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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