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ECOSTAR Résumé de rapport

Project ID: 502578
Financé au titre de: FP6-SUSTDEV
Pays: Germany

Final Report Summary - ECOSTAR (European Concentrated Solar Thermal Road-Mapping)

The ECOSTAR project had three major objectives:
- to identify the potential European technical innovations with the highest impact on Concentrating solar thermal power (CSP) cost reduction;
- to focus the European research activities and the national research programs of the partners involved on common goals and priorities;
- and to broaden the basis of industrial and research excellence, capable to solve the multidisciplinary CSP specific problems.

Recognising both the environmental and climatic hazards to be faced in the coming decades and the continued depletion of the world's most valuable fossil energy resources, CSP can provide critical solutions to global energy problems within a relatively short time frame and is capable of contributing substantially to carbon dioxide reduction efforts. Among all the renewable technologies available for large-scale power production today and for the next few decades, CSP is one with the potential to make major contributions of clean energy because of its relatively conventional technology and ease of scale-up.

While scenario approaches estimate cost reduction potential and the total market incentives needed to achieve full compositeness with conventional choices, they do not help to identify specific innovations that may enable these reductions. Other recent cost reduction studies have already pointed out that approximately half of the cost reduction potential for CSP can be attributed to scale-up to larger plant sizes and volume production effects, whereas the other half is attributed to technology R&D efforts.

Today several CSP technologies (like parabolic troughs and central receiver using different heat transfer media) are at the phase of a first commercial deployment for bulk power production in Europe. In addition to those technologies, several others are also included in this investigation if they have had a successful proof-of-concept demonstration, have undergone comprehensive engineering studies, and if industry is promoting a commercial plant.

The approach is to analyse the impact on cost of different innovations applied to a reference system in order to identify those with the highest impacts. Cost and performance information of the reference systems are currently at a different level of maturity. Therefore, the evaluation focused on the identification of the major cost reduction drivers for each of the considered reference systems and identified the impact of technical innovation approaches. This lead to recommendation on R&D priorities as well as on recommendation on changes in the political framework needed to achieve a successful deployment. These findings should serve as input for the definition of future R&D and demonstration programs also support the adaptation of a political framework on the national and European level to accelerate commercial deployments.

The essential figure of merit is the levelised electricity cost (LEC) which is calculated according to a simplified IEA Method using current Euros. The goal of this study was the comparison of different technical innovations, therefore any project specific data (e.g. tax influences, or financing conditions) were neglected. The approach was kept simple, but it appeared to be appropriate to perform the relative comparison necessary to quantify the impact of different innovations. For each reference system, a detailed performance and cost model has been established in Microsoft Excel. The model uses common assumptions for the site, meteorological data and load curve. It calculates the annual electricity production hour by hour, taking into account the instant solar radiation, load curve, part load performance of all components (depending on load fraction and ambient temperature), operation of thermal energy storage, and parasitic energy requirements. The reference size of all systems was assumed to be 50 MWel net.

The innovations considered within this study may be divided into several groups:
- Scale up of of plant size to 50 MWel: This measure is required because only the parabolic trough HTF system has been demonstrated at a 50 MWe size. All other technologies considered here are planned at a scale of 15 MWe or smaller for initial commercial demonstrations. For these technologies, it is assumed that several smaller plants are co-located at one site to reach the 50 MWe reference size and provide a common basis for computing O&M costs. Increasing plant scale to 50 MWe for those systems would provide a significant efficiency increase and cost reduction.
- Modification of structures, application of new materials and simplification of the concentrator system are measures of the second group of innovations.
- Integration of thermal storage for several full load hours, together with new storage materials and advanced charging / discharging concepts allow for increased solar electricity production without changing the power block size. Provided that the storage is sufficiently inexpensive, this would lower the LEC, and additionally increase the dispatch ability of the electricity generation.
- Further development of the cycle with increased temperatures, or additional superheating for the CRS saturated steam plant is considered. These measures provide higher efficiencies and solar fractions.
- For all CSP reference systems the most promising innovations are combined (as far as possible) and the cost reduction potential for this combination of selected measures has been calculated.

The innovations have different probabilities of success and are in different stages of development; some of are already conceptually proven and some are only a concept. This uncertainty is addressed by providing optimistic and pessimistic bounds on the input data for the performance and cost model, resulting in appropriate bounds for the LEC values and cost reduction percentages presented here.

Many of the systems considered in this research are planned for commercial deployment in Spain, which recently enacted an incentive of around 21 cents EUR/kWh for solar thermal electricity. The most mature technology today is the parabolic trough system that uses thermal oil as a heat transfer medium. Several 50 MWel units using thermal energy storage based on molten salt are currently planned in Spain. The present ECOSTAR evaluation estimates levelized electricity cost of 17- 18 cents EUR/kWh for these initial systems, assuming a load demand between 9:00 a.m. and 11:00 p.m. These cost estimates may deviate from electricity revenues needed for the first commercial plants in Spain because they were evaluated using a simplified methodology including the financing assumptions recommended by the IEA for comparative studies like this.

