Solar Panel Calculator

The mathematical foundation of solar sizing relies on converting your annual kilowatt-hour consumption into daily generation needs, adjusted for environmental variables. First, the daily energy requirement is calculated by dividing your annual kWh usage by 365 days and further dividing by your location's average daily peak solar hours. This value is then scaled by your target bill offset percentage and divided by panel efficiency to yield the required solar array size in kilowatts (kW). Finally, the total system capacity is divided by the power rating of an individual panel (in watts) to determine the exact number of physical panels required, which is rounded up to the nearest whole integer.

Imagine you live in a region with an average of 4.5 peak solar hours per day. Your household consumes 10,000 kWh of electricity annually, and you want to achieve a 100% bill offset (1.00). Using standard modern residential panels rated at 400 watts each, with a baseline system efficiency factor of 85% (0.85), we compute the system size as follows: First, find the daily energy demand: 10,000 kWh / 365 = 27.39 kWh per day. Next, divide by daily sun hours: 27.39 / 4.5 = 6.08 kWh daily production needed. Adjusting for efficiency and offset yields a solar array size of approximately 7.15 kW. To find the required panel count, multiply the array size in kW by 1,000 to get watts (7,150 W) and divide by the individual panel power rating (400 W), resulting in roughly 17.87 panels. Rounding up, you will need 18 panels to fully offset your annual electricity consumption.

When planning your solar installation, always account for future electricity consumption increases, such as purchasing an electric vehicle or installing a heat pump. Additionally, verify your roof's structural integrity, orientation (south-facing is ideal in the Northern Hemisphere), and potential shading from nearby trees before finalizing your panel layout. Finally, check local utility net-metering policies to ensure you receive fair credit for excess energy sent back to the grid.