Skip to main content

Distributed CHP generation from Small Size Concentrated Solar Power

Final Report Summary - DIGESPO (Distributed CHP generation from Small Size Concentrated Solar Power)

Executive Summary:
The DiGeSPo concept is a modular 1-3 kWe, 3-9 kWth micro Combined Heat and Power (m-CHP) system based on innovative Concentrated Solar Power (CSP) and heat engine technology.
This m-CHP CSP should provide electrical power, heating and cooling for single and multiple domestic dwellings and other small commercial, industrial and public buildings. It relies on small scale parabolic trough collectors (PTC) with thin mirrors, moving, tracking components and solar absorbers inside vacuum receivers, a heat transfer fluid, a Stirling heat engine with generator, and heating and/or cooling systems. It should be incorporated into buildings in an architecturally acceptable manner, provided of low visual impact.
The project has covered the whole of the R&D chain: from concept formulation to development, modelling and simulation of each sub-system; production and testing of prototype sub-systems; integration and field testing of full system prototype. Since the beginning of the project, the system has been designed using off-the-shelf components. Contemporarily a research programme on subcomponents was running. The improved components coming from the research results have been integrated in the system along time during the project activities.
In the DiGeSPo system, the solar radiation is concentrated onto a selective absorber inside a vacuum tube collector. The absorber was coated with a specific nano-structured Ceramic Metal layer (Cer.Met.) based on TiO2 – Nb material, stable at intermediate working temperatures up to 350°C (measured absorptance = 0,94; measured emittance = 0,08 @ 350°C).
The Cer.Met. was developed to minimize the radiation losses from the receiver. This allows very high efficiency conversion of the solar radiation into thermal energy, which is transferred to a thermal vector fluid (Therminol 66 by Solutia).
The receiver is a vacuum tube of 50 mm in diameter. The absorber is coated on a stainless steel tube-in- tube, on the external surface with a diameter of 12 mm and special realized design for management of hot oil flow.
The high temperature fluid flows to the hot end of a high energy density Stirling-cycle heat engine, where its energy is converted in a rotary cinematic power, and then into electrical power via the generator. During project execution the Stirling technology has been demonstrated to produce 350 W of electrical power with a cycle efficiency of about 6%. At the cold end of the engine, heat is rejected at a lower temperature (about 50°C), to be used in domestic heating and/or hot water. The system may operate on solar energy alone, or in hybrid mode with fuel such as natural gas or biomass. The latter would increase the cost effectiveness, potential markets and impact of both systems.
The DiGeSPo technology may have additional potential markets where it may be introduced, such as:
- Production of steam and process heat for industries;
- Small solar fields (MW power size), for communities and districts;
- Integration with sorption chillers, for cooling generation;
- Support to cogeneration in rural communities, in hybrid, off-grid systems.
Project Context and Objectives:
The objectives at the onset of DIGESPO were:
# Cer.Met coating: R&D on an innovative absorber inside the vacuum solar receiver. New nano-composite Cer.Met. layer, stable and efficient up to 300-315°C. The efficiency targets are absorbance greater than 0,93 and emissivity smaller than 0,06;
# concentrator optics: modelling and development of the optical components. They comprise a very high efficiency, low profile parabolic trough reflector using new, chemically treated, flexible and low cost thin glass mirrors, with concentration ratio of about 12:1. The efficiency targets are reflectance higher than 0,93 and intercept factor higher than 0,93;
# thermal vector fluid: R&D on a suitable fluid that maximises heat transfer efficiency from the Cermet layer to the Stirling engine; reducing the NTU deficit, Number of Transferred Units (of heat), to a minimum;
# full solar collector: modelling and optimisation of an existing vacuum solar receiver, integrating an absorber with the improved, new high temperature Cer.Met. layer. The overall efficiency target is 75% (thermal power transferred to fluid / direct solar radiation on receiver);
# heat engine: modelling, development and assessment of two novel engine options. One is a high energy density Stirling-cycle engine; the second is a rotary, modified Stirling cycle engine based on scroll compressor technology. The best candidate between the two identified solutions will step forward to realization and integration.
# full system integration: integration of the sub-components into complete system, first using mostly off-the-shelf components, secondly integrating components from the research programme.
# demonstration of the complete system in a high impact and visibility location in the middle of the Mediterranean area (Arrow Pharm in Malta).

# WP1, development of a new absorber material for the vacuum solar receiver. All planned activities have been positively concluded including theoretical modelling, realization of samples and tests (including long term tests), optimization process and selection of best candidates for up scaling;
# WP2: the activity is divided in three main tasks: i. development of the optical system, ii. Research on a new thermal fluid and iii. Development of the receiver. A full optical module has to be developed and realized, together with tracking system and controls. The vacuum solar receiver has been investigated, modified and engineered with off-the-shelf and new improved Cer.Met. absorbers. Thermal fluid research has excluded at the moment the possible application of a heat transfer fluid with nano-particles. The thin glass cold tempered mirrors have been manufactured and tested at the demonstration site since summer 2013.
# WP3: two heat engines concepts have been developed by two project partners: i. a high energy density Stirling engine and ii. a Scroll based heat engine. Both engines were engineered on main components and the Stirling engine was selected for final manufacturing and integration in the DiGeSPo system. A full monitoring and control system is ready and available for variable speed control of the Stirling engine. Manufacturing of the Stirling engine was completed in June 2013. The engine was tested and partly validated up to a rated efficiency of about 6%, and then installed in Malta until the end of the project.
# WP4: the system integration between the full solar collectors, a custom developed hydraulic system, and the new high energy density Stirling engine has been realized, together with the definition and management of all safety high pressure issues of the system;
# WP5: the demonstration site has been identified in the industrial plant of Arrow Pharm, a Maltese company subsidiarity of a US pharmaceutical corporation. The solar collectors, optical modules, steam generation system and monitoring and control system were initially installed and tested. The demonstration site in Malta started to work with off the shelf components and has been progressively implemented with several DiGeSPo results, such as new absorbers, receivers, mirrors, Stirling engine, thermo regulation unit;
# WP6: a wide dissemination activity has been realized, mainly through the project website, a project brochure, a leaflet and other information material, a first newsletter delivered to more than 400 recipients, the participation to international events and Congresses (among others, ISES SWC 2013, SOLAR PACES 2013). A second press release and updated dissemination material has been prepared. The Consortium has paid particular attention to exploitation of the project results. A Technology Transfer Board has been established. The board was participated by industrial and market stakeholders on CSP technologies and supported by some research Institutes. A final dissemination Conference was organized in September 2013 during the Solar Heating and Cooling Conference organized by ESTIF and IEA in Friburg.

