Solar Supercritical Organic Rankine Cycle

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The Solar Supercritical Organic Rankine Cycle project demonstrates an innovative CST system’s ability to provide 24/7 electricity. The project will use integrated solar thermal storage while operating as an automated plant with a gas heater.Key resultsDirect HeatingWorld first demonstration of direct heating a supercritical organic working fluid in a parabolic solar trough.An auxiliary thermal fluid transfer system is absent because it has complexity, cost and efficiency losses.Development of a semi-hermetic high speed Turbine GeneratorThe turbine generator uses state-of-the-art magnetic bearings to support the turbine and generator rotor without the need for oil lubrication. This very low friction bearing allows the shaft to spin at speeds over 40,000 rpm to deliver up to 30 kW of electricity. The generator is directly coupled to the turbine which eliminates a reduction gearbox. The unit is sealed in a semi-hermetic pressure tight casing to eliminate any mechanical seals. This design is ultra-low maintenance and high efficiency.Low cost energy storageThe thermal energy from the sun is stored and released as required because it uses low cost materials such as clay paving bricks. The storage tank can provide another hour of continuous full power or several hours of low power output. A back-up heat source can be added and in Wallsend, an LPG burner is in use to run the plant after cloudy periods.Maximum system efficiency by delivering power in both electricity and heatOf the solar thermal energy, less than 20% goes to electricity and about 70% is rejected as heat due to Thermodynamic limitations. The Wallsend public swimming pool is an example of how the this heat is useful. The remote communities can obtain a cost effective option with small-scale concentrating solar thermal (CST) systems.Project innovationThe Solar Supercritical Organic Rankine Cycle project demonstrates an innovative CST system’s ability to provide 24/7 electricity. The project will use integrated solar thermal storage while operating as an automated plant with a gas heater.The project develops, demonstrates and tests a small-scale CST system. It combines Granite Power’s GRANEX technology with a process to produce a supercritical organic fluid through parabolic trough solar collectors (which ‘collect’ sunlight). This is Direct Supercritical Fluid Generation (DSFG). As a result, the CST system provides both heat and electricity.GRANEX generates electricity from low and medium grade heat sources such as industrial heat. For this reason, it is more efficient and cost effective than conventional technologies. It also uses a wide range of heat sources. GRANEX achieves higher thermodynamic efficiency using specialised fluids operating in the supercritical state.The demonstration plant at the Wallsend swimming complex has a 200 kilowatt field of parabolic trough solar collectors and a GRANEX plant. The plant will generate 30 kilowatts of electrical output and over 150 kilowatts of heat for the swimming pool. The plant’s efficiency will increase with the use of organic DSFG as the supercritical fluid can:reach a greater range of temperatures, andlower costs by eliminating the need to use expensive thermal oils.The project is the test-bed and launch platform for a commercial product.BenefitThe plant provides thousands of hours of operating data and will increase investor and customer confidence in the emerging technology.

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