Asking the question ‘do solar panels work in winter?’ is a reasonable one. As energy costs soar, and more and more homeowners are considering installing solar panels on their roof in a bid to save on energy bills, it’s only right to question how they will work and how much energy they can generate day-to-day, especially during the winter months.
Solar panels are growing in popularity again not least because the expected payback time has reduced as electricity costs rise. However, unlike sunnier climes, the UK weather can be temperamental and we are prone to dull, cloudy days. So, will you get the most out of solar panels on your roof, especially in winter?
Our guide answers this question, and more, to help explain how solar PV panels work in winter.
So, do solar panels work in winter?
The simple answer is yes, solar PV panels do work in winter. Despite the sun being lower in the sky, and the days being potentially cloudier and rainier, solar panels will still generate electricity, just not as much electricity as they would during summer because the amount of daylight hours is reduced. But, they will still work. And here’s why.
Understanding how solar panels work is important first. Solar panels are made from wafers of silicon, a semiconducting material in which electrons are stimulated in response to photons of light, thereby generating electrical energy.
That is all light, not just direct sunlight, because solar cells will also react to diffuse light which is light that has been scattered by particles such as rainclouds in the atmosphere. Which is why solar panels will still operate in the winter months, without direct sunlight.
Indeed, rainy weather can benefit solar panels by washing away accumulated dirt and grime on the surfaces that would otherwise restrict the amount of light, potentially enabling the panels to work more efficiently.
Solar panels generally need at least four hours of direct sunlight to operate at their peak performance. According to Yes Energy Solutions, this is based on 1,000W/m2 of sunlight for peak output.
However, as mentioned previously, this doesn’t mean that solar panels won’t work at all in anything less than direct sunlight. In fact, just this year, scientists at Stanford University in the US developed solar panels that actually work at night, using infrared light.
In general, throughout the year, the most suitable roof for a solar panel array is one that faces south or south east, thereby orientated towards the morning and noon sun. A roof that faces south-west or west may still be suitable, but in those directions, the sun will be in decline as it moves towards setting. Any danger of shading the panels might be mitigated by locating the panels in a ground array in the garden or yard rather than on the roof.
How much electricity do solar panels generate in the winter?
According to The Green Age figures produced by the Energy Saving Trust suggest a 3 kilowatt solar system facing due south will produce around 300 kilowatt hours (kWh) in June and July but only 75 kWh in the deep winter months of December and January. This amounts to about a fifth of the electricity generated during the summer months.
Solar panels generate less electricity in the winter for several reasons:
- First, there is less sunlight available during the course of the day.
- Secondly, the sun is usually lower in the sky and therefore the light reaching the panels is weaker.
However, on some winter days, more electricity may be generated than on a summer day during a heatwave, because too much heat can adversely affect a solar panel. (Solar panels also work in hot desert countries because of inbuilt safeguards against ‘heat induced degradation’.) In more northerly regions though, the cold combined with bright sunlight can actually benefit solar power generation. (Teach Engineering explain all about it in this PDF.)
The UK receives an annual average total amount of sunshine of 1,339.7 hours, representing just under 30 percent of the maximum possible amount (approximately 4,476 hours during the course of a year). Due to its geographical location and climate, UK skies are frequently cloudy.
Unsurprisingly, the northern regions of the UK receive less sunlight than the south. Dorset, Hampshire, Sussex and Kent being the sunniest parts of the country, receiving an average total of around 1,750 hours per year.
Sea fog in coastal areas and high pressure weather systems called anticyclones may also present a problem.
How much solar PV energy do you need to power a house?
So can you run a house on solar power, and in winter? “This is a very good question, and an essential piece of information to feed into the design process,” says energy efficiency expert Tim Pullen. “We need to know how much energy the house requires before deciding how much we can or want to generate.”
If we take that figure of 75kWh generated by a 3kW solar panel system in the deep winter months and give some context: a flat screen TV uses 0.1kWh/hr (hour); a fridge uses 1.6kWh/day and according to Which? an electric mid-sized car or SUV like the BMW iX consumes 20.4kWh per 100km. As such, solar power is not going to provide all our generation needs in the winter in particular.
“However, at best these are only a starting point,” explains Tim. “What is wanted is a detailed and accurate calculation of the energy demand based on the building and the people in it. This ideally needs to be completed by a specialist, as working out how much electricity is needed for lighting, appliances, etc, and so on is a tricky process.”
What temperature do solar panels work best?
Solar panels are most efficient at temperatures between 15°C (59°F) and 35°C (95°F), according to Action Renewables, but still work in the colder winter months.
This also means they will still generate efficiently during a (thankfully rare) UK heatwave as experienced recently. However, solar panels will start to lose efficiency as it grows hotter beyond those temperatures but this will not normally be a problem in the UK.
Do solar panels work when it snows?
A solar panel that is covered in snow is not as great a problem as you might think. In most cases, the residual heat generated by the panel will melt the snow sufficiently so that the snow just slides off, although excessively heavy snowfall will require the snow to be cleared off the panel surface manually.
Another potential danger is that frozen water could damage solar panels in cold conditions causing cracks in the solar cells and adversely affecting soldered joints and damage components.
However, solar panel manufacturers generally tailor their products to specific regions, thereby taking into account local climatic conditions. In most cases then, your solar panels should be able to withstand freezing temperatures.
This is not normally a problem in the United Kingdom, except perhaps for some regions of northern Scotland.
How can you maximise solar panels in the winter?
The best way of maximising electricity generation from solar panels in winter is to support the system with a solar battery energy storage system. This will enable storage of excess electricity generated during the summer for later use in the winter, and electricity produced in the day to be used at night.
It will also reduce amount of electricity sourced from the grid during the winter months. Some energy companies have launched ‘time-of-use’ tariffs so that electricity can be stored in a battery while it’s cheap (such as overnight).
Batteries can also be affected by the cold weather, as they are mostly meant for indoor use. One example is the Panasonic Evervolt system, which has an operating temperature range of 0°C (32°F) to 50°C (122°F).
The risk to batteries from colder temperatures can be mitigated by locating them in a sheltered place such as a garage or insulated building or indoors in a house. This will keep them operating efficiently.
Other options for maximising electricity generation from solar panels include reorientating the tilt angle of the panels (assuming that is possible, it may not be if they are roof mounted) to take advantage of the lower level of the sun in the winter sky. Cleaning panels regularly is also important, but usually the rain will do that for you.
