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How Do Solar Panels Work?

Solar panel efficiency has increased by 22.3% since 2012

Solar panels can work in many different types of climate even snow

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The Smart Export Guarantee (SEG) launched on 1st January 2020 to replace the old Feed-in Tariff. Check out our guide to the SEG here to find out how much you could earn.

Solar panels are powered by the sun. The Pope also lives in the Vatican, and water is indeed wet. Knowing this, it would be easy to figure that solar panels do their best work on a hot sunny summer’s day, while basically sitting idle on a chilly winter’s afternoon.

But how valid is this? What’s the science behind solar panel efficiency, and is this preconception true? Does a cold dreary day actually affect your solar panels’ output enough to render them “not worth it”?

Let’s take a look at how solar panels work, what their ideal conditions are, and whether snow and cloud are really a problem for this renewable energy source. To start collecting free quotes for solar panels, enter your details into this quick form, and our suppliers will be in touch.

solar panel being made in factory

What's on this page?

How do solar panels work?

We won’t mince words here – the science behind solar panels is complicated and confusing for those of us who aren’t engineers. So we’re going to do our best to make it as simple as possible, for your sake and ours.

So the sun emits heat and light – this much we all know. And light, you may also know, is made up of tiny particles called photons. Meanwhile, every solar panel is essentially a magnetized sandwich, with each slice of “bread” being a sheet of densely packed atoms. When photons from the sun hit a solar panel, the design of the panel causes the photons to knock electrons off of these atoms. This generates an electric current, which then powers your house or gets stored in a battery.

Infographic on how solar panels work

Solar panel components

A typical solar module usually sits snug in a glass casing, which offers a much-needed layer of protection for the silicon PV cells. Under this glass exterior is a layer of insulation, as well as a protective back sheet this makes sure no heat is lost, and prevents humidity building up inside the panel. 

Solar panels also have an anti-reflective coating that increases sunlight absorption, allowing the cells to soak up more sunlight. 

How do solar panels connect to the grid?

Once your solar panel system is set up, your installation company will supply all of the necessary information to your District Network Operator (DNO). After a few checks, the DNO will make sure you're able to connect to the National Grid.

Connecting your solar PV system to the grid allows you to take advantage of the Smart Export Guarantee, which gives you money for each kWh of electricity you generate. On top of these payments for energy generation, you also receive a sum of money for feeding any surplus energy into the grid. 

In total, you could stand to earn £340 per year by connecting a 4kWp solar panel system to the grid.

Do solar panels need heat or light?

Solar PV panels work by absorbing the light not the heat from the sun, and turning it into usable electricity. 

There are, however, solar water heating systems that use solar thermal panels. These panels do collect heat from the sun, and use it to heat up water that is stored in a hot water cylinder. A boiler or immersion heater can be used as a backup to heat the water further to reach the temperature you want.

What is a solar inverter?

Every solar panel produces direct current (DC) electricity, but your house requires alternating current (AC), which is why you need a solar inverter. This clever bit of kit converts DC into AC, so you can use it to power your home. Your two options are a string inverter or a micro inverter, but which should you choose?

String inverters are lone operators, receiving the DC electricity from all of your solar panels at once, before converting it to AC. This puts a lot of pressure on the string inverter, and means that the output of your solar panels is dictated by the performance of your weakest panel.

For example, if a bit of shade or dirt is affecting the output of one of your panels, this will consequently affect the output of all of your panels. Keep them clean and unobstructed.

A string inverter tends to come with a 5-year or 10-year warranty, so it will typically need replacing at least once during the lifespan of your solar panels. Replacing a string inverter typically costs between £500 and £1,500.

Micro inverters operate as a team. Each of your solar panels is assigned an individual micro inverter, which means the DC-AC conversion happens at the point of energy creation, rather than at a later stage. With micro inverters installed, a weak performance from one of your panels will not affect the rest of them.

Given that micro inverters have to deal with significantly lower voltages, they tend to last much longer than string inverters (i.e. 20 or so years, instead of 5-10). When you do eventually need to replace your micro inverters, it’s about £50-£100 per unit, so it would cost about £1,500 to refit a 14-panel system with new ones.

taking solar panel measurements

What are solar panels made of?

Perhaps you’re curious as to how these things are actually put together.