DiGeSPo has confirmed the main objectives planned. Particularly:
# Cermet coating: after identification of best candidates and selection of the material for up-scaling the coating and realize full scale receivers, the results have been mostly achieved. The up scaled material has been reported to have absorptance of 0,94 and emissivity of 0,08 at 350°C;
# Concentration optics: flexible and cold tempered mirrors have been realized with thickness of 0,95 mm with an optical efficiency of 0,945. New thinner glasses (0,55 mm) have been manufactured and integrated in the solar panels in substitution of off-the-shelf aluminium based mirrors. Four full modules including 16 parabolic troughs with a total aperture area of about 13 square meters were manufactured;
# Heat engine: a high energy density Stirling engine has been modelled, engineered and finally manufactured. Validation of new selective laser melting (SLM) heat exchangers has been done both in small samples and full-scale prototypes. A second scroll-based engine has been modelled and engineered, but not selected for final improvements and manufacturing. The high energy density Stirling engine has been tested and partly validated. Some improvements are yet necessary and FBK will continue the work. The electrical efficiency from the Stirling engine of 12 – 15 % can be achievable indeed in close time and on the basis of the manufactured prototype.
Potentially interesting market solutions that could be exploited by the project partners are:
- High efficiency and low cost Cermet coating and mirrors: several sub components may be utilized for license agreements and be part of a specific business for project partners;
- Sustainable system based on solar radiation for industrial process heat: the solar technology has been demonstrated in steam production for industrial processes within the pharmaceutical plant. Other applications may be related to the integration in medium temperature industrial process heat (200 – 300 °C) using different thermal fluids (e.g. mineral oil);
- Novel compact solution for small to medium solar fields suitable for small and rural communities: small solar fields can benefit of the modularity and simplicity of DiGeSPo technology, developed with the concept of plug and play system. It is scalable, modular and simple.

Project Results:
A new absorber was part of the research programme of DiGeSPo due to scarcity of available market specific solutions in the application sector of medium temperature solutions. This sector requires enhanced performances and cost effectiveness. At the present, in the market solutions are available in one or the other option, but not on both at the same time.
UU was the responsible for activities, supported by FBK and POLIMI.
The selection of coatings was made considering cost effectiveness in large-scale production. According to the specifications the coating has been developed based on a nano-technology-based Cer.Met. (ceramic – metallic) composite layer.
The following four candidates were chosen for coating preparation: Nb-TiO2, W-SiO2, (W or Zr)-ZrO2 with Mo IR reflector. A short description of the candidates is as follows:
1) Base layer (70 nm) with a volume fraction of 50% Nb and 50 % TiO2
2) Middle layer (35 nm) with a volume fraction of 10 % Nb and 90 % TiO2
3) Antireflection coating of Al2O3 (75 nm)
Solar absorptance: 0.94; thermal emittance: 0.06
1) Base layer (70 nm) with a volume fraction of 45 % W and 55 % SiO2
2) Middle layer (65 nm) with a volume fraction of 20 % W and 80 % SiO2
3) Antireflection coating of SiO2 (75 nm)
Solar absorptance: 0.93; thermal emittance: 0.06
1) Base layer (90 nm) with a volume fraction of 50 % W and 50 % ZrO2
2) Middle layer (55 nm) with a volume fraction of 15 % W and 85 % ZrO2
3) Antireflection coating of SiO2 (95 nm)
Solar absorptance: 0.95; thermal emittance: 0.06
1) Base layer (70 nm) with a volume fraction of 25 % Zr and 50 % ZrO2
2) No middle layer
3) Antireflection coating of SiO2 (90 nm)
Solar absorptance: 0.91; thermal emittance: 0.06
Motivation to the candidate list: the absorber was decided in WP2 to be a stainless steel tube. The consequence of choosing stainless steel (SS) instead of copper or aluminium is that an infrared high reflecting (i.e. low emitting) layer must be deposited under the absorbing coating. Copper and aluminium have high IR reflectance but stainless steel does not. Using bare stainless steel as IR reflector increases the emittance to more than 0.10 and hence 0.06 in thermal emittance would be out of reach. This issue is solved by means of depositing a thin metal film with a lower emittance on the stainless steel tube. In previous STE collectors with SS absorber tubes Mo has been used and proved to be stable at STE operational conditions.
The samples made by the UU group (all but Nb-TiO2 cermets) were prepared in a Balzer UTT400 sputtering unit. The chamber has a base pressure of 10-7 mbar after backing. Argon, nitrogen, or oxygen can be sprayed into the chamber from different nozzles controlled by a mass flow controller. The pressure in the chamber can be adjusted by a manual valve mounted between chamber and pump and is measured by a capacitance diaphragm gauge. The sample holder can be rotated to even the film thickness. The unit can be operated with dual targets both in rf and dc mode.
The Nb-TiO2-cermets were prepared in an on-site constructed sputtering unit at FBK. Substrates of SS absorber tube materials covered with 100 nm Mo were prepared at UU. Optical measurements and determination of optical constants of thin Nb and TiO2 films on glass was performed at UU in the same way as for W and SiO2. The theoretical optimization of the coating using these experimental optical constants was also made in the same way as for W-SiO2. The AR coating on the cermet was SiO2 and was deposited at UU after that FBK had deposited the Nb-TiO2 cermet. The result was a solar absorptance of 0.93 in combination with thermal emittance (350°C) of 0.09 for the small sample. An annealing test of 72 h showed a small initial change in reflectance.
The results for the Nb-TiO2 Cer.Met. showed just as for W-SiO2 that the modelling using optical constants from the thin films gives a different optimal spectral reflectance but in this case a higher absorptance from 0.90 to 0.93. Comparing with the sputtered coatings the values of reflectance are following the modelled reflectance very well (same values in solar absorptance of 0.93 in combination with thermal emittance of 0.09). Considering temperature stability, also the Nb-TiO2 cermet is a promising candidate with just a small initial change in reflectance after heating at 350°C.
It was not possible to reach the original goal of WP1 to combine a solar absorptance of at least 0.93 with a thermal emittance of maximum 0.06. This failure to reach the original goal is a consequence of using stainless steel substrates and introduction of molybdenum as infrared reflector that intrinsically has a higher emittance than copper or aluminium.
Calculations were made (September 2011 at FBK) in order to investigate the consequence on absorber efficiency of altering the optical performance. These results show that an increase of thermal emittance from 0.06 to 0.08 (keeping the solar absorptance constant on 0.93) gives an efficiency-drop from 79.5 % to 78.1 % for a solar direct normal irradiation of 850 W/m2. It was therefore concluded that the results obtained in WP1 on optical performance with solar absorptance of 0.91 to 0.93 and thermal emittance of 0.07 to 0.09 is satisfactory for the project. Finally, the upscaled absorbers were realized by Polyteknik and gave back a transmittance of 0,94 and an emissivity of 0,08 @ 350°C.

