Off-grid solar and battery sizing for Hastings
A 1 kW array in Hastings produces about 1,249 kWh a year — but that annual figure is not what sizes a system. June is, and in June the same array makes only 1.3 kWh a day, against 5.4 in January.
What do you need?
Battery bank
12.9 kWh
268 Ah at 48V
Solar array
3.04 kW
about 7 panels of 450W
Summer only
0.76 kW
if you only use it January-ish
Sizing by household
Year-round systems in Hastings, 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 | 1.01 kW | 3 |
| Basic off-grid living The above plus a small fridge and a few hours of television |
3.0 kWh | 12.9 kWh | 3.04 kW | 7 |
| Comfortable off-grid home Full-size fridge-freezer, washing machine, pumps, laptops |
6.0 kWh | 25.7 kWh | 6.09 kW | 14 |
| Everything except heating A normal household load, with heating and cooking on gas or wood |
10.0 kWh | 42.9 kWh | 10.14 kW | 23 |
Why June 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 | 5.37 kWh/day | 0.76 kW | |
| February | 4.55 kWh/day | 0.90 kW | |
| March | 3.49 kWh/day | 1.17 kW | |
| April | 2.55 kWh/day | 1.60 kW | |
| May | 1.78 kWh/day | 2.28 kW | |
| June (worst) | 1.34 kWh/day | 3.04 kW | |
| July | 1.53 kWh/day | 2.66 kW | |
| August | 2.30 kWh/day | 1.77 kW | |
| September | 3.30 kWh/day | 1.23 kW | |
| October | 4.42 kWh/day | 0.92 kW | |
| November | 5.14 kWh/day | 0.79 kW | |
| December | 5.33 kWh/day | 0.76 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 June 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 New Zealand
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.