Cheaper hybrid concentrated solar power plant design put to the test

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MHPS is testing out a hybrid concentrated solar power system that combines a a solar power tower with a low-temperature, low-cost Fresnel evaporator

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Concentrating solar power (CSP) plants focus the sun's thermal energy to produce steam that drives a turbine to generate electricity. Now, Mitsubishi Hitachi Power Systems (MHPS) is testing the performance of a new hybrid system that is designed to increase efficiency and lower costs by combining a solar power tower with a low-temperature Fresnel evaporator.

Conventional CSP systems are made up of arrays of heliostats, mirrors that track the sun to ensure the reflected light is always pointed at a specific target. While they're more complex and costly than photovoltaic setups, CSP systems can better deal with fluctuations in the strength of the sunlight, and their energy production is more stable at night or in cloudy conditions as the thermal energy can be stored and used to continue producing power long after the sun has set.

Laid out over 10,000 sq m (107,639 sq ft), MHPS's test facility is made up of 150 heliostats, a superheater built into a tower, and a low-cost Fresnel evaporator. Of the overall sunlight collected at the plant, the evaporator pulls in 70 percent, thanks to a plane of mirror surfaces with adjustable angles. Using the resulting thermal energy, the Fresnel evaporator heats water to produce steam at temperatures of around 300° C (572° F).

That steam is then channeled into the superheater located at the top of a small tower, where it is further heated to 550° C (1,022° F) via sunlight focused by the heliostats. Since the steam is already pre-heated, a smaller array of heliostats is required to superheat the steam, so it can do so at a lower cost than previous CSP systems. MHPS says its hybrid test system is capable of generating the equivalent of 300 kW of electricity.

Working at its Yokohama Works facility under contract from Japan's Ministry of the Environment, MHPS will run tests until March 2017 to verify if its hybrid sunlight collection system can improve on the efficiency of existing CSP technologies. Testing of a high-temperature thermal energy storage system will also begin in October to test whether the system can stably supply power without the help of fossil fuel-based systems.

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