Panel count + output + roof fit
How Many Solar Panels Do I Need?
Use monthly electricity consumption, not a generic home-size rule. See panel count, system kW, output per panel and a first-pass roof-space check with every assumption visible.
1. Convert use to an annual target
Monthly kWh × 12 × target offset. Use 12 actual bills when seasonal heating or cooling is material.
2. Estimate output per panel
Panel kW × peak sun hours × 365 × (1 − losses). State values are screening proxies, not address weather files.
3. Round up and check the roof
Panel count rounds up to a whole module. Roof fit uses entered dimensions plus a 15% allowance; code and design determine the final layout.
Solar Panel Count & Output Questions
There is no reliable national answer for one home. Panel count depends on annual kWh use, local solar resource, roof orientation and shade, system losses, desired bill offset and panel wattage. Enter monthly kWh rather than house size whenever possible.
A 400-watt panel produces 0.4 kW multiplied by local peak sun hours and the system efficiency factor. At 5 peak sun hours and 14% losses, the screening estimate is about 1.72 kWh per day. Actual output varies by weather, orientation, temperature and shade.
A common residential panel around 69 by 45 inches occupies roughly 21.5 square feet before spacing. This calculator adds 15% for a simple planning allowance, but real layouts need roof-plane measurements, setbacks, pathways and obstruction clearance.
Sometimes, especially if you expect an EV, heat pump or other electrification. But utilities may limit oversizing and excess exports may be credited below the retail rate. Check interconnection and export rules before targeting more than current annual use.
Method benchmark: PVWatts-style capacity × solar resource × loss calculation. For address-level weather and roof geometry, use PVWatts and a qualified site design.