Why are solar panels 'only' 20% efficient?

Solar cells can only capture certain wavelengths of light. The theoretical maximum (Shockley-Queisser limit) is 33% for single-junction cells. 20-22% is excellent relative to this limit — and improving each year.

Does low efficiency mean solar is bad?

No — efficiency matters when space is limited. For rooftop solar: a 20% efficient panel produces more than enough electricity from a typical roof. Fuel cost is zero. The efficiency figure is not a measure of value.

How much CO₂ does solar save?

Each kWh from solar replaces a grid kWh (currently ~200g CO₂ in UK). A 4kW system saves 1.5-2 tonnes CO₂/year. Over 25 years: 37-50 tonnes. The lifecycle CO₂ of manufacturing the panel is repaid within 2-3 years.

Solar vs Power Stations

By Home Solar Guide Team|Updated 18 March 2026|educational

Independently written | Evidence-based | Sources cited

Solar vs power stations — Solar: 20% efficient but FREE fuel. Coal: 33% efficient with expensive, polluting fuel.

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How efficient are solar panels compared to power stations?

Solar panels vs power stations efficiency comparison: COAL: 33% efficient. Fuel cost: high. CO₂: 900g/kWh. Status: UK phasing out by 2024 (done). GAS (CCGT): 55% efficient. Fuel cost: volatile. CO₂: 400g/kWh. Status: still 35% of UK grid. NUCLEAR: 33% efficient. Fuel cost: low. CO₂: 12g/kWh. Status: reliable baseload. WIND: 35-45% capacity factor. Fuel cost: FREE. CO₂: 11g/kWh. Status: UK's largest generator. SOLAR: 20-22% efficient. Fuel cost: FREE. CO₂: 20-50g/kWh (lifecycle). Status: fastest growing. KEY INSIGHT: Efficiency percentage is misleading. Solar's fuel is FREE and unlimited. A 33% efficient coal plant burns expensive fuel and pollutes. A 20% efficient solar panel converts free sunlight into free electricity forever.

Frequently Asked Questions

Related: Home Heating Systems

Solar panels are most powerful when combined with an efficient heating system. Heat pumps use solar-generated electricity to heat your home at 300-400% efficiency — making them the ideal partner for solar.

how heat pumps work

A heat pump converts 1kWh of electricity into 3-4kWh of heat.

From our sister site Home Heat Pump Guide