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A cost effective and efficient approach for a new generation of solar dish-Stirling plants based on storage and hybridization

Final Report Summary - BIOSTIRLING-4SKA (A cost effective and efficient approach for a new generation of solar dish-Stirling plants based on storage and hybridization)

Executive Summary:
The BIOSTIRLING - 4SKA (B4SKA) is a demonstration project for the implementation of a cost-effective and efficient new generation of solar dish-Stirling plants based on hybridization and efficient storage at the industrial scale. The main goal of the B4SKA demonstration project is the generation of electric power using simultaneously solar power and gas to supply an isolated system and act as a scalable example of potential power supply for many infrastructures, including future sustainable large scientific infrastructures.

B4SKA build an interdisciplinary approach to address reliability, maintainability and costs of this technology. B4SKA successfully tested the first world Stirling hybrid system providing about 4kW of power to a phased array of Square Kilometre Array (SKA) antennas, overcoming challenges in Stirling and hybridization and smartgrid technologies.

B4SKA achieved the final implementation of one integrated unit dish-reflector with hybrid receiver and Stirling engine and associated PCU+electrochemical storage (batteries) in order to validate a new commercial solar dish technology at demonstration scale. The B4SKA Consortium, with fourteen companies from six European countries, has performed the engineering, construction, assembly and experimental exploitation of a solar concentration system powering a set of demonstration astronomical EMBRACE - MFAA antennas installed in Contenda Forest (Moura, Portugal).

The power provision developed a cost effective and efficient new generation of solar dish-Stirling plant based on hybridization and efficient storage at the industrial scale, combining solar concentration, gas and batteries for night operations.
B4SKA has driven innovation in the following areas:
• Hybrid Stirling motor.
• Development of passive cooling system and smart load sequencing to minimise demand side energy requirements.
• Generation of serendipitous radio frequency interference shielding, interfacing with grid supplies and land use.
• Distribution and reticulation design for price/reliability trade-offs.
• It has improved the conversion efficiency above 24%, through the new design of the parabolic concentrator, innovations in the coating materials to replace the conventional mirrors and increase reflectivity, modelling and optimisation of operation, and definition of a control system to implement all aforementioned improvements.

Besides the testing of dispatchability and compatibility with a radioastronomical system, B4SKA actually implemented the first world example of a hybrid concentrator engine, opening new avenues for further innovations of green autonomous radioastronomical systems with greater economic impact.
Project Context and Objectives:
B4SKA is a demonstration project dealing with the implementation of a cost-effective and efficient new generation of solar dish-Stirling plants based on hybridization and efficient storage at the industrial scale. The B4SKA run between June 2013 and until April 2017. The B4SKA Project is based on the achievement of four targets simultaneously: to reduce costs, to increase the efficiency, to optimize the dispatchability and to increase the life-time, in order to validate a new commercial solar dish technology at demonstration scale. The project demonstrator is the Square Kilometre Array (SKA)

The SKA is the approach for the next generation of Radio Astronomy telescopes that enables innovative approaches to a reduced power footprint. This is done through pushing innovative approaches to renewable energies as well as to low power computing with improved algorithms, in a domain were high density big data processing and imaging computing is mandatory. The Energy Sustainability of large-scale scientific infrastructures led to consider the impact of their carbon footprint and Power costs into the respective development path and lifetimes.

Solar dish-Stirling systems have demonstrated the highest efficiency of any solar power generation system, by converting nearly 31.25% of direct normal incident solar radiation into electricity after accounting for parasitic power losses. Therefore, the solar dish-Stirling technology is anticipated to surpass parabolic troughs by producing power at more economical rates and higher efficiencies. However, the aforementioned technology is not commercially exploitable to date as other Concentrated Solar Power (CSP) technologies, such as tower and parabolic solutions. This is because the current solar dish-Stirling technology still presents several limitations: high costs, limited lifetime, low system stability and reliability. Since solar dish-Stirling systems are modular, each system is a self-contained power generator, which can be assembled into plants ranging in size from kilowatts to 10MW. The solar dish-Stirling plants are a hybrid solution to produce energy. This hybrid solution is a mix among different green energies, solar dish-Stirling technology as the main one, together with biomass or similar, in order to be able to produce energy 24 hours per day, which is of special interest infrastructures requiring 24/7 power availability. The initial goal of the B4SKA demonstration project was the generation of clean electric power using simultaneously solar power and biomass energy in the form of biogas or fuel, to supply an isolated system and serve as a scalable example of power supply for future developments and potential inclusion or consideration in large scientific infrastructures.

The SKA radiotelescope, to be installed in Africa and Australia will be once built the largest scientific infrastructure on Earth, with high and very stringent energetic demands. Hence, it has been considered an ideal framework to have new radioastronomical concept demonstrators as reference loads for B4SKA, and to guide some of the specifications of the plant. Additionally, a demonstrator of one of SKA related radiotelescope technologies, installed at Moura (Portugal), has been used as a real existing demonstrator to be fed by means of B4SKA plant. These collaborative activities coupled to Large science projects such as the planned Square Kilometre Array enable innovative approaches to decarbonisation of large scale infrastructures.

The objective of B4SKA is to research, develop and implement new solar dish-Stirling technology suitable for large-scale commercialization with the following overall goals: i) to implement a cost effective and efficient new generation of solar dish-Stirling plant based on hybridization and efficient storage at the industrial scale and ii) to study compatibility of innovative power production units with the strict Radio interference requirements of modern radiotelescopes and related radioastronomy SKA-like technologies.

This project in Moura developed and commissioned a prototype with an expected average power of up to 9kW. The demonstrator has served as an excellent testbed to verify the adequacy of the Biostirling energy system as a potential clean energy source for part of the SKA antennas. The hybrid solar dish-Stirling solution is a highly efficient solar and/or gas-to-electricity energy conversion unit capable of providing 24/7 electrical power. It consists of:
• A solar concentrator (Dish Unit), which concentrates the solar radiation on its focal point.
• A solar receiver placed at or in the surroundings of the concentrator focal point, which converts the concentrated solar radiation to heat by increasing the internal energy of a working fluid.
• A gas burner, which burns gas stored but thought for biomass and produces sufficient heat to run a Stirling engine on the heat generated.
• A hybridization apparatus, which makes it possibly to seamlessly run the Stirling engine at continuous power on any mix of heat from the two sources above.
• The Stirling engine turns a generator from which electrical power is distributed. To be able to control the unit there has to be an engine control unit (ECU). The ECU contains a microprocessor carrying necessary control software, power supplies, sensor interfaces, safety functionality etc.

The B4SKA prototype has been tested with the SKA demonstrator in Moura. This demonstrator consists of a set of medium-frequency antennas that are in a technology development phase and which will form part of SKA phase II. This demonstrator has been installed in the National Park of Contenda, in Moura (Southeast of Portugal), whose radiofrequency spectrum is similar to that of the deserts of South Africa and Australia where SKA will be installed.

