Enter your power needs and get a recommended system size instantly.
* These are estimates. System sizing depends on your specific equipment efficiency, local weather patterns and usage habits. We recommend adding 20-25% buffer to all values.
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It depends on your daily watt-hours and your local peak sun hours. Add up each appliance's watts times hours used per day to get daily watt-hours, then divide by your sun hours and by about 0.8 for system losses to get the panel wattage needed. Divide that by the wattage of a single panel (for example 400W) to get the number of panels. This off-grid solar calculator does that math for you.
System sizing has three parts: panels, battery bank, and inverter. Panels are sized from your daily watt-hours and peak sun hours. The battery bank is sized from your daily watt-hours times the days of backup you want, divided by system voltage and usable depth of discharge. The inverter is sized to handle your largest simultaneous load with roughly a 25% safety margin.
Peak sun hours are the number of hours per day that sunlight averages 1,000 watts per square meter, the standard used to rate panels. It is not the same as daylight hours. A location with 4 peak sun hours means a 400W panel produces roughly 1,600 watt-hours on an average day. Fewer sun hours means you need more panel wattage to make the same energy.
Panels determine how much energy you can harvest each day; batteries determine how long you can run without sun. Size panels to replace your full daily usage during your worst realistic sun hours, then size the battery bank for the number of cloudy or no-sun days you need to ride through. Undersizing either one leaves you short, so most reliable off-grid builds add a 20 to 25 percent buffer to both.
Bugs, confusing bits, or ideas — all welcome. Thank you!
