A small company in Las Cruces, New Mexico is partnering with a large development institute in China for the development and manufacture a low-cost system to collect extra power from the sun, in the form of both electrons and heat, and put them into microgrids.
The solar system developed by Focused Sun in Las Cruces uses a low-tech panel of mirrors to concentrate sunlight onto a tubular collector. The innovation is in the construction of the collector, two alternatives of which can be swapped in to work at either relatively low temperatures, in the hot water range, or at temperatures around 300 degrees C.
Developer Shawn Buckley explains that the low temperature version of the collector has PV cells attached to the underside, to take advantage of the concentrated sunlight from the reflectors, and also channels water through it to collect heat that can be stored and used for space heat. Normal configuration would be one or two modules with a capacity around 500 W electricity and 1500 W heat, suitable for an off-the-grid cottage.
The other configuration leaves out the photovoltaics, which do not work at the higher temperatures, and instead pipes mineral oil through the a vacuum-jacketed tube at 300 degrees, and feeds the heat to a turbogenerator in a type of thermodynamics called a Rankine cycle. A specialized medium allows the engine to make efficient use of the relatively low-grade heat, where a typical steam turbine uses heat around 1000 degrees in the same thermodynamic cycle. A microprocessor operating small and inexpensive servomotors controls the angle of the reflectors to maintain a constant temperature in the collector in this version. Here also the heat can be stored, in Focused Sun’s design using slabs of concrete, for use when needed. The normal configuration for the high-temperature model is hundreds to thousands of units, for a system size up to 10 MW.
Focused Sun’s partner, Xiang Yang Institute, is interested in using the package in microgrids in China, where the potential market is in the tens of millions. From China’s perspective, microgrids would help China’s smog problems by replacing burning coal cakes – a major source of heat energy in Chinese cities – with clean energy from the sun.
The system produces both electricity and hot water and can pay for itself in as little as two years. The Focused Sun concentrators are made locally bringing local jobs plus cheap, clean energy. For every dollar spent, four times more solar energy is captured.