- Mirrors efficiency and optical accuracy
The efficiency of a solar concentrator is significantly affected by its optical performance. Hence, obtaining the maximum concentrated solar flux on the receiver requires a precise alignment of the mirror facets. The alignment includes the adjustment of the normal direction of the mirror surface. This orientation alignment is very important due the large influence of Direct Normal Irradiance (DNI) concentrated on the receiver. By means of canting the mirror surface, the alignment of mirror facets can be achieved. Several methods have been developed and applied for the different types of CSP collectors (i.e. parabolic trough, linear Fresnel, power tower and dish/Stirling). Basically, there are three main types of alignment: On-sun alignment, mechanical alignment and optical alignment. In order to execute the canting process, a single facet has been calibrated as a reference during sun tracking as described earlier. Following this process, the tracking mode has been deactivated and manually directing/aligning the collector with fire tower (750 m distant).
In summary, the dish structure and the optical accuracy have been verified allowing to proceeding with engine commissioning, storage integration and all related activities to performance monitoring an evaluation.

On-site installation, integration and commissioning tasks can be summarized as follows:
• Measurement and evaluation of the static misalignment level linked to the dish main structure.
• Integration, adaption and adjustment of the steel adapters to the dish main structure.
• Compensation of misalignment by adjusting the mounting pins of the steel adapters.
• Preparation, integration and pre-canting of mirror facets.
• Laser-based evaluation of dish structure geometry.
• Application of sophisticated Canting of mirror facets.
• On-site burning test: validation of optical accuracy (e.g. reflectivity, tracking accuracy, focal length and spot size).

- Energy Management System (EMS) Installation
The EMS box controls and measure the flux of energy coming from the public grid and also the power being produced by the plant and injected into the public electrical grid. The rest of the boxes are meant to measure the power consumed of given by the Stirling engine, the Storage System and the antennas providing the power load.
All the equipment is also connected with communication cables. The cables used are Ethernet CAT 5 cables. It is also needed to install a switch in order to establish communication with all the meter boxes (Stirling, storage, antennas and public grid). The boxes already have a network RJ45 connector.

- Storage System
The storage system is composed of 25 modules of batteries, of 29,3 kg each, that are positioned on a 57,8 kg bank. The total weight is around 800 kg. The EES, converter and inverter system works has a UPS in order to have a backup source power in case of power loss. It has been designed and sized to supply power to tracking system, auxiliaries and SKA Demonstrator antennas in the experimental plant (when the Stirling engine fails). It can feed all the consumptions (considered) during more than 3 hours.
For its installation, two groups of cables were put out from the main switch, one going for the UPS and another for the Stirling switch.

- Engine Installation and Commissioning
The final design consists of 48 wickless thermosyphons oriented in two concentric circles, enabling both a tubular sun receiver and a radial gas flow through the pipes. The design included the development of a high temperature thermosyphon capable of using two different heat sources.
Before sending the engine to site for its commission, the prototype was deeply tested in the manufacturing facilities with very positive results:
• The first hybrid receiver prototype was tested successfully in combustion only mode, generating a maximum electrical power output of 7.7kW with an electrical efficiency of 17% in January 2016.
• Different heating powers were evaluated at an inclination of 15° and all results indicated that the developed receiver will also perform well when heated only from the sun or from both sun and gas simultaneously.
• At the first test run of the unit in hybrid mode, the output power increased from combustion mode at 1,5 kW to hybrid mode producing 3 kW proving that the concept is working but the weather was not sunny enough for fully testing.
Before installing the Hybrid Stirling Engine, a solar version of a Stirling engine was installed in order to check the proper functioning of the system. The solar engine had been used before and was ready to run after checking and filling working gas and cooling water. No real commissioning of the engine was done since the main purpose was to check all other systems before moving on to the hybrid.

- Impacts & Innovation drivers
The main impacts of B4SKA in terms of energy-related developments are the following:
• A hybrid dish-Stirling engine that works simultaneously using solar power and gas energy. This is a very important step in order to obtain a solar-energy system that can work 24x7.
• Our solar dish-Stirling prototype has an electrical power of 10Kw (1-9 kW in gas mode, 2-10 kW in solar mode), what can provide energy supply isolated systems and serve as a scalable example of power supply for future developments of larger infrastructures.
• Several important improvements on the structure of the dish by reducing its weight and improve tracking precision.
• Regarding optical parameters, the concentrator has been evaluated with an average reflectivity of more than 95,5% and an average optical slope error of 1.7 mrad at maximum.
• Assuming 20% efficiency from gas chemical energy to power, the chemical energy demand is 250 kWh.
• A new energy storage system able to work simultaneously with the hybrid technology, hence able to avoid non-desirable energy peaks.
• An innovative control system that achieves a highly reliable and fully renewable hybrid solution.

