Question 1

How much electricity does a solar panel produce?

Accepted Answer

Production ≈ system size (kW) × daily peak sun hours × 365 × a derate of about 0.8 for real-world losses. For example, an 8 kW system at 4.5 peak sun hours makes roughly 8 × 4.5 × 0.8 ≈ 28.8 kWh a day, or about 10,500 kWh a year. A single 400-watt panel in those conditions makes around 1.4 kWh per day.

Question 2

What is the derate factor?

Accepted Answer

It's the share of nameplate output a system actually delivers after losses: inverter conversion, wiring, heat, soiling, panel angle, and mismatch. A common figure is about 80% (0.8), close to the PVWatts default of 86% before shading. Lower it for hot climates, heavy shading, or a non-ideal roof angle.

Question 3

Why is winter output so much lower than summer?

Accepted Answer

Shorter days and a lower sun angle mean far fewer peak sun hours in winter, often less than half the summer figure. The summer and winter day estimates here are rough swings around your annual average to show the range; your actual seasonal profile depends on latitude and weather.

Question 4

Do solar panels lose output over time?

Accepted Answer

Yes, gradually. Panels degrade roughly 0.5% per year, so after 25 years they typically still produce about 85–88% of their original output. The lifetime figure adds up production across the panel's life with that yearly decline factored in.

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