Estimate the solar system you need. Enter your daily electricity use and local sun hours. You get the array size, number of panels, rough roof area, inverter size and, if you want one, the battery bank.
Planning estimate only. Real output depends on shade, tilt, dust, temperature, wiring and inverter. Get a site survey and a quote from a qualified installer before you buy.
Formulas and assumptions
- Array size (kW): daily kWh divided by (peak sun hours times system efficiency)
- Panels: array watts divided by panel watts, rounded up
- Area: about 4.8 square metres per kW of modern panels
- Inverter: highest simultaneous load times 1.25, rounded up to a standard size
- Battery energy: night energy divided by usable depth of discharge (90 percent lithium, 50 percent lead acid) and by 0.9 for losses
- Battery Ah: battery kWh times 1000, divided by battery voltage
Example
A home using 20 kWh per day with 5 peak sun hours and 75 percent system efficiency needs a 5.33 kW array. With 550 W panels that is 10 panels (5.5 kW) covering about 26 square metres. With a 6 kW peak load an 8 kW inverter fits, and if 35 percent of the energy is used at night, a lithium bank of about 8.6 kWh (180 Ah at 48 V) covers it.
Frequently asked questions
How many solar panels do I need for my home?
Divide your daily kWh by the peak sun hours and the system efficiency to get the array size, then divide by the panel wattage. A home using 20 kWh a day with 5 sun hours usually needs roughly 5 to 6 kW of panels.
What are peak sun hours?
They are the hours per day when sunlight is strong enough to count as full power. Many sunny regions have 4.5 to 6.5. Check a local solar map for your city.
Do I need a battery?
Not with a grid-tied system, which uses the grid as storage. A battery helps if the grid fails often or if you want to use solar energy at night.
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