March 26, 2018 Solar Energy Written by Greentumble Editorial Team
How well do solar panels work in the winter
One might think that solar panels would

generate the most electricity in a hot, sunny climate. But a closer look at how solar panels actually work quickly dispels this notion.

Solar panels are also commonly referred to as PV panels. A solar panel contains many solar or PV cells. PV stands for photovoltaic. Photovoltaic means that the cell is capable of converting a photon into an electrical charge.

What is a photon?
The sun releases packets of electromagnetic radiation (light) that travel the 93 million miles from the sun to the earth in eight and half minutes. These packets of energy are called photons. A photon is a particle of light defined as a discrete bundle (or quantum) of electromagnetic (or light) energy [1]. That speed alone gives one an idea of how much energy a photon contains. A solar panel is ready to take advantage of that energy and turn it into usable electricity [2].

A solar panel is made up of many solar cells. At present, the dominant semiconducting material used to make solar cells is silicon. Solar cells are made primarily of crystalline silicon containing a positive layer and a negative layer to create an electric field. When the photons hit a solar cell, they knock electrons loose from their atoms. If conductors are attached to the positive and negative sides of a cell, it forms an electrical circuit. The electrons flow through this circuit, creating electricity. The faster the electrons flow, the higher the voltage output.

It is the sunlight, not the heat that the solar cell uses. In fact, heating the material through which the charge flows can cause resistance, slowing down the flow of electrons.

There is a lot of research being conducted in the solar industry to improve efficiency of solar panels under different conditions. This includes experimenting with different materials.

Because of the resistance created, solar panel becomes less efficient when the temperature rises above 25 degrees Celsius or 77 degrees Fahrenheit. This is considered the ideal efficiency temperature for solar panels and is the parameter upon which efficiency ratings are based. It is referred to as the Standard Test Condition or STC.

For a more comprehensive explanation of the Standard Test Condition rating in the solar industry, and how to understand the efficiency of different panels on the market, read more at Effect of Temperature on PV Panel Efficiency.

Conversely, resistance decreases with decreasing temperatures. For example, in polycrystalline PV panels, if the temperature decreases by one degree Celsius, the voltage increases by 0.12 V [3].

So, actually, solar panels operate more efficiently in cold weather [4].

Polycrystalline solar panel in winter

Polycrystalline solar panel in winter


 

But what happens to solar panel efficiency in snow?

The positive side of snow is that the reflection of sunlight on snow can mean more available light for the solar panel to convert into electricity [5].

The difficulties arise when snow has fallen onto the panels and blocks sunlight from reaching the solar cells. Because a cell begins heating once sunlight hits it, even just removing a small amount of snow from a panel can kickstart the heating process and hasten snow melting from the rest of the panel.

Another consideration in the speed of melting snow and the availability of electricity is whether the system of panels has a single inverter for the entire array of panels or has a micro-inverter for each panel. An inverter is the mechanism which converts the direct current of electricity produced within the PV panel from direct current (DC) to alternating current (AC) used by American households. Central inverters were the norm until recently. A problem on one solar panel would diminish performance of the entire array or system.

Micro-inverters optimize energy conversion per panel so even if one solar panel has an issue, like snow build-up, the remaining panels can still perform efficiently [6].

So, if you know that one side of the roof is going to heat up enough to melt the snow, you might not bother trying to get the snow off the panels on the other side as it just may not be worth the effort, opting instead to let rising temperatures over the next few days do the work for you.
 

Removing snow from solar panels

Solar panels have smooth surfaces. They become slippery when wet. And they are typically installed facing south or southwest, so when the sun comes out snow should quickly melt and slide off on its own [7]. If, however your solar panels are not easily accessible, like on the roof and are not at a sufficient angle that gravity readily encourages the snow to slide off, then one must consider how to remove the snow as technological improvements are not yet in place to help out.

Silly and potentially harmful ideas for manually clearing snow from solar panels abound on the internet. For example, throwing a nerf ball to begin a cascade of snow. That might take a while. Other suggestions include hosing the snow off, but freezing temperatures may compromise the materials. Objects such as rakes may well scratch and damage the surface of the panels.

And then there is the safety issue. A rooftop is generally high enough to cause a safety risk getting up there in favorable weather, let alone when it is wet or icy outside. One must also consider where the avalanche of snow will land once dislodged.

The best two alternatives at this point are a soft snow removal rake with a long, flexible handle specifically designed for snow removal from solar panels or you may opt to utilize a maintenance company to clean dirt, debris and snow from your solar panels [8].

So, while intuitively one might think solar panels work better in hot climates, the fact is that they can produce more power on a sunny winter day in New Jersey than a blazing hot summer day in Arizona.

Snowfall on the ground can create more available reflective light and it is the light from the sun that is converted into electricity, not the heat. The most significant problem occurs when sunlight is blocked from hitting the solar panel due to snow drifts.

At present, either patience or manual removal is the most feasible option.

 


References

[1] https://www.thoughtco.com
[2] https://us.sunpower.com/blog/2016/12/06/yes-solar-panels-work-winter/
[3] https://www.teachengineering.org/content/
[4] https://www.nrgcommunitysolar.com/blog/solar-panels-work-winter/
[5] https://www.theecoexperts.co.uk/do-pv-panels-work-cold-weather-conditions
[6] https://news.energysage.com/solar-panels-in-winter-weather-snow-affect-power-production/
[7] https://us.sunpower.com/blog/2016/12/06/yes-solar-panels-work-winter/
[8] https://www.nrgcommunitysolar.com/blog/solar-panels-work-winter/