A 10kWh solar battery can provide many hours of backup during load shedding, but there is no single runtime that applies to every South African home.
The answer depends mainly on how much electricity your home is using while the grid is off, how much of the battery capacity is actually usable, inverter losses, and whether your solar panels can recharge the battery during the day.
A home using only lights, Wi-Fi, a refrigerator, security equipment and a television can get substantially more backup time from a 10kWh battery than a home also running a geyser, kettle, pool pump or air conditioner.
How much usable energy does a 10kWh battery provide?
The first thing to understand is that the 10kWh figure is normally the battery's rated capacity. You should not assume that the full 10kWh will be available to your home on every cycle.
Modern LiFePO4 batteries commonly operate with a high usable depth of discharge. Depending on the battery and its settings, a 10kWh battery may provide roughly 8–9.5kWh of usable energy before allowing for the system's operating limits and conversion losses.
That is why battery comparisons should look at usable capacity, not just the number printed on the front of the battery.
The simple way to estimate battery runtime
The basic calculation is:
Runtime in hours ≈ usable battery capacity in kWh ÷ average load in kW
For example, if your 10kWh battery provides 9kWh of usable energy and your essential loads average 500W, or 0.5kW:
9kWh ÷ 0.5kW ≈ 18 hours
That is a simplified estimate. Real-world runtime will be affected by inverter efficiency, battery reserve settings, changing appliance loads and the fact that appliances do not all consume power continuously.
What can a 10kWh battery run?
A 10kWh battery is often well suited to a carefully selected essential-load backup circuit. Typical loads might include:
- LED lights
- Wi-Fi router and fibre ONT
- Televisions and entertainment equipment
- Refrigerator and freezer
- Alarm, cameras and electric gate equipment
- Laptops and phone chargers
- Selected kitchen appliances used briefly
The important point is that runtime is determined by the total load, not simply by the number of appliances connected.
10kWh battery runtime examples
Consider a battery with approximately 9kWh of usable energy. These examples illustrate how dramatically the load changes the result:
| Average load | Approximate runtime | Typical situation |
|---|---|---|
| 500W | About 18 hours | Essentials such as lights, Wi-Fi, fridge and TV |
| 1kW | About 9 hours | Essentials plus additional household use |
| 1.5kW | About 6 hours | More active household during an outage |
| 2kW | About 4.5 hours | Several moderate loads running together |
| 3kW | About 3 hours | Heavy household load |
These are planning examples rather than guaranteed runtimes. Actual results vary with the battery, inverter, appliance duty cycles and system configuration.
Why a kettle can change the calculation
High-power appliances can use a surprising amount of battery energy in a short period.
A kettle, microwave, geyser element, heater or air conditioner can draw substantially more power than lights, Wi-Fi and a refrigerator. A kettle may only operate for several minutes, but repeated use can noticeably increase the energy consumed during an outage.
The same principle applies to pumps and compressors. A pool pump, borehole pump or air conditioner may have a high running load and can also have a starting surge that the inverter must be able to handle.
What about running a geyser from a 10kWh battery?
An electric geyser is one of the biggest loads to consider when designing backup power.
A typical geyser element can draw around 2–3kW while heating. If it runs for two hours, it can consume roughly 4–6kWh of energy. That can represent a large portion of the usable energy in a 10kWh battery.
For many homes, it makes more sense to heat the geyser while the solar panels are producing electricity and keep the geyser off the battery-backed circuit during load shedding.
Can a 10kWh battery run an air conditioner?
It can, provided the inverter and battery are designed for the required power, but air conditioning can reduce backup time quickly.
An air conditioner can consume considerably more power than the basic essential loads in a home. If a 10kWh battery is supporting lights, refrigeration, entertainment and an air conditioner at the same time, the average load can rise substantially.
This is why battery capacity and inverter capacity must be considered together. A battery may have enough stored energy but the inverter may still be unable to supply all the appliances simultaneously.
Does the inverter affect how long the battery lasts?
