Equatorial and sub-equatorial regions have a great potential when it comes to solar energy generation. As such areas are characterized by very high annual solar irradiances, it was estimated that solar modules installed in these regions could potentially produce 50% more energy compared to what they would otherwise generate if placed in Europe or North America. This should be enough encouragement to move all solar power generation businesses to these regions. However good these numbers, solar power growth in the equatorial and sub-equatorial regions has not yet lived up to global expectations.
So, what is hindering the great potential of solar PV in these areas? One point is the heat. Sub-equatorial and equatorial regions are characterized by very high temperatures, which during the summer can even reach 50C. Why is that negative for solar PV? Solar panels loose a % of their efficiency as their operative temperature rises above 25C, which is the standard temperature at which they are tested to determine their “nominal” efficiency. Standard Si modules (which represent over 90% of the market) loose in average 0.6 % in power conversion efficiency for every C increase in their working temperature. To put this in an example, a solar module with a proven efficiency of 20% at 25C, has at a working temperature of 60C an efficiency of only 15.8%, meaning that it loses more than 20% of its original capability of producing electricity. It is also important to note that the outside temperature is not the only factor that determines the operative temperature of a solar module. Under standard operation, a solar module, other than producing electricity, generates a lot of heat. Imagine that in a 20%-efficient solar module, almost 60% of the incoming energy is turned into heat. As this heat is not converted into electricity, it raises the temperature of the solar panel, thus negatively affecting its capability to produce electrical power. It is not unusual then that solar panels in the equatorial regions reach, during the summertime, temperatures above 75C. Under this condition, solar modules can loose over 30% of their original power conversion efficiency.
The PV community has embarked on different paths to reduce heat-related losses and thus maximise the performances of solar panels in high-temperature regions. The first path consists in improving material quality with the scope of bringing down the temperature coefficient of a solar module. This has produced Si solar modules with temperature coefficients as low as 0.3-0.35 %/C, with the caveat of being more expensive due to higher manufacturing costs. The second path consists in using alternative materials with lower temperature coefficients. Thin-film materials (like CIGS and CdTe) exhibits temperature coefficients as low as 0.2 %/C, which are considerably lower than that of Si modules. Although thin-film modules have also a competitive price, their low efficiencies and reduced durability represent today strong limiting factors, which are ultimately discouraging their use.
We at Solar Bankers undertook a different path, focusing on the source of the problem, the light, rather than solar cell materials. The sunlight is made of different colors, also called wavelengths, which together compose the sunlight spectrum. Among these wavelengths there are visible and invisible, infrared (IR) colors. Silicon solar modules can convert the visible spectrum and only a small portion of the IR light. The remaining wavelengths pass undisturbed trough silicon, but are turned into heat at the electrodes, which cover the back surface of solar cells. As a result, not only these wavelengths are not converted into useful electricity, but they also reduce the performance of the module, as they increase its operative temperature. Solar Bankers developed and patented a high-tech solution to get rid of unwanted, efficiency-lowering wavelengths, thus achieving better performance than standard modules even in high-temperature environments. The product consists in a nanostructured optical film that efficiently selects the light colors suitable for photovoltaic conversion and bends away those that only produce heat. The film, produced in large scales and at a very low cost, can be installed on existing modules or can be in alternative integrated on stand-alone panels. Field tests have confirmed that Solar Bankers film can reduce the difference between the module operating temperature and that of the ambient by almost 35%, leading to the recovery of the previously lost power output of up to 30% depending on solar cell quality.