Off-grid solar and battery sizing for Nairobi
A 1 kW array in Nairobi produces about 697 kWh a year — but that annual figure is not what sizes a system. January is, and in January the same array makes only 1.3 kWh a day, against 2.5 in May.
What do you need?
Battery bank
12.9 kWh
268 Ah at 48V
Solar array
3.08 kW
about 7 panels of 450W
Summer only
1.62 kW
if you only use it May-ish
Sizing by household
Year-round systems in Nairobi, 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 | 1.03 kW | 3 |
| Basic off-grid living The above plus a small fridge and a few hours of television |
3.0 kWh | 12.9 kWh | 3.08 kW | 7 |
| Comfortable off-grid home Full-size fridge-freezer, washing machine, pumps, laptops |
6.0 kWh | 25.7 kWh | 6.15 kW | 14 |
| Everything except heating A normal household load, with heating and cooking on gas or wood |
10.0 kWh | 42.9 kWh | 10.26 kW | 23 |
Why January 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 (worst) | 1.32 kWh/day | 3.08 kW | |
| February | 1.47 kWh/day | 2.77 kW | |
| March | 1.63 kWh/day | 2.50 kW | |
| April | 2.12 kWh/day | 1.93 kW | |
| May | 2.51 kWh/day | 1.62 kW | |
| June | 2.47 kWh/day | 1.65 kW | |
| July | 2.27 kWh/day | 1.80 kW | |
| August | 2.07 kWh/day | 1.96 kW | |
| September | 1.82 kWh/day | 2.24 kW | |
| October | 1.79 kWh/day | 2.27 kW | |
| November | 1.82 kWh/day | 2.24 kW | |
| December | 1.61 kWh/day | 2.54 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 January 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 Kenya
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.