How home batteries and inverters can impact your electricity bill: South African insights

Installing an inverter and battery system without solar generation capacity may lead to a significant increase in your monthly electricity bill, warns a recent study. While batteries provide households with electricity during periods of load-shedding, their usage can cause unexpected spikes in consumption. A MyBroadband analysis reveals the cost of recharging lithium-ion batteries ranging from 1.2kWh to 5.5kWh across major South African metros. With electricity tariffs varying between providers, residents of Cape Town face the highest charges at R3.51 per kWh, while City Power offers the lowest tariff at R2.41 per unit. The study emphasises the importance of factoring in load-shedding frequency and the overall impact on costs for accurate budgeting. This article was republished courtesy of MyBroadband.

How much a home battery and inverter can increase your electricity bill

South Africans that plan to install an inverter and battery system without solar generation capacity should be prepared to see a significant increase in their monthly electricity bill.

This is expected, as having the battery gives households access to electricity during periods they otherwise would not have.

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However, what I didn’t fully expect was how much more electricity I would use every month after installing a battery and inverter system earlier this year.

Even during Eskom’s lower stages of load-shedding — Stage 1 to Stage 4 — recharging common battery sizes can significantly increase your electricity bill, depending on how much capacity you use and your electricity provider.

MyBroadband calculated how much it would cost to recharge a range of typical lithium-ion battery sizes, from 1.2kWh to 5.5kWh, for households who receive power directly from Eskom or municipal power providers for South Africa’s biggest metros.

These include City Power (Johannesburg), the City of Tshwane, the City of Cape Town, and eThekwini Municipality.

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The table below provides the cost of a single recharge of various battery capacities.

Our calculations assume the batteries are lithium-ion with an 80% depth of discharge (DoD) and disregard the efficiency of the charging system. We used the electricity tariff blocks for customers averaging 600kWh per month.

The City of