Solair World

Does Solar Heater Work at Night?

If you use our links to purchase something, we may earn a commission. Learn more.

It is no secret that solar heaters draw their energy from the sun. Equally important, one can’t expect the sun at night for obvious reasons.

Under such circumstances, does a solar heater work at night? It is good to know before buying one, especially if you mostly use a heater at night.

Fortunately, you have come to the right place for the answer to this million-dollar question. Is it a yes or a no, and why?

There is only one way to discover and eliminate doubt about it. Look at this discussion for answers and a better understanding of how a solar heater works.

Will My Solar Water Heater Work at Night?

How does a solar water heater work, to begin with? It has soar collectors responsible for absorbing heat from the sun.

It then transfers the heat it absorbs through solar radiation to the water heating system. The system can either have a flat plate collector or an evacuated tube collector, but the latter is quite common.

The system starts heating the water flowing through its components. The most significant component is the heat exchanger responsible for heating water through convection.

If these solar collectors need the sun to work, does that mean the solar water heater won’t work at night? Interesting, that’s not the case.

Why Does a Solar Water Heater Work at Night?

There are various reasons why solar water works at night. That’s despite the solar collectors being unable to heat the transfer liquid.

The following explains why that’s the case;

The Storage Tank

Once the solar water heater heats the water, you may not need to use it immediately. That’s where the storage tank comes in since it ensures the water stays hot.

It means the solar water heater will heat the water when the sun is available during the day, whereas the storage tank will keep it hot until you use it at night. It explains why the heater works even at night.

How long the water remains hot depends on your area’s climate and the manufacturer. However, finding one that can’t keep the water hot for at least a night is impossible.


A storage tank isn’t enough if the insulation is missing or inadequate. After all, it greatly determines how long your storage tank keeps the water hot.

Ensure you choose a system with a well-insulated storage tank for a long hot water supply. Otherwise, working at night will be hard for your solar heater.

The insulation material should be strong to withstand an enormous temperature difference. At one juncture, the water will be extremely cold, but that’s bound to change drastically once it is heated.

The minimum rating should be 200 degrees Celsius, if not more. The material you choose also determines how effectively the insulation prevents heat loss.

Insulation recommendations include thermoplastic, foam, and fiberglass. It is equally important to avoid any leakages to enhance insulation.

Besides the storage tank, you should insulate other components. Then include pipelines and solar collectors since insulating them reduces heat loss and extends the water’s hot period.

Correct Size

How much hot water do you need in your household? If it exceeds the capacity of your storage tank, then there is a problem.

It won’t hold enough water to last you, even at night. So, ensure you have the correct size when choosing a storage tank.


Sometimes, the solar water heater does not provide hot water at night. On the contrary, the electric water heater serves as a backup.

The good thing is that it only works when the solar heater can’t. Its role is to promote convenience when the green solution is unreliable due to weather and other factors.

Whereas it means high utility bills, combining a solar and an electric water heater is way cheaper than using the latter exclusively. Besides, there is no joy in the benefits of a solar heater when it can’t provide the hot water you need for whatever reason.

Can a Solar Heater Work on a Freezing Night?

Despite working at night, it can become hard when it is freezing. That’s because most insulations may be rendered useless under such circumstances.

That doesn’t mean you won’t find a solar heater working excellently, even on an extremely cold night. The main determinant is the insulation’s strength, not forgetting its installation and whether there are leakages.

How Long Does It Take for Solar Heater to Work?

You shouldn’t expect hot water at the right temperature from a solar heater until it heats all the water in the storage tank to that point. It usually takes between 5 and 6 hours to heat the entire tank capacity when the sunlight is normal.

Do Solar Water Heaters Work in the Morning?

The answer to this question depends on the efficiency of your solar water heater. That’s why it is crucial to choose one wisely lest it disappoints you.

Solar water heaters store water in an insulated storage tank after heating it to the ideal temperatures. Since it uses the sun’s thermal energy to heat water, it will only heat it for the day.

So, let’s say the time between sunset and the next sunrise is around 12 hours. As long as the storage tank can maintain the temperature for such a period, you will have hot water the next morning.

It is rare to find a solar water heater that can’t hold the temperatures for such a period. So, one can say that most, if not all, solar water heaters work in the morning.

How Long Does Water Stay Hot in a Solar Water Heater?

A solar water heating system has various components, and one of them is the storage tank. It is responsible for storing the heated water and ensuring it maintains that temperature for as long as necessary.

However, don’t expect the storage tank to keep the water hot forever. In most cases, it can keep the water hot from 72 to 80 hours but narrows down to your manufacturer.