Project Results:
As presented before, the BioStirling-4SKA (B4SKA) Consortium has successfully accomplished the implementation of a hybrid Stirling plant that can supply electrical power 24/7 combining the use of renewable sources such as sun and biomass (in the form of biogas).
The main science and technology results are directly reflected in the prototype.
1) There has been accomplished the manufacturing of an optimized steel structure and tracking system that reduces its costs when manufactured with mass production, making the technology competitive against others existing.
2) The latest advances in reflective technology have been applied to the reflective surface, manufacturing high efficiency mirrors that use innovative coating materials to replace the conventional mirrors and increase reflectivity, as well as endurance and durability.
3) The challenge of been able to build a hybrid Stirling engine has been widely overcome with the hybridization of the solar CLEANERGY V161 Stirling Motor.
4) The coupling of a compatible Storage System (SS) that optimizes the functioning of the whole plant. This SS has to assure the supply of electric energy to the SKA, by either storing the surplus produced by the Stirling dish, and also, when the production from the sun is low, being as a backup supply source for the SKA.
5) And the programming of an Energy Management System that optimizes the production of electrical energy based on the energy demand in each moment, by evaluating the production and demand, studying different operation strategies in order to provide reliable energy supply to the load.
As a result, the first Hybrid Stirling dish plant has been built.
WP1. KPIs & specifications (RTD)
The BioStirling-4SKA project consists of eight differentiated blocks, called Work Packages; in which the main components of the demo plant have to be defined. In order to prepare the development of all the aspects and subsystems of the project, the start of the project begins with the definition of the bases of all the elements that compose it.
In this sense, WP1 leads the way to set the first requirements and specifications for the Solar Dish Concentrator (reflected surface and tracking structure), Hybrid Engine, Storage System and Energy Management System; as well as the preliminary guidelines for the manufacturing process, operation and maintenance and the demo SKA Sensor Infrastructure needs.
A Hybrid Stirling Dish (HSD) is a highly efficient power production solution capable of providing 24/7 electrical power from either solar, gas or a solar-gas combined renewable source.
The HSD consist of:
• a reflective dish-shape surface composed of forty one-meter-square mirrors which concentrates the solar radiation into a focal point;
• a tracking system that turns the reflective surface towards the sun, tracking it from dawn to dusk
• a receiver, placed in the surroundings of the concentrator focal point to convert the concentrated solar radiation into heat by increasing the internal energy of a working fluid;
• a green-gas burner, which produces sufficient heat to run a Stirling engine on the heat generated.
• an hybridization system, which makes it possible to run the Stirling engine at continuous power whether the income heat source comes from the sun or the gas subsystem.
• A Stirling engine that turns the thermal power into electrical power.
The BioStirling Consortium has managed to build the first Hybrid Stirling Dish prototype ever made, by going through a very deep and extensive background research process for finding the best solution for the development of all the components for the prototype.
The reflective surface attached to the tracking system is one of the components with the greatest potential of improving the global performance of the system; that is why the dimensions, weights, wind/snow loads, reflective materials, mirrors reflectivity and manufacturing tolerances, have been meticulously defined for successfully achieving the chosen Key Performance Indicators (KPI).
These chosen requirements called KPIs will, at the end of the project, be used to evaluate the degree of achievement of the project objectives.
The Hybrid unit has been based on an existing solar CLEANERGY V161 Stirling Motor. The challenge of the BioStirling project lies in being able to build a hybridized burner that operates seamlessly from 100% solar to 100% gas fueled power, keeping the efficiency when working only with sun, increasing the working hours by burning biofuels in no sun conditions, and even burning gas in low radiation conditions to reach at any time and conditions, the nominal power of the engine in a constant manner.
The Hybrid System consists of:
• a solar receiver for absorbing the solar heat flux of energy,
• a combustor, where the biogas is burned to produce heat,
• a hybridization system which makes it possible to seamlessly use heat from two sources, solar and gas burner,
• a core engine with crank drive, engine block and the Stirling specific heat exchangers,
• a working gas control system which regulates the gas pressure,
• a cooling system consisting of a fan, radiators, and circulation pump,
• an electric generator, and
• an Engine Control Unit (ECU).
Besides the dish itself, the BioStirling Power Plant also has an Energy Storage System (ESS) and an Energy Management System (EMS). The ESS contributes to the dispatchability of the supplied electricity to the SKA by providing extra power in case of production failure. The EMS manages and controls the energy flow demanded and produced, in a way that production is optimized, minimizing energy costs.
The main source of power comes directly from the sun; however, as it is not available 24/7, in order to produce a constant amount of power all day, it is combined with the heat that the biogas burnt provides. Moreover, as the demand of power may not be constant 24/7, the surplus of energy produced is stored in batteries, so it can also be used as a backup power source, besides ensuring stability to the inner grid.
The EMS works optimizing this process in the time range of minutes. It provides an optimized energy flow to the loads in order to hold frequency and voltages within an allowed range. It also collects energy related data from the subsystems and makes it available a standardized interface.
The way all these components for the prototype have been manufactured, goes in line with the main objectives of the BioStirling-4SKA project, reducing costs, optimizing production systems for mass manufacturing processes, making this technology competitive against other existing (central solar receivers, parabolic troughs, photovoltaic, Fresnel, etc.).
For the proper functioning of the whole plant, an Operation & Maintenance Plan in needed. The guidelines will be defined among all partners involve, throughout the course of the project.
WP2. Solar Dish and Concentrator RTD.
The principal of WP2 was to develop an innovative parabolic dish. The elaboration of the conceptual design and basic engineering of the parabolic dish concentrator pursued the following specific objectives:
• Optimization of concentrator dimensions.
• Improvement of the concentrator optical efficiency.
• Characterization of the flux distribution onto the receiver.
• Reduction of the Levelized Cost of Energy (LCOE).
• Optimization of the overall system performance
Results: new solar dish design
The main results obtained within this task are the following:
• Identification of a strong relationship between the size and number of the mirror facets and the total cost of the mirror due the adjustable connectors to the support structure. For dishes within the given boundary conditions, 9 to 12 pie slices provide the best results in terms of size, shape, and cost for sandwich composite mirrors. MT designed a segmented sandwich mirror facet consisting of three segments bonded together (Figure 1). The segmentation is a result of actual manufacturing limits mainly due to stresses produced by bonding the glass mirrors to the curved surface.
• First conceptual design of the B4SKA dish (Figure 2). The main boundary conditions of the investigated dish models are the focal lengths (in the range of 4.5 to 8 m) and the reflecting surface area which has been set to be in the range of 50 to 70 m².
Results: High efficiency reflective materials
• Silvered silicate mirrors with a thickness of 1mm and a reflectivity of 95.5 % has been identified as the best material for this purpose. Simulations of the stress and constraints in the sandwich and the mirror have been performed for pie slice-formed facets. The stresses in the sandwich and the mirrors have been calculated.
• Different potential protective coating of the glass and different protection concepts were evaluated and tested to decrease soiling and potential haze by sand and dust abrasion.
• The preliminary evaluation of wind tunnel experiments with a simplified dish model showed promising results for a kind of wind fence at the back of the dish structure. The use of anti-soiling coatings is promising for the future.
• Different foam materials and glues/sealants of the integrated sandwich composite mirror had been tested. Up to now, accelerated life cycle tests showed no changes of dimensions, no relevant deformation, and no cracks of the samples after 2.5 simulated years in an arid environment. These life cycle tests and field tests are ongoing.
Results: New solar dish designs and configurations
• The basic design of the B4SKA dish is shown in Figure 3. The structure was designed taking into account structural and operational factors.
The connection of the reflective surface to the structure was analysed in detail. For the 11-facet design, the attachments pins are placed in different parts of the structure and mirrors, having always three canting points per facet (Figure 4).
Results: Optical modeling
The optical model of the system was developed using a ray-tracing tool, Tonatiuh (Figure 5). The main results in this task are:
• The concentrator final version, for the receiver design has a double focal length (5.5 m outer focal length and 5.4 m inner focal length), an inner diameter of 2.2 m and an outer diameter of 8.97 m.
• The aperture of a cone-shaped cavity with a depth of 0.1 m depth is placed at the inner focal length. The inclusion of this surface ensures the utilization of the entire receiver walls.
• The optical performance of the concentrator was simulated with a reflectivity 95.5 %, 1.7 mrad slope error and 0.5 mrad of specularity error. The diffuse reflectivity of the Inconel and the insulation material is taken in 7 % and 80 % respectively.
• The flux distribution on the cylinder walls should be relatively homogeneous, with a maximum peak flux of 430 kW/m2 close to the aperture plane. The flux on the plate at the bottom of the receiver is restricted. The flux distributions on the bottom plate and the cavity walls for a cavity aperture of 150 mm are shown in Figure 7.
WP3. Full renewable hybrid engine RTD.
The aim of WP3 was to assess feasibility of, and develop engineering specifications to enable sourcing and installation of the envisioned 100% renewable power system for SKA in Moura, Portugal in WP6.

There were two main areas of development:

• A gas generation plant producing syngas or biogas, using biomass readily available locally in Moura, Portugal
• A Hybrid Stirling unit, capable of seamlessly operating across the full range from 100% powered by the sun using the concentrator developed in WP2, to 100% powered by burning the generated biogas.

- Results - Gas Generation Plant
A tentative design of the wood gas production process was defined by JYU and ALENER as part of the feasibility study and presented as part of D3.1.
Technically, gasification of available specific bio-mass in Moura and combustion of the resulting gas in the Stirling engine combustor were judged to be feasible. However, sourcing and adaptation equipment for gasification suitable for the project is concluded to be not economically feasible, given the budget frame as defined in the DOW. Equipment for small scale gasification, delivered by credible and proven suppliers, is difficult to find ready at the market, only a few options with limited track record exist.
As a part of this process, the “Carbon conversion predictor” tool was adapted and used by JYU to predict the syngas composition from the biomass available in Moura. The expected syngas composition over the full range of biomass mix was analyzed and delivered as part of D3.1 and separately as D2.2.
For the continuation of the Project, the Partners made the assessment that the combined top-level objectives of demonstrating a new technology for a cost effective hybrid solar / gas Stirling unit, and delivery of a power plant for the SKA array in Moura, Portugal, outweighs the objective of demonstrating syngas production. Therefore, the originally planned syngas plant in Moura was replaced by a solution where a combination of externally produced bio-methane and natural gas. This solution was designed as part of the Work Package.

