How Many Solar Panels Do You Need for an Off-Grid System?
A practical worksheet for sizing the PV array of an off-grid inverter system — daily load, sun hours, derating and a worked example with the numbers our engineers use.
The single most common sizing mistake we see in off-grid projects is an undersized solar array. Panels are cheaper than batteries and inverters to replace later, so getting this number right matters more than any other part of the design.
Step 1: Find your daily energy need (Wh/day)
List every load, its power draw in watts, and the hours it runs per day. Multiply and add: watts × hours = watt-hours per day.
Worked example:
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Lights | 40 | 5 | 200 |
| Refrigerator | 150 | 8 | 1,200 |
| TV | 100 | 4 | 400 |
| Phone chargers | 15 | 4 | 60 |
| Water pump | 300 | 1 | 300 |
| Total | 2,160 Wh/day |
Step 2: Adjust for system losses
Off-grid systems lose energy to conversion, wiring and battery charging. A conservative design multiplies the load by 1.3 (a 30% derating) to get the energy the array must actually deliver:
2,160 Wh × 1.3 = 2,808 Wh/day needed from PV
Step 3: Estimate your sun hours
“Peak sun hours” is the daily equivalent of full-strength sunlight for your location. This is not the same as hours of daylight. Typical values:
- Northern Europe: 2.5–3.5
- Central Europe: 3.5–4.5
- Mediterranean: 4.5–5.5
- Middle East / North Africa: 5.5–6.5
- Southeast Asia / equatorial: 4.5–5.5
- US Southwest: 5.5–6.5
Use a conservative figure — the worst month, not the annual average, unless you have a generator backup.
Step 4: Calculate the array size
Array watts = daily PV energy ÷ sun hours ÷ derating
With 2,808 Wh needed and, say, 4.5 sun hours:
2,808 ÷ 4.5 = 624 W minimum array
We recommend adding a margin of 10–20% on top for cloudy streaks and panel degradation, bringing the example to roughly 700–750 W of panels.
Step 5: Match the array to the inverter / controller
- Check the MPPT operating voltage range of your off-grid solar inverter and size the string voltage to sit in the middle of that range.
- Keep array power within the controller’s maximum PV input rating.
- Wire string current below the controller’s rated input current.
Our off-grid solar inverters include a built-in MPPT charge controller — you can read the PV input range directly from the specification table on each product page, so the array math above slots straight into the actual model you are quoting.
If you would rather not work through the steps by hand, our off-grid system sizing calculator runs the same derating and battery maths and returns a recommended array size, inverter rating and battery bank alongside matching catalog models.
Quick reference: panels per inverter
These figures assume ~550 W panels and 4.5 sun hours, with the 1.3 derating:
| Inverter size | Typical array (W) | Panels (~550 W) |
|---|---|---|
| 1.5–2 kW | 900–1,200 | 2 |
| 3 kW | 1,500–1,800 | 3 |
| 5 kW | 2,400–3,000 | 5 |
| 8 kW | 3,600–4,500 | 7–8 |
Solar array sizing — FAQ
What happens if my array is undersized?
The batteries may not fully recharge on cloudy days, and the system relies on grid or generator backup more often. In off-grid systems this shows up as premature low-voltage cut-offs.
Can I oversize the array safely?
Yes, within the MPPT input limits of the inverter. Oversizing helps winter production and keeps batteries full; the controller clamps excess power. Stay inside the rated PV input voltage and current.
Do panels need to match the inverter wattage one-to-one?
No. The array is sized for daily energy, while the inverter is sized for peak load. A 3 kW inverter often runs with a 1.5–1.8 kW array in our sizing examples.