California-based SolFocus shines at generating renewable energy with sophisticated, reliable solar panels.
SKF does solar
Since it embarked on expanding its renewable energy portfolio in 2008, SKF has developed a solar linear actuator that enables reliable precision tracking for up to 20 years. SolFocus is the first customer incorporating the unit for its CPV panels. The SKF CASD-60 actuator integrates a linear screw with gearbox, motor, bearings, lubricant, seals, limit switches, hall sensors and a circuit board. The actuator is protected in a sealed housing for optimal performance even in extreme conditions, including winds in excess of 160 kilometres per hour. As a plug-and-play solution, the system can be quickly installed and requires no downtime for part changes or relubrication. In order to become a one-stop shopping solution for clients such as SolFocus, SKF will offer rotary drive and other mechanical systems for CPV panels.
Mahdi Sebti, Mahdi.Sebti@skf.com
Cutting-edge solar technology is all about small movements done right. Take the concentrating photovoltaic (CPV) panels developed by SolFocus. The US company, based in San Jose, an innovation hotbed in the heart of Silicon Valley, builds a rectangular array of cells that each contain a chip no bigger than a fingernail. The sun’s rays bounce off a larger primary mirror at the bottom of each cell before being concentrated in a smaller secondary mirror and then shot onto an optical system that takes up just one square centimetre at the centre of each cell.
This design enables SolFocus to concentrate sunlight at 650 times and generate renewable energy with twice the efficiency of a regular roof-bound PV (photovoltaic) panel. There’s one catch, though, as Steffen Jensen, director of Systems Engineering at SolFocus, points out: “With a CPV system, you only cover a small part of the sky, so it’s crucial that the system can follow the sun from sunrise to sunset.”
That’s where actuators come in. Stand next to a SolFocus panel and you’ll notice that the array of 4×7 panels constantly readjust their position to maximize the yield, tilting every so often up or down, left or right. Like a robotic ballet moving to its own muted hum, each CPV panel is steered by a linear and a rotary drive in the back to stay pointed within 0.1 degree of the sun’s incoming rays. While regular PV panels do not require tracking the sun, and they have optimal efficiency at a broader range (one to three degrees) of pointing accuracy, CPV panels are much more sophisticated installations that provide much greater panel efficiency (29 percent) with a relatively small footprint.
SolFocus is considered one of the leaders in the CPV field. Founded in 2005, the company released its first prototypes in January 2006 and has since introduced the third generation of its panels. The most recent models feature an array of 4×9 cells in one panel. The company has raised 161 million US dollars (128 million euros) in venture capital to date and also secured a 2.2-million-dollar (1.8-million-euro) grant from the US Department of Energy – evidence that technologists and energy experts are betting on CPV, which has the potential to harness the sun’s energy with just one-thousandth of the solar cell material used in traditional PV panels.
What’s more, 97 percent of the glass and aluminium used in SolFocus panels is recyclable, further reducing the environmental footprint of the technology. As a modular system, CPV farms can range from several hundred kilowatts to more than 50 megawatts in capacity. SolFocus systems are already up and running in 13 countries around the world, from the United States (the Hawaiian island of Kona as well as California and Colorado) to Crete and all the way to Saudi Arabia, Malaysia and Australia.
“Hot and dry locations with plenty of direct sunlight are the type of environment where CPV outperforms other technologies,” says Jensen. Most CPV systems are also in remote locations where regular maintenance is a chore; it involves sending out a truck to make sure that wild temperature swings, high winds and the onslaught of corrosive sea breezes or dust particles have not damaged the mechanical parts. Misalignments due to faulty tracking or, worse, downtime for repairs to the mechanical system can be costly.
SKF provides the company with a custom-designed linear actuator that constantly adjusts the concentrator to track the sun. The actuator is lubricated, sealed and assembled for life and therefore alleviates reliability headaches. “We chose the SKF actuator because it’s easy to install, reliable, sturdy even in high winds and, most importantly, maintenance-free for 20 years,” says Jensen. “SKF brought the expertise to the table that enabled us to design and build a better product faster.” SolFocus is currently testing a total of 15 units fitted with the new SKF linear actuator in indoor and outdoor settings, with an additional 30 to 40 units on the way.
SolFocus President and Chief Operating Officer Robert Legendre sees the development work on the new linear actuator as the beginning of a strategic partnership. “The solar industry is challenged by price competitiveness,” he explains. “CPV can compete on reliability and performance, but we have to drive costs down. Having a system that’s maintenance-free impacts our entire value chain. So we’re very excited to work with SKF to integrate other solutions into our products.”