Solar System Sizing Calculator
Enter kWh from your bill or a device list; get panel size (kWp), inverter, LiFePO4 battery and roof area for on-grid, hybrid and off-grid systems.
System type
Energy use
Read the kWh figure on the bill. Use a 3–12 month average, or a hot month (March–May) to be safe.
Offices, shops and factories are often 60–80%. Homes empty during the day are often 30–40%.
Homes 30; offices open Monday–Saturday about 26.
Sun and panels
Laos and Thailand average about 4.5–5.5; lower in the rainy season.
What is left after heat, dust, wiring and inverter losses. About 0.75–0.80 in hot, dusty conditions.
Current panels are mostly 550–650 W.
Electricity rate (optional)
Enter it to estimate monthly savings. Leave 0 to skip.
Results
Recommended array
1.80 kWp
3 × 600 W panels
Inverter
3kW
Approximate roof area
9–13m²
Energy produced per day
6.3kWh
Per month
190kWh
Share of the bill covered
32%
How we calculate
1. Daily energy (kWh) ≈ kWp × PSH × PR. With PSH 4.5 and PR 0.78, 1 kWp gives about 3.5 kWh a day.
2. On-grid: daytime load (kW) = monthly kWh × daytime share ÷ days in use ÷ 9 h, then kWp = daytime load ÷ 0.75, because at noon in hot weather 1 kWp delivers about 0.75 kW. Inverter ≈ kWp ÷ 1.2.
3. Hybrid: kWp = daily kWh ÷ (PSH × PR). Battery = backup W × hours ÷ 0.81 (DoD 0.9 × inverter 0.9) ÷ 0.8 (ageing). Inverter ≈ the larger of kWp ÷ 1.2 and backup W × 1.25.
4. Off-grid: kWp = daily kWh ÷ 0.85 ÷ (PSH × PR) × 1.25 so the battery recovers after a dull day. Battery = daily kWh × days ÷ 0.8 (DoD). The inverter covers total watts × 1.25 plus motor starting surge (about 3×).
5. Panels round up to whole panels, the inverter to a standard size and the battery to 5.12 kWh modules. A metal-sheet roof needs about 5–7 m² per kWp.
The full method and three worked examples are in our solar system sizing guide.
These results are estimates to help with planning and budgeting. Our engineers will verify everything on site before final design and equipment proposal.
The same rules of thumb our engineers use for a first design. Good enough for budgeting; the final numbers come from a site survey.
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Open calculatorSend us a floor plan or a few photos of the site
We’ll come back with a few questions, then a first design. The first consultation is free, in Lao, Thai or English, on WhatsApp or our Facebook page.