How Do Solar Panels Work?
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Solar panels turn daylight into electricity using a process discovered in the 19th century and refined ever since. You do not need to understand the physics to benefit from them, but a little knowledge helps you ask installers the right questions and judge whether a quote makes sense.
The photovoltaic effect, in plain English
A solar panel is made up of many photovoltaic (PV) cells, each one a thin wafer of silicon. When daylight strikes the silicon, the energy in the light knocks electrons loose. Because of the way the cell is constructed, those electrons can only move in one direction, and that flow of electrons is an electric current. The brighter the daylight, the more electrons are freed and the larger the current. Crucially, panels respond to light, not heat — which is why they work perfectly well in cool British conditions and, in fact, lose a little efficiency when they get very hot.
The electricity a panel produces is direct current (DC), the same kind that comes from a battery. Your home, however, runs on alternating current (AC), the kind that comes from the grid. That is where the inverter comes in.
The four parts of a solar system
1. The panels
Mounted on your roof, the panels are the part everyone recognises. A typical modern domestic panel is rated at around 400 to 450 watts, and a standard home system uses ten to twelve of them to reach roughly 4 kilowatts-peak (4kWp). "Peak" refers to the output under ideal test conditions; real-world output varies with the weather and the time of year.
2. The inverter
The inverter converts the DC electricity from your panels into the 230-volt AC electricity your home uses. It is the brain of the system, and its quality matters: a cheap inverter is a common reason for early system faults. Some homes use a single "string" inverter; others use micro-inverters or power optimisers, which can help if part of the roof is shaded.
3. Your consumer unit (fuse board)
From the inverter, the AC electricity flows into your home's consumer unit and is used by whatever appliances are switched on at that moment — your fridge, router, kettle and so on. Solar electricity is always used first, before any is drawn from the grid, so you automatically reduce what you buy from your supplier.
4. The meter (and optionally a battery)
A smart meter measures both the electricity you import from the grid and the surplus you export back to it. Any electricity your home cannot use at the moment it is generated flows out to the grid, and under the Smart Export Guarantee your supplier pays you for it. If you fit a battery, that surplus is stored for later instead, so you use more of your own power.
What happens on a typical day
On a bright morning, your panels may produce more electricity than your home needs. The excess charges your battery (if you have one) or is exported to the grid for payment. By early evening, when generation falls and demand rises as people return home, your battery discharges to cover that demand, or you simply draw the shortfall from the grid as normal. The system manages all of this automatically — there are no switches to flick and nothing for you to do day to day.
Do they work in winter and on cloudy days?
Yes to both. Generation in December is naturally lower than in June because the days are shorter and the sun is lower, but the panels still produce useful electricity throughout the year. On a cloudy day output drops compared with bright sunshine, yet it does not stop. Over a full year a well-sited UK system performs reliably; the seasonal peaks and troughs simply balance out. You can read more on our pages about whether solar panels work in the cold and generating electricity in daylight hours.
How roof direction and pitch affect output
A south-facing roof is ideal because it captures the most daylight across the day, but it is far from essential. East and west-facing roofs typically produce around 15% less than south-facing, which is still very worthwhile, and an east-west split can actually spread generation more evenly across the morning and afternoon. A pitch of roughly 30 to 40 degrees suits most UK homes. The bigger enemy is shading — from a chimney, tree or neighbouring building — because shade on even one panel can drag down a whole string unless optimisers are fitted. See does my roof need to face south and what is shading for detail.
Monocrystalline panels and what you will be offered
Almost every domestic installation today uses monocrystalline panels, recognisable by their uniform black appearance. They are more efficient than the older blue-tinged polycrystalline type, meaning they produce more from a given roof area — which matters in Britain, where roof space is often the limiting factor. You may also hear about "half-cut" cells and PERC technology; both are refinements that improve performance and resilience to partial shading. You need not memorise the terminology, but it is reasonable to expect a reputable installer to fit good-quality monocrystalline panels with a sensible performance warranty of around 25 years.
How much electricity will a system produce?
As a rule of thumb, each kilowatt-peak of well-sited panels generates roughly 850 to 1,000 units a year in the UK, with the south and south-west at the higher end and Scotland a little lower. A 4kWp system therefore produces somewhere around 3,400 to 4,000 units annually — enough to cover a large share of a typical household's demand, especially if you shift some usage, such as the dishwasher or washing machine, into daylight hours. A battery removes the need to time appliances so carefully by storing surplus for whenever you need it. For more on what reduces output, see what affects solar panel power generation.
The bottom line
A solar system is simple to live with: daylight in, clean electricity out, with surplus either stored or sold. The technology is mature, the components are well understood, and a quality installation should run with little more than the occasional clean and an inverter replacement around the twelve-year mark. Once you understand these basics, the rest of your decision comes down to cost, savings and choosing a reputable installer — all of which we cover elsewhere on this site.