WP2 had the objective to realize the full solar PTC collector. Three main tasks are related to: the optical system (T2.1) the thermal fluid (T2.2) and the solar receiver (T2.3) a fourth to the full solar collector (T2.4) including all sub-components integration. NARVA is WP leader, while the activities ran mainly under the responsibility of different Task leaders, ELMA for T2.1 POLIMI for T2.2 and NARVA itself for T2.3. FBK has provided support on all tasks to all partners.
The main subcomponents of the optical system are:
i. Reflection optics: the first version used high reflectance aluminium; the second one used thin cold tempered glass mirrors, installed by the demonstration site on August 2013;
ii. Tracking system: both hardware and control software were developed. The solar algorithm has been completed and modified by measurement of the solar resource, both direct and diffused. The initial version used 2-axis tracking. The second one, with a small loss in annual total energy gain, only azimuth tracking;
iii. Support structure: required to be resistant to extreme weather conditions.
Due to market constraints and material availability, the task has been completed using 0,55 mm thin glass, realized through the planned cold tempered processes. There are indeed cost issues. The full mirror would cost more than a
Photovoltaic collector considering actual amount of ordered components and respect market availability and utilization of the 0,55 mm thin glass. Thicker glasses (0,95 mm, used in big CSP panels) have problems of bending and surface defects for DiGeSPo smaller mirrors. While aluminium modules are cheaper and easier to install, because they are pre-calendered, chemically-treated glass is more expensive and it needs to be glued on a metal substrate, then bent and inserted inside the parabolic structure. Considering mirror technology based on chemical tempered glass, ELMA performed the following tests:
1. Glass with thickness of 0,55 mm, glued on metal sheet 1mm thick, using 3M tape;
2. Glass with thickness of 0,55 mm, glued on metal sheet 2mm thick using 3M tape;
3. Glass with thickness of 0,95 mm, glued on metal sheet 1mm thick using 3M tape;
4. Glass with thickness of 0,95 mm, glued on metal sheet 2mm thick using 3M tape.
Results are as follows:
1) and 2) are very difficult to be glued due to their low thickness, there are aberration issues even with minimum surface pressures. The first prototype had problems in maintaining the shape, and at the very end of the project, all mirrors have been substituted with the older ones, using new guiding sliders realized in aluminium. 3) and 4) are easier to be glued on the substrate due their higher resistance, moreover they are cheaper than the previous ones. 4) has been broken with a lower deformation than the necessary to fit parabolic modules.
A different design and layout of mirrors, as proposed by the end of the project by ELMA and not yet realized, may mitigate and possibly solve the costs and technical issues quite efficiently.
The option of adding high conductivity nano-particles to traditional vector fluids was investigated. After the analysis of the technical literature on nanofluids, a suspension of nanoparticles on Therminol 66 oil was selected. The operation was conducted with the collaboration of Solutia USA which supplied Therminol 66 oil and Meliorum Technology (USA), manufacturer of nanomaterials and nanoparticles.
It was decided to prepare a dispersion of Zinc Oxide nanoparticles in Therminol 66 oil. The choice of Zinc Oxide nanoparticles was justified from the expected compatibility and suspension stability with oil. From Meliorum and from the technical literature there was no direct experience with oil as a solvent. A three-liters suspension was prepared and the concentration of the nanoparticles was 5% vol ± 0.05%. By photon correlation spectroscopy, the size of the diameter of each particle was measured and estimated to be 13.9 nm as an average value with a standard deviation of 5.6 nm. The estimated price of the suspension is 1194,00 $/l.
According to the ASTM D1298-85 Standard the density of the suspension was measured at 40°C and was estimated to be 1.038 g/cm3 . According to the ASTM D445-94 Standard, the kinematic viscosity at 40°C was measured: a value of 43.08 cSt was found. Following this cited standard, the time is measured for a fixed volume of liquid to flow under gravity through the capillary of a calibrated viscometer under a reproducible driving head and at a closely controlled and known temperature. The kinematic viscosity (determined value) is the product of the measured flow time and the calibration constant of the viscometer. The thermal diffusivity of the suspension was measured by Therm Test TPS 2500 S Hot Disk Conductimeter at 20°C and at 30°C. Three measurements for each temperature were carried out. The standard deviation was lower than 1%.
Finally, the nanofluid was analysed by DLS (Dynamic Light Scattering) for evaluating the dimensional distribution of the particles. DLS is used to measure particle and molecule size. This technique measures the diffusion of particles moving under Brownian motion, and converts this to size and a size distribution using the Stokes-Einstein relationship. From the analysis and according to the measured viscosity value, 408 nm particles were found. It means that the nanoparticles tend to form clusters, which is a well-known problem for the nanofluid. Also, measurements at high temperature were difficult because the suspension tends to be unstable.
The research has highlighted some promising properties of a nanofluid for solar applications, but several limiting factors as above illustrated, related to costs and technical issues such as clustering of nanoparticles. At the present, these are unsolved problems.
The development of a new design of vacuum receiver is motivated by the miniaturization down to the size of a low temperature solar tube of a technology usually managing fluids and thermal power at bigger scales. Different steps have led to the proposed final technology.
- Design of the receiver: in the beginning of the project a receiver with a sheet absorber was proposed. But due to relative big surface of the sheet absorber the efficiency drops strongly with the temperatures required by DiGeSPo. A direct coating on the tube was necessary. It was decided to design the receiver with only one glass metal seal, with both the inlet and the outlet at one end of the receiver tube. This solution can prevent cracks from the dilatation of the tube at high temperature. The absorber is a coated pipe in an evacuated space, protected by an envelope glass tube. Because there is only one fixing of the absorption pipe, the extension between absorber pipe and cover glass tube has not to be compensated. To efficiently extract energy from the vacuum receiver, a second tube is inserted in the absorber pipe, so that the flow of the working fluid can go in and out like in a coaxial or u-shape design. The end of the absorber pipe is vacuum tight closed.
- Glass envelope of the vacuum receiver: NARVA operate a factory for the production of the
glass tubes for the lamps sector. The glass has a really high transmittance, equal to 0,96 averaged on
the solar spectrum. A special soda-lime based glass already realized in NARVA is applied as envelope of the tube. Both technical (e.g. transmittance) and economic issues (e.g. the cost of the glass) were at the basis of the selection. Several problems were therefore solved:
a) Development of a robust glass to metal seal for higher temperatures;
b) Special coating to prevent oxidization of the glass by moisture and other weather/environmental agents;
c) Special production process for glass, to improve the transmission to the maximum achievable.
To reach objective of items b) and c) the company has developed a coating process for Silicon dioxide nano particles using a sol gel process. NARVA used water as solvent, to avoid any environment impact by an organic solvent and any danger of explosion in the factory. NARVA coats the glass on both sides, internal and external. The applied coating has demonstrated that no influence on trasmissivity was caused by condensed water. The coating brought an additional advantage. Transmissivity improved its value of about 4%.
After coating process of the envelope tube the silica dioxide layer is soft and easily scratchable. To reach the necessary hardness of the surface, a sintering process is necessary. The sintering process is done through a thermal process, contemporarily to the evacuation.
- Glass to metal seal: weakness is one of the main problems for most of glass to metal seals, particularly against lateral forces. The reason is that the diameter of the connection pipes of glass and metal is small. In this case lateral forces, as wind, create a big bending stress and the glass very often break. NARVA tried to solve the problem by a metal lid with the same diameter of the envelope tube.
To realize a strong connection between the glass and the metal seal, the edges of the envelope glass tube are heated up. Then the heated edges are folded around the edges of the lid using special process tools. The result is a very strong vacuum tight glass to metal seal. NARVA has protected this invention in an international patent. The velocity of heat transfer on contact between glass and metal must be properly controlled to prevent fractures.
The soda lime glass will be destroyed in case the speed is too high. During a test, the receiver was heated up using a 1 m parabolic trough in stagnation conditions. In 5 min the absorber pipe reached 500°C. The temperature close to the glass - metal seal increased with a speed of 0,3 K/s preventing any danger due to radiation intensity.
- The absorber pipe: at the beginning, the absorber pipe was made by copper. The pipe was coated with a TiNOX coating. Mechanical stability was low, so the material for absorber pipe was changed to stainless steel. To get a low emissivity, it was necessary to polish the stainless steel pipes before the application of the Cer.Met. coating.
- Means to get uniform temperatures on the surface of the absorber pipe: since stainless steel has a low thermal conductivity, the surface of the absorber pipe had no uniform temperatures over the whole length and diameter. On many points the return flow pipe touched the internal wall of the absorber pipe. This caused the stop of the oil stream within the absorbing tube and heat was not removed properly. The effect was an extremely high temperature on the inner tube wall, damaging the selective coating and altering the properties of the thermal oil. The problem was solved inserting a wire winded around the internal pipe. A pitch of 150 mm was selected after tests.
To optimize the design at the end of the tube, at that point a pitch of 50 mm was selected. The selection of the pitch is a compromise between high Reynolds-Figure, efficient heat transfer and the minimal pressure drop in the pipe. For the heat transfer from the wall of the absorber pipe in the working fluid a MathCad calculation program was developed. Basic figures are as follows:
- Mass flow: 180 l/h Thermal oil
- Reynolds figure: 6766
- Working temperature: 300°C
- Temperature difference between working fluid – wall: 22.5 K
- Heat transfer: 425 W
- Thermal resistance wall – working fluid: 0.053 K/W
The temperature of the absorber pipe was estimated 322,5 °C ( 300°C+22,5 K).
- Reactive sputtering of the SiO2 AR layer. UU investigated properties of anti-reflection layer deposited from a silicon target in oxygen instead of SiO2. The advantage with reactive sputtering is an increased deposition rate. It was demonstrated that quality and properties were equivalent between the two processes.