Each solar panel is made up of approximately 32-48 solar cells, which are in turn made from a semiconducting material called silicon. Most panels either use monocrystalline or polycrystalline silicon, “mono” offering a higher level of performance than “poly”.

The solar cells are then connected together using soldered metal, creating an impressive matrix-style structure. If that’s the sandwich filling, all you need now is the bread. A layer of glass (approx. 7mm thick) goes on top, and a polymer-based backsheet goes on the back. Stick on a strong aluminium frame with EVA glue, and you’ve got yourself a solar panel.

For more information, check out our guide to the three main types of solar panel.

Did You Know?

You can save more than £400 each year, just by switching your home’s energy supplier. If you’re looking to cut down your bills, this one’s a bit of a no-brainer.

That’s why we’ve partnered with Switchd. With four different price plans (including a free option), Switchd will find you cheaper, greener energy suppliers in no time.

Do solar panels need direct sunlight?

That’s where it gets a little tricky. No one could blame you for thinking that a solar panel does its best work on a hot summer’s day. However, seeing how complicated these devices are, you can assume they're pretty capable of functioning in different types of weather.

Part of this is true. Solar panels (obviously) need the sun to operate; the more sun that shines down onto the panel, the more efficient it will be at producing energy. That much is easy to figure out.

The surprising part is that solar panels are actually less efficient in intense heat. Yes, we know – a device that operates best in direct sunlight is impeded by high temperatures. It’s certainly a bit of a design flaw – perhaps an obstacle for future solar panel generations.

It doesn’t take much heat to start lowering a panel’s efficiency. In fact, all solar panels have a “Pmax temperature coefficient.” This refers to the amount of power a solar panel will lose as the temperature rises 1°C above 25°C.

We’ve found Pmax numbers for some of the bigger solar panel models and listed them here.

Pmax Coefficient (%/°C)
Sunpower Maxeon 3
Panasonic N330
Canadian Solar HiKu
TrinaSolar Duomax

Information updated in July 2019.

As you can see, a solar panel in 26-27°C won’t have a noticeable drop in output – but in a place like Nevada or Egypt, the sweltering heat would reduce a panel’s efficiency by a considerable amount.

How hot do solar panels get?

Just as with any other electronic device, solar panel performance declines as the panel gets hotter. Home solar panels are tested at 25°C, meaning solar cells will produce at maximum efficiency at this temperature. If you live in a hotter climate, however, your panels can get as hot as 65°C, at which point solar cell efficiency will be hindered. 

Manufacturers rate their products’ susceptibility to temperature with a “temperature coefficient”, which varies from model to model this is expressed as a percentage per degree Celsius. 

Since it's standard practice to test solar panels for power output at 25°C, if a panel is rated to have a temperature coefficient of -0.50% per °C, that panel’s output power will decrease by a half of a percent for every degree the temperature rises above 25°C (77 °F). 

Do solar panels work in cloudy weather?

People in the UK are no strangers to cloudy weather, but does this mean that they shouldn’t consider solar panels?

The idea that “solar panels stop working on cloudy days” is a common misconception. Remember that light is a spectrum, and solar panels want all of it. While clouds can obstruct visible light, there are still multiple different wavelengths of light that can penetrate through even the thickest of cloud.

After all, when clouds coat the sky, it’s not like we’re all stumbling around in darkness – it’s very much still bright. That means your solar panels will still be getting suitably juiced up throughout the day.

There’s also the ‘edge-of-cloud’ effect, a bizarre phenomenon that causes clouds to intensify the strength of the sun’s light. Just as a cloud starts to pass in front of the sun (or just as the sun starts to emerge from a cloud), something very special happens. The sunlight actually refracts as it glances off the edge of the cloud, causing a sudden boost in its intensity.

So, while the fluffy centre of a cloud might not be ideal for your solar panels, the wispy edges are basically like big magnifying glasses.

Solar panels for cloudy climates

Since clouds have the potential to stunt your panels’ efficiency, you want to make sure you invest in a solar panel system that will be able to absorb as much sunlight as possible. 

That’s why we’ve compiled a list of the most efficient solar panels in 2020. 

Solar panel manufacturer
Maximum efficiency
Canadian Solar
BiKu CS3U-365PB-FG
X22-370 DC
HIT® N340
Yingli Solar
PANDA Bifacial 60CL
NQ-R Series 258W
JA Solar
72-cell Mono PERC

Information updated in January 2020.

