Free solar panel estimator. Enter daily electricity use, peak sun hours and panel wattage to estimate panels needed and total system size.
Your results will appear here.
Enter your values and press Calculate.
The estimator divides your daily electricity use (kWh) by your location's peak sun hours to get the raw system size in kilowatts, then divides that by your chosen panel wattage and rounds up to a whole number of panels. The result shows panels needed and the actual installed system size. These are planning estimates for budgeting, a professional roof survey finalises any real installation.
Sizing starts with energy, not roof space: first find how much electricity you use per day, then divide by peak sun hours to get the kilowatts of panel capacity needed. The panel count is system kW times 1,000 divided by one panel's wattage, always rounded up, you cannot install half a panel.
Worked example, a home using 30 kWh a day with 5 peak sun hours needs 6 kW of capacity. With 400 W panels that is 6,000 ÷ 400 = 15 panels, i.e. a 6.0 kW system.
This is a raw estimate before real-world losses (inverter, wiring, dust, heat), which is why installers usually add margin on top, treat the number as a solid starting point for quotes.
Enter your average daily electricity use in kWh, take your monthly bill total and divide by 30. Then enter your location's peak sun hours per day (most places sit between 3 and 6; the US average is about 4–5) and pick a panel wattage.
Click Calculate to see how many panels you need and the resulting system size in kW. Try a higher wattage to see how fewer, more powerful panels shrink the roof area you need. Use it as a quick home solar size guide before requesting quotes.
Peak sun hours are not the same as daylight hours, they are the equivalent hours of 1,000 W/m² sunshine, the standard test condition panels are rated at. Six hours of hazy daylight might equal only 3–4 peak sun hours, which is why this single input moves the panel count so much.
Typical ranges: the US Southwest gets 6–7.5 peak sun hours a day, the Midwest about 4–5, the Northeast 3.5–4.5, and much of Europe and the UK 2.5–4. Free solar irradiance maps and NASA POWER climatology data give a figure for your location.
Residential panels commonly run 250–550 W; 400–450 W modules are the 2026 mainstream sweet spot. Monocrystalline panels convert 15–22% of sunlight and need the least roof space, while polycrystalline panels are cheaper but sit around 13–16% efficiency.
Higher wattage means fewer panels for the same system size, a 6 kW array needs 24 panels at 250 W but only 11 at 550 W. Fewer panels also means fewer mounts, less wiring and lower labour cost.
A standard residential panel covers roughly 17–18 square feet, plus spacing for access and wind clearance, budget about 20 square feet per panel when eyeballing roof space. In the northern hemisphere panels should face true south, tilted near your latitude angle; even 10–15° off optimal loses only a few percent.
Shade is the real killer: a single shaded panel can drag down a whole string. And no system produces its rated output all day, temperature, dust, inverter losses and panel ageing (about 0.5% a year) mean real output runs 75–85% of nameplate. Always get a site survey before buying.
Net metering explained simply: with an on-grid system your excess daytime power flows back to the utility and spins your meter backwards, earning credits you use at night, the cheapest setup where the grid is reliable. A hybrid system adds batteries for backup during outages, which is popular where load-shedding is common.
Off-grid systems skip the utility entirely but need batteries sized for several cloudy days, which roughly doubles the cost. Payback periods commonly run 3–10 years depending on tariffs and subsidies, every year after payback is essentially free electricity.
Divide your daily kWh by your peak sun hours to get the system kW, then divide by panel wattage and round up. A typical US home using 30 kWh a day with 5 sun hours needs about 15 panels at 400 W. Enter your own numbers above for an exact figure.
Peak sun hours are the equivalent hours of full 1,000 W/m² sunshine, not total daylight. Most US locations average 3–6 a day; the Southwest reaches 6–7.5. They are the single biggest location factor in system sizing.
Roughly panel watts times sun hours times an 0.8 real-world factor: a 400 W panel at 5 sun hours makes about 1.6 kWh a day. Multiply by your panel count for daily system output.
Allow about 17–18 square feet per panel plus spacing, roughly 20 square feet each. A 15-panel 6 kW system needs around 300 square feet of clear, unshaded roof.
Heat (output falls above 25°C), shading, panel angle and direction, dust and soiling, inverter and wiring losses, and ageing at about 0.5% a year. Real-world output is typically 75–85% of the panel's rated capacity.
On-grid with net metering is cheapest where the grid is reliable. Hybrid adds battery backup for outages. Off-grid suits remote areas with no grid but costs much more because batteries must cover cloudy days.
No, it is a planning estimate for budgeting and comparing quotes. Roof geometry, shading, wiring runs and local codes all change the final design, so a professional site survey is essential before purchase.
The solar payback period, the time for electricity bill savings to repay the system cost, is usually 6 to 10 years for a home installation, depending on panel cost, electricity rates, peak sun hours and net-metering rules. After the payback period ends, the remaining 15+ years of panel output are essentially free electricity.
See how your savings grow with compound interest over time.
Find percentages, percentage change and reverse percentages instantly.
Convert between metric and imperial length units.
Measure investment performance with total ROI, net profit and annualized ROI.