- Results - Hybrid Stirling Unit

The development of a Hybrid Stirling unit, capable of seamlessly operating across the full range of sun/biogas power input was assessed to be feasible and has subsequently been conducted successfully.

The approach was to use Cleanergy´s proven core Stirling engine and MILD combustion burner with as few major re-designs as possible to minimize the risks and keeping TRL at reasonable levels.

The major designs and technology development achieved:

• Adaptation of the MILD burner to syngas fuel instead of methane based fuel and Cleanergy had a prototype burner specifically developed for syngas which has been tried and proven to be fit for purpose, which made the redesign more straight-forward. The key differences are significant differences in proportions between fuel gas and air which changes the properties of pre-heater and mixing tube. The design was completed but abandoned following the PMC decision to change the gas type from H2 based syngas to CH4 based biogas or natural gas.

• Adaptation of the standard CH4 burner comprising the changes in length of the burner including mixer tube, and the need for change of gas channel geometry to facilitate the insertion of the hybridization unit in the burner assembly.

• Development of thermosyphon technology, new-to-the world in its application where heat input is provided at multiple points along the length of the thermosyphon tubes. This work also produced a new understanding of the function of the thermosyphon function over the range of heat input mix and inclination not before studied. The research and technology development also resulted in the publication of several scientific papers in cooperation with the Universities of Brighton and Florianopolis, respectively.

• Development of a novel technology to facilitate heat transfer from thermosyphons to the Stirling working gas heat exchanger. This was a necessity after deducting that geometrical constraints made direct conduction through metal impossible. The solution comprises a “slurry” of metal balls and molten glass to make it possible to engineer heat transfer rates and ascertain conductive contact. It was found to work well in practice.

• Design of a solar receiver geometry matching the Solar Concentrator developed in WP2.

• Integration of the thermosyphon technology and heat transfer technology into a hybrid assembly where a solar receiver is combined with a gas burner and a Stirling Engine.

• Integration of the Hybrid Unit with control systems, gas supply systems and cooling systems into a unit which can be installed and operated on the Solar Concentrator developed in WP2.

• Development of a control system for the hybrid receiver that seamless switch between gas and solar power.
WP4. Power conversion unit integrated with a storage system RTD.
The main technical objective of energy storage system is to assure the supply of electric energy demand of SKA. In normal operation, Stirling dishes supply the energy demand of SKA, if energy produced is higher than energy demanded, the surplus energy is sent to energy storage system. In the opposite way, if the energy produced by Stirling engines is lower than SKA electric demand, the defect is extracted from the energy storage system.
Other objectives of the energy storage system:
• The system has to serve as a grid stabilizer, due to an operation of grid as an ‘island’. The voltage of grid is 400 V (AC). The electric energy produced and demanded by grid are variable in time, so fluctuations of frequency and voltage of grid occur. These fluctuations have to be limited in order to not produce the collapse of grid.
• If there is a problem in Stirling dishes that makes a full defect of energy in grid, the energy storage system has to assure the energy demanded during an enough period of time to permit the connection of grid to the general Portuguese net.

In this task, several alternatives of Storage Systems have been analyzed to be coupled with the Stirling Engine. Final options considered were:
• Hydrogen storage system with small batteries set (for transient switch).
• Batteries storage system.

Hydrogen storage system with small batteries set
A scheme of this system is shown in FIGURE 8. The components of the system are:
• Hydrogen technology: electrolyser, hydrogen storage and fuel cell.
• Batteries.
• Power management: AC/DC converter, DC/AC inverter.
• Auxiliaries: Water purifier, water storage and water pump.
• Control system.

In this alternative, the massive storage system is the hydrogen technology and batteries are used to assure the stability of AC Bus (frequency and voltage). The operating principle is:
• If electric energy produced by Stirling-engines is higher than electric demanded from SKA-sensors, the surplus energy is sent to storage system. The first system to charge is the batteries set, if it is not in its maximum state of charge (SOC), and the second the hydrogen storage system (via the electrolyser).
• If electric demanded from SKA is higher than energy produced by Stirling-engines, the deficit of electric energy is supplied by the fuel cell, which consumes hydrogen and air (from ambient). The batteries set is destined to stabilize the AC bus during the transient time of switching-on the fuel cell.
The control system is the responsible for carrying out this scheme of principle, and follow the orders issued by the EMS.
The electrolyser, the batteries set and the fuel cell work on DC current, so an AC/DC converter and a DC/AC inverter are needed. In this proposal scheme, all these components have to work with the same DC voltage, so a careful designing and sizing of components has to be done.
Batteries storage system.
The second storage system proposed is only composed by a batteries set. The batteries have to assure the grid stability and take the roll of massive storage system. To reach these two objectives the size of the batteries set have to be higher compared with previous system.

In a batteries storage system, a bidirectional AC/DC converter is needed. This kind of power converters is more expensive compared with traditional converters, but only one is needed (in previous system two converters are used).

Taking into consideration the components of system, several operation principles can be considered. First scheme is when the whole system works as an isolated grid:
• If electric energy produced by Stirling-engines is higher than electric demanded from SKA-sensors and auxiliaries, the surplus energy is sent to batteries storage system.
• If electric demanded from SKA is higher than energy produced by Stirling-engines, batteries will supply the deficit of electric energy.

Second, if a net grid is available near SKA antennas, the storage system works as an UPS (Uninterruptible Power Supply):
• The Stirling engines (electric source) and SKA antennas and auxiliaries loads (electric demands) are connected to net grid.
If a failure happened in national grid or Stirling engines, the control equipment of storage system creates an isolated grid and SKA antennas and auxiliary loads are connected to the grid created

Analyzing both options, and taking into account the difficulties to use the hydrogen produced in electrolyze to be used as a fuel in Stirling Hybrid Receiver, Batteries set option was selected.

For assuring the integrity of Stirling engine in experimental plant, the second operation principle are selected. If the complete system is disconnected from net grid the Storage system must give enough power to defocus the dish concentrator (and move it to safe position) and give the electric energy to SKA antennas and auxiliaries.

Finally, for the experimental plant a commercial solution has been selected: ABB DPA UPScale RI 11. The main characteristics of storage system are presented in TABLE 1. This model works as an UPS, and have integrated the two operation modes described above.

The forty batteries of 12 V each are connected in serial to reach 480 V (DC). At full capacity, the storage system has a capacity of 3.84 kVAh. The general specifications and electrical specifications of each battery are shown in TABLE 2.
In FIGURE 10, a real image of Storage system in experimental plant is shown.
WP5. Plant Control System.
The main goal of this work package was the development of a concept for the Energy Management System (EMS) to ensure a highly reliable fully renewable hybrid power supply for an astronomical antenna array by employing a dish Stirling system as a main energy source in combination with of a storage unit. This included:
• Exploration of the overall electrical system topology and configuration, identification of the multiple loads, load profiles and other electricity demanding equipment.
• Defining the system control unit as well as control and operation strategies in order to provide reliable energy supply to the load.
• Set up of a simulation environment and models for the SKA power supply system
• Supporting the hardware development and implementation of the EMS control unit (work package 6).

