Solar Technology Breakthrough

 

The system makes it possible to power state of the art combined cycle power plants by both natural gas and solar energy. Gas fired power plants built today with provision for the addition of solar collectors will be usable in the future as solar powered power plants. When powered by solar energy, the efficiency of the plants will be much higher that of photovoltaic cells.

 

BOEING, as the project team leader, is responsible for system integration, the heliostat field, the master control system, the tower and tower reflector. ORMAT is responsible for the power conversion system and for the fluid loop integration, and Rotem is responsible for the air receiver and its associated optics. The Weizmann Institute of Science through its commercial arm, Yeda, will transfer the unique solar technologies to industry and will also host the prototype system in the Institute's solar test facility. The prototype plant construction will be completed by the end of 1999.

Electricity transport has recently become competitive with natural gas pipelines for transporting electricity to distances of up to 5,000 km, making it possible to site power plants near the gas wells, rather than near the electricity consumers. Wherever gas fields are developed in sparsely populated areas with high solar intensity, there is a substantial advantage in constructing power plants close to the gas field: the initial investment in conventional gas fired plants, at competitive prices (with only minor modifications in the combustion systems), can be enhanced in the future, as gas fields deplete, by adding solar collectors and using the plants as solar powered plants. This will extend the useful life of the plants and power transmission lines for decades beyond the exhaustion of the gas resources.

In the conventional approach, where gas is transported to consumption areas, gas pipelines and power plants become useless when gas reservoirs are used up. Using the proposed strategy, the life of power plants can be extended, avoiding the expense of de-commissioning power plants and pipelines. This innovative scheme can thus provide truly sustainable power supply to densely populated areas.

The new system is implemented in a pilot solar plant, the first of its kind in the world, which uses solar energy for directly powering gas turbines in order to produce electricity. It is located at the Weizmann Institute of Science and will be completed by the end of 1999.

The pilot plant is being set up as a collaboration between the Weizmann Institute, the U.S. company Boeing and Israel's Ormat and Rotem Industries. It makes use of technologies, particularly special optics and an innovative air receiver, developed on the basis of research conducted at the Weizmann Institute's Canadian Institute for the Energies and Applied Research. These technologies reflect, concentrate, and convert sunlight to provide the high temperatures necessary to directly power gas and steam turbines in a combined cycle and thus generate electricity.

The innovative solar system is equipped with highly reflective mirrors (heliostats), which track the sun in two axes and reflect sunlight up to another reflector atop a central tower. This reflector redirects the sunlight back down to a matrix of optical concentrators, capable of concentrating the light 5,000 to 10,000 times, compared to natural sunlight reaching the earth. The concentrated radiation then enters a unique group of solar receivers, located on the ground, which heats up compressed air to be used for driving the turbogenerator that produces electricity.

The pilot system's advantages stem from a unique combination of technologies. Firstly, the production facilities, including the concentrators, receivers and turbogenerator, are located on the ground rather than at the top of the tower (as they were in previous systems). This innovation will make construction of the tower, whose sole function will be to support the reflecting mirror, significantly simpler and cheaper.

Secondly, the sophisticated design of the concentrators, based on pioneering research at the Weizmann Institute, will make it possible to concentrate sunlight sufficiently in order to heat the air to the temperature needed for driving advanced gas turbines.

A third innovation is the use of the Weizmann Institute-designed solar receiver (nicknamed "Porcupine") that contains hundreds of ceramic pins arranged in a geometric pattern that maximizes the collection and use of sunlight. Compressed air that flows across the pins is heated and channeled to the gas turbines. Sunlight enters the device through a special cone-shaped quartz window that can withstand higher pressure than can a similarly designed steel cone.