How to read your prepaid meter’s kWh—and size solar from it
Turn the units on your South African prepaid meter into a useful daily energy profile before choosing an inverter, battery or solar array.
VumaTech editorial team · 6 October 2026
The short answer
One prepaid electricity unit is one kilowatt-hour (kWh). Record the meter balance at the same time on two different days, subtract the later reading from the earlier one, and divide by the number of days. That daily kWh figure is the most useful starting point for solar and battery design.
Start with energy, not inverter size
A 5 kW inverter describes how much power it can deliver at one moment. Your meter records energy used over time. Those are related, but they are not interchangeable. A sound design needs both your peak load in kW and your consumption in kWh.
Take readings for at least seven ordinary days. A full month is better because weekends, geyser use, cooking and laundry can distort a single-day snapshot.
A simple reading method
Write down the remaining units and time before you buy electricity. Repeat at the same time later, without adding a token between readings. The difference is the energy used during that period.
- Beginning balance: 240 kWh
- Balance seven days later: 156 kWh
- Energy used: 84 kWh, or 12 kWh per day
- Indicative monthly use: about 360 kWh
What the number can—and cannot—tell you
Daily use helps estimate the battery energy and solar generation you may need. It does not reveal which appliances run together or the surge from pumps and motors. An installer should still map essential circuits, high-demand equipment and the hours when you use power.
For backup, isolate the energy used during outages or overnight. For bill reduction, look at the portion you can shift into daylight hours. Those two goals often produce different systems.
Bring these readings to an assessment
Bring a recent municipal bill or prepaid purchase history, seven to thirty days of readings, and a list of essential loads. Also note any future additions such as an electric vehicle, borehole pump, air conditioner or heat pump.
Questions people ask
Is one prepaid unit the same as one kWh?
Yes. One electricity unit represents one kilowatt-hour of electrical energy.
Can monthly kWh determine my inverter size?
Not by itself. Inverter size depends on the loads that may operate simultaneously and their starting surges; monthly kWh is mainly an energy-capacity input.
How many days should I measure?
Seven days is a useful minimum, while a full month gives a more representative baseline. Seasonal bills are even better when available.