While there are several high-profile companies who are betting on solar-thermal technology for utility-scale systems, Kalahari Greentech, Inc. is one of the few, and perhaps the only company intent on applying it to small-scale residential, agricultural, and small commercial markets. The company has announced its intention of demonstrating a production prototype of a rugged, inexpensive and scalable solar thermal generating system that uses a common automotive refrigerant as it working fluid some time in mid-2011. Kalahari contends that the lack of any moving parts in its passive tracking solar collector and the Rankine-style turbine system will enable their "Tri-Brid" solar-thermal generator to be built at a much lower cost-per-Watt than an equivalent photovoltaic system.  Current estimates for the initial retail price of a complete pad-ready 4kW (peak capacity) 120VAC generating system will be about $10,000, with significant room for improvement as sales volumes increase.

Matt Tyson, Director of Product Development at Kalahari Greentech, explained that the heart of the system is a unique passive solar thermal collector that has been under development at the company for several years. Unlike the parabolic reflectors which are commonly used today, Kalahari’s collector looks more like a more like a “mini-greenhouse”. Tyson says that the collector acts like a Fresnel lens but is very different in construction. Able to track the sun with no moving parts, the collector demonstrates good thermal capture efficiency across a wide range of sun angles. In recent tests at Georgia Tech, a prototype collector demonstrated an average efficiency of 65% and 74% maximum performance during a 4-hour peak sun period.

For solar-electric applications, the collector’s will be used to drive a generator using a common automotive refrigerant as a working fluid. Several candidate generators are under evaluation but  the production units will likely use a Rankine-style turbine similar to those produced by Infinity Turbine which works well with temperature differentials as low as 40C. Although Rankine systems have a lower theoretical efficiency than engines based on the Stirling cycle, Kalahari’s technical staff feels that their simpler architecture offers higher reliability and much lower cost per Watt. Tyson says that Kalahari is also exploring the possibility of an optional water heating stage (domestic hot water or space heating) which would run downstream of the generator and actually enhance the systems’ generating efficiency.  

The Kalahari system will be a self-contained 4’x4’x2’ skid-mounted unit that can be installed on a simple concrete or gravel pad – similar to those currently used for fossil-fueled gensets. Besides dramatically reducing installation costs, the modular form factor makes it easy to transport to remote sites using a standard pickup truck. Tyson also expects that the system’s simplicity will make it reliable and long-lived with little or no maintenance - even under rugged conditions. Current estimates that the first-generation system will enjoy a service life comparable to a typical residential central air conditioner, about 15 years. 

This fits into Tyson’s long-term goal of producing low-cost solar-electric systems for use in developing economies where fuel, transportation and skilled labor are relatively scarce commodities. Kalahari’s initial plan is to produce a complete generator system, up to and including the wall outlet (120 VAC) which will be used in grid-tied applications. He says that the company’s long-term goal is to provide inexpensive, reliable power sources for small-to-medium-scale commercial and agricultural applications in developing economies. As production volume grows and economies of scale begin to take hold, Kalahari intends to produce both grid-tied and off-grid systems of various capacities up to around 100kW - about the largest output that’s feasible for an unattended system.

Kalahari contends that their long-term plans will be supported by the healthy demand for low-cost reliable solar-electric systems in North America and Europe. A recent study by the Sustainable Energy Industry Association (www.seia.org) revealed that overall U.S. solar electric capacity, including both photovoltaic and concentrating solar power installations, increased by 37% in 2009. This growth drove total solar industry revenues to $4 billion; a 36% increase over 2008, with continued growth anticipated during 2010.

More information can be found on the company's website, www.kalaharigt.com.