About

Switching to renewable energy involves balancing consumption with production capacity. This calculator assists homeowners in dimensioning a Photovoltaic (PV) system. By analyzing monthly energy usage (kWh) against regional Peak Sun Hours, it determines the precise number of panels required to achieve net-zero energy.

Key variables include the wattage of selected panels and system efficiency losses (inverter inefficiency, wiring, and dust). The tool also features a roof area mapper to verify physical feasibility and a battery sizing estimator for off-grid resilience. Correct sizing prevents over-expenditure on hardware while ensuring sufficient power generation during winter months.

Formulas

The daily energy requirement is derived from the monthly bill:

E_daily = Monthly Usage (kWh)30

The required system size (kW) accounts for Peak Sun Hours (H) and System Inefficiency (L, typically 1.2 to 1.4):

P_req = E_daily × LH

Finally, the number of panels is:

Count = ceilP_req × 1000Panel Wattage

Reference Data

Region (USA)	Avg Peak Sun Hours (hrs/day)	System Size Factor
Southwest (AZ, NM)	6.0 - 7.5	Low (Efficient)
California / Florida	5.0 - 6.0	Moderate
Midwest / Texas	4.0 - 5.0	Standard
Northeast (NY, MA)	3.5 - 4.0	High
Pacific NW (WA)	3.0 - 3.5	Very High

Frequently Asked Questions

Peak Sun Hours are not just the length of daylight. One Peak Sun Hour equals 1000 watts of solar energy per square meter for one hour. A 14-hour summer day might only deliver 6 Peak Sun Hours due to the sun's angle and atmospheric intensity.

Standard industry loss is about 20-25% (Factor 1.25). This accounts for inverter heat, wiring resistance, dirt on panels, and temperature coefficients. If you live in a very hot climate, efficiency drops further.

If you want to go "Off-Grid" or have backup during outages, you need batteries. The calculator estimates the storage needed (kWh) to run your house for 24 hours without any sunlight.

The ROI (Return on Investment) estimator provides a raw payback period based on energy savings. It does not automatically deduct the Federal Solar Investment Tax Credit (ITC), which is currently 30% in the US, as this varies by year and jurisdiction.