- The up-scaling of coating has been followed by FBK, in collaboration with UU and NARVA. When doing a PVD process up-scaling there are a lot of factors that must be controlled. For a CSP stack the layer thickness and optical properties of the individual layers, the substrate temperature and the deposition pressure have to be carefully controlled. After the thickness of each layer was successfully targeted and deposited, the overall optical properties were measured with an FT-IR and compared to the expected values. The properties of the deposited Cermet are: absorptance = 0,94 and emittance = 0,08@ 350°C.
NARVA manufactured the full vacuum receivers, and finally installed them in Malta. Here below follows a description of improvements performed on the receiver:
- Quality of vacuum: after tests in ELMA, possible loss of vacuum from the glass tube may have occurred. NARVA verified if the problem could have occurred within the production line. Iit has been found that the metal getter at the bottom of the receiver had a colour change and the areas of the getter were reduced.
To solve that problem the following action was proposed and implemented. It is well known that during the exhausting processing the materials should reach high temperatures to allow desorption of gasses and water bounded on the inner glass surfaces. Without the heating process, it is not possible to reach a good vacuum level. If the heating of the receiver is not on the right level with regard to time and temperature, the gasses in the receiver will harm the selective coating of the absorption pipe and reduce the quality of the glass tube respect optimal thermal behaviour. Process temperatures during the exhausting had been analysed and measured. To leverage the temperature of the absorber pipes to a higher value, tests with a special high temperature getter were carried out. SAES’ St 787 was used. Such getters are used in high power receivers for power stations. To activate the special getter to its maximal efficiency a temperature of 500 °C and an activating time of 10 min are necessary. During tests, a temperature of 350°C and a time of 15 min have been used for activation values, as process parameters of DiGeSPo system.
- T Connection element: it is necessary to connect the influx (“cold oil”) and reflux (“hot oil”) to the manifolds. The connection element must be compliant to work at 350°C and must be oil tight. The element was developed in several steps and stages. The first option was the connection elements welded directly to the receiver. Secondly, to allow maintenance and substitution of solar tubes, NARVA developed a new solution. The new connection elements used ball screwing, which is simple to handle and oil tight. The inner pipe was screwed in by a standard thread. This was changed now to fine screw thread. To prevent corrosions a special steel (No 1.4571) was used.
- New distance holder (absorber pipe- cover glass tube): the cover glass tube is not completely straight. That´s why during the development of the receiver bending of the absorber pipe by its own weight was calculated. Three distance holders were installed, improving the quality of alignment considerably.
The full solar collector has been realized by ELMA with the support of FBK. Tests were performed to select proper hydraulic connections and fittings and final components were identified to guarantee the sealing of the connections at the working temperature and pressure of the thermal oil. NARVA has supported the final supply of components as indicated by FBK and ELMA.

The activity on micro cogenerating unit had the objective to develop a heat engine based on an efficient thermodynamic cycle at pressure and temperature conditions properly selected and at rated power for the cycle itself. The heat engine should be provided of robustness, reliability, flexibility and cost effectiveness.
The work ran on two different proposed technologies, the first is working on a scroll-based m-CHP heat engine (SES), the latter is working on a high energy density Stirling engine (FBK).
Following first measures on initial prototypal realizations, a decision was made to proceed only with the High Energy Density Stirling engine. Below some main topics of engine development:

- Characterization of Selective Laser Melting (SLM) AISI 316 steel
FBK and POLIMI designed samples in order to investigate the microstructural and mechanical properties of SLM production process. The objective of the investigation was the characterization of SLM manufactured AISI 316 steel, which was the candidate for the manufacturing of the heater and cooler of the project. Two samples were designed: one dedicated to the static tensile tests and the other for fatigue tests.
The characterization was carried out by the following tests:
- analysis of the presence of microstructural defects (pores) by Light Optical Microscope (LOM) and Scanning Electron Microscope (SEM);
- microstructural analysis by LOM;
- porosity measurements by LOM;
- surface roughness measurement by Taylor Hobson surface profilometer;
- hardness test by Wolpert Hardness Test Machine;
- tensile strength at room temperature and at 350°C according to UNI EN ISO 6892:09;
- rotating bending fatigue test at ambient temperature by the Stair Case Method with 10 millions run-out cycles (UNI 369 – ISO 12017);
- analysis of the fracture surface by SEM.
Finally, on some samples, a thermo-mechanical treatment called Hot Isostatic Pressing (HIP) was performed. HIP was carried out at 1250°C and with 140 MPa pressure, using Argon as atmosphere.
By LOM, the residual porosity was measured and compared with the initial one.
Summary of observed results:
- Tensile tests were performed on SLM specimens so obtaining the mechanical strengths at ambient temperature and at 350°C;
- Rotating bending fatigue tests have been performed on as-sintered round specimens;
- The obtained fatigue limit is strongly influenced by residual porosity which is mainly external and open/interconnected (observed by LOM and SEM);
- This porosity was not observed in the tensile specimens (prismatic) characterized by closed porosity;
- HIP tests were performed on fatigue and tensile specimens;
- HIP was successful in densifying the tensile specimen (closed porosity), NOT successful in densifying the fatigue specimen (open and interconnected porosity).
In summary, the results on mechanical properties of components realized by SLM process was good and sometime above expectations (yield stress). Some problem of porosity has been mostly solved through HIP process. The surface roughness in case of heat exchangers is an added value due to a net increase of surface wettability.

