Plan your solar array with confidence quickly. Tune panel size, sun hours, and performance assumptions. Download summaries, compare scenarios, and decide your next step.
Fill the fields, then press Calculate. For best results, use annual averages or long-term utility data.
The calculator converts your energy use to a daily target, then estimates the DC system size needed to produce that energy based on solar resource and efficiency.
E_target = E_base × Coverage × (1 + Growth)kWh/kW/day = PSH × PR × η_invkW_req = E_target ÷ (PSH × PR × η_inv)N = ceil((kW_req × 1000) ÷ W_panel)If you provide roof area, the tool also estimates a practical maximum panel count after applying a spacing factor.
A_eff = A_panel × (1 + Spacing)N_max = floor(A_roof ÷ A_eff)N_rec = min(N, N_max) when roof area is set.For grid-tied systems, use long-term averages. For off-grid designs, add battery and autonomy checks before final sizing.
These sample scenarios illustrate how sun hours and panel wattage affect the panel count. Use them as starting points, not guarantees.
| Daily Usage (kWh/day) | Peak Sun Hours | Panel Rating (W) | Performance Ratio | Estimated Panels Needed |
|---|---|---|---|---|
| 10 | 5.5 | 450 | 0.80 | 6 |
| 15 | 5.0 | 550 | 0.80 | 7 |
| 20 | 4.5 | 550 | 0.78 | 11 |
| 25 | 4.0 | 600 | 0.80 | 14 |
| 35 | 5.0 | 550 | 0.75 | 19 |
Panel quantity depends on three levers: consumption, offset target, and the energy each panel can deliver. If monthly use is 450 kWh, the daily baseline is about 14.8 kWh/day. Choosing 100% coverage and 10% growth turns that into roughly 16.3 kWh/day. Because the tool sizes in kW first, increasing coverage from 80% to 100% raises required capacity by 25%, while growth adds directly (1.10× for 10%).
Peak Sun Hours (PSH) is daily solar energy expressed as “equivalent full-sun hours.” A site averaging 5.0 PSH can produce about 5.0 kWh per installed kW DC before losses. Locations with 4.0 PSH typically need 25% more capacity than 5.0 PSH for the same demand. Use an annual average, since winter and monsoon seasons can temporarily reduce output.
Performance Ratio (PR) bundles real-world losses: temperature derate, dust, wiring, mismatch, clipping, shading, and downtime. Clean, well-ventilated arrays often land near 0.75–0.85; harsh heat or soiling can push PR lower. The calculator estimates delivered energy with PSH × PR × inverter efficiency, so a PR change from 0.80 to 0.72 reduces expected production by 10% and increases panel count accordingly.
Roof area limits become important when the energy-based panel count is high. Many modern modules occupy roughly 1.9–2.2 m², but usable roof is always less than measured roof because of setbacks, vents, and access paths. The spacing factor adds practical clearance; with 10% spacing, each 2.0 m² panel effectively needs 2.2 m². On a 30 m² roof, that reduces the maximum from 15 to 13 panels.
Use the estimate as a planning baseline, then validate inputs with site data. Confirm PSH from local solar maps or installer simulations, and refine PR using roof tilt, shading, and cleaning frequency. If you are area-limited, options include higher-watt panels, optimizing layout, adding a carport structure, or improving PR through maintenance. Export CSV or PDF to lock assumptions, compare quotes, and track revisions across scenarios over the year.
Use a long-term annual average for your city or nearest weather station. Many regions fall between 3.5 and 6.0 hours/day. If you only have monthly values, use the lowest-season average for conservative sizing.
Start with 0.80 for a typical grid-tied rooftop. Use 0.75 for hot, dusty, or lightly shaded sites. Well-ventilated, frequently cleaned arrays may reach 0.85. Treat PR as a planning factor, then refine after a survey.
The tool first computes required kW. A higher-watt module provides more kW per panel, so fewer panels reach the same capacity. Total system kW stays similar; the physical count and area often improve.
They are planning estimates using averages. Real output varies with shading, tilt, temperature, soiling, and equipment limits. Use the result to compare options, then confirm with an installer simulation and a site inspection.
If net metering is strong, 90–110% can be practical. Without net metering, match daytime loads more closely to avoid exporting energy you cannot use. Start at 80–100%, then adjust based on bills and usage patterns.
Leave roof area blank to get an energy-based panel count. Later, measure usable space excluding setbacks, vents, and access paths. Re-run with spacing factor to see whether the design fits or becomes area-limited.
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.