Solar panels generate electricity through the photovoltaic effect, not heat
When sunlight reaches a solar panel, it is not the heat but the light itself that produces power. Sunlight is composed of tiny energy packets called photons, each carrying a specific amount of energy. When these photons strike the silicon cells inside a solar panel, they knock electrons loose from their atoms, creating a flow of freed electrons. This flow is direct current (DC) electricity (Energy Saving Trust, 2026).
Solar panels generate electricity through the photovoltaic effect, where photons in sunlight knock electrons loose in silicon cells to create direct current (DC) electricity. This process works from daylight, not heat, and panels still produce 10–25% of peak capacity on cloudy days.
- Sunlight photons knock electrons loose in silicon cells to create DC electricity.
- Solar panels work from daylight, not just direct sun, producing 10–25% on cloudy days.
- Monocrystalline cells achieve 20–22% efficiency; polycrystalline cells reach 15–18%.
- A solar panel layers glass, EVA encapsulant, silicon cells, backsheet and aluminium frame.
- Shading reduces output; bypass diodes in the junction box prevent power loss.
- Solar panels generate electricity through the photovoltaic effect, not heat
- The key components inside a standard solar panel
- How DC electricity from panels becomes AC for your home
- Quick numbers typical UK solar panel output and efficiency
- How do solar panels generate electricity — the plain-English answer
- The role of the National Grid and solar export
- How to verify a solar panel installer in the UK
- Realistic lifespan and degradation of solar panels
This process is called the photovoltaic effect. It is important to note that solar panels do not need direct sunlight to generate electricity. They produce power from daylight, though output is lower in cloudy conditions. A typical UK home system will still generate roughly 10–25% of its peak capacity on an overcast day, depending on cloud thickness (Energy Saving Trust, 2026).
The key components inside a standard solar panel
A modern solar panel is a layered assembly. The top layer is tempered glass, which protects the cells from weather and impact while allowing light through. Beneath this is an encapsulant layer, usually ethylene-vinyl acetate (EVA), that bonds the glass to the silicon cells and prevents moisture ingress. The silicon cells themselves are the active layer where the photovoltaic effect occurs. Below the cells is a backsheet, typically a polymer layer that provides electrical insulation and weather resistance. The entire assembly is held in a lightweight aluminium frame (MCS, 2026).
The silicon cells come in two main types. Monocrystalline cells are cut from a single silicon crystal, giving higher efficiency (typically 20–22%) and a uniform black appearance. Polycrystalline cells are made from multiple silicon crystals melted together, offering lower efficiency (15–18%) at a slightly lower cost. A junction box on the back of the panel contains bypass diodes, which prevent power loss when part of the panel is shaded (MCS, 2026).
How DC electricity from panels becomes AC for your home
Solar panels produce DC electricity, but UK homes and the National Grid use alternating current (AC). This mismatch means every solar PV system requires an inverter to convert DC to AC. Without an inverter, the electricity from your panels is incompatible with your home’s wiring and appliances (Energy Saving Trust, 2026).
Two common inverter types exist. A string inverter connects all panels in a single series, sending their combined DC output to a central unit that converts it to AC. This is the most cost-effective option for roofs with consistent, unshaded sunlight. Microinverters attach to each panel individually, converting DC to AC at the panel itself. This approach improves performance when panels experience partial shading, as one shaded panel does not drag down the output of the entire string (Energy Saving Trust, 2026).
Quick numbers typical UK solar panel output and efficiency
| Metric | Typical value | Source |
|---|---|---|
| Panel wattage (2026 typical) | 400 W | DESNZ, 2026 |
| Annual kWh per kWp installed (UK average) | 850–950 kWh | Energy Saving Trust, 2026 |
| Panel efficiency (monocrystalline) | 20–22% | Energy Saving Trust, 2026 |
| Number of panels for a 3.5 kWp system | 9–10 panels | DESNZ, 2026 |
| Average daily generation (summer) | 12–15 kWh | Energy Saving Trust, 2026 |
| Average daily generation (winter) | 2–4 kWh | Energy Saving Trust, 2026 |
How do solar panels generate electricity — the plain-English answer
Solar panels turn daylight into electricity using silicon cells that release electrons when hit by light. Those electrons flow as DC electricity, which an inverter changes into AC electricity your home can use. The process has no moving parts, is silent, and requires no fuel — the energy comes from the sun. This is the fundamental principle behind every solar PV system installed on UK homes.
