Turbines – A Different Spin on Solar Energy
August 21, 2008
On July 29, 2008 Capstone Turbine announced the receipt of an order from Israel based HelioFocus for the modification and development of a C65 microturbine to operate on solar energy. While much of the investment community and press in general is focused on the development and implementation of photovoltaic (PV) based solar systems, this announcement considers an alternate way of capturing solar energy.
In Capstone’s recent Q4 conference call it was indicated that solar turbines are considered an area of great interest, where solar energy would be used as a heat source instead of the burning of a fuel. It was also indicated that the turbine could also be operated using fuel when there is insufficient solar energy, such as at night. The concept seems, on the face of it, quite simple. However, the details likely lie in the ability to impart a sufficient temperature rise to the compressed air and the ability to integrate a solar collector, solar receiver and microturbine.
Let’s consider a couple of patents that outline technology that might be involved in this solar turbine. United States Patent 6,748,742 (‘742 patent), assigned to Capstone, discloses a turbine system that is capable of using multiple fuel sources, a control system therefore and a method of operation thereof. Of interest here is Figure 5, which presents a partial section end view of a turbine that incorporates an external heat source 600. In Figure 5 connection 376 collects air from the compressor. The air then flows through compressor discharge port 376P, travels through heat exchanger/ mixer 606 where it is heated by external heat source 600, and is brought back to the turbine via inlet port 384. In this case the external heat source 600 would be solar energy and the exchanger 606 would be a device appropriate for transferring this energy to the compressed air.
Research around HelioFocus led to the research of Prof. Jacob Karni and United States Patent 7,042,857 (‘857 patent) issued thereto. The ‘857 patent discloses a Solar Receiver with a Plurality of Working Fluid Inlets, which might be suitable for use as the exchanger 606. Figure 1 of the ’857 patent presents a solar receiver 2, having a receiver chamber 12, inlet ports 17a-17d and outlet port 18. The nature of the fluid flow from inlets 17a-17d is discussed, as is the use of solar absorbing particles within the fluid to assist in the transfer of energy to the fluid. It is also mentioned that the receiver may implement a single inlet for working fluid, which may be free of absorbing particles. Test results presented in Table 1 indicate that air had an exit temperature of 1630 ºC for a particle loading of 4.5 g/m³.
Of interest would be the final configuration of the various elements including the turbine, receiver and parabolic solar concentrator. In the end we will be looking at the usual parameters, including system cost, efficiency and real estate requirements. However, one very compelling attribute of the proposed system is the ability to operate on different sources of energy to provide for a continuous output of power.