Britain isn’t exactly renowned for its crystal clear skies, so you might want to make sure you choose one of the options above. To get up to date on how efficient solar panels can be, head over to our solar panel efficiency page, where you’ll find everything you need to know before making the leap.

Do solar panels work in snow?

Even though we don’t get blizzards upon squalls in the UK, snow can still rear its head when you least expect it, in months as late as April. The thing is, snow is the worst possible environment for solar panels. It can cover the panel entirely, meaning no light gets through, and if enough snow piles up, it can break the panel altogether.

To make sure you know what kind of chilly punishment a solar panel can take, we’ve taken some of the bigger solar panel brands and had a look at how much snow their top models claim to be able to handle.

Snow load (Pascals)
Sunpower Maxeon 3
6,000 Pa
Panasonic (All models)
5,400 Pa
6,000 Pa
Canadian Solar HiKu
5,400 Pa
TrinaSolar Duomax
5,400 Pa

Information updated in July 2019.

Firstly, if the unit “pascal” means nothing to you, then you should know that one pascal is equal to one newton per square meter. And if you don’t remember your Year 7 science lessons, a newton is the amount of force needed to accelerate a one kilogram mass at the rate of one metre per second squared.

1 Pa is approximately 0.1 kg/m². This means that panels with a 6,000 Pa load can handle 611.8kg/m² of snow before something goes wrong. Panels with a 5,400 Pa maximum can take 550.6kg/m². As you can see, this is a lot of snow – more than we’re ever likely to get over the course of one night. Even if we do experience a cold snap, it won’t be hard to brush some snow off every day to minimize the risk of damage to your panels.

The best conditions for solar panels

You can’t control the weather, but there are four key things you can do to ensure you get the best out of your solar panels.

1. Point them south

The direction that your solar panels are facing is the number one most important factor when setting up a solar PV system. If there’s a portion of your roof that’s south-facing or even southwest/southeast-facing, this is where your panels should be going. Since the sun rises in the east and sets in the west, south-facing panels have the best chance of capturing the most sunlight across the day.

2. Angle them at 30°

Solar panels always operate at maximum performance when the sun is directly perpendicular to them. You want the sunlight to be hitting your panels as directly as possible. In the UK, this basically means that a 30-45° angle is ideal.

Obviously, as the sun changes its position in the sky throughout the year, the optimum angle for your solar panels changes. For example, in the winter they should be positioned at a steep 60°, while in the height of summer a low 20° is best. However, once your panels have been installed, it’s not that easy to readjust the angle every few months (unless you hire a professional installer to do it for you).

That’s why 30° is the recommended permanent position for your panels.

3. Remove the shade

There’s no point in getting the perfect direction and angle for your solar PV system if it’s just going to sit in shade. Be sure to clear away anything that might cast a shadow on your panels, particularly any big trees. If the obstruction is in your neighbour’s garden, you’ll just have to ask them nicely, or reconsider where your panels are going.

4. Keep them clean

As dust and dirt build up on your panels, this will gradually make them less effective. The sunlight will find it harder to reach the solar cells beneath the grime, and consequently you’ll have less electricity to use at home.

Naturally, the best thing to do is to keep your solar panels clean. Manufacturers recommend that you give your panels a scrub once or twice a year, and you can either do this yourself, or pay approximately £100 for professionals to do it for you. Of course, rainfall in the UK helps to keep solar panels pretty clean, but there’s only so much lichen, plant sap, and bird droppings that rain can run off.

Life expectancy of solar panels

The vast majority of residential solar panels typically come with a 25-year warranty, although they are built to last around 40-50 years.

Fortunately, solar panels have no moving parts, so the risk of something breaking is extremely minimal. This can make maintenance costs as low as £0 for decades at a time (other than the cost of replacing the inverter, and a little bit of cleaning). Insure your solar panels, though, just in case.

Finding an installer

If you think that the switch to solar sounds like the right move for you and your household, you've picked a great time to do it.

65% of people are likely to buy a house with solar panels, according to our latest National Home Energy Survey.

And we can help you make the switch. Simply fill in this short form, and our professional installers will be in touch with their quotes.

Duncan Lambden Senior Writer

Duncan’s world-saving style comes in the form of energy conservation. Whether it’s solar panels or energy efficient bulbs, Duncan knows how to save energy.

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