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ore and more homeowners are lured by the idea of harnessing solar power and generating green energy at home, which fuels the demand for solar panels. But here's the thing – evening hours after sunset is often the time when electricity is needed most, which leads to the question of whether solar panels can work at night. In this guide, we'll break down everything you need to know about nighttime solar energy.

How do solar cells generate energy?

To find out if solar panels work at night, it is essential to understand the core principles of solar energy generation.

Solar panels are comprised of photovoltaic (PV) cells – the basic working units of a solar system. These cells convert solar radiation into electricity using a process known as the photovoltaic effect. A solar cell is made from a semiconducting material, most commonly silicon. Thin wafers of silicon are doped with boron or gallium on the back side – these elements have one electron less than silicium, making the cell positively charged. On the front side, solar cells are doped with phosphorus, which, on the contrary, has more electrons than silicium and hence creates a negative charge. That builds a negative-positive junction which makes an internal electric field.

When the light hits a solar cell, electrons within it are moved from their regular positions, creating “holes”—the empty places left behind them. And as that happens within the electric field, the current of electricity is generated.

What happens to solar panels at night?

From the explanation above, you can see that solar PV cannot work after dark, as at night solar panels simply have no light to absorb. Without sunlight, the electrons can’t be knocked off their positions, so energy generation is impossible. And since solar panels stop working, your solar system will shut down automatically.

Can solar panels collect moonlight?

At night solar panels can’t generate power, but what about generating energy by harvesting moonlight? Well, that doesn’t work as well. This is because the moon doesn’t produce its own light, and the glow we see at nighttime is just a reflection of the sun’s rays. The number of photons reaching the Earth is too small to cause the photovoltaic effect within solar cells, which means solar panels can’t produce energy using moonlight.

At night solar PV doesn’t work, but you can still use solar power

Even though your PV panels can’t produce solar energy at night, you can still keep your lights on during the nighttime. Solar owners have two options for powering their homes at night, which can be used separately or combined.

Installing a grid-tied solar system

Some solar energy systems work autonomously and don’t depend on a local power grid. Such panels are often installed in areas without access to the transmission lines or where these lines are old and unreliable.

Other solar systems are grid-tied, meaning they are connected to the grid. This type of solar panel installation gives its owners more flexibility: they can either send any surplus energy their solar panels generate to the grid and get credits offsetting their utility bill or draw energy from the grid whenever needed. This means that at night solar owners can keep powering their homes even though their solar panels don’t work.

Pairing solar modules with a solar battery bank

Another solution to the night solar problem is using battery storage. On sunny days PV panels often produce more power than you might need, so you can keep the surplus for later and use this solar power at night.

Using the grid and solar battery together

Combining connection to the grid and solar battery storage is the most solid option for providing yourself with electricity at nighttime, as you can take energy from the grid or the battery – the latter may be the case during grid power outages, for example.

Bonus: night solar panels exist, but so far inefficient

Even though we’ve just determined that at night solar panels can’t produce power, this isn't entirely true. Scientists have recently designed innovative solar modules that can generate electricity even at night. These nighttime solar panels utilize the same concept as traditional solar but reversely. Solar panels heat up as they harvest solar radiation during daylight hours, and then emit infrared light back into space at night.

The novel night solar cell is called a thermoradiative diode – a device that generates electricity by emitting power instead of consuming it, as the current and voltage flow in the opposite direction.

This night solar technology is in its early stages and showcases a very low efficiency equal to 0.001% of the energy produced by a traditional solar panel. However, this tech can potentially change the solar energy market by providing homeowners with renewable energy even at nighttime.

Posted 
May 9, 2023
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