Do Solar Panels Work At Night?

By Michael Olenick
March 15, 2017
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The short answer is: no, solar energy systems only operate during the day. This is because the power from the sun is key to how a solar panel turns light into electricity. However, that does not mean that solar cannot power your home day and night! Wait, what?

How Do Solar Panels Work - A Technical Explanation

Solar panels are made up of a collection of solar cells. Each cell is capable of producing electricity, which is made of two thin wafers of semiconductive material, usually silicon. Since silicon is not a great conductor by itself, each wafer is “doped” with impurities to make them more effective. One wafer is doped with phosphorus to create more free electrons, making the wafer more negative. The other wafer is laced with boron which has more receptor holes for electrons, meaning that it is more positive. When the two sides are connected, free electrons move from negative to positive wafers until balance is reached.

An electric field is created that moves other free electrons away from the positive side and back to the negative one. This is where the sun comes in. Light from the sun travels as photons, or packets of energy. When a photon hits your solar cell, it dislodges an electron creating an electron space. The electron just wants to fill the space, but the electric field moves the space to the positive side and the free electron to the negative side. In order to get back, the electron has to travel the long way around to get back. These travelling electrons are the current in your PV system and the electric field creates the voltage. The current from the cells flows out of each panel and the current from all the panels powers your home. Without the sun’s energy to dislodge the electrons from their happy state, there is no electron flow, no current, and no power to your home.

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Other Sources of Light

So light makes solar panels work. There are sources of light at night, such as streetlights, the moon, and the stars. You may wonder if these can make your solar panels run as well. Technically, it can happen. Moonlight is sunlight reflected off the moon’s surface. While the human eye is very good at adjusting to a full moon, making it appear almost as bright as day sometimes, the intensity is much less than the sun. A small trickle of power is possible, but with small system sizes, the total current is unlikely to be enough to reach the minimum to activate the system’s inverter to change the energy to AC power that your home can use. For practical purposes, other sources of light just are not strong enough to make electricity production useful.

Full Energy Offset From Solar

Then how can you get solar power all day and night? Since solar energy production is only practical during the day, some form of energy banking is necessary. The most common form is called “net energy metering”. Solar systems are designed to produce more energy than needed during the day and in the summer, which is then exported to the grid at the time that it is produced. Solar system owners are issued credits for excess generation by the utilities that manage the grid, and when those system owners take energy from the grid (at night), those credits are used. The balance of credits and debits are settled once a year during a true-up period. Other system owners rely on batteries to store excess solar energy to be either independent of the grid or only rely on the grid very infrequently. Some utility scale solar operations even use thermal banking to heat molten salt during the day and then discharge the stored energy at night. A power plant generates electricity from the heat of the molten salt even into the early hours of the night.

While the sun is the only source of power for solar systems, there are ways that your nighttime power usage can be offset by solar produced during the day.

View our 2018 Solar Starter Guide

 

Michael Olenick

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Michael Olenick

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