Solar panel calculator
Size a grid-tied solar system from your annual electricity use and the peak sun hours where you live.
How it is calculated
kW = annual kWh × % covered / (PSH × 365 × PR)
panels = kW × 1000 / panel watts
Peak sun hours are the daily hours equivalent to 1000 W/m² of sunlight: about 3 in northern Europe and over 6 in deserts. System efficiency (PR) is typically 75–85 %.
Covering 100 % of usage without a battery only pays off where net metering credits your exports. Otherwise, part of the energy is produced when you are not using it.
Face the panels south in the northern hemisphere (north in the southern), tilted close to your latitude.
Frequently asked questions
How many solar panels do I need for 10,500 kWh a year?
With 4.5 peak sun hours and 80 % efficiency, about 8 kW: 18 panels of 450 W to cover 100 %, or 13 for 70 %.
How much roof space does a panel need?
A 450 W panel measures about 1.9 × 1.1 m (75 × 44 in): roughly 2 m² or 22 ft².
Which direction should panels face?
South in the northern hemisphere, tilted roughly at your latitude. East or west produce about 10–20 % less.