Once upon a time, solar concentrating photovoltaic (CPV) technology – the use of mirrors to direct sunlight onto solar cells – received ridicule for its promise to deliver cheaper solar electricity. But CPV is winning over more customers these days and attracting new entrants such as SunPower, a long-time maker of traditional solar panels that on Tuesday launched its first CPV system.
SunPower calls the new offering its C7 Tracker, which includes a set of curved mirrors that concentrate and direct sunlight onto a row of solar cells to produce electricity (see video). This whole set up sits on top of a tracker that rotates the mirrors and cells to follow the sun’s movement – CPV technology works best under direct sunlight in cloudless days.
The new system concentrates the sunlight seven times and uses SunPower’s silicon solar cells, which are 22.8 percent efficient. The use of the mirrors means SunPower can use smaller solar cells to produce the same amount of energy. The company says a 400 MW project that uses its C7 Tracker will need less than 70 MW of its solar cells. The C7 Tracker also comes with a wireless monitoring and control system.
A historical connection
Using trackers has been a SunPower specialty. The company has designed trackers for its conventional silicon solar panels for years. The company often uses the trackers for large-scale projects on the ground (as opposed to the rooftop). Its tracker design experience is an advantage. A tracker for a CPV system must have a precise aim at the sun to harvest direct sunlight. A tracker for conventional solar panels doesn’t have to be so accurate in order to produce ample power because those solar panels can make use of indirect and reflected light.
SunPower is working on lining up utilities as customers – the company not only sells equipment to distributors and developers, it also develops solar farms.
The company made it known that it was interested in CPV earlier and showed off its early designs at conferences last year. It’s no stranger to the technology long before that. SunPower worked on a CPV technology in the early 90s but found little customer interest. It then shifted its focus to develop solar cell technology that led SunPower to become the producer of the most efficient silicon solar cells today.
Most of the solar panels today are made with silicon cells. The price of silicon used to be sky high about six years ago, and that prompted a slew of startups and investors to find ways to reduce the cost of solar cell materials. CPV seemed promising because less solar cell materials are needed when you can use mirrors to concentrate sunlight and produce the same amount of electricity. But as with many early-stage technology approaches, many CPV companies took more time and money to nail down their designs, and during that time the price of silicon fell dramatically and rendered traditional solar panels a whole lot cheaper.
In the past two years, some CPV companies were able to complete the first installations of their equipment and that was important to show there was customer interest for CPV. SolFocus built a 1 MW project at a community college in California in 2010 – that was the largest CPV project in the country then. Rival Amonix has since broken that record with a 2 MW system it completed earlier this year. The company also is supplying its equipment for a 30 MW project in Colorado by Cogentrix, which has gotten a $90.6 million federal loan guarantee for the project.
Those early installations, if they perform as promised, will help to convince banks and utilities to invest in CPV technology.
The use of curved mirrors to concentrate sunlight isn’t a new concept – many companies have been developing various versions of concentrating solar technologies that use flat or curved mirrors. Companies such as BrightSource Energy uses the mirrors to concentrate the sunlight to heat water and produce steam, which is then piped to drive a turbine generator for electricity production (this type of technology is called concentrating solar thermal).
Although CPV technology is competitive against other solar technologies, it can deliver that cheaper electricity only in parts of the world that see a lot of direct sunlight. In other words, the technology doesn’t like cloud covers, where as conventional solar panels can still produce some electricity on cloudy days. As a result, the best locations for CPV power projects include the American Southwest, parts of Middle East, southern Europe and Australia.
Photos courtesy of SunPower (first two images) and Amonix