According to the main goals different sub tasks were performed during the first phase of the project:
• Interfaces and software protocols
• Loads and subsystems analysis
• Definition of the hardware architecture for the communication and control infrastructure
• Development of the operation and storage algorithm
• Development of the demand management and load control algorithm
Interfaces and software protocols
To enable a proper communication between the different sub-systems (Stirling unit, electrical storage, antennas (load) and public grid interface) of the BioStirling for SKA power plant there are in principal two possibilities. Because a decision for a specific component / sub-system (like the Stirling dish) includes intrinsically its available interfaces, there is on the one hand the option to choose (only) components / sub-systems with compatible interfaces or – on the other hand – to create “translating” gateways. The research activities within this project has been shown to better leave the option of creating gateways between the sub-systems / components in order to minimize hardware and implementation requirements (and thus costs). So this end up in the necessity to very carefully choose the devices for energy measurement and control. In a decision making process it turned out that is was of foremost importance to be compatible with the communication abilities of the (chosen) Stirling sub-system, as this was not substitutable. Taking in to account all of these boundaries Modbus TCP as a communication platform appeared to be the best choice. Modbus is a serial communication protocol/interface, it is simple and robust, has a good track record in field bus application and has become a de facto industry standard for communication over the years.
Connecting devices with Modbus TCP is as easy as with every standard TCP/IP infrastructure. Further suitable components utilizing a Modbus TCP interface could be identified and used at a later stage of the project. In a next step an appropriate set of data points and parameters which have to be exchanged between the devices / sub-systems was defined. In order to easily configure every device, a table with all Modbus and assignment properties has been developed.
Loads and subsystems analysis
In co-work with the partners IAA and CSIC loads and sub-systems of the power supply were defined, analysed and documented; multiple factors that may affect the different sub-systems regarding short-term and long-term loads were studied. Due to the high cost involved in energy storage, the development of the optimal solution is closely linked to the long-term load of the system. Considering this initial premise, a detailed study has been carried out to determine the work-flow and the process to be implemented in the integral control system. The analysis included:
• Antenna processing control elements:
• Central Signal Processing (CSP)
• Science Data Processor (SDP)
• Telescope Manager system (MGR)
• Signal & Data Transport (SaDT)
• Provision of power and cooling of the CSP, SDP, MGR & SaDT data processing racks
• On-site communication
Definition of the hardware architecture for the communication and control infrastructure
To care for a reliable and efficient power supply system the micro grid is controlled in two stages:
• The grid control (GC) is the first stage and cares for a stable reliable grid by controlling electric power flows in timeframe smaller than seconds.
• The energy management system (EMS) is the second stage with the task to monitor and optimize energy flows and acts in timeframe of minutes.
Many possible solutions for GC were discussed and analysed. From the outcome of this process a concept for GC to build up a secure and reliable micro grid was developed. GC is performed by a grid building bi-directional battery inverter with integrated micro grid control software. The battery based bi-directional inverter controls electric power flows in timeframe smaller than seconds in cases of a sudden change of generating power or changes of the load demand. Additionally it functions as an uninterruptable power supply with batteries and a grid fault back switch. Task of the EMS is to monitor and optimize energy flows to minimize fuel consumption of the biogas burner and to maximize lifetime of the components. The optimization is done with generator (Stirling) and load control with the assistance of the battery storage. To fulfil these requirements a communication with a fieldbus system between EMS and all system components is necessary. As already pointed out a Modbus via TCP/IP communication protocol was found to optimally fulfil the communication requirements.
In turn the EMS monitoring system is integrated in the “OpenMUC” software framework. The OpenMUC software framework (FIGURE 11) is an open source package based on Java programming language. OpenMUC already has implemented a Modbus driver, data logging ability and the possibility to use a graphical user interface (GUI) and a plotter to see measurement data from all connected system components online. Further the OpenMUC allows integrating individual developed control and SCADA systems like EMS. Additional power analysers were used in cases where specific measurement data could not be provided by the system component or a Modbus interface of a component did not exists.
The OpenMUC Framework is integrated in an embedded system; in turn the embedded system is connected to the Modbus communication bus via TCP/IP. A wide range of embedded systems are available with different possibilities of adding communication hardware and running operation systems. After a long investigation process, the choice fell on the Raspberry Pias an embedded hardware to run OpenMUC. The Raspberry Pi platform is cheap and popular and much supported through a worldwide community. Although the processing speed is quite low, it is adequate to drive the software platform sufficiently.
The EMS monitors the overall system and allows access to control specific components. It cares for a reliable and efficient operation of the storage and reduction of fuel consumptions by controlling the BioStirling generated energy depending on needed load power. To minimize fuel consumption a load management system will be integrated, but load control is very limited as all components (antennas and computing system) are always in use. Only A/C is variable depending on the ambient temperature. In future stages of the SKA project, load management could be easily extended and adapted to further requirements or control needs.
Finally, the implemented communication infrastructure connects Meter Boxes (power analysers), EMS, PLC (Programmable Logic Control) and the sub-systems Stirling power engine, Battery/UPS and Antenna in order to collect data and have access to their control mechanisms. A remote control via GSM rounds-up the picture. FIGURE 12 shows an overview of the communication infrastructure.
Operation and storage algorithm development
The control strategy of the EMS is divided in grid control (GC) for efficient operation of the supply units (Stirling) and a load management / load control to optimize the use of direct solar energy and thus minimize fuel consumption. The GC will be done by giving frequency depending set points to the Stirling generator. The GC unit varies frequency between 48 and 52 Hz. Between 49 and 51 no control action happens, between 49 and 48 power from generators will be increased from 0% to 100% of nominal power from 51Hz to 52Hz power will be decreased from 100% to 0% as so called “droop control”.
Demand management and load control algorithm development
The goal of the load management system is to maximize direct use of solar energy through optimized scheduling and operation of shiftable loads. A genetic algorithm (GA) was developed which arranges loads in an optimized manner in hourly or 15 minute slots depending on different side conditions for optimal use of direct solar power. The GA was optimized for the BioStirling project in order to BioGas fuel saving. Input parameters are power plant control with rules of varying fuel powering of the Stirling engines, prognosis of solar production and load profile for the next 24 hours, possible shiftable loads with side conditions of running time, time of needed continuous operation, time slot of allowed operation and load power. With this input parameters a daily load schedule is calculated by the GA to run BioStirling in optimized conditions.
In the second phase of the project the hardware development and implementation of the EMS control unit was supported. Thus three Meter Boxes and one EMS/Meter Box for data acquisition and control were developed and built, based on the results of WP5.
Hardware Implementation
With the help of colleagues from ALN, the Meter Boxes, current transformers and an Ethernet Switch has been installed on-site at Contenda (FIGURE 13), FIGURE 15 shows an overview of the complete finally implemented BioStirling4SKA power supply system.
Visualization of the captured data via OpenMUC
OpenMUC is used as a data framework for data collection and visualization.FIGURE 14 shows a screenshot of the graphical user interface of OpenMUC.

