How Do Solar Panels Work?

The Basic Principle: Sunlight to Electricity

Solar panels convert light into electricity using the photovoltaic (PV) effect. Each panel is made up of many photovoltaic cells, typically made from silicon — the same material used in computer chips. When light photons hit a silicon cell, they knock electrons loose from their atoms. This flow of electrons is electricity.

Importantly, solar panels work with daylight, not heat. They actually perform slightly better in cooler temperatures. A bright but cool spring day can generate more electricity than a blazing hot summer afternoon. This is why solar works well in the UK despite our moderate climate.

What Is Inside a Solar Panel?

A typical residential solar panel contains 60 or 72 photovoltaic cells arranged in a grid. Each cell produces about 0.5 volts, and they are wired together to produce a useful voltage (usually 30–40 volts per panel).

The cells are sandwiched between a sheet of tempered glass on top (for protection) and a back sheet underneath. An aluminium frame holds everything together. Modern panels are designed to withstand hail, snow loads, and high winds for 25–30 years.

The two most common types of solar cell are:

• Monocrystalline — made from a single silicon crystal. More efficient (20–22%), more expensive, and recognisable by their uniform dark appearance. Most common in residential installations.
• Polycrystalline — made from multiple silicon crystals melted together. Slightly less efficient (17–19%), cheaper, and have a blue, speckled appearance. Less common now as monocrystalline prices have dropped.

The Inverter: DC to AC Conversion

Solar panels produce direct current (DC) electricity, but your home’s appliances and the national grid use alternating current (AC). An inverter converts the DC output from your panels into AC electricity that can be used in your home.

There are two main types of inverter:

• String inverter — a single box (usually mounted in the loft or garage) that converts the output from all panels at once. This is the most common and cheapest option. The downside is that if one panel is shaded, it can reduce the output of the entire string.
• Microinverters — a small inverter attached to each individual panel. Each panel operates independently, so shading on one panel does not affect the others. More expensive (20–30% premium) but better for roofs with partial shading or multiple orientations. They also typically come with 25-year warranties.

A third option is power optimisers (like SolarEdge), which sit between a string inverter and microinverters in terms of cost and performance. Each panel gets an optimiser that maximises its individual output, but conversion still happens at a central inverter.

The Generation Meter

A generation meter measures the total amount of electricity your solar panels produce. This is usually built into the inverter or installed as a separate meter near your consumer unit (fuse box). It shows you how many kilowatt-hours (kWh) your system has generated — daily, monthly, and lifetime.

Most modern inverters also connect to Wi-Fi, letting you monitor generation through a smartphone app. You can see real-time output, daily totals, and historical performance. This is useful for checking that your system is working correctly and understanding your generation patterns.

The Export Meter (Smart Meter)

Your smart meter measures two things: how much electricity you import from the grid, and how much you export back to it. The export reading is what your energy supplier uses to calculate your Smart Export Guarantee payments.

You need a smart meter (SMETS2) that records half-hourly import and export data. If you do not have one, your energy supplier is obligated to install one free of charge. Without a smart meter, you cannot receive SEG payments, so make sure one is installed before or at the same time as your solar panels.

How It All Connects: The Grid Connection

Your solar panel system remains connected to the national grid at all times. Here is what happens during a typical day:

1. Morning: As daylight increases, your panels start generating. If generation exceeds your current usage, the surplus flows automatically to the grid. Your smart meter records this export.
2. Midday: Peak generation. On a sunny day, a 4kW system can produce 3–4 kW of power. If you are using 1 kW for the fridge, router, and other baseload appliances, 2–3 kW is exported.
3. Afternoon/Evening: As the sun drops, generation falls. When your usage exceeds solar generation, you automatically draw the shortfall from the grid. This switch is seamless — there is no flicker or interruption.
4. Night: No solar generation. All electricity comes from the grid (or from a battery if you have one).

There is no on/off switch and no manual intervention needed. The system automatically prioritises using solar electricity in your home, only exporting what you cannot use and only importing when solar is insufficient.

What About Cloudy Days and Winter?

Solar panels still generate electricity on cloudy days, just less of it. A heavily overcast day might produce 10–25% of a sunny day’s output. Light cloud or haze might only reduce output by 20–30%.

In winter, shorter days and lower sun angle mean less generation — December and January typically produce about 10–15% of what July produces. However, the panels themselves are more efficient in cold weather, and even modest winter generation saves you money at the highest electricity rates of the year.

Over a full year, a well-positioned 4kW system in England generates 3,400–4,000 kWh. In Scotland, 2,800–3,400 kWh. The annual totals are consistent from year to year — a bad month is usually balanced by a good one.

How Long Do Solar Panels Last?

Solar panels are warranted for 25–30 years but typically last 35–40 years. They degrade slowly, losing about 0.5% of output per year. After 25 years, a panel will still produce around 87% of its original output.

Inverters have a shorter lifespan. String inverters typically last 10–15 years and may need replacing once during the panel’s lifetime (cost: £800–£1,500). Microinverters usually last 20–25 years and may not need replacement at all.

There is no regular maintenance required. Panels are self-cleaning in the rain. In very dusty areas or under trees, an annual clean with a hose can help, but is rarely necessary.