Solar Panels

How much electricity do your panels make in a year, and when have they paid for themselves? Based on the panel rating, the sunshine where you live and the losses in a real system.

EnergySolar powerPayback

Inputs

Input examples

Peak sun hours: the yearly sunshine on the panels expressed as hours per day of full sun (1000 W/m²). About 3 in the Netherlands and Germany, 5 in Spain, 6 in Arizona. PR covers losses from heat, wiring, the inverter and dirt.

The system

Number of panels

Rated power per panel (Wp)

Peak sun hours per day

Performance ratio (%)

Money and CO₂

Electricity price (€ per kWh)

System cost (€)

CO₂ of grid electricity (g per kWh)

Watts Peak and Sunshine

A panel’s rating in watt-peak (Wp) is what it delivers in full, perpendicular sunlight of 1000 W/m² at 25 °C. Over a year the sun gives far less on average, so engineers count peak sun hours: the yearly sunshine squeezed into hours of full sun per day.

Real systems lose 15–25% on the way — hot panels work less well, and wiring and the inverter waste a little — captured by the performance ratio. In the Netherlands one kWp typically yields 850–950 kWh a year.

1 kWp≈ 900 kWh/yr (NL)

PR 75–85%real-world losses

heatpanels like it cool

southbest direction (north of the equator)

Savings Over the Years

€

cumulative savings

system cost

Result

Enter the values above

Key Relations

Yearly Energy

Peak power in kW times the equivalent hours of full sun per year, times the performance ratio.

Example:

Simple Payback

Years until the saved electricity has paid for the system, ignoring price changes and panel ageing.

CO₂ Avoided

Each kWh from your roof replaces one from the grid.

Sources & Verification

References

G. M. Masters, Renewable and Efficient Electric Power Systems, 2nd ed., Wiley, 2013