Does Solar Thermal Work In The Winter/Snow?

We get asked this question a lot, and it’s understandable considering solar thermal panels rely on energy from the sun to heat water. The short answer is yes, solar thermal works in winter. However, the panels don’t work as efficiently during the winter months, which means they may not be able to provide all your hot water needs.

For this reason, you should always have a conventional boiler or immersion heater installed as a backup system – most boiler and hot-water-cylinder systems are compatible with solar thermal, however if your boiler is a combination (combi) boiler and you don’t currently have a hot-water tank, then solar thermal may not be compatible. Having a backup system will ensure you have enough hot water during those long cloudy days when your solar thermal system is not able to generate enough heat.

How much energy will a solar thermal system produce in winter?

A modern solar thermal system should be able to provide around 70% of your total hot water needs over 12 months. But this includes the summer months when solar thermal systems are at their most efficient.

A typical solar thermal system will provide around 90% of your hot water needs during the summer but this can fall to as low as 25% during the winter.

The drop in performance is due to several factors including shorter daylight hours and increased cloud cover. The sun is also lower in the sky during the winter months which reduces the amount of direct sunlight hitting the panel.

Are solar thermal panels affected by frost?

No – Most solar thermal systems installed in the UK are either indirect or closed-loop systems. Both types of systems use eco-friendly antifreeze in the heat transfer fluid which prevents it from freezing as it circulates through the collector and heat exchanger.

Typically this antifreeze is capable of withstanding temperatures as low as -28ºC. This should ensure your system keeps working even during the coldest winter nights.

We are sometimes asked if the antifreeze needs changing. While it is true that antifreeze degrades over time, it should last for more than 10 years. But as a precaution, the antifreeze should be checked at each service interval.

Do solar thermal panels still work in the rain?

Solar thermal panels require direct sunlight to generate heat, so the performance of your panels will be affected by rain clouds. But because modern systems are extremely efficient you only need a small amount of sunlight to generate enough energy to heat your water.

So it is only on heavily overcast days when there is no sunlight at all, that your system won’t be generating energy. On days of intermittent sunshine and showers, there should still be enough sunlight around to provide enough energy for your needs.

Are solar thermal panels affected by snow?

Snow acts as a filter preventing sunlight from reaching the collector. This can have a detrimental effect on heat transfer. However, according to the Met Office, snow is only on the ground for approximately 15.6 days a year in the UK. And because the snow melts off the panels quickly, they should only remain covered for a few days at most.

So snow shouldn’t cause any problems long term, although where performance is concerned flat plate collectors deal with snowy conditions better than evacuated tube collectors – this is thanks to the flat plate collector’s absorber plate, which will capture any light that makes it through the snow causing it to melt and slide off more quickly. Sadly this isn’t the case with evacuate tube collectors as they have a form of vacuum insulation designed to reduce heat loss, hence they won’t be as affective when it comes to melting snow.

Is it worth installing solar thermal in the UK?

YES – provided it has been installed by an MCS Certified Solar Thermal Installer, a typical evacuated tube solar thermal system should be able to provide around 70% of your total hot water requirements over the year. This represents a huge saving on your energy bills and will significantly lower your carbon footprint.

While the amount of heat produced will fall during the winter months, modern solar thermal systems are incredibly efficient and will still contribute towards your heating and hot water requirements, even during the depths of winter.