Solar panels and weather

Do solar panels always need direct sunlight?

The renewable energy industry and solar in particular are still young. This is why people ask all sorts of questions about how PV modules work. One of this kind is "Do solar panels always need direct sunlight to work?" The short answer is "no, they don't". The long one is this article, where we explore the relationship between the Sun and panels and how shade and weather affect it.

Solar panels work as long as there is daylight

Solar panels work as long as there is daylight
Panels produce the maximum amount of energy when sunlight strikes them at a 90° angle. This is why positioning and angle are so important for a solar installation. In the northern hemisphere solar panels should face south for maximum energy production. The inclination of panels can be equal to your latitude. In the USA, an angle between 30° and 45° generally works fine.

However, panels don't necessarily need direct sunlight to work. Even when there are heavy clouds in the sky, modules still produce energy: panels make use of more than just visible sunlight. The Sun gives off radiation of different wavelengths, some of which can't be perceived by the human eye. This invisible radiation penetrates the clouds to go straight to PV modules. As long as it is daylight, solar panels continue to produce energy. So, if you can't install solar panels under direct sunlight, they will still work, just at a lower capacity.

Shading decreases energy production drastically

Shading decreases energy production drastically
If there is something between the sun and your panels, that's another story. Solar panels in shade produce much less energy, because solar cells in a panel are interconnected. If the performance of one cell goes down, the ability to produce electricity of the whole module suffers. The performance of a panel may fall by more than 75%. Constant shading also shortens the lifespan of modules, because some cells have to work more than others and eventually burn out. Manufacturers addressed the problem of shading by implementing bypass diodes into PV modules. They split panels into several sectors, normally 3 or 4. If a cell in one sector is shaded, diodes don't let it influence the other sectors. For example, Panasonic HIT 330W with 4 bypass diodes will lose only 25% of its power output if one cell gets shaded. A solar panel with 3 diodes would lose a third of its production.

A shaded panel can become a problem if modules are connected in series and a string inverter is used. Bad performance of one panel drags down the power output of others. To avoid it, you can use microinverters instead, or combine a string inverter with power optimizers for every panel in the string.

Some modern panels are barely affected by clouds

Some modern panels are barely affected by clouds
On a cloudy day, the performance of solar panels falls by 10-25%. However, it's not unreasonable to go solar in cities and towns which can't boast of the abundance of sunlight. The profitability of a solar PV system also depends on the electricity price: the higher it is, the shorter the solar payback period. This is why a solar installation in cloudy New York city might pay for itself quicker than in sunny Arizona.

What is more, the design and construction of PV modules has improved a lot over the last years to make them more tolerant to freaks of nature. For example, Canadian Solar panels retain around 95% of their power output even when the sky is full of clouds. Good energy conversion rate in cloudy conditions ensures that your solar panels will pay for themselves quickly even in places where they wouldn't seem like a good idea.
7-8 years – the average solar payback period in the US

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Illustrations – Marina Fionova

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