It is certainly not for want of trying… After all, the benefits are compelling. The PV module works better when cooled, additional energy can be applied to thermal loads, and the overall panel efficiency goes from below 20 percent to above 60 percent. A single PV plus thermal (PVT) module can deliver over 1,000 watts of PV and thermal energy with all the roof space, installation and cost-of-sales efficiencies that come with a combined system.
For decades many companies have spent many tens of millions of dollars attempting to combine PV and solar thermal into one panel. So why has a commercially successful PVT product been historically elusive?
A good guy to ask might be Dan Shugar, founder of Powerlight and currently CEO of NexTracker. Dan and his team designed, tested and patented an early PVT system almost 20 years ago. In Dan’s words, “It always comes down to cost. Maximize performance, relentlessly reduce cost and be sure it lasts for 30 years.”
Ah, if only it were that easy! The first problem is absorbing the heat from a PV module. The second is doing so efficiently at low cost. The third is what to do with the heat. Common wisdom suggests thermal energy applications benefit from high temperatures, but we need to keep the PV module cool. Suppose there is too much heat? What about aesthetics? What happens if the installer needs to replace a PVT panel in the middle of an array? How can the system realize even flow through all the PVT panels with low back pressure to minimize parasitic losses? Is it light enough to handle easily and meet roof load requirements? Even if we get the product right, what is the best market in what region through what channel?
One of the reasons the promise of PVT has been unrealized is a misconception about the difference between temperature and heat. End users don’t buy temperature; they buy heat energy. Heating the water flowing to a central boiler from 70 to 85 degrees Fahrenheit uses the same amount of energy as heating the water from 170 to 185 degrees Fahrenheit . It’s just much less expensive to heat the water at the lower temperature. Heeding the physics and Shugar’s low cost mantra, the successful PVT system must be able to cost-effectively and efficiently preheat water flowing through the PVT array on its way to the thermal load.
Once the relationship between thermal energy and heat is understood, ideal PVT applications become clear. PVT needs to be cost competitive with alternative sources of energy, which means the ideal applications use large amounts of heated water daily in warm to hot climates with high energy cost. Typically this means islands or other regions that rely on high cost imported fossil fuels for energy used in such applications as bottle washing, textiles, food processing, pharmaceuticals, bath/shower/laundry heated water for destination resorts, etc. Commercial and residential pools are ideal. Local incentives and absence of tariffs play a part as well.
Commercial Benefits of PVT
What does PVT do for PV module manufacturers, selling and installing dealers and especially the end users? The end user gets about four times the energy from the same roof or rack area at a better ROI. Pool owner Jerry Pollard in Sarasota, Fla., commented, “As a CPA, I ran the numbers comparing a CoolPV system with other options; I get more electrical energy and a cold pool is an unused pool. However, now we enjoy our FAFCO CoolPV solar heated pool!”
When asked about his involvement with PVT, Mukesh Dulani, president of SolarWorld Americas Inc., commented, “PVT appeals to SolarWorld by enhancing the performance of our modules while also providing far more total energy to our end users, the majority of whom have thermal loads.”
What is the dealer appeal of PVT? Bryan Raymond of Diablo Solar in Martinez, Calif., stated: “We have nearly 20,000 solar pool heating customers and many find PVT appealing as a way to reduce or virtually eliminate their electric bills while heating their pools using the same valuable and often limited roof space. Many also find the aesthetics better than provided by solar pool heating panels alone.”
Clearly the solar industry manufacturers, installing dealers and especially end user customers can benefit from a commercially successful PVT solution. When asked exactly what the optimum PVT solution would look like, let’s ask a PV dealer without prior thermal experience. Josh Aldrich of DelSol energy in Brentwood, Calif., stated: “The PVT solution we have chosen uses components made in the USA, is easy to install and is tested, certified and locally code-compliant. It has a class A fire rating with patents pending.”
Clearly PVT is not for everybody. Increased electrical output ranges from 3-20 percent. The additional thermal energy from a 285-watt PVT panel is usually an additional 800 watts. But the system must be designed to optimize both electrical and thermal performance. Both the electrical and thermal energy must be conducted to their respective loads. PVT systems must be installed and serviced to the manufacturer’s specifications. It just may be that FAFCO and SolarWorld have built on the experience of those who have gone before to offer what we hope will be a breakthrough PVT solution called CoolPV. Time will tell.