A] High energy density FBK Stirling engine
The design of the specific Stirling engine derived from a cross configuration realized with four pistons in a double effect configuration, where pistons are respectively positioned at an angle of 90° degrees one by the other. The thermodynamic design of the engine defined some main characteristics and realization parameters:
• Value of the expansion and compression volumes;
• Connection between the different working volumes;
• Rotation speed at 250 rpm;
• Mean pressure of charge gas (Nitrogen) in the thermodynamic cycle;
• Expansion max temperature set to 300°C.
The Stirling engine main sub-components are:
- Assembly of cylinders and pistons
- Heat exchangers / Regenerator
- Crankshaft
- Engine structure and basement
- Flywheel
- Guides and seals
- Auxiliaries, measure and control systems
- Electrical generator
The development and integration of all these components have been performed along the whole project. Manufacturing of the Stirling engine started at the end of 2012 and completed at the end of May 2013. The validation started in mid-June 2013 and the engine was shipped to Malta by the end of September 2013.
The manufacturing has been performed within LA.ME. tool machinery in Motta di Livenza (Tv). FBK supervised the tool machinery during the manufacturing. Some parts of the engine were manufactured by other suppliers:
- Heat exchangers using Selective Laser Melting (SLM) process, by Texer Desing (Treviso);
- Seals and rings by Elring Klinger (Germany)
- Electrical Generator by MOOG Industries (Genova, Italy)
Some pressure tests on the engine for heat exchangers and cylinders were performed partly in LA.ME. and partly in MAXIMATOR (300 Bars pressure).
Assembly of cylinders and pistons
After the design of cylinder and piston, multi-physic modelling was performed in order to compensate thermal effects (temperature differences and stress on the components) and optimize fluid dynamics during engine operation. The cylinder and piston assembly includes a structure supporting the moving parts and connecting the assembly to the main crankcase. It is designed to properly connect to the crankshaft through a crosshead and a connecting rod. The piston rod is in between the piston head and the crosshead at the bottom. Guides are located on the crosshead and on the piston rod, while seals are located on the pistons, dividing the expansion volume from the compression volume. The two volumes, due to the double effect configuration, are related to different thermodynamic spaces. The kinematic configuration has a design of a 90°C shift from one cylinder to the next one. To properly dimension thickness and other aspects of the engine, specific structural mechanic analyses were performed. An internal coating on the cylinder has been applied to reduce the thermal conductivity and realize a surface hardness coefficient according to values required by the seals manufacturer.
Heat exchangers / regenerator
The heat exchangers are one of the most strategic elements of the engine. Energy enters by this way to circulate throughout the cycle. The heat exchangers have been designed and modelled to realize a high heat transfer coefficient maintaining compactness and robustness. They have been manufactured using SLM technology and process. This allows a high degree of freedom in shape, design, geometry.
A full assembly of the exchanger was finally realized through welding of machined components. The configuration of the assembly changed from a first version (using connecting tubes and fittings) to a second version (full in – line configuration). The regenerator of the engine has been installed in an appropriate volume in between the hot and cold heat exchangers and realized in a thin mesh of stainless steel foils.
The crankshaft has the function to transmit the actuation received by the four pistons to the flywheel and contemporarily to the electrical generator. Any deviation from a perfect alignment is converted into friction and energy losses. It was very important to define minimum tolerances and maximum requisites of precision.
A roller bearing between the rod and the crankshaft was installed, as the optimal solution for contemporary condition of high forces coming from the four pistons to the crankshaft and unlubricated seals and guides. In parallel the potential application of bushings was considered, but due to high stresses and low reliability not implemented in final design.
Geometric tolerances were the main critical aspect on the final realization and assembly of the crankshaft. The crankshaft and the the connecting rod were checked with a comparator to verify the coaxial alignment. Some optimization steps occurred until the maximum threshold on tolerance was confirmed. DEA machine has been utilized to properly measure the shaft alignment and evaluate possible errors.
Engine structure and basement
A block of aluminium was realized to support the four pistons group and the crankshaft. This part has been machined using a milling machine. This element has been realized with some windows/openings to allow the operator to check the shaft and add some lubricants to the bearings.
The rotating engine has a variable torque. It is lower than in internal combustion engines. Relevant friction, mechanical stresses and unbalanced motion along the rotation may occur. For this reason a flywheel was included, to absorb energy when the torque is high and give it back when the torque decreases and becomes negative. Considering the already mentioned double engine effect, and the specific configuration of the four cylinders 90°, the effective torque on the FBK’s Stirling engine is always positive on the crankshaft. This aspect has allowed a considerably reduction of the overall dimension and weight of the flywheel, and so the objective of compactness of the engine was respected.
Guides and seals
In the designed Stirling engine, a list of guides and seals was defined, both on moving and static elements. The description will concentrate on the dynamic guides and seals, due to high pressure that has to be maintained within the thermodynamic cycle.
There are several dynamic seals, as from the below list:
- 2 seals with bi-directional effect on the piston;
- 2 seals with mono-directional effect on the piston;
- 2 guides on the piston;
- 1 lip seal with bi-directional effect on the piston rod;
- 2 guides on the crosshead.
The 6 segments on the piston have to separate the expansion volume from the compression volume of two different thermodynamic cycles, and the guides have to maintain a balanced and centralized actuation reducing all possible frictions. The same applies for the two guides on the crosshead. The seal on the piston rod is the most critical element because it has to maintain a pressure difference up to 200 Bars. Any gas loss is a real leakage of the cycle, so it must be compensated by a pressurized cylinder.
Auxiliaries of the engine are all the external parts that realize both the hydraulic circuit (all oil and water connections, all gas connection and fittings) and the electric and control circuit (sensors and actuators).
A list follows including main components:
# Gas circuit:
- Balancing valves for the different circuits: there are some volumes in between the Nitrogen cylinder and the internal part of the engine and some back pressurized ducts (e.g. in between the expansion and compression volumes) to properly adapt pressure conditions and create the highest pressure gradient in between different components together with the smallest pressure difference. This has to reduce to a minimum cycle losses and gas losses;
- Charge and discharge valves: some valves have been installed to automatically and remotely maintain internal pressure conditions and charge in the working volumes of the Stirling engine;
- Connection to the cylinder and pressure reducers.
# Oil circuit:
- Tubes and fittings for 300°C and 4 bars conditions;
- Insulating material;
- Interfaces for temperature sensors;
- Security options as break seals.
# Water circuit:
- Tubes and fittings;
- water flow retrofitted with target cooler temperature by water flow rate control;
- Interfaces for temperature and flow sensors.
# Sensors:
- Temperature sensors (at all levels of engine cycles, gas, oil and water circuits);
- Pressure sensors, in the gas circuit and inside the engine for each thermodynamic cycle;
- Flow sensors, in the oil and water circuits;
# Actuators:
- Valves in the gas, oil and water circuits;
- Balancing valves in the 4 thermodynamic cycles;
- Electric controls on the generator.
The engine has been finally assembled and checked within the tool machinery LA.ME. Quality checks were performed on components’ tolerances, on cycles tightness, on cylinders and exchangers resistance to maximum pressurization (up to 300 Bars), to rotation effect of the engine. Finally the engine was shipped to FBK in Trento to be integrated and validated within the FBK test bench.
# High pressure testing
The engine was designed for 200 Bars of max internal pressure. Even if not required by actual standards, FBK has performed pressure test in controlled ambient. Tests were performed both using water and nitrogen at 300 bars (1.5 times the maximum pressure). Specifically, heat exchangers were tested in Nitrogen to a pressure of 300 bars.

