Switch to renewable energy with confidence. Calculate your total PV array size, panel count, and required roof space in seconds.
This tool estimates the solar system you'd need based on your monthly electricity usage, average daily sunlight hours, panel wattage, and a real-world efficiency loss factor (accounting for inverter losses, wiring, temperature, and dust). It returns the system size in kW, the number of panels required, the roof area needed, and a rough annual generation estimate.
If your home uses 900 kWh a month (10,800 kWh a year), your array needs to produce at least that much. Panels don't run at full rated output all day, so the calculation uses "peak sun hours" — in most temperate regions that's 4-5 hours per day, even though the sun may be visible for 10-12 hours. Dividing your daily energy need by peak sun hours (adjusted for system losses) gives you the required system capacity in kW.
Most residential installs are grid-tied, meaning the system stays connected to the utility and any excess power can often be sold back through net metering. An off-grid system instead relies on battery storage to keep the lights on at night or during outages, and is typically sized 20-30% larger than a grid-tied system to keep batteries charged through cloudy stretches.
Not every roof performs equally. In the northern hemisphere, south-facing roofs get the most direct sun; east- or west-facing roofs may need 15-20% more panels to make up for lower output. Roof pitch matters too — a tilt close to your latitude generally gives the best year-round production. The "System Efficiency Loss" field in this calculator lets you account for these real-world factors rather than assuming a perfect installation.
Most homeowners weigh system cost (after any available incentives) against their current electricity bill to find a payback period, commonly somewhere between 6 and 10 years depending on local rates and system cost. After that point, the electricity the system produces is essentially free, and solar has also been shown to support home resale value in many markets.
Q: How much roof space does a 5kW system need?
A: A standard 5kW system using 400W panels consists of about 13 panels. At roughly 2 square meters per panel, that's about 26-30 square meters (280-320 sq ft) of unobstructed roof space.
Q: Do solar panels work at night?
A: No. Solar panels need sunlight to generate power. For power at night you need either a grid connection or a battery storage system like a home battery unit.
Q: What is a solar inverter?
A: A device that converts the direct current (DC) electricity your panels generate into the alternating current (AC) your home appliances use. Inverter sizing must match your total panel capacity.
Q: How long do solar panels last?
A: Most modern panels come with a 25-year performance warranty. They rarely fail outright, but their efficiency gradually declines over decades.
Determine exactly how much power you need.
Plan safe cable gauges for solar arrays.
Calculate roof area for panel mounting.