Size: 50 to 250 MW

Proven utility scale technology

Commercial operation since 1984

Preferred technology for new plants in the USA, Spain and North Africa (Morocco, Egypt and Abu Dhabi)

These plants use line-concentrating parabolic trough collectors which reflect the solar radiation into an absorber tube. Synthetic oil circulates through the tubes and is heated up to approximately 400°C.

Parabolic trough collectors are the most commonly used thermoelectric technology in the market. Its track record began in the 80’s in the USA with a total power installed of about 350 MW. New plants have been constructed in the last years, such as the 65 MW plant of the Spanish company Acciona in Nevada (USA). In January 2009, 15 plants are under construction in Spain which amounts to more than 700 MW, and a number of new projects are being developed in the USA. In addition, two plants in Algeria and Morocco of 50 MW electrical equivalent power for two solar bottomed combined cycles have been awarded to Spanish companies as a result of an international tender and a 20 MW plant is under construction in Egypt. A tender for a 100 MW plant is under way in Abu-Dhabi as well as additional expressions of interest from the Middle East, China and other sunny countries. The current total investment for the aforementioned projects is close to 3,000 M€.

This technology is commercially and technically viable, plants are being financed by the banks on a regular basis. Nevertheless public promotion and support schemes by means of direct investment, tariff increase (feed-in) or by means of mandatory targets are still necessary. The Spanish case is a good example of an effective legal framework: 27 c€/kWh in feed-in tariff scheme for plants up to 50 MW and the possibility of using 15 % natural gas or in hybridisation with 50% biomass to improve the dispatchability.

Investment and land use depend strongly on the solar field collector surface and the storage capacity ratio.

Some of the Spanish 50 MW power plants under construction have been designed to produce not only the nominal power during sunny hours but also to store energy, allowing the plant to produce an additional 7.5 hours of nominal power after sunset, which dramatically improves the integration of solar thermal power plant into the grid. Molten salts are normally used as storage fluid in a hot-and-cold two-tank concept.

The maximum power output of a single plant is theoretically not limited by any physical constraint and power levels of some hundred MW with a unique power group are being designed. The commonly seen 50 MW figure in all of the ongoing Spanish plants is the limit fixed by Spanish legislation and by no means a technical limit.

The expectations on the reduction of the kWh generating costs are based upon the efficiency increase based on higher working fluid temperature, a more efficient use of the generation group by means of the storage, new concepts for the collectors design and/or the contribution of the other primary sources (gas or biomass) and by the size optimization, and also by market evolution, without artificial administrative barriers (such as the 50 MW limit in Spain).

The maximum nominal efficiency of these plants is currently about 16 % and it is limited by the working fluid temperature. R&TD activities are being carried out in order to find more efficient fluids such as direct steam generation or molten salts. These technologies are not commercially available today, but there are many ongoing development initiatives, which are expected to be commercially available shortly. Europe has the world leadership in these technology development initiatives, carried out by R&D institutions and industry, with the support of the EU R&TD Framework Programmes.

The cost of the energy produced is directly related to the available solar radiation resource, which has to be taken into account when defining the feed-in tariff scheme. At the end of 2008 more than 12,000 MW of projects under development were registered in Spain.