Realized Power System
FIGURE 15 shows an overview of the electrical design of the BioStirling4SKA power supply system as it was finally implemented on-site in Contenda.
It could be shown that the chosen hardware platform is a feasible solution for EMS and metering tasks for the electrical supply of remote systems. The embedded system on a Raspberry Pi hardware platform provides sufficient computing power to run an open source data framework like OpenMUC on the one hand and to take over communication task via TCP/IP and ModBus TCP on the other hand.
ModBus TCP allows a simple connection of components and sub-systems on a communication level. Thus, allowing the further extension of the system with additional components (and sub-systems) as well as replacement of components for optimization or adaptation purposes. In general the PLC can overtake EMS tasks in order to control energy flux from generation to storage and load.
The implemented VPN router allows the remote access to the system in order to share the data for remote control or visualization (SCADA) in combination with OpenMUC. Furthermore, the UPS installed in the plant as storage system cares also for frequency and voltage stability, statically as well as dynamically.
WP6. System integration (DEM).
WP6 is the construction and implementation of the 7 kW BioStirling Power Plant. As introduced before, it is a hybrid plant that can manage power production coming from a solar, a gas or a storage source.
First, the civil works were carried out, then the installation of the prototype and finally its commissioning and start up.
With the concentrator fully operative, several tests have been performed in order to check the proper functioning of all the components before installing the Hybrid Stirling generator:
• QA tests of optical accuracy
• Tracking system tests
• Energy Storage System tests
• Solar engine tests
• Hybrid engine tests
• System monitoring tests
Furthermore, before commissioning the hybrid engine, it is decided to test the concentrator by installing a solar unit and testing it as long as possible, in order not to damage the one and only manufactured hybrid unit. After this commissioning, the whole BioStirling plant is put into operation with satisfactory results, having successfully achieved the following KPIs:
(Note 1) During the first half of the project it was decided that it was not going to be feasible the construction of a syngas generation plant inside the facilities of the BioStirling power plant, as it had enormous costs that could not be beared within this project. It was then concluded that the hybrid engine would not be tested in Contenda burning syngas, and instead it was decided to use some biogas or even propane. In the end the fuel used at the demo tests was commercial propane, and accordingly, the results in efficiency have been better than using syngas. The constructed Hybrid Stirling Engine has over 99% burner availability (the gas only unit has barely any burner-caused-incidences during a year). What's more, the hybrid engine had no burner-stops during the tests performed in Åmål and Contenda.
(2) In the midterm review it was already indicated that this KPI made no sense as the use of a fuel cell in the BioStirling plant was discarded. The system that has been installed, a storage system with batteries and a UPS, has an overall efficiency of around 96%, reaching values near 98% when functioning in eco-mode configuration.
(3) Due in part to the difficulties encountered throughout the project, it was not possible to directly measure the DNI that is the amount of direct solar radiation at the receiver of the engine. That is why we don't have exact values of the overall efficiency of the plant. This KPI-9 addresses the overall efficiency of the B4SKA power system, comparing the energy feed-in to the grid respectively to load and battery, related to the input (solar irradiation).With the limited time and budget of the project, and having received some components / sub-systems delivered delayed, in the end, we have not been able to perform a test of the B4SKA power system on a system level and gain the necessary data in order to calculate the overall system efficiency according to KPI-9.
The project has had some difficulties during its life cycle; including one warning stage for 6 months due to some uncertainties in the demo stage as the manufacturing of components took more time than expected. This warning was overcome due to the hard efforts of all the partners in completing the project achieving the objectives initially set.
Many other hurdles had to be taken during the course of this project, not only of technical nature, but also administrative and organizational difficulties had to be overcome.
For example, the definition of the final location of the demo plant has delayed some tasks of WP6. Furthermore, there have been considerable planning and budget issues, as the early DOW was not comprehensive enough to reflect all the work and effort needed in the project, nor did the budget in relation to the actual technology development challenge balance out among all the partners; that is one of the reasons the DOW had to be amended.
The Consortium, also, even lost two strategic partners (Lógica and CTAER) along the way. And a redistribution of tasks was needed among the partners in order to be able to finally achieve all the objectives of the project.
Besides, a large portion of the work was marked by the continuous and constant finding process concerning the technical characteristics of the power system to be developed and which requirements should be fulfilled. E.g. it was discussed for a long time, if a pure Off-grid system should be developed or if a grid connected variant should also be considered.
The answer to these questions was, among other things, dependent on the location finally chosen for the functional model of the B4SKA (location with or without existing grid).
Due to the cost frame (natural budget limitations) and technical challenges which could not be solved, the project objectives had to be discussed and adapted over and over again, and new solutions had to be found.
Furthermore, the goal of the project was in a constant state of flux, as various technical approaches had to be abandoned soon (e.g. Hydrogen or fuel cells storage, Syngas production), and new tasks were added.

In conclusion, and despite all the difficulties that the partners have faced during the course of the B4SKA project, the main result of the project is that the BioStirling Consortium has technologically been able and successful in building an environmental sound power supply system for a demo SKA that can be realized in a realistic approach.
The demonstrator was successfully deployed and tested coming the RTD to reality ready for commercialization, achieving the overall project objectives and making the BioStirling system a real renewable energy alternative generation system for the SKA. Besides, the accomplished functional model of BioStirling power supply system is scalable and adaptable to many diverse requirements, e.g. purely off-grid, grid connected or hybrid power systems, and therefore can be fitted to different types of SKA.

Potential Impact:
Dissemination has been considered a key factor for this Project because the promotion of the renewables is a must for the EC objective H2020 for a 20% of energy in Europe produced by renewables.
That is the reason why Dissemination contemplates a full work package in Biostirling-4SKA project. The objectives for this activity is:
1. Raising awareness and promoting the project results across industry groups, geographical markets and different stakeholders.
For the promotion of the project results across industry groups different documents were issued such us brochures for showing the solution, datasheet for checking the main features of the system, videos for explaining the workflow, pen-drive for storing and promoting the information given for B4SKA. Other main communications such as the press releases.
Other activity was the presence in fairs such as Solarpaces or Intersolar where the complete B4SKA solution was shown and explained.
The creation of a network of Stirling experts were done during the project especially by identification of plants with this technology.
2. Promoting the results by focusing on the technologies developed the demonstration results and their potential applications across different sectors.
Main activities for this field were the articles in specialized magazines as well as participation in conferences.
Article examples are:
• A Sustainable approach to large ICT Science based infrastructures; the case for Radio Astronomy, IEEE-EnergyCon., Croatia, May 2014, arXiv:1402.2783
• Power Monitoring and Control for Large Scale Projects; SKA, a case study, Proc. SPIE Vol9910, Astronomy. Telescopes& Instrumentation /Observatory Oper.: Strategies, Processes, and Systems VI, Session 6: Site and Facility Operations I, paper 9910-25, AS16,Edinburgh, Scotland, June , doi:10.1117/12.2234496
• Publication in European Energy Innovation Magazine is the communication platform designed with one purpose in mind: to put energy and transport stakeholders in touch with each other.
• 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 12-15 June, 2017, Iguazu Falls, Brazil EXPERIMENTAL STUDY OF A SODIUM TWO PHASE THERMOSYPHON
• Hybrid Stirling Systems: Development of a Solar/Combustion Thermosyphon Receiver
• Possibilities of increasing the overall efficiency of a Solar dish Stirling system
• Optical test of the DS1 prototype concentrating surface
• Other Publications in Different Magazines
3. Encouraging synergies with China, to open possibilities in this market.
China has been identified as one of the market targets. Accordingly workshops with Chinese companies were held both in China and Europe where different approaches were shared in order to the synergies for the initiatives in both countries.
4. Preparing market take-up of the critical results using business-oriented commercialization plans which include dedicated business plan models for the demonstrated technology.
The exploitation plan includes the business plan for showing the market the feasibility of the Biostirling-4SKA solution. The complementation of this activity with the commercial documents such as the brochures, the videos and fliers ensure the proper penetration in the market.
5. Securing the future successful commercial exploitation of the results of the project.
The exploitation plan is part of this commercial exploitation by the anticipation of results for the project.

