The phrase “water, water everywhere and not a drop to drink” conjures images of floods and monsoon-like rainstorms, but the fact is that even in the most dry and landlocked cities, there is indeed water everywhere.
What most people don’t know if that many municipal waste treatment facilities (think potable and sewage) are just walled off and fenced away far from the prying eyes of the public. Though these facilities, not to mention water around dams, are performing inarguably important functions, new technology in the world of solar energy is making it possible for them to do even more.
Solaris Synergy’s floating photovoltaics—essentially solar arrays designed to float—are creating power potential for facilities that would otherwise lack the ability to contribute to a municipality’s energy diet.
The Israeli company founded in 2008 began with a novel approach toward rethinking solar power generation. Rather than looking to develop a new kind of solar cell or power generation system, Solaris Co-Founder and Chief Technology Officer Yuri Kokotov started an entirely different question: How can a solar array be more effectively cooled?
“Yuri [Kokotov] was trying to solve a different problem,” says Elyakim Kassel, Business Development Manager at Solaris. “He was looking at concentration systems, and he understood that cooling was a major expense. Fundamentally we have to solve the cooling problem. So he solved the cooling problem by using water.”
Keeping it cool
As great as solar’s potential is, one of its more notorious challenges is heat gain. What’s more, silicon cells—the most common and most affordable—require a great deal of land to capture substantial solar energy, and silicon doesn’t perform well under concentrated heat.
High-concentration photovoltaics require less space, but also are made of more expensive materials and have additional related expenses such as extremely precise tracking systems and advanced cooling systems. Simply put, traditional land modules come with a host of costs.
“One of the disadvantages of concentrating photovoltaics in general is that if you concentrate 1000 suns on one material, it gets pretty darn hot,” says Raphael Bouskila, an engineer and physicist at Inerjys Ventures. “You need to cool it somehow, which can be tricky. That’s one of the advantages of them keeping it on water; it’s inherently cooler there.”
Solaris’ system allows the photovoltaic cells to face down toward a mirror that concentrates the sun’s power 20 times.
The floating system Solaris developed takes full potential of that cooling effect. Not only does it float atop a cooler surface, but it also includes an evaporative cooling system that makes the water do double duty. The patented closed-loop design consistently delivers cooling water to the cells. Solaris’ system allows the photovoltaic cells to face down toward a mirror that concentrates the sun’s power 20 times.
“Our cooling system brings us back to the ability to use silicon, and that’s what makes it more economical,” Kassel says.
Although the cooling system is an important advancement, it also allows for a number of other solutions in the design of the product. For instance, because the cells face downward, they are less exposed to the elements. The concave mirrors are designed in such a way that rainwater can help keep them clean (read: efficient). And because the module is medium concentration, it relies on a simpler, cheaper tracking system.
All told, the system uses technology in such a way that it requires about five percent of the silicon used in traditional PV systems. Couple that with its use of inexpensive materials, and by Solaris’ calculation, the system is about 30 percent cheaper per kilowatt than a traditional array, and the company says the system’s cooling properties make the cells 25 percent more efficient, leading to a 10 to 15 percent increase in energy output.
Building solar farms requires a significantly greater expense than creating solar modules. Land acquisition is an obvious one, but environmental impact is a less well-considered one. Battles have happened between different camps of environmentalists and other interest groups, even leading to court cases.
Solaris’ target locations include those related to power utilities, such as cooling ponds, hydroelectric dams and pumped water storage facilities, as well as sewage water reclamation reservoirs and sewage treatment plants.
“We prefer installing our system on bodies of water that otherwise would not be used because of purity level or safety issues,” Kassel says. “We would not like to interfere with recreational activities or harming a picturesque landscape.”
It’s a move Rick Borry, Chief Technology Officer at Principal Solar, agrees is smart. Prior to his work at Principal Solar, Borry spent three years at an industrial wastewater treatment plant, where he designed a parabolic concentrating solar distillation unit that turned saltwater into drinking water.
Notably, the system decreases water evaporation and it can also reduce algae growth and preserve water freshness.
“They’re right on the money as far as acquiring space to put solar,” he says. “You have wide open spaces, no shading issues, it’s perfectly flat so there are no grading issues, no alternative use issues, and it should have very low environmental impact studies.” In the U.S., permitting alone can be a third of the cost of a solar project.
Kassel says Solaris learned of additional benefits after the product was developed.
“It was only after we had the floating system that we met with the utilities and understood that, beyond the technical solution to the problem, there were a lot of benefits involved with combining solar and water,” he says. Notably, the system decreases water evaporation and it can also reduce algae growth and preserve water freshness.
In 2010, Solaris partnered with EDF Group, the world’s largest utility company, to install its floating concentrated photovoltaics on a reservoir in Provence, France. The pilot project will help determine the feasibility of stacking power-generation opportunities and, hopefully, uncover new ways to produce more power from existing facilities rather than affecting new ecosystems.
“We learned EDF has a strategic decision to try and create maximum capacity without having to destroy the landscape,” Kassel says. “Their goal is to maximize power at existing plants.”
Under the partnership, a research team will test the system’s productivity and evaluate performance under different weather conditions and other variables for nine months. The results are expected to be ready for release by June 2012.
Illustration by Timothy Hunt