Sizing Your Solar Panel System
Properly sizing a solar panel system requires balancing your electricity consumption with the energy production potential of your location. The key factors are your monthly kWh usage, available peak sun hours, the wattage of your chosen panels, and system efficiency losses from inverters, wiring, and environmental factors.
The average US household consumes approximately 900 kWh per month. To offset this entirely with solar power in an area receiving 5 peak sun hours per day, you would need a system rated at approximately 6-7 kW, which translates to about 15-18 standard 400W panels covering roughly 30-35 square meters of roof space.
Sizing Formula
Common Panel Wattages
| Panel Type | Wattage | Size (m²) | Best For |
|---|---|---|---|
| Standard Residential | 350-400W | 1.7-1.9 | Most homes |
| Premium Residential | 400-450W | 1.7-1.9 | Limited roof space |
| Commercial | 450-550W | 2.0-2.4 | Large roofs, ground mount |
| Portable/RV | 100-200W | 0.5-1.0 | Off-grid, camping |
Frequently Asked Questions
Should I offset 100% of my electricity?
Many homeowners choose to offset 80-100% of their usage. Net metering policies in most states credit you for excess production, but some utilities cap net metering benefits. Consider future energy needs (EV charging, heat pumps) and potential rate increases when sizing your system.
How much does a residential solar system cost?
As of 2025, the average cost of residential solar in the US is $2.50-3.50 per watt before incentives. A typical 7 kW system costs $17,500-24,500 before the 30% federal tax credit, bringing the net cost to $12,250-17,150. Prices vary significantly by region, installer, and equipment quality.
Do I need batteries with solar panels?
Batteries are optional if your utility offers net metering. They are valuable for backup power during outages, time-of-use rate optimization, and maximizing self-consumption. A home battery system (like Tesla Powerwall) typically adds $10,000-15,000 to system cost.