The sad fact of solar PV electricity generation is, the more sunlight the panels get, the hotter they become. And the hotter they become, the lower the efficiency, which directly affects power output.

A test to determine just how much is lost as a result of heat stress was carried out, showing that – above 42 degrees Celsius (or 107.6 degrees Fahrenheit) – panels lost about 1.1 percent of their energy for every degree of temperature added.

NASA, which designs solar cells to withstand the higher solar radiance of space, has determined that higher bandgap materials (i.e., gallium, indium, silicon) are preferred, as they result in less degradation. In doing the work, the agency calculated a loss of about 0.177 percent per degree of temperature increase.

Solimpeks, which makes the Volther Powervolt 175/460 and the Powertherm 155/680 (the latter featuring extra solar glass and greater long-term efficiency), offers both solar PV electricity generation and solar hot water by using between one and two liters of water to absorb the extra heat that prevents panels from performing in their optimum range.

According to Inhabitat, the temperature coefficient is actually 3.5 degrees F, and the resultant water-cooled PV panels reportedly deliver efficiencies of up to 28 percent while also providing 140 to 160-degree (F) water (the normal setting on a hot water heater is between 120 °F and 140 °F). Solar PV efficiencies in the laboratory setting are now approaching 25 percent, their theoretical upper limit; in the real world, they are still confined to about 22 percent, and you get what you pay for.

According to Solimpeks, a Turkish manufacturer that started as a boilermaker and expanded into renewable energy technologies, keeping the panels cooled with water also extends lifespans and reduces payback times by factoring in the (reduced) cost of hot water.

Source: Solar Calfinder.