Another target audience was identified as the general public. Accordingly some activities were thought for the promotion of the B4SKA project as well as renewable energies:
• Biostirling-4SKA project conference near the demo location where the general public could be introduced in the project and visit the demo plant.
• A TV documentary for general public for promoting the renewables as well as specifically the Biostirling-4SKA project.
Compiling actions that were done during the project:
• Project website: A Project Web site was designed and implemented providing project overviews and highlights, up-to-date information on intermediate and final project results, including public reports and synthesis reports drawn from selected confidential material, information on project events such as user group meetings, conferences and workshops.
• Project Identity: A Project Logo was designed as well as communication templates. Besides, an informative brochure (including a presentation of the project, objectives, partners, etc.) was designed, electronically distributed and available at the Project website.
• Promotional literature: leaflets, brochures, reports and press releases will be created and distributed in dissemination events.
• Video shortcuts: a set of video shortcuts were produced and distributed via Internet to show the evolution of the project through the participation of researchers, engineers and general public.
• TV Documentary production: a 50 minutes documentary about the project based in the internet audio-visual shortcuts, to be distributed in different TV channels, especially in educational programs as well as in Research Institutions focused in education.
• Presentation in sectorial events: Attendance to key conferences, congresses, exhibitions and commercial meetings, to present and promote the results of the project in the field of Renewables Energies, as well a Astronomy and Sensors events to show the results of the implementation with the SKA pilot plant.
• Scientific publications: Relevant results will be published in international and national impact scientific and technical journals (e.g. Science, Solar Energy, Energy Policy, Journal of Power Sources, Industrial and Corporate Change), subject to respect the intellectual property rights of each partner.
• Presentation in public scientific events: an open day to visit the installations of the pilot plant.
• Creation of a Network of Experts across policy makers, managers, professionals, industry and stakeholders to support areas working on Renewables Energy and its implementation in smart grids.
• Organization of a BIOSTIRLING event: The project held a scientific-technical conference at the end of the project near the location of the demonstrator in Moura, to promote the results to main Solar Energy stakeholders.

Regarding the exploitation, different activities were done in order to support and boost the solution from the prototype to the market. It was identified potential customers for the hybridized technology and accordingly, the strategy for approaching the market targets.

The identification of the potential customers for the technology and products is the first step of the plan for introducing the knowledge into the market through new or improved products. The knowledge comes from the outcomes that result from the different work packages and the merging with potential customers creates a new market or introduces the new products into the market. The Biostirling-4SKA project is on a high TRL basis and so it needs to assure that the knowledge is transferred to goods and services.

The proof of concept of this project is related to the high cost of these systems. Strategies such as smaller mirrors, lighter structure as well as hybridization approach the objective for being a reality. On the other hand the rest of technologies have been improving their costs and breakdown during the project duration. The storage and hybridization is the key factor of the project and adds the value for the technology competitiveness even at potential higher costs than other renewables.

Regarding the business plan, some topics were identified as key factors:
• A SWOT Analyses
• Defining the Pricing Strategies
• Marketing Channels

The proposed strategy for Biostirling-4SKA changed from the proposed exploitation plan: the demo is finally composed by one unit fully operative. The fact of the scalability is an important point for customers understanding of the potential of the project and demo.

The introduction of the product in the niche market will be through the strong position of the industrial partners as well as through high quality of the demo with a very low slope error.

A complete business plan was issued in order to support the commercialization of the B4SKA solution.
• Simulated sales of the project.
• Simulated structure cost of the project.
• Simulated manpower costs of the project.
• Simulated profits and losses of the project.
• Simulated balance sheet of the project.
• Simulated summary sheet of the project.
• Simulated working capital of the project.
• Simulated investments of the project.

The conclusion is a positive feedback of the project even with one unit working.

The impact of BIOSTIRLING-4SKA project is focused on society, beyond Science, in the broader context of large scientific infrastructures and the opportunity that sustainable energy sources can bring in for energy production in rural areas.
It is well understood that the research and development associated with large scientific infrastructures (e.g. the SKA telescope), as well as their construction and operation, is impacting skills development, employment and economic growth in science, engineering and associated industries, not only in the countries that host the infrastructures but also in all partner countries. For instance, in the case of SKA, the SKA website enumerates as benefits of SKA beyond Science [SKA- FAQ]: the use of sustainable energy sources, the development of energy-efficient processing, new data processing techniques on the cloud, new data communication strategies and technologies to distribute large packets of data quickly around the world, the development of human capacities and capabilities or the enhancement of global and transcultural collaboration in the advancement of knowledge.

Although the work performed in BIOSTIRLING-4SKA has been rooted in the needs and objectives of SKA, the final results have opened the door to considering that it is not mainly large scientific infrastructures who can benefit from these results, but also other situations where the combination of biogas and solar technology can be exploited in order to generate power islands or to contribute to smart grids. In general, infrastructures as hospitals, university campus, technological parks, etc. can benefit of the scalability, power and dispatchability of the biostirling-4ska solution. Small and medium communities, especially in remote and isolated areas, can benefit in addition, due to the energy autonomy of this device.

From all these areas, we especially focus on two aspects that have been underlined and that are strongly related to BIOSTIRLING-4SKA results: the provision of electrical power through the use of sustainable (renewable) energy sources as the solar power and the potential impact on human development, in terms of capacities and capabilities. These aspects are discussed next.

Provision of electrical power through the use of renewable energy sources
Large scientific infrastructures usually have considerable energy needs. In some cases (e.g. SKA) much of that energy demand concentrates in remote areas. Furthermore, there are many rural areas that are not hosting such scientific infrastructures but in any case have low to medium continuous energy demands that may benefit from research and innovation in the area of renewable energy, and particularly in solar energy. Further advantages would be the independence of the general supply, scalability, power and the low ecological impact of the BIOSTIRLING solution.

The use of renewable energy in all these cases provides the opportunity to pioneer remote power generation with low running costs, accelerate technology development in the areas of scalable energy generation and storage, distribution, efficiency and demand reduction, and provide a launch pad for commercialization of innovative green energy technologies.

A solar dish-Stirling prototype such as the one developed in BIOSTIRLING-4SKA may be adequate as an energy source for a large part of the antennas that will be deployed in Africa and Australia during SKA phases 1 and 2, as well as for energy production for remote areas in general, where it is not possible or very difficult to connect to the general supply.

BIOSTIRLING-4SKA acts as an innovation driver in the area of renewable energy in the following aspects:

• A model that may be applied to large areas of land, remote from conventional power supplies but with good solar insolation. A solar dish-Stirling plant can be, from an energy point of view, a very suitable solution for remote and isolated places that have sufficient irradiance from solar power and that need a continuous power range between 10 and 50 KWh. Furthermore, this solution allows working both in an isolated manner or connected to the electric grid. It is also easily scalable in power (adding more units) and with a simpler maintenance than that of a conventional power plant.

