From the photovoltaic effect inside a solar cell to the usable AC power in your sockets, this guide covers everything you need before requesting quotes.
Photovoltaic panels, often called solar PV panels, are the same technology most people picture when they hear "solar panels". The two terms are used interchangeably in the UK market. The word photovoltaic comes from the Greek for light and the name of the physicist Alessandro Volta, describing panels that turn light directly into electricity.
This sets them apart from solar thermal collectors, which capture heat from sunlight to warm water. A photovoltaic panel generates electrical power; a solar thermal panel heats a fluid. Most UK homeowners asking about solar energy are asking about the photovoltaic kind, because it is the one that reduces an electricity bill and earns export payments.
Understanding how photovoltaic panels work starts at the cell level. Each panel contains dozens of photovoltaic cells made almost entirely from silicon, a semiconductor. Silicon atoms are arranged in a crystal lattice. When a photon of sunlight strikes a cell with enough energy, it knocks an electron loose from its atom.
The cell is built in two layers with opposing electrical charges, creating an internal electric field. That field pushes the freed electron in one direction, producing a flow of electrons, which is direct current (DC) electricity.
A single cell produces a small voltage. Cells are wired together in a module, and modules are wired together in a string to produce a useful voltage and current. The output at this stage is still DC, at a voltage that depends on the number of cells and the intensity of the sunlight hitting them.
Your home runs on alternating current (AC) at 230V. The DC output from the panels must be converted before it can power your appliances or flow into the grid. That job belongs to the inverter, a box typically installed in the loft or garage.
A string inverter handles the whole array as one unit. Microinverters attach to each panel individually, which can improve output when part of the roof is shaded. A hybrid inverter does the same conversion job but also manages a battery, storing surplus DC power before it is converted.
The inverter is the component most likely to need replacing during the system's life. Panels typically carry a 20 to 25 year product warranty, while inverters typically carry a warranty of around 5 to 15 years, according to the Energy Saving Trust and Which?.
Output is measured in kilowatt-peak (kWp), which is the panel's rated power under standard test conditions. Real-world generation is always lower than this figure because it depends on roof orientation, pitch, shading from trees or chimneys, local cloud cover, and the time of year.
A south-facing roof at a pitch of around 30 to 40 degrees produces the most electricity in the UK. East- or west-facing roofs produce roughly 15 to 20 per cent less over a year. Shading has a large effect because shaded cells can drag down the output of an entire string, not just their own section.
These factors explain the wide range in potential annual benefit. Which? puts it at up to £605 to £675 a year on an ideal south-facing roof, or £410 to £470 east-facing or shaded (bill savings plus Smart Export Guarantee export payments, June 2025 prices). Roof age matters too: installers generally recommend replacing a roof within 10 years of its expected end of life before fitting panels, since removing and refitting a system adds cost and complexity. Knowing how many photovoltaic panels you need for your specific roof is therefore a conversation worth having with an MCS-certified installer before you commit.
When your panels produce more electricity than your home is using at that moment, the surplus flows out to the grid. The Smart Export Guarantee (SEG) requires electricity suppliers with at least 150,000 domestic customers to offer a tariff that pays you for each unit exported. The rate is set by the supplier, not by the government, and it must always be above zero. Rates vary widely between suppliers, so comparing tariffs before you choose one is worthwhile.
To qualify for SEG payments, your installation must be certified under the Microgeneration Certification Scheme (MCS) or an equivalent scheme. This means using an MCS-certified installer is not just a quality marker but a practical requirement for earning export income. For a full breakdown of how the Smart Export Guarantee works, your installer can walk you through the supplier options relevant to your area. SEG is an export payment earned per kilowatt-hour, not a grant or a one-off subsidy.
A typical domestic system costs £5,000 to £10,000 installed, according to the Energy Saving Trust (July 2026 prices). The final figure depends on system size, roof access, panel type and the inverter chosen. Residential solar installation currently attracts 0% VAT, zero-rated to 31 March 2027, which reduces the upfront cost relative to most home improvement work. For more on what drives the price, see the section on solar panel costs in the UK.
Payback depends heavily on how much of the electricity you use directly, rather than exporting it. The more you can shift consumption to daytime hours, the faster the system pays for itself. On an ideal roof, the Energy Saving Trust puts the typical payback period at 9 to 12 years; east-facing or shaded roofs take longer.
A battery can close that gap by storing midday generation for evening use, though solar panels with battery storage add to the upfront cost. Getting quotes from several MCS-certified installers and comparing the system sizes and payback assumptions in each proposal is the most reliable way to judge whether the numbers work for your home.
Illustrative payback on a mid-range domestic solar installation
| 2027 | -6,875 £ |
|---|---|
| 2029 | -5,625 £ |
| 2030 | -5,000 £ |
| 2032 | -3,750 £ |
| 2033 | -3,125 £ |
| 2035 | -1,875 £ |
| 2036 | -1,250 £ |
| 2038 | 0 £ |
Assumed: installed cost £7,500, annual benefit £625 (bill savings plus SEG export payments), over 12 years. Illustrative example, calculated from the assumptions in the text, not figures from a source.
Illustrative example
Most domestic solar installations in England and Wales qualify as permitted development, meaning you do not need to apply for planning permission. The rules changed under amendments to the General Permitted Development Order (GPDO), but the broad principle is that panels flush with the roof on a standard residential property are permitted.
Frame-mounted systems, ground-mounted arrays, listed buildings and properties in conservation areas can require full planning permission. It is worth confirming your position with your local planning authority before committing.
Building regulations approval is separate from planning permission and is typically handled by your MCS-certified installer as part of the process. If your roof is older, an installer may also recommend a structural survey to confirm it can carry the additional load. Checking these points early is a straightforward part of understanding how photovoltaic panels work in practice for your specific property.
The trade-offs, in short.
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Answers to the most common questions.
There is no practical difference for most homeowners. Both terms refer to the panels that convert sunlight into electricity. Solar thermal panels, which heat water rather than generate power, are a distinct product. When an installer or energy supplier says solar panels, they almost always mean photovoltaic panels.
A typical domestic system costs £5,000 to £10,000 installed (Energy Saving Trust, July 2026 prices). The exact figure depends on system size, roof type, inverter choice and access. Residential installation currently attracts 0% VAT, zero-rated to 31 March 2027, which reduces the effective upfront cost.
There is no single answer, because it depends on your annual electricity consumption, roof area, orientation and how much generation you want to cover. A typical three-bedroom home might use a 3 to 4 kWp system, but an installer will size the system to your actual usage and roof after a survey.
Yes, and more than most people expect. Shaded cells can pull down the output of an entire string, not just the shaded section. Microinverters or power optimisers on each panel can limit this effect. An installer should assess shading from trees, chimneys and neighbouring buildings before recommending a system size.
Most domestic roof installations in England and Wales are permitted development under the GPDO, so no formal planning application is needed. Listed buildings, properties in conservation areas and ground-mounted systems are exceptions. Always confirm your specific situation with your local planning authority before installation.
A battery stores surplus daytime generation for use in the evening, which increases the share of solar electricity you consume directly. That raises the financial return, but batteries add to the upfront cost. Whether the numbers work depends on your consumption pattern, system size and the battery price at the time of your quotes.
