Solar Panel Calculator
Estimate panel count, solar array and inverter size, optional battery capacity, roof area and yearly generation from a bill or appliance list.
What is the solar panel calculator?
A solar panel calculator gives an early estimate of the photovoltaic array needed for a home's electricity use. Enter monthly or daily kWh from a bill, or list appliances with their quantity, wattage and hours of use. The estimate includes panel count, installed array capacity, inverter size, optional battery capacity, approximate roof area and yearly generation. It is a planning aid, not a site survey or equipment specification; local conditions and installer design determine the final system.
How it works
Monthly energy is divided by 30 to get an average daily load; appliance mode sums quantity × watts × hours ÷ 1,000. The target daily energy is multiplied by the offset percentage, then divided by peak sun hours and the system efficiency assumption to estimate array kW. Panel count is rounded up to a whole module, and the inverter estimate applies a 25% margin to the larger of the array and peak simultaneous load before rounding to a common size. For off-grid and hybrid systems, backup energy is daily use × autonomy, and nominal battery kWh is backup energy ÷ depth of discharge; Ah is kWh × 1,000 ÷ battery volts. Roof area uses about 2 m² per panel. Annual generation uses installed array kW × sun hours × 365 × efficiency. A simple payback appears only when both electricity price and system cost per watt are entered.
Worked example
For 900 kWh per month, daily use is 900 ÷ 30 = 30 kWh. With 5 peak sun hours, 80% efficiency and a 100% offset target, the required array is 30 ÷ (5 × 0.80) = 7.5 kW. Using 450 W panels gives ceil(7,500 ÷ 450) = 17 panels, or 7.65 kW installed, and about 34 m² of panel area. If the entered peak load is 8 kW, the inverter estimate is max(8, 7.65) × 1.25 = 10 kW after rounding. Estimated yearly generation is 7.65 × 5 × 365 × 0.80 = 11,169 kWh before any export or seasonal adjustment.
Frequently asked questions
How many solar panels do I need for my home?
Divide daily kWh use multiplied by your offset target by peak sun hours and system efficiency to estimate array kW. Divide that result by panel kW and round up. The calculator does these steps from bill data or appliance loads; actual production depends on the site.
What are peak sun hours?
Peak sun hours express a day's solar energy as equivalent hours at strong, standard sunlight; they are not the same as daylight hours. The right value depends on location, season, shading and panel orientation, so use local solar data for design.
What is the difference between on-grid, off-grid and hybrid?
On-grid systems connect to the utility and this calculator does not include a battery for them. Off-grid systems operate with storage, while hybrid systems combine a grid connection and batteries. The tool estimates battery capacity for the backup duration you enter.
How is battery capacity calculated?
Backup kWh is daily electricity use multiplied by backup hours divided by 24, or by backup days. Nominal battery kWh is that energy divided by depth of discharge; amp-hours are nominal kWh × 1,000 ÷ battery voltage. Charging and inverter losses are not included.
Can I use this for a mobile home or a 1,000-watt panel?
Yes. Enter a mobile home's bill or appliance loads, and choose custom panel wattage to model a 1,000 W module. The estimate does not check roof weight, vehicle wiring, battery chemistry compatibility or equipment availability.
How is the payback estimate worked out?
When both costs are entered, estimated system cost is installed array watts × cost per watt. Annual bill value uses estimated generation capped at the entered offset of your yearly use, multiplied by cost per kWh. The result excludes incentives, financing, maintenance and export credits.
Does this estimate solar farm or ground-mounted project costs?
No. It is a household load and array planning estimate, not a solar farm development cost model or an industrial solar panel design. Ground-mounted layouts, structural work, permits, grid studies and commercial costs need a project-specific assessment.
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