MHPS Tests World’s 1st Tower-fresnel-hybrid CSP Generation System

Mitsubishi Hitachi Power Systems (MHPS) Ltd announced Aug 4, 2016, that it has completed a test facility for light/heat collection with a concentrating solar power (CSP) generation system at its Yokohama Plant (Naka-ku, Yokohama City) and started a demonstration test.

The company combined (1) a “tower type,” which is suited for production of high-temperature steam, and (2) a “fresnel type,” whose facilities are low in cost, and realized a hybrid-type system for the first time in the world.

A CSP generation system generates electricity by using mirrors to collect sunlight, producing high-temperature vapor and turning a steam turbine. With a CSP generation system, the short-period output fluctuation caused by change in solar irradiation is small, compared with solar (photovoltaic) power generation systems. Therefore, when a heat storage device is used, it can stably output electricity even on cloudy days and during nighttime hours.

On the other hand, the facility cost of a CSP generation system is high because it is a complicated system.

MHPS aims to effectively produce high-temperature steam while reducing facility cost by combining tower-type and fresnel-type CSP generation systems.

For a tower type, many heliostats, which track the sun and concentrate reflected light at one point, are installed in front of a tower-like heat collector. It is possible to produce superheated vapor with a temperature of 500°C or higher by collecting reflected light at the receiver located on the top of the tower.

For a fresnel type, strip-like mirrors are laid on the right and left sides of a heat-collecting pipe. The angles of the mirrors are changed in accordance with the position of the sun so that sunlight is reflected to the heat-collecting pipe. As a result, it can produce vapor with a temperature of up to 300°C.

A tower type can produce high-temperature steam and, therefore, increases the thermel efficiency of steam turbine generation. However, when it is applied to a large-scale facility, it is necessary to increase the height of the tower and array an enormous number of heliostats, increasing facility cost.

On the other hand, a fresnel type has a relatively low facility cost. But the temperature of vapor is low, making it difficult to increase thermal efficiency.

This time, with the hybrid-type CSP generation system, a fresnel type is used to produce saturated vapor with a temperature of 240-300°C and send it to the receiver of a tower type. Then, light reflected from heliostats is intensively applied to the vapor to produce superheated vapor with a temperature of about 550°C.

The fresnel and tower types collect 70% and 30% of the total heat, respectively, making it possible to lower the height of the tower and, thus, facility cost. MHPS aims to realize a power generation cost equivalent to that of solar (photovoltaic) power generation.

The demonstration facility was built on about 10,000m2 of land. The number of heliostat mirrors is 150. The height of the heat-collecting tower is 20m. It has a heat collection capacity equivalent to 1,000kW and can generate about 300kW of electricity.

However, this time, the facility is used for the light/heat collection test and does not have power generation equipment. A heat storage device (about 10kW) is scheduled to be installed in October 2016, and molten salt will be used as a heat storage material.

The fresnel-type vaporizer and the tower-type superheater were designed by Hitachi Zosen Corp and MHPS, respectively. The heliostat is a product of an Australia-based firm.

The demonstration project was selected for the “CO2 emission reduction leading technology research and development program” of the Ministry of the Environment. The subsidy for the project is about ¥800 million (approx US$7.96 million). The project period is from fiscal 2014 to fiscal 2016.

“After establishing the hybrid type at the demonstration plant, we will first aim to receive orders from sunbelt regions, which are suited for commercializing CSP generation,” MHPS said.

Sunbelt regions are areas where the intensity of direct sunlight is high. They include Spain, North Africa, South Africa, the Middle East, the US West Coast, Chile, Australia, India and China.

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