One of the advantages of thin-film PV is the superior high-temperature performance, which results in higher efficiency compared to standard crystalline wafer-based silicon PV. For all solar cells, the efficiency begins to drop once the panel temperature exceeds 25oC (77 oF). and this drop is quantified using a metric known as the “temperature coefficient.” The temperature coefficient gives the loss in efficiency observed for each one degree increase in the temperature (ie. % / oC). The general relationship is that higher solar cell temperatures lead to a decrease in performance from the maximum efficiency, which can be generally described as:
The result in electrical output decreases by two factors: 1.) under strong sunlight the solar cell temperature will increase, and 2.) if ambient temperatures are high, then the solar module will have a decreased ability to vent waste heat. The consequence of higher solar cell temperatures is not only lower electrical output, but also an accelerated degradation of the solar cell.
For traditional PV, the typical observed high-temperature performance degradation is:
- for crystalline-silicon: about 0.45% decrease in efficiency per degree centigrade (°C); and
- for CdTe and CIGS: about 0.3% decrease in efficiency per degree centigrade (°C).
For example, if a traditional crystalline-silicon solar cell that performs at 20% efficiency at 25°C (77°F), and we place that in a high sunlight environment (e.g., Abu Dhabi, UAE, or Phoenix, Arizona) at noon, where the internal solar cell temperature can reach 85°C (185°F) and higher, the efficiency would drop from 20% down to about 14.6%.
High temperature can also occur in urban areas during the summer months.
As the solar cell thickness decreases, the impact of the high-temperature on electrical performance also decrease. The main driver of this benefit for thinner PV is that thinner solar cells have a higher surface area in proportion to volume. This enables thin solar PV to remove excess heat more rapidly, enabling a lower cell temperature, which not only keeps the module closer to the rated efficiency but also reduces the stress on the cell. Reducing crystalline Si Solar PV by about a half has been shown for one product on the market to reduce this temperature coefficient by about a half.
For PI Energy’s ultra-thin solar cell, at about 1/40 the thickness of traditional crystalline-silicon, We expect the temperature coefficient to be significantly lower, enabling higher performance in high-temperature conditions, which are common when solar energy resources are plentiful.