Solar: It’s not just a bunch of hot air…

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Thinking colder winter temperatures reduce solar panel output? Think again!

Panels actually thrive in colder weather, while the sun, lower on the horizon and contributing less daylight, reduces output on a typical winter day.

The sun’s rays striking the panel’s silicon cells cause their electrons to be released as electricity. Higher temps mean more excited electrons before the sunlight strikes.  These hot electrons require less energy from the sun than cold electrons to be released as electricity, generating lower voltage, hence making less power when the outdoor temperatures rise.

The rated power for a solar panel power is measured at 25 deg C (77 deg F). A temperature coefficient is assigned to each panel model, indicating the drop in rated power for each degree the outdoor temperature rises. This is an important consideration when designing solar for property owners in regions with hot average temperatures.

Manufacturers have been reducing this coefficient with technology improvements, so be aware of the best-performing panels. Average panels have a temperature coefficient at or slightly below -0.40%/ deg C. The best available panels have a temperature coefficient of -0.25%/ deg C.

The difference in performance between an average 350-watt panel versus the same rating in a best available panel on a 110 deg F day in Phoenix would be 325 watts for the average panel versus 334 watts for the best available panel. So, where the average daytime temperature spends seven months of the year above the standard conditions of 77 deg F, the difference in power produced over 25 years becomes significant. Panel selection is an important consideration.

Power optimizers and inverters suffer from a higher incidence of failures as temperatures increase. Critter guards around panel arrays are discouraged, unless required, as they obstruct cooling air from circulating beneath the panels and around power optimizers. Similarly, inverters are best located on an outside north wall for maximum shade and coolest temperatures.

When considering the quality of panels for your solar system, it is often the case that temperature coefficient is as important as their design rating. Find a panel with the lowest $/kWh price, long warranty, low temperature coefficient and excellent power production guarantee to yield earlier payback and better economics.

Look at the system price compared to estimated power production over the 25+ year system life for a few different panel models to see if the result always leads back to the same choice.

Who knew that winter had solar benefits!

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