Yes. The battery stores DC electricity, while most household appliances use AC electricity. The inverter converts the battery's DC energy into usable AC power, and that conversion has losses.
Your inverter also has a maximum continuous output and a surge capability. A system that has enough battery energy but an undersized inverter may not be able to run several high-power appliances together.
For this reason, Solar8 looks at energy capacity and power demand together rather than choosing a battery from its kWh rating alone.
What happens when the solar panels are producing electricity?
A major advantage of a solar-and-battery system is that the battery does not necessarily have to supply the entire outage from stored energy.
During daylight, the solar panels can supply household loads and, where the system design allows it, recharge the battery. This can extend the practical backup period during a long outage.
For example, a household might use battery energy overnight and then use daytime solar production to support the home and replenish some of the battery before another outage.
How much recharge is possible depends on the panel array, sunlight, household consumption, battery state of charge and inverter configuration.
How long will a 10kWh battery last overnight?
For a household using an essential-load circuit, a 10kWh battery can provide a useful overnight backup period.
For example, a 600W average load over 10 hours requires approximately:
0.6kW × 10 hours = 6kWh
That can fit within the usable capacity of a suitably configured 10kWh battery, leaving some reserve for system losses and battery protection.
But if the household averages 2kW throughout the night, the same calculation becomes:
2kW × 10 hours = 20kWh
In that situation, a single 10kWh battery would clearly not be enough for a full ten-hour period.
10kWh vs 15kWh vs 20kWh for load shedding
A 10kWh battery is not automatically the right size for every home.
- 10kWh: a useful starting point for homes wanting substantial essential-load backup and some flexibility during longer outages.
- 15kWh: better suited to homes with higher essential loads or longer overnight backup requirements.
- 20kWh: more appropriate where the household wants to keep a larger selection of appliances running for longer periods.
These are broad planning categories. Your actual battery requirement should be based on the appliances you want available, their power consumption and the length of backup you are targeting.
How to make a 10kWh battery last longer
If you already have a 10kWh battery, a few simple operating choices can make a significant difference:
- Keep the geyser off the battery-backed circuit where practical.
- Use LED lighting.
- Switch off unnecessary entertainment equipment.
- Avoid running multiple high-power appliances simultaneously.
- Use the washing machine and dishwasher during solar-producing hours where possible.
- Run pool pumps during the daytime rather than from the battery.
- Use solar production to recharge the battery whenever conditions allow.
- Keep a sensible battery reserve rather than repeatedly draining it to the absolute minimum.
What if load shedding lasts longer than expected?
A battery should be designed around the type of backup you actually want. If you want only essential loads protected, a 10kWh battery can provide substantial runtime. If you want near-normal whole-home operation for extended outages, significantly more storage may be required.
It is also important to consider what happens after the battery reaches its reserve level. A hybrid system may be able to recharge from solar during daylight, while a system without sufficient solar generation may eventually need the grid or another backup source.
Is a 10kWh battery enough for your home?
For many South African homes, 10kWh is a useful and practical battery size. But the right answer depends on your electricity consumption and your backup expectations.
If your priority is keeping the fridge, lights, Wi-Fi, security, television and selected small appliances operating, 10kWh can provide a strong level of protection.
If you want to run geysers, air conditioners, pool equipment, electric cooking and other high-power loads throughout a long outage, you may need a larger battery bank and a higher-capacity inverter.
The bottom line
A 10kWh solar battery can provide anything from several hours to well over a day of backup depending on the average load. A useful planning assumption is that a modern 10kWh LiFePO4 battery may provide around 8–9.5kWh of usable energy, before accounting for all system losses and reserve settings.
The most important question is therefore not simply “How long does a 10kWh battery last?” but “How much power does my home need while the grid is off?”
That is the calculation that determines whether 10kWh is appropriate — or whether you should consider a smaller or larger battery system.
Find out how much battery backup your home needs
Solar8 can assess your electricity usage, appliances, backup priorities and property to determine the appropriate combination of inverter and battery storage for your home.
Get My FREE Solar8 Assessment and find out what type and size of battery-backed solar system makes sense for your property.