Plan solar panels for your energy goals. Compare roof space, losses, and budget options quickly. Get a clear count to start quoting confidently today.
| Scenario | Daily Use (kWh) | PSH (h) | Panel (W) | Derate (%) | Estimated Panels |
|---|---|---|---|---|---|
| Small apartment | 6.0 | 4.5 | 450 | 80 | 4–5 |
| Family home | 15.0 | 5.0 | 550 | 78 | 7–9 |
| Home + small office | 28.0 | 4.2 | 600 | 75 | 15–18 |
Accurate daily consumption is the foundation for a reliable plan. Convert your monthly bill to kWh per day, then decide what portion you want solar to cover. Peak sun hours translate local irradiation into usable production time. When peak sun hours drop seasonally, the same array produces less energy, so sizing should reflect realistic averages rather than best days. For households with variable loads, using a conservative daily value reduces the chance of undersizing.
Modules rarely deliver nameplate power continuously. Losses from wiring, inverter conversion, soiling, mismatch, and downtime reduce delivered energy. This calculator combines those effects using an overall derate chain, multiplying efficiency terms into a single performance factor. If you can measure inverter efficiency and estimate site losses, the derate becomes more representative. A small change, such as moving system losses from 12% to 18%, can shift required capacity by several hundred watts.
Once required DC size is determined, panel quantity is the required watts divided by panel watts, rounded up. Rounding up matters because partial panels cannot be installed, and any rounding also provides slight headroom against uncertainty. Higher-watt modules reduce the number of panels for the same capacity, which can simplify mounting and wiring. However, higher-watt panels may be larger, so roof fit should always be checked alongside quantity.
Area planning is often the first constraint for residential systems. The calculator compares required panel area to usable roof area after setbacks, obstructions, and shading zones. If the plan does not fit, options include selecting higher-watt panels with similar dimensions, reducing the solar fraction, improving derate assumptions through better hardware, or relocating panels to ground mounts. Including a small buffer for maintenance access and airflow improves long-term serviceability.
Early budgeting benefits from a simple panel cost estimate, even before full balance-of-system pricing is known. Adding a backup margin can represent planned storage, future load growth, or a preference for extra generation. Use the exported CSV to compare scenarios across different panel ratings and performance assumptions, and use the PDF when sharing with installers. Revisiting inputs after a site assessment typically tightens the estimate and improves procurement decisions. Document assumptions, then refine them after quotes and commissioning measurements.
Peak sun hours represent equivalent full-sun hours per day. Use values from local solar maps, installers, or performance reports, then choose a realistic annual average for your mounting angle and location.
Real systems lose energy to heat, wiring, dirt, mismatch, and inverter conversion. Combining these into one derate reflects delivered energy more honestly than nameplate power alone.
Not always. Some users target 60–90% to manage roof limits, budgets, or net-metering rules. Start with your goal, then compare panel count and fit across scenarios.
Try higher-watt panels, improve orientation, reduce losses with better components, or lower the solar fraction. If needed, consider a ground mount or a second roof surface.
No. It simply adds extra capacity to cover future growth or storage charging. You can keep the margin at zero if you only want a grid-tied offset estimate.
It is an early-stage sizing tool. Accuracy improves when your sun hours, shading, and losses match real conditions. A site survey and production simulation will refine final equipment selection.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.