Solar Panel Calculator
Estimate the required solar PV system size (kW), total panel count, and expected daily generation to cover your electricity needs.
How to Size a Solar PV System
Designing a reliable solar photovoltaic (PV) system starts with understanding your daily energy footprint. Utility bills usually state monthly consumption in kilowatt-hours (kWh). Dividing this monthly value by 30 gives your target average daily energy requirement.
The Solar Sizing Formulas
To ensure your solar array generates adequate energy under real-world ambient conditions, we apply an efficiency derate factor (η) to compensate for thermal loss, inverter conversion losses, and voltage drops across cables.
1. Array Capacity Requirement:
$$P_{\text{array}} = \frac{E_{\text{daily}}}{H_{\text{sun}} \cdot \eta}$$2. Total Panel Count Calculation:
$$N_{\text{panels}} = \left\lceil \frac{P_{\text{array}} \cdot 1000}{W_{\text{panel}}} \right\rceil$$Where:
- Parray = Required continuous PV array size in kilowatts (kW)
- Edaily = Target daily consumption in kilowatt-hours (kWh)
- Hsun = Equivalent peak sun hours per day in your area
- η = Total system efficiency factor (e.g., 75% = 0.75)
- Wpanel = Nominal rated wattage of a single PV panel (Watts)
- Npanels = Total required panel count (rounded up to the next integer)
Frequently Asked Questions
What are Peak Sun Hours?
Peak sun hours measure solar irradiance intensity rather than standard daylight duration. One peak sun hour corresponds to 1,000 Watts of photovoltaic power per square meter hitting the module surface in 60 minutes.
Why is the efficiency factor necessary?
Solar panels are rated under standard test conditions (25°C). In real outdoor operating conditions, heat buildup, inverter DC-to-AC conversion losses, dirt accumulation, and wiring resistance reduce net output by 20% to 30%.
How do panel tilt and orientation affect energy yield?
For maximum energy generation in the northern hemisphere, solar arrays should face true south at a tilt angle approximately equal to the local latitude.