B] SES Scroll Engine
The SES Scroll Engine is at the same time an interesting and challenging technology, and a really difficult thermodynamic problem to be solved. In the first part of the project the research was concentrated on:
- Developing the thermodynamic modelling; modelling showed scroll engine cycle as Brayton, with lower efficiency than the Stirling Ericsson cycle;
- Engineering of the scrolls: Sanden dual AC compressor for Honda accord was identified as suitable basis for project.
-Engineering of SLM heat exchangers: the initial heat exchanger failed at minimum wall thickness of 0.3 mm. They were rebuilt at 0.5 mm. They held pressure, but much too thick for financial viability. The search for reasons behind poor performance - identified alloy constituents as priority. Initial trials of heat exchanger ducts inside SLM walls to represent walls of scrolls were performed. Work started on wetted Cu alloys to improve thin wall porosity and control surface finish.
- Engineering of Scrolls & test rig: design of proof of concept system was completed. The initial models showed a net power with temp. >200°C. At 300-350°C and 11 kWt input, 1.4 kWe into the compressor, 2.0 kWe expander output with a net power of 600 W. Power input and output were separated to ensure that component efficiencies and losses could be analysed and understood, as no data are available on scroll performance. Commercial Exhaust Gas Recirculation (EGR) heat exchangers were purchased to operate as heater and cooler. Initial test bench was designed for direct electrically heating. But volume constraints meant a shift to electrically heated Therminol oil in large tank as heating medium. Later complexity, costs and potential safety issues shifted the design back to hot air supply using 12 kWe heater.
The output load is managed via 12V DC automotive alternator. When operating below self-exiting speed, the scroll engine uses separate voltage for excitation.
# The Input temperature controller sensors could not accept high DC voltage of motor driver, so lack of control of working gas temperature derived.
# Compressor motor drive unit limited to 110V instead of specified 140V, limiting maximum power to drive motor.
# Compressor housing temperature much higher than expected because of heat soak from expander. So changed to completely separate compressor for initial trials.
- SLM Heater, Recuperator and Intercooler/interheater Compact Heat Exchanger (CHX) requirements are:
Thin walls of ~0.1 mm, zero connected and very low unconnected porosity. Initially, minimum 0.5 mm thick walls needed for zero leakage was not competitive. The heat exchangers can anyway tolerate small amounts of porosity, even if connected.
Control of surface finish. Surface finish typically 7-12 RA – much rougher than plate. This can increase heat transfer in laminar flow, but also increases pressure drop. Most SLM parts have thick walls and/or accessible surfaces and post-process control of surface finish is possible.
Progress so far: modification of alloy constituents:
• Two alloys – CuSn and CuNi – modified by adding wetting agent.
• Test pieces built with reducing wall thickness.
• Assessed with Scanning Electron and Laser Confocal Microscopy.
• Test tubes with reducing wall thickness tested to 4 bar.
Preliminary conclusions.
• Addition of wetting agents improves porosity but, so far, not roughness.
• Machine and setup may affect minimum wall thickness as much as alloy constituents.
• If scan pattern builds contours and fills in, danger of incomplete build at <0.3 mm.

FBK has designed and realized a system capable to test under experimental controlled conditions the main components for the final prototype; specifically the solar collectors, realized by NARVA and ELMA, and the Stirling engine unit. The working fluid selected for the DiGeSPo Project is Therminol 66, which has a maximum bulk and film temperature respectively of 345 °C and 375 °C. The maximum temperature for the oil inside the circuit will be approximately 300 °C; all the materials and components have been chosen to meet those requirement.
The test bench can be used for different validation and characterization purposes, by changing its configuration from:
1) Electrical Generation – Final Configuration
2) Solar collector efficiency testing (from single parabola to the whole module)
3) Stirling engine testing and characterization
Gate valves installed on the hydraulic circuit allow manually switching from one configuration to the other. FBK was involved in the realization of the integration layout, while ELMA was involved in the development of the control system of the engine and in the support to tests and validation.
The test bench is equipped with sensors to measure performance parameters. The final prototype integrated some sensors with the control system, to provide feedback and check security status. All the sensors have been selected to meet the requirements defined by the standard UNE EN 12975-22006, the guideline for efficiency testing and certification of solar collectors.
The list of sensors installed on the test bench is:
- 2 temperature measures, Pt 100, at the inlet/outlet of the solar collector;
- 2 temperature measures, Pt100, at inlet/outlet of the thermoregulation unit;
- Absolute Pressure after the recirculation pump;
- Differential pressure for the whole hydraulic system;
- Ambient Temperature;
- Wind Speed;
- 1 Pyranometer for direct radiation;
- 1 Pyranometer with shadow ring for diffuse radiation;
- 4 temperature measures, Pt 100, for outlet module temperature;
- Pluviometer;
- Coriolis mass flow meter.
The thermoregulation unit, also referred to as “Centralina”, is the system designed to decouple the testing for the solar collector and the engine. It can be set a fixed temperature in the system, thanks to a PID controller, which regulates the thermal power in the system. The main components are a water heat exchanger, which is used to extract power during solar collector’s efficiency testing, and an electrical heater, which is used for Stirling engine performance characterization and preheating purpose. The thermoregulation loop is driven by a magnetic drive pump, while the flow delivered to the system is set by a secondary pump, the rotation velocity of which is controlled with an inverter. This configuration allows proper control of the response of the system and avoids the risk of oil degradation.
To avoid the contact of hot oil with atmospheric air, which can lead to oxidation of the fluid starting
at 70 °C, an open expansion tank of about 50 litres is located upon the unit . The connecting small pipe acts as a thermal insulator. The hydraulic system is open to atmosphere and it is not pressurized. Temperature in the expansion tank is further controlled with a secondary water heat exchanger, which is automatically activated if a temperature sensor is triggered. Total power is 14 kW for electrical heater and 25 kW for the cooler heat exchanger.
The test bench can be used to measure the thermal efficiency of the solar collectors. In this configuration the engine is put offline and thermal power is extracted through the heat exchanger located in the termoregulation unit. The unit provides temperature control in order to run tests in thermostatic conditions (e.g. 150 °C, 200 °C, 250 °C, 300 °C).
The engine was delivered to FBK and integrated in the test bench in a similar layout of the demonstration plant in Malta. The test methodology of the Stirling engine has followed a common pattern of tests along the whole Improvement steps, to have a similar and comparable term of reference.
At each modification of the layout, similar tests have followed the below scheme:
- Test of the Stirling engine at ambient temperature, maintaining a hot temperature at about 50°C and a cold temperature at about 10°C. During the tests, the charge pressure is increased by 5 Bars each step. This test provides information on the fluid dynamic of the engine and the specific energy required without any supply to the thermodynamic cycle;
- Test of the Stirling engine at increasing temperature, step by step from ambient temperature to 300°C. The specific test gives back information on the behaviour of the engine with regard to the thermal energy introduced in the thermodynamic cycle and the temperature difference between the hot and cold heat exchangers.
The tests were performed at some fixed conditions such as:
- Speed of the engine, maintained at 250 RPM;
- Mass flow of the water;
- Mass flow of the oil;
- Typology of charge gas utilized in the Stirling engine (generally, nitrogen. Some comparison tests have been performed with the use of helium too, to validate the specific design of the engine addressed to nitrogen).
Engine testing in FBK included the following data and results achieved:
- Mechanical losses, cold test (no thermal cycle activation), and no pressure charge and no working cycle: 200-300 W. This is a good result, since it means that the mechanical part of the engine works properly, when no charge pressure is applied;
- The thermodynamic cycle achieved the expected theoretical performances in terms of power generation from cold to hot operation: 2 kW @ 80 bar , 3.5 kW @ 135 bar;
- Each of the high energy density heat exchangers achieved 3,5 kW thermal power, temperature drop from source to gas less than 25°C (delta temperature measured), total volume less than 1 liter. The SLM heat exchanger concept proved as efficient and robust;
- Still, mechanical losses prevent having net positive power, which is achieved only with a high charging pressure: 300 W @ 135 bar. In Malta improved performances of 350 W @ 110 Bars were achieved.

