Work out the solar array size in kWp, number of panels, yearly generation, battery bank and inverter for grid-tied, hybrid or off-grid systems from your energy use.
Peak sun hours are the average daily solar energy on the panels expressed as hours at 1,000 W/m². They vary with location, tilt and season; for a site-specific figure use PVGIS (Europe, Africa, Asia) or NREL PVWatts.
| Location | Peak sun hours | kWh per kWp per year (PR 80%) |
|---|---|---|
| Riyadh, Phoenix | 6.0 – 6.5 | 1,750 – 1,900 |
| Dubai, Cairo | 5.5 – 6.0 | 1,600 – 1,750 |
| Karachi, Los Angeles | 5.0 – 5.5 | 1,450 – 1,600 |
| Delhi, Lahore | 4.5 – 5.3 | 1,300 – 1,550 |
| London, Berlin | 2.5 – 3.0 | 730 – 880 |
Approximate values on an optimally tilted surface, for early sizing only.
Estimate the daily energy with the Residential Electrical Load Calculator or the AC Running Cost Calculator, and size the battery-backed loads with the UPS Sizing Calculator.
Divide your daily energy use by peak sun hours and the performance ratio to get the array size in kWp, then divide by the panel rating. For 30 kWh/day, 5.5 sun hours and 80%: 6.82 kWp, or 13 panels of 550 W.
About 4–5.2 kWh per day (1,450–1,900 kWh per year) in sunny regions such as the Middle East and South Asia, and about 2–2.4 kWh per day in Northern Europe, at a performance ratio of 80%.
The ratio of actual output to the theoretical output at standard test conditions. It covers temperature losses, inverter and cable losses, dust and mismatch, and is typically 75–85%. Hot, dusty sites are at the lower end unless the panels are cleaned often.
Battery kWh = energy to back up × days of autonomy ÷ (usable depth of discharge × round-trip efficiency). Divide by the bank voltage to get amp-hours. 30 kWh for 1 day with lithium at 90% depth needs about 35 kWh, or 731 Ah at 48 V.
At least the peak simultaneous load plus about 25%. For grid-tied systems the inverter is often 80–100% of the array kWp; check the surge rating if it must start motors such as AC compressors or pumps.
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