Linear Fresnel reflector (LFR) also based on solar collector rows or loops. However, in this case, the parabolic shape is achieved by almost flat linear facets. The radiation is reflected and concentrated onto fixed linear receivers mounted over the mirrors, combined or not with secondary concentrators. One of the advantages of this technology is its simplicity and the possibility to use low cost components. Direct saturated steam systems with fixed absorber tubes have been operated at an early stage of use of LFR technology. This technology eliminates the need for HTF and heat exchangers. Increasing the efficiency depends on superheating the steam. Superheated steam up to 500°C has been demonstrated at pilot plant scale and first large commercial superheated LFR plants have begun recently their operation.
Since the steam is the working fluid, LFR technology is usually fitted with steam storage system. Molten salt storage system can be also implemented. Furthermore, PCM storage systems are currently demonstrated at pilot plant scale.
There are almost more than 200MW LFR plants in operation or under construction. After a first pilot scale application in Australia, a few new pilot plants have been tested in Spain and in the United States. In 2012, the first commercial 30-MW Puerto-Errado 2 plant began its operation in Spain. France has already implemented two linear Fresnel pilot plants and is currently building two new commercial plants with this technology of 9 and 12 MW respectively, named Llo and Alba Nova 1 plants constructed respectively by CNIM and SOLAR EUROMED. In Australia, there are two plants running with this technology of 6 and 9.3 MW respectively. There is also one 44-MW plant under construction at Kogan Creek. In India, Reliance has completed and connected to the grid in November 2014 at Dhursar in Rajasthan a 125MW CLFR plant designed and constructed by AREVA Solar.
Compared to other technologies, the investment costs per square meter of collector field using linear Fresnel technology tend to be lower because of the simpler solar field construction, and the use of direct steam generation promises relatively high conversion efficiency and a simpler thermal cycle design. The Fresnel design uses less expensive reflector materials and absorber components. It has lower optical performance and thermal output but this is offset by lower investment and operation and maintenance costs. The Fresnel system also provides a semi-shaded space below, which may be particularly useful in desert climates for agriculture. Acting like a large, segmented blind it could shade crops, pasture and water sheds to protect them from excessive evaporation and provide shelter from the cold desert sky at night. Many improvements in the absorber tubes and the geometry are under development. Some of those ongoing improvement efforts relate to the shape and the disposition of mirrors to accommodate some of the peculiarities of this technology.
Therefore LFR offers high thermal performance and low cost, as well as various cost competitive thermal energy storage solutions. Hence, LFR is becoming one of the CSP technologies capable to achieve very low LCOE costs.
In addition to electricity generation, linear Fresnel technology is also quite useful for direct thermal applications, such as cooling or industrial process heat applications. Very low cost LFR collectors are providing 200-300°C steam solutions at competitive cost for process heat application such as desalination, food processing and pharmaceutical industries. Low cost LFR collectors are providing 250°-500°C steam solutions at very competitive cost to hybrid CSP – fuel fired combined cycle or Enhanced Oil Recovery applications.