Question: Recently I was at a boat show and saw a new boat equipped with some of the semi-flexible solar panels. I’ve heard that as solar panels heat up their electrical efficiency is reduced. I’ve also read that to help minimize the heating effect it’s a good idea to allow for ventilation and air circulation on both sides of the panels. I was looking over the installation shown here and it seems to ignore these issues. Furthermore, it seems to me that the dark color of the cells in the panels will actually absorb the sun’s rays and contribute further to heat build-up. What’s your take on this?

Flex Solar Panel

Trade-off: Installations like this can conform to curved surfaces and are hardy, but a lack of airflow under the panel can reduce output in hot conditions.

Answer: You have a sharp eye and are generally quite right in your assessment of the installation: It may not be the most efficient electrically. In a very general sense, flexible and semi-flexible  solar panels are not quite as electrically efficient as their rigid cousins, although new technology semi-flexible panels (what we see in your photo) are much better than earlier versions in that regard.

As for the color, well, absorption of more light rays can also help to generate more power. That said, you definitely reach a point of diminishing returns in terms of heat build-up. In tests that I’ve conducted over the years, at a panel surface temperature of about 125 degrees F and above, panel efficiency begins to drop quite noticeably. So there is a definite benefit to ventilation, and air circulation to help keep things cool.

Perhaps the biggest gain in solar power efficiency today has less to do with the panels themselves and much to do with the type of charge controller an installer uses with a panel installation. The type of charge controller can make a big difference in the overall efficiency of the system. The buzzword here is actually an acronym: MPPT, which stands for “maximum power point tracker." Within the MPPT realm, things can be further broken down into two categories, digital and non-digital units. Given the choice, always go with the digital, micro-processor controlled variety for this application.

MPPT controllers perform their magic by carefully monitoring both battery voltages and panel output, and  matching them so that the final power output amperage is maximized under all conditions. This is a continuous adjustment done in real time that in the end squeezes the absolute most out of whatever panel array is connected to the controller.

So, although the type of solar panel (rigid vs. flexible) as well as panel surface temperature are indeed factors in determining overall system efficiency, the biggest efficiency gain today can usually be achieved by connecting to a “smart” charge controller. To learn more about MTTP controllers, check out units made by companies like: Genasun, Outback, Xantrex, and Blue Sky Energy, to name several.