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Solar Panel Temperature Affects Output – Here's what you need to know
Solar panel temperature is one of the important factors that affects how much electricity your panels will produce. It's ironic – but the more sunshine you get, the hotter the panels get and this in turns counteracts the benefit of the sun. In some cases the heat factor can reduce your output by 10% to 25% depending on your specific location. Of course, not all solar panels are affected by heat equally and luckily some do much better at coping with the heat than others. Here's what you need to know.
If you look at the manufacturer's data sheet you will see a term called "temperature coefficient Pmax". For example the temperature coefficient of a Suntech 190 W (monocrystalline) solar panel is –0.48%. What this means is that for each degree over 25˚C … the maximum power of the panel is reduced by 0.48%. So on a hot day in the summer – where solar panel temperature on the roof might reach 45˚C or so – the amount of electricity would be 10% lower. Conversely, on a sunny day in the Spring, fall, or even winter – when temperatures are lower than 25˚C – the amount of electricity produced would actually increase above the maximum rated level. Therefore, in most northern climates – the days above and below 25˚C would tend to balance each other out. However, in locations closer to the equator the problems of heat loss could become substantial over the full year and warrant looking at alternatives. Note:For those of you who want to use their solar panels to charge their RV or boat batteries – you'll will need to make sure that the voltage produced by your panel (under high heat scenarios) will be sufficient to recharge your battery – so it's best to order higher voltage solar panels to offset the temperature losses – and also keep the panels clean for maximum output.
The solar panel temperature affects the maximum power output directly. As solar panel temperature increases, its output current increases exponentially while the voltage output is reduced linearly. Since power is equal to voltage times current this property means that the warmer the solar panel the less power it can produce. The power loss due to temperature is also dependent on the type of solar panel being used. Typically, solar panels based on monocrystalline and polycrystalline solar cells will have a temperature coefficient in the –0.44% to -.50% range. Sunpower (Monocrystalline) does the best in this regard with a temperature coefficient of –0.38%. It is also the most efficient commercially available solar panel – making it an excellent choice for high temperature areas. Amporphous Silicon does a bit better. For example, the Sanyo HIT hybrid cells and bifacial cells, which consist of a layer of monocrystalline silicon covered with a thin coating of amorphouse silicon have a lower temperature coefficient of –0.34% - making them another good choice for people looking for high efficiency solar panels in areas closer to the equator. The best so far in terms of dealing with high temperatures are the Cadmium Telluride solar panels – with a temperature coefficient of –0.25%. However, while they are good with dealing with temperature changes – they are not as efficient at converting sunlight into electricity. Newer technologies such as CIGS and some of the 4th generation solar cell technologies being developed show show promise of also being less affected by the temperature – but we have to wait until their datasheets are published to know for sure.
Because of the problem of loss of electricity as a result of heat buildup – most installers make sure it is possible for air to flow above and below the solar panels to help keep them cool. I've recently received plans from a company in India that has developed a mounting rack that cools the panels – and they claim they can boost the output by 30% to 60% in the lab by keeping the panels cooled. Whether they raise the money they are looking for to take their invention to the market remains to be seen – but I suspect such solutions will eventually become available in the not too distant future.
While we've focused primarily on the impact of heat on the solar panel production I wanted to also bring up the issue of inverters. Until recently, large multi-panel installations required a larger inverter with larger capacitors to convert the DC to AC current. These too can also run hot … and will usually require a cooling fan that will suck in the air (and airborne dust, pollen and pollution) and can decrease the lifespan of the unit. Microinverters (which are usually installed on the backs of individual panels) use more efficient electronics, don't require internal fans and therefore are a better choice for high heat areas that are likely to push the solar panel temperature to the manufacturer's upper limits – not only from an efficiency point of view but also from a durability and heat resistance point of view.
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