Solar power can be a great addition to a home – it certainly saves you money in the long run and will help cut your bills. We all know that solar power uses the suns energy however, and during the winter, the sun isn’t out as much – and it isn’t as strong, so just how much can you expect of your solar PV or solar thermal during those long winter months?
Solar PV relies on light not heat
Many people think that a hot sunny day will produce more electricity than a colder sunny day. This just isn’t the case. Solar PV relies on the light of the sun, but higher temperatures actually reduce the effectiveness of the panels. So cold and bright are actually ideal conditions.
Having said that, the lower the sun is in the sky, the less energy will reach the panels. In winter, the sun will always be lower in the sky, and therefore will produce that bit less energy. Couple that with the fact that winter days are shorter and unfortunately you can guarantee that the panels will not be as effective in winter.
So what are the figures? The Energy Saving Trust have published some figures which suggest a standard 3kW system facing due south, producing around 300kWh during June and July, will produce around 75kWh in a winter month like December or January. So you are talking about a 5th of the energy production in the winter months.
Another quick tip – make sure you clear the snow off your panels if you do happen to have snow – you will produce zero energy if the panels are covered.
Does solar thermal work in winter?
So solar PV may not produce the kind of electricity you get in the summer, but it is still producing some energy. Let’s now compare this to solar thermal. Solar thermal heats water using the heat of the sun, so you would expect it to produce far less usable heat in the winter.
And again this is the case. We looked at a typical Viesmann solar thermal system, and they suggest that solar thermal should provide about 60% of your hot water needs as an annual average, with about 90% during the height of summer, and about 25% during the winter. Solar thermal is affected by the loss of direct sunlight a bit more than PV and realistically you should not expect too much from your solar thermal during winter. They are also affected by cloud considerably more than solar PV, so a cloudy winter day you should not expect your solar thermal to do much at all.
You should note that evacuated tubes tend to work much better than the older style solar thermal systems in winter conditions, so whilst they will still only produce a small amount of your hot water, a modern evacuated tube system will provide more heat.
Can you optimise your panels for winter?
During winter, the optimal angle for your panels will be lower, because the sun is lower in the sky. Some systems will allow you to alter the angle over the year to optimise the system, though this will depend on the mounting used. Some systems will track each day with the sun, whilst others will allow for infrequent manual altering of the tilt over the year. Most systems are fixed on roofs for domestic customers, so unfortunately there won’t be anything you can do.
Can you rely on solar in winter?
Unfortunately solar is not going to provide all your energy needs in winter, but people are sometimes surprised by just how much you can get out of some of these systems during the colder months.
Don’t rely on your panels in winter to heat your hot water or run your electric heating, but remember that the savings over the whole year should pay for the system in less than 10 years!