Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has launched verification testing of the sunlight and thermal energy collecting performance of a unique solar thermal power system at dedicated facilities newly completed within its Yokohama Works. The testing will be conducted through March 2017 under contract from the Ministry of the Environment as a FY2016 project under its “Low Carbon Technology Research and Development Program.” The project calls for verification of a) efficiency improvement enabled by higher-temperature steam than that produced by earlier systems, and b) optimal control of the high-temperature thermal energy storage system. Development of these and other new technologies for the system will advance the achievement of stable power supplies at low cost.
The verification testing being performed by MHPS is on what is known as a concentrating solar power (CSP) system. In a CSP system, a sunlight concentrator is used to collect solar thermal energy, producing high-temperature steam that drives a steam turbine, generating power (Note). CSP offers a number of advantages over conventional photovoltaic power generation: less fluctuation in power output relative to fluctuations in solar radiation intensity, and stable power supply even under cloudy or nighttime conditions as the thermal energy, collected when available, can be stored. Challenges still needing to be addressed include the greater complexity of the CSP system and relatively higher equipment costs compared to photovoltaic power generation.
The sunlight and thermal energy collection method adopted in MHPS’s CSP system is a proprietary hybrid system combining a low-temperature Fresnel evaporator which collects sunlight while changing the angles of multiple mirror surfaces arranged on a plane, and a tower-type superheater which collects sunlight by heliostats. The result is the ability to produce higher-temperature steam at lower cost than earlier CSP systems. In this configuration, approximately 70 percent of all concentrated sunlight is collected by the Fresnel evaporator — which is low in cost — and the remainder is collected by the superheater. The newly completed testing facility covers an area of approximately 10,000 square meter, in which are located the evaporator, the superheater, and 150 heliostats that track the sun’s movements and use mirrors to reflect the sunlight to the focus point on the superheater. If connected to a generator, this system has the capacity to generate the equivalent of 300 kilowatts (kW) of electric power.
At the testing facility, verification of the hybrid sunlight collection system’s technology will be carried out in the following manner. First, the low-temperature Fresnel evaporator will heat water to initially produce steam near 300°C in temperature. The steam will then be sent to the superheater installed atop the small tower, where, by heliostat-based sunlight collection, it will be further heated to 550°C. Testing of the high-temperature thermal energy storage system will get underway in October, to investigate the viability of nighttime power generation.
The main challenge to be addressed under this project is to verify the feasibility of a system capable of supplying power stably using abundant solar thermal energy without relying on CO2-emitting fossil fuels. Through the newly launched verification testing, MHPS aims to establish low-cost and outstandingly practical CSP technologies through the combination of a hybrid sunlight collection system and high-temperature thermal energy storage technologies.
(Note) CSP systems exist in a variety of types: the type described here is the most prevalent system commercialized outside Japan.