The role of the National Grid and solar export
When your solar panels generate more electricity than you are using at that moment, the surplus is automatically exported to the National Grid. This export is metered by your smart meter or a dedicated export meter. The Smart Export Guarantee (SEG) requires licensed electricity suppliers to pay you for every kilowatt-hour (kWh) you export, with rates set by each supplier rather than a fixed national price (Ofgem, 2026).
Without an export arrangement, any surplus generation is simply lost unless you have a battery storage system. A typical 3.5 kWp system in a home where someone is present during the day might export 30–50% of its total generation, depending on usage patterns. Installing a battery can capture this surplus for use in the evening, reducing your grid imports further.
How to verify a solar panel installer in the UK
To ensure your installation qualifies for SEG payments and most finance options, the installer must be certified under the Microgeneration Certification Scheme (MCS). You can check an installer’s MCS status on the public register at mcsregister.co.uk (MCS, 2026). Additionally, look for TrustMark registration, which provides consumer protection and ensures the installer follows industry standards (TrustMark, 2026).
For the electrical work involved, the installer should be registered with NICEIC or NAPIT for compliance with Part P of the Building Regulations. Part P covers electrical safety in domestic properties, and using a registered electrician ensures the work is inspected and certified (GOV.UK, 2026). How to choose a solar panel installer in the UK
Realistic lifespan and degradation of solar panels
Most solar panels come with a 25-year performance warranty, typically guaranteeing at least 80% of the original output after 25 years. In practice, degradation rates average 0.5–0.7% per year, meaning after 25 years a panel still produces about 85% of its original power (Energy Saving Trust, 2026). This slow decline is due to microscopic defects in the silicon cells and exposure to UV radiation and temperature cycles over time.
Inverters have a shorter lifespan, typically needing replacement after 10–15 years. This is because inverters contain electronic components that experience more thermal stress than the panels themselves. A replacement inverter for a typical 3.5 kWp system costs roughly £800–£1,200 installed, depending on the type (Energy Saving Trust, 2026). Solar panel maintenance and lifespan guide
Frequently Asked Questions
Solar panels do not generate electricity at night because they need daylight to produce power. The photovoltaic effect requires photons from sunlight or daylight to free electrons, so no light means no electricity output. According to the Energy Saving Trust, panels produce zero power in full darkness.
No, solar panels do not need direct sunlight to generate electricity. They produce power from daylight, though output drops to 10–25% of peak capacity on overcast days, as the Energy Saving Trust reports. Direct sun gives maximum generation, but panels still work in cloudy conditions.
The photovoltaic effect is the process where photons from sunlight knock electrons loose from atoms in silicon cells, creating a flow of freed electrons that becomes direct current (DC) electricity. The Energy Saving Trust explains that this effect occurs from light, not heat, and is the core mechanism behind solar panel power generation.
Monocrystalline solar panels are 20–22% efficient, while polycrystalline panels achieve 15–18% efficiency, according to MCS standards. Monocrystalline cells are cut from a single silicon crystal, giving a higher efficiency and uniform black look, whereas polycrystalline cells are made from multiple crystals at a lower cost.
A solar panel consists of tempered glass top layer, an ethylene-vinyl acetate (EVA) encapsulant, silicon cells (monocrystalline or polycrystalline), a polymer backsheet for insulation, and an aluminium frame. A junction box with bypass diodes prevents power loss from shading, as specified by MCS guidelines.
