Off-grid solar and battery sizing for Vacoas
A 1 kW array in Vacoas produces about 1,426 kWh a year — but that annual figure is not what sizes a system. July is, and in July the same array makes only 3.2 kWh a day, against 4.4 in December.
What do you need?
Battery bank
12.9 kWh
268 Ah at 48V
Solar array
1.26 kW
about 3 panels of 450W
Summer only
0.92 kW
if you only use it December-ish
Sizing by household
Year-round systems in Vacoas, three days of autonomy, lithium.
| Use | Per day | Battery | Array | Panels |
|---|---|---|---|---|
| Weekend cabin LED lights, phone charging, a laptop, a small water pump |
1.0 kWh | 4.3 kWh | 0.42 kW | 1 |
| Basic off-grid living The above plus a small fridge and a few hours of television |
3.0 kWh | 12.9 kWh | 1.26 kW | 3 |
| Comfortable off-grid home Full-size fridge-freezer, washing machine, pumps, laptops |
6.0 kWh | 25.7 kWh | 2.52 kW | 6 |
| Everything except heating A normal household load, with heating and cooking on gas or wood |
10.0 kWh | 42.9 kWh | 4.19 kW | 10 |
Why July decides everything
Array needed to cover 3.0 kWh a day, month by month. The tallest bar is the one your system has to survive.
| Month | Yield per kW | Array needed | |
|---|---|---|---|
| January | 4.26 kWh/day | 0.96 kW | |
| February | 4.24 kWh/day | 0.96 kW | |
| March | 4.04 kWh/day | 1.01 kW | |
| April | 3.88 kWh/day | 1.05 kW | |
| May | 3.47 kWh/day | 1.17 kW | |
| June | 3.25 kWh/day | 1.25 kW | |
| July (worst) | 3.24 kWh/day | 1.26 kW | |
| August | 3.55 kWh/day | 1.15 kW | |
| September | 4.08 kWh/day | 1.00 kW | |
| October | 4.23 kWh/day | 0.96 kW | |
| November | 4.24 kWh/day | 0.96 kW | |
| December | 4.44 kWh/day | 0.92 kW |
What the numbers assume
- Battery capacity allows for inverter losses, round-trip efficiency, and a usable depth of discharge — 80% for lithium, 50% for lead-acid. Nameplate capacity is always larger than the energy you can actually use.
- Array size includes a 25% margin over the bare requirement. A system that exactly meets demand on an average day of July never recovers from a run of cloudy ones.
- Yield figures are measured, not modelled — PVGIS satellite and reanalysis data for 2005–2023, at the optimal angle for this location, with 14% system losses already deducted.
Other cities in Mauritius
Limitations
- No shading. Trees, terrain and buildings are not modelled and can dominate everything here.
- Nothing about heating. Electric heating or cooking multiplies these figures several times over. Off-grid systems almost always use gas or wood for heat.
- Batteries age. Capacity falls over years; installers commonly oversize to allow for it.
- This is an estimate, not a design. A real installation needs a survey, local electrical regulations, and someone accountable for the result.