The original plan for testing was to install initially at the demonstration site the solar collectors and an off the shelf Stirling engine capable of operating with temperatures of 300 degrees C (hot supply) and 20 degrees C (cold sink). Due to problems with the COOL ENERGY Stirling engine, this plan was modified to include a further preliminary stage of generating steam for feeding into the ArrowPharm steam header as a first step. This had the benefit of allowing the project team to start testing the solar collector modules and oil performance.
In order to generate steam a steam generator (hot oil to water/steam heat exchanger with related circulation pumps and control systems) was purchased and tested by FBK and ELMA in Italy prior to shipment to Malta.
Installation, phase 1
First three solar modules: In November 2012 the first three modules where shipped to Malta for installation at ArrowPharm and in preparation for the final installation. After the installation the modules were "mothballed" by covering the evacuated tubes with aluminium foil and spraying a protective oil layer on all steel surfaces.
In order to perform the lifting of the modules on the roof of ARROWPHARM it was necessary to prepare a method statement for clarity of actions to be taken as well as for the insurance company and ARROWPHARM.
A further measure that was taken to protect site integrity was to install large trays below the modules whose function is to collect any leaking oil coming out from the modules in a worst case scenario.
These are all interconnected through pipe work to one outlet. The outlet is connected to a spring loaded three way valve whose normal position results in any fluid within the trays being fed into a waste collection tank. In the case that there is rainfall the position of the valve switches to the waste water outlet position automatically.
Installation, phase 2
In July 2012 the remaining equipment (steam generator and final solar modules) were shipped to Malta for final installation and included a number of people from the different partners of the project (FBK, NARVA and PIM).
Final modules: The modules were lifted into place and aligned to face perfect south after levelling them out. With perfect alignment the shadows of the tubes should be perfectly centred on the reflecting mirrors. To do this perfectly sized and marked paper sheets were prepared and taped to the mirrors and the modules set to tracking. The modules were aligned one by one by matching the tube shadows to the determined central positions on the paper shapes both at the bottom of each parabolic mirror as well as at the top to ensure good positioning.
Once the modules were aligned it was possible to focus on changing the 16 vacuum tubes to the latest versions from NARVA. The internal receivers also needed to be changed to the versions with a spiral on the outside to ensure that they remained as concentric as possible within the outer steel tube.
To maximise the possibility of having the central heat collection tube at the centre of the vacuum tube it was necessary to always have the tubes aligned with the supporting steel clips being orthogonal to the passage of the sun. The few centimetres of tube also needed to be insulated with glass fibre insulation mat and tied around it with glass fibre strands.
After the tubes were installed on the modules it was necessary to also insulate the area around the tube holding 3 point valve on the manifold well. This was done using rock wool and attached using aluminium duct tape and aluminium covers to fasten done the insulation.
Several tests on the modules were performed. As a synthetic efficiency value, latest data on the last version of the receivers and on one single collector composed by 4 parabolic troughs, in a solar radiation close to 800 W/m2, gave back the below values.
Hot temperature [°C] Average efficiency [%] Peak efficiency [%]
215 33 42
261 38 45
From such data, it is clear that the system suffers from input losses and in such direction should be optimized first, cause the temperature, even considering lower temperature values, is not affecting in a relevant way the overall collector efficiency.
Installation, Stirling engine and full final tests
Finally, in September 2013, the Stirling engine was installed in the demonstration site in Malta. Auxiliaries were connected, such as Nitrogen pressurized in cylinders, hot oil connections passing through the solar plant and warm water circuit connected to a water boiler and then to a pre-heating system installed in Arrow Pharma.
Several tests were performed, where the Stirling engine demonstrated power generation up to 350 W, equivalent to a cycle efficiency of 6%.

WP1. Cer.Met. coating R&D to enhance absorption of solar radiation
1.1 Emittance of the material: 0,06 @ 350°C 0,08@350°C
1.2 Absorptance of the material > 0,93 0,94
1.3 Long term stability Up to 350°C confirmed by lab tests
WP2. Development of Solar Collector
2.1 Optical reflectance > 0,93 0,945 (measured)
2.2 Optical intercept factor > 0,93 0,95 % of aluminium mirror surface on target
2.3 Thermal fluid application custom fluid research only at lab scale level
2.4 Thermal fluid working T up to 400°C 320 °C
2.5 Evacuates solar tube, high T up to 350°C confirmed
2.6 Full overall efficiency: up to 70% @300°C up to 40%@300°C peak
WP3. Development of CHP generator and definition of the thermodynamic cycle
3.1 Identification of Stirling’s cycle limit of 2 solutions 1 realized by FBK
3.2 Power conversion efficiency up to 28% 6 %
WP4. System Integration
4.1 Electric efficiency up to 15 – 20% 3 %
4.2 Thermal efficiency up to 45 – 50% 35 %

Potential Impact:
The transnational cooperation prompted by DIGESPO has managed to mobilise and promote the sharing of existing capabilities among the partners, in terms of experts, institutions and related resources such as laboratories.
The project has produced considerable impact on the related industry and research disciplines, in events where members of the DIGESPO consortium participated and presented the project objectives and results. Feedback from the public can be distinguished in the following categories:
# Research: people asking for information on the project in order to complete research papers, dissertations, for use in related research prototypes or to be better informed about the project innovations and objectives.
# End-users: people asking for information as potential end-users willing to try out the project results
# Working/collaborations: people asking for job opportunities, or declaring interest for collaborating in new initiatives
# Commercialisation: established big players enquiring about collaboration in order to develop or market the final DIGESPO products.
It is also important to note that impacts of research, capacity building and innovation projects like DIGESPO are also long-term in nature and the contribution to socio-economic development can not only unfold with immediate direct results but also via indirect ones that may become visible only years after research activities have ended. Besides the obvious impact in terms of new technologies/products produced, DIGESPO has also helped in ensuring further knowledge sharing and capacity building projects between typically unconnected research partners established in North Europe and those in the South - thus contributing towards the development of skills and institutional capabilities of partners. Similarly some effort has been undertaken to generate and influence policy-making, while promoting policy dialogue and learning in the area of CSP and energy in general.
The list below illustrates the major innovative developments achieved:
-New ceramic metal coatings for better thermal absorption of concentrated thermal energy.
-Use of flexible glass as a reflecting surface that can be easily snapped in place reducing costs and increasing concentration.
-Modified Stirling engine and compact heat exchanger to improve thermal energy conversion efficiency.
-Improved control system for better performance and solar tracking.