• A showcase that may encourage operators of many high technology, mission-critical infrastructures to switch to renewable energy sources. Currently, many such operators are reluctant to make the change because of concerns about technology maturity and power quality. An eventual working system for the SKA, running 24/7 on renewable energy, would show how those concerns could be addressed. A hybrid dish-Stirling engine that works simultaneously using solar power and gas energy is a very important step in order to obtain a solar-energy system that can work 24x7.

More specifically, some of the main technical advantages that our current prototype offers, which contribute towards its commercial (and social) impact, are:
• The current prototype has an electrical power of 10Kw (1-9 kW in gas mode, 2-10 kW in solar mode), what can provide energy supply isolated systems.
• Several important improvements have been made on the structure of the dish, especially in relation to its precision and on the reduction of its weight.
• Regarding optical parameters, the concentrator has been evaluated with an average reflectivity of more than 95,5% and an average optical slope error of 1.7 mrad at maximum.
• Induction engines that are used in kinematic Stirling engines connected to high-voltage electricity grids can provide alternating electric power (single phase or three phase), at 230 V or 400 V. The conversion efficiency is around 94 %.
• Assuming 20% efficiency from gas chemical energy to power, the chemical energy demand is 250 kWh.
• A new energy storage system able to work simultaneously with the hybrid technology, hence able to avoid non-desirable energy peaks.
• An innovative control system that achieves a highly reliable and fully renewable hybrid solution.

The new technological developments of this project will allow a large scale and low cost production of this type of devices, which leads to a significant economical impact in industry, in potential commercial clients and in the rest of involved actors.

There is also an ecological impact that can be considered in this equation, related to the characteristics of the plant and its potential location:
• Reduction in waste during the activity. The activity does not generate any type of waste: solid, liquid or gaseous. Rather this installation prevents a series of emissions to the environment or nuclear waste that would occur if the energy injected by this installation is produced by a thermal or nuclear power station. A fuel/biogas storage and a set of hydrogen batteries are necessary.
• Reduction in waste during construction. During the execution of the works and necessarily at the end of the same, will be the cleaning of all land occupied by the manpower and facilities collecting all kinds of waste from the same as packaging, remnants of pipes, drivers, unused concrete, etc.
• Lack of incidence to the flora and fauna. There is no significant vegetation, trees or fauna in the area where the installation is located, and hence there are no incidences on them.
• Low acoustic impact. The installation activity does not exceed the noise level of LWA = 67 dB per engine.
Human development
An important angle to be considered from the possibility of applying the BIOSTIRLING-4SKA results in the context of large scientific infrastructures (e.g. SKA) is the fact that new skills and knowledge about renewable energies will need to be transferred to the local population for the deployment of the new energy production plants. This will allow creating new jobs and types of businesses with higher levels of skills that are not generally present in the areas where the deployment of antennas will be done.
Indeed, Astronomy has already been recognized as a driver for the human capital and economic development in areas such as Africa, as discussed by the International Astronomical Union in its Strategic Plan 2010-2020 [IAU]. Therefore, this additional angle in terms of renewable energy skills and capacities may provide an additional boost for these economies. Since these technologies will be commercialized in the next 10-20 years, young African (and Australian) people currently working on the project will find themselves in high demand around the world.
As discussed on the SKA website, the South African partners have also been investing in developing skills for MeerKAT and the SKA through their dedicated Human Capacity Development Programme. Around 700 people, ranging from artisans to postgraduate students and postdoctoral fellows, have already received bursaries and grants from the project. This is causing a surge of interest in studying mathematics, engineering and astrophysics at local universities, and attracting top students and academics from around the world to South Africa. Many of these students will use SKA to conduct cutting edge research in South Africa. This illustrates how the results from BIOSTIRLING-4SKA can be also relevant for career development.

On the other hand, the implementation of dish Stirling farms in remote areas would provide energy for the development of new industry and infrastructures, as well as the development of man power in the installation and maintenance of this type of devices and the know-how in renewable energies, engines, production of biogas, etc. ... for the social and labor community.

BIOSTIRLING-4SKA stakeholders and the impact on them
The project conducted an analysis of the range of stakeholders and how they can be impacted by the project results. Figure 16 summarizes graphically this set of stakeholders.
• Society, in general, will benefit from the project results, with a focus on specific segments of the population (by age, interest in ecology, etc.) that are especially sensitive to renewable solar energy. There is an additional indirect impact from the project results derived from the need of fundamental science projects such as SKA as an engine of technological and social development.
• The renewable energy sector, including industry and R&D centres. The hybrid solar dish-Stirling plant has a cost that is sufficiently adequate to start industrial production: its mass production cost is lower than 2 Euro/watt. This has a direct impact on the manufacturing process, distribution and sales of this type of solutions. Therefore SMEs as well as large national and international companies that are currently developing and distributing solutions for the production of renewable energy, especially in the area of Concentrated Solar Power (CSP), may be interested in exploiting further the project results. Furthermore, the knowledge generated in the project around solar energy can benefit R&D groups and centres focused on renewable energy. The project has accelerated new technologies in the field of CSP solutions, which will be the basis for new developments and future research. It has driven innovation in the following areas: hybrid Stirling motor, new alternative storage system based on Hydrogen technology, development of passive cooling system and smart load sequencing to minimise demand side energy requirements, generation of side radio frequency interference shielding, interfacing with grid supplies and land use, distribution and reticulation design for price/reliability trade-offs, and improvement in the conversion efficiency above 24%, through the new design of the parabolic concentrator, innovations in the coating materials to replace the conventional mirrors and increase reflectivity, modelling and optimisation of operation, and definition of a control system to implement all aforementioned improvements.
• Public administration (city councils, regional authorities, foundations), especially on rural or local areas where a solution like ours may be optimal from an energy production and demand point of view. This also includes local development and employment agencies, working on remote developing areas, and environment-protection agents (government agencies, associations, ecologists, etc.), which are generally interested in a clean and renewable energy production system.
• Scientific infrastructures. A modular, autonomous and 100% manageable 24x7 small solar power plant consisting on a hybrid dish-Stirling will allow a distributed generation, with a long lifetime. This constitutes hence a perfect solution for scientific and technological infrastructures (observatories, big laboratories, particle accelerators, etc.) and the optimal way to get a real “clean” science. It constitutes as well a showcase that may encourage operators of many high technologies, mission-critical infrastructures to switch to renewable energy sources.
• Potential commercial customers that require renewable energy where there is a need for scalable, self-sustained energy production, with a power range and demand peak that is small or medium. The project results have provided the option to have a CSP technology that is competitive with respect to photovoltaic technology, as well as much more efficient in the case of places with a good solar irradiance.
• The educational sector, since an installation like a solar dish-Stirling plant is a good opportunity for the educational development at the local level, due to its ecologist message on clean energy.

List of Websites:
Name, title and organisation of the scientific representative of the project's coordinator :
Mr. Luis Saturnino González
Project Manager
Gonvarri MS Corporate, S.L.
Tel: + 34 985 12 82 00
Fax: + 34 985 50 53 61
Project website address: