Size a reliable solar array from daily energy. Fine tune derating, efficiency, and degradation easily. Compare outputs, then download CSV or PDF instantly here.
| Daily kWh | Sun hours | Panel W | Losses % | Efficiency % | Panels | System kW |
|---|---|---|---|---|---|---|
| 12.0 | 5.5 | 400 | 14 | ~80.0 | 7 | 2.800 |
| 20.0 | 4.8 | 450 | 18 | ~75.5 | 13 | 5.850 |
| 30.0 | 6.0 | 550 | 12 | ~82.5 | 12 | 6.600 |
1) System efficiency
System_Efficiency = (1 − Losses%) × Inverter% × Temp% × Soiling% × Aging%
2) Required array size
Required_Array_W = (Daily_kWh × 1000) ÷ (Peak_Sun_Hours × System_Efficiency)
3) Panel count
Panels = ceil(Required_Array_W ÷ Panel_Watt)
Oversize applies after required array sizing, adding headroom to DC power.
Accurate sizing begins with a realistic daily energy figure. Use billing data, smart meter exports, or appliance logging to estimate average kWh per day, then separate weekday and weekend behavior. If loads spike seasonally, compute a weighted monthly average and plan for the worst month. This calculator converts that kWh target into required DC array watts using your chosen sun hours and efficiency factors.
Peak sun hours represent equivalent hours at full solar irradiance, not clock time. A site with 5.5 sun hours can deliver the same daily energy as 5.5 hours at one kilowatt per square meter. Use local solar maps, long term weather datasets, or installer assessments. Conservative inputs reduce underproduction risk, while optimistic inputs reduce panel count but may increase grid reliance on hazy days.
Real systems lose energy through wiring resistance, module mismatch, inverter conversion, soiling, and high temperatures. Instead of a single guess, the calculator multiplies individual derate factors to form a composite system efficiency. For example, 14% general losses, 96% inverter efficiency, 92% temperature derate, 98% soiling, and 98% aging yields about 0.80 effective efficiency. Small changes matter because the required array watts scale inversely with efficiency.
The required array result is a DC wattage target that meets the daily kWh goal under average conditions. Panel count is the ceiling of required watts divided by panel watt rating, ensuring you never fall short due to rounding. Installed kW DC helps compare designs and roof space. The estimated production value shows what the chosen panel count should generate given the same assumptions, supporting quick sensitivity checks.
After finding panels required, validate physical feasibility. Check roof area, orientation, and shading, then confirm string sizing and inverter limits. If you expect winter deficits, add modest DC oversize or incorporate storage. For commercial sites, align sizing with demand charges and net metering rules. Finally, document assumptions and export results, so stakeholders can review inputs and update them as better data becomes available. Include panel spacing, walkways, and maintenance access, and verify local codes, permits, and grounding requirements carefully before purchasing equipment today.
Daily kWh, peak sun hours, and overall efficiency dominate the result. Lower sun hours or lower efficiency increases required array watts, which raises the rounded panel count. Panel watt rating changes how many modules you need for the same array size.
Use a long term average for your exact location. Installer proposals, solar maps, or meteorological datasets are useful. If you want a conservative design, enter a slightly lower value to account for haze and seasonal variation.
Separating losses helps you model real conditions. Inverter efficiency, temperature derate, soiling, and aging behave differently and can be improved independently. Multiplying them produces a more transparent system efficiency than a single blanket estimate.
DC oversize adds extra module capacity beyond the calculated requirement. It can improve winter and morning output, but it may increase clipping if the inverter is smaller. Keep it modest and validate inverter limits and string design.
No. It sizes the PV array for average daily energy under your assumptions. If you add storage, adjust the daily kWh target for battery round trip losses and desired autonomy, then rerun the calculation with updated inputs.
The calculator already rounds up to whole panels. You may still add margin for future load growth, shading uncertainty, or module availability. Confirm roof layout and electrical constraints before increasing the design size.
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.