The other technologies analysed are currently planned in significantly smaller pilot scale of up to 15 MWel. The LEC is significantly higher for these small systems ranging from 19 to 28 cents/kWh. Assuming that several of the smaller systems are built at the same site to achieve a power level of 50 MW and take benefit of a similar O&M effort as the larger plants, LEC estimates of all of the systems also range between 15 and 20 cents/kWh. The systems achieve a solar capacity factor of up to 30 % under these conditions (depending on the availability of storage). One significant exception is the integration of solar energy into a gas turbine / combined cycle, which at the current status of technology can only provide a solar capacity factor of 11 % and needs significant fossil fuel (20 % -25 % annual solar share depending on load curve) but offers LEC of below 9 cents/kWh for the hybrid operation (equivalent to 14 cents/kWh for the solar LEC). Due to the low specific investment cost of the gas turbine / combined cycle together with a high efficiency, the system is specifically attractive for hybrid operation. Further development of the receiver technology can increase the solar share significantly in the future.

Since the absolute cost data for each of the reference systems are relatively close and are based on a different level of maturity, choosing technologies for R&D prioritization (e.g. troughs versus towers) doesn't appear feasible. This competition between technologies will be left to industrial entrepreneurship and market forces. However, the evaluation has identified the major cost reduction drivers for each of the considered reference systems and has identified the impact of technical innovation approaches.

For all systems considered technical innovations were identified and translated into component cost and performance estimates to calculate the LEC. For example the utilisation of thin glass mirrors in parabolic trough collectors impacts the following:
- the mean reflectivity is left unchanged at 0.88 / increases to 0.89;
- the specific investment costs are reduced to 95 % / 90 % of the reference value;
- the O&M equipment cost percentage is increased to 1.1 % / left unchanged at 1.0 %.
The first of the above mentioned parameter values, is the pessimistic estimate and the second one is the optimistic one. The most promising options were combined to evaluate the overall cost reduction potential.

Based on the limited number of approaches suggested in the scope of this study, cost reductions of 25 - 35 % due to technical innovations and scaling up to 50 MWe are feasible for most of the technologies. These figures do not include effects of volume production or scaling of the power size of the plants beyond 50 MW unit sizes, which would result in further cost reductions.

For parabolic trough technology the Sargent & Lundy study estimated a cost reduction of 14 % from larger power blocks (400 MW) and 17 % by volume production effects when installing 600 MW per year. Assuming similar figures also for the other technologies, an overall cost reduction of 55 - 65 % can be estimated in the next 15 years.

Summarising the detailed findings for the individual systems we may see that improvements in the concentrator performance and cost most drastically impact the LEC figures. Since the concentrator is a modular component, development of prototypes and benchmarks of these innovations in real solar power plant operation condition in parallel with state of the art technology is a straight forward strategy. New reflector materials should be low cost and have the following traits:
- good outdoor durability;
- high solar reflectivity (> 92 %) for wave lengths within the range: 300 nm - 2500 nm;
- good mechanical resistance to withstand periodical washing;
- low soiling coefficient (< 0.15 %, similar to that of the back-silvered glass mirrors).

The supporting structure of the concentrators also needs improvement. New structures should fulfil the following requisites:
- lower weight
- higher stiffness
- more accurate tracking
- simplified assembly.

Scaling to larger power cycles is an essential step for all technologies except for parabolic trough systems using thermal oil, which have already gone through the scaling in the nine SEFS installations in California starting at 14 MWe and ending at 80 MWe. Scaling reduces unit investment cost, unit operation and maintenance costs, and increases performance. The integration into larger cycles specifically for power tower systems means a significant challenge due to the less modular design. Here, the development of low-risk scale-up concepts is still lacking.

Storage systems are a second key factor for cost reduction of solar power plants. Development needs are very much linked to the specific requirements of the systems in terms of the used heat transfer medium and the required temperature. In general, storage development needs several scale-up steps generally linked to an extended development time before a market acceptance can be reached. Requirements for storage systems are:
- efficient in terms of energy and energy losses;
- low cost;
- long service life;
- low parasitic power requirements.

Especially challenging is the development of storage systems for high pressure steam and pressurized, high temperature air that would lead to a significant drop in electricity costs. Higher temperatures also lead in many cases to higher system performance. The current status of receiver technology, however, does not exploit the full performance potential.

Significant improvements in the performance of high temperature receivers are possible, whereas the room for performance improvements in the temperature range below 400 degrees Celsius is relatively small (cost improvements are possible).

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