# FBK patent related to modified Stirling cycle (“injection Stirling”): "Apparatus particularly for obtaining electricity from solar energy", Publication info WO2008146109, 2008-12-04.
# FBK patent related to Evacuated Solar Tubes: "Solar collector for heating a thermo vector fluid", Publication info WO2008090461, 2008-07-31;
# "Solar collector for heating a thermo vector fluid", Publication info WO2008090454, 2008-07-31.
# SES - Integration of heat exchangers with heat engine components. Filed in Nov 2011 - UK; Global
# FBK / Uppsala- TiO2Nb as spectrally selective absorbing coating for low and intermediate temperature applications. Filed in May 2012 – Italy.
There are several options to commercialize the DIGESPO platform, varying from selling it as a standalone product to incorporating it into existing products. These steps are envisaged to bring the developed technologies to market as an integrated system after the basic and applied research conducted for DIGESPO under the FP7 funding:
# Solar array frame weight reduction using carbon hollow sections, and sleeker design.
# Easier manifold and insulation access.
# Stirling engine cycle efficiency improvements and weight reduction.
# Adhesive improvements in flexible solar mirrors
# Miniaturisation of control systems
# CE marking
There are several options to commercialize the DIGESPO platform. All the options the consortium considers viable are described below. Potential commercialisation pathways for DIGESPO include:
Pathway Advantages
1. Outright sale Simple, immediate income
2. Consulting Personal to the expert
3. Licensing Exclusive or not, long term income, simple
4. Joint Venture company Agreed equity stakes, sharing in future development
5. Independent Spin-out company Agreed equity stakes, best returns including from future R&D
At the moment it is deemed that the commercialisation pathways best suited for the DIGESPO results are primarily the Spin-off route and the licence route, with the opportunity of outright IP purchase for the single components. Some of the technologies introduced at micro-scale (buildings, small appliances, SMEs) will include details which possibly need a standardisation approval and that are acceptable with national regulatory frameworks. The DiGeSPo project has assessed particularly the aspects related to the regulatory frameworks and standards, and will customise its final prototype to make the necessary changes where applicable.
These may include:
# Safety related standards:
# Maintenance procedure standardisation: instructions related to the maintenance procedure for the system will include:
i. definition of lifetime of each spare component and/or system (Stirling engine, thermal fluid, mechanical parts);
ii. definition of terms of use for the system.
# Regulatory framework assessment.

Commercialisation requests and further funding opportunities
Optical system and Stirling engine
# Request to help the Malaysian goverment's efforts towards promoting CSP solar projects in Malaysia and the implementation of a prototype unit of parabolic troughs that could lead to the setting up of a100MW CSP plant.
# Request to provide optical systems to generate hot water for an absorption cycle by the EU funded DIDSOLIT-PB Project (“Development & Implementation of Decentralised Solar Energy-Related Innovative Technologies for Public Buildings in the Mediterranean Basin Countries” - which aims to cover a cooling demand of approximately 13kWc (absorption parameters 95ºC "inlet", 90ºC outlet). The thermal requirements are 28kWt (hot water production /140-150ºC/). DIGESPO was invited to establish collaboration with CITEA – UPC who have a similar interest to study solar concentration technologies, focusing on dish stirling systems, parabolic trough systems and related cooling systems, with the idea to integrate them in public and private buildings.
# DIGESPO was requested to provide information to a company located in Lebanon and interested in the marketing/distribution of the micro cogeneration system for the Lebanese market.
# DIGESPO was requested to provide a quotation to Energy Resources (Italy) for a demonstration project using DIGESPO technology on a new commercial outlet that is currently under construction in Pescara (roof space area of 5000m2).
# DIGESPO was requested to provide a feasibility study for a potential installation for a single family building requiring 3Kw of power.
# DIGESPO was requested to provide a feasibility study for the use of the DIGESPO Stirling engine with a wood chip stove in a rural dwelling, in collaboration with the Dipartimento di Macchine dell’Università di Roma.
SLM heat exchangers and scroll engine
# Successful application to Finance South-East for funds for further development of SLM heat exchangers. September 2011.
# Application to Center for Defense Enterprise (CDE) to develop SLM aerospace heat exchangers based on DiGeSPo developments – successful. November 2011.
# Application to Engineering and Physical Sciences Research Council for boiling 2-phase fluids in micro-channels using SLM for the heat exchangers - successful. March 2012.
# Application to Technology Strategy Board (TSB) under Low Carbon Vehicle’s Integrated Delivery Programme for SLM heat exchangers for Micro-Turbined Range Extender (MiTRE) for electric vehicles – successful. June 2012.
# Agreement to licence SES’s SLM IP in heat exchangers and their integration with other engine components to HiETA Technologies Ltd in exchange for 45% of HiETA shares. August 2012.
# Application to CDE to develop new alloys for SLM heat exchangers based on DiGeSPo experience – successful. August 2012.
# Application to TSB to develop SLM heat exchangers based on DiGeSPo work to solve thermal and water management problems in PEM fuel cells – successful. January 2013.
# Application to TSB to develop SLM heat exchangers based on DiGeSPo expereince for use in micro-turbines, scroll engines and internal combustion engines – Selective Laser Melting Engines (SLaME) – successful. February 2013.
# Application to TSB under High Value Manufacturing call for Additive Manufacturing: Selective Laser Melting Micro-Turbine (SLaMMiT). Further development of SLM recuperator for micro-turbine based on DiGeSPo work – successful. March 2013.
# Application to TSB to develop SLM variable conductance heat pipes and heat exchangers based on DiGeSPo experience for Thermal Control Management in micro-CHP systems (Thermac) – successful. October 2013.
# Request from City University, London, to supply SLM heat exchanger (recuperator) using DiGeSPo experience for micro-turbine in OMSoP project (EC FP7 – Optimised Micro-turbine Solar Power system). October 2013.
# Throughout this period meetings to examine and pursue with many companies, including Rolls Royce, EADS, Intelligent Energy, Arcola Energy, Bladen Jets. Three presentations made to potential investors. Stalls at Bristol VentureFest October 2012 and October 2013.
NARVA and PiM: production and testing of vacuum tubes with heat pipes with a switch-off temperature of 95 - 97°C for Mediterranean countries.

The Technology Transfer Board is a horizontal structure defined at the beginning of the project between the Coordinator (FBK), the project partners, and external industrial parties interested in exploitation of the project results and in developments after the project closure. The TTB’s task is to ensure full exploitation of the project results. The Technology Transfer Board is expected to meet again.

- the coating is a real value of DiGeSPo project, matching the requirements of low cost and high performances at the same time. The product has been patented and it can be licenced, sold or directly manufactured through a start up company promoted by FBK
- the innovative heat exchangers have been characterized and the process of manufacturing studied. Knowledge allows a specific development of products in the same topic. The know-how could be opened to the market for the realization of new SLM based products, and / or to transfer the technology of miniaturized and highly performing heat exchangers realized for the specific Stirling engine.
- The solar receiver is a unique product of its kind. No CSP collector has an absorber with 12 mm in diameter, and at the same time provided with a simple and efficient design. It can be sold by NARVA as an OEM product, like the manufacturing of standard vacuum solar thermal receivers.
- When demonstrated, the integrated technology may be exploited in the market as a stand alone technology, as a support to distributed energy generation in buildings, as a regenerating technology for solar chillers, as a technology for small scale solar fields, as a thermal collector for medium temperature industrial process heat.

List of Websites:

Coordinator details:
Luigi Crema
Head of REET unit (Renewable Energies and Environmental Technologies)
Fondazione Bruno Kessler

Via alla Cascata, 56/C
I-38123 Trento - Italy

Phone: +39 0461 314922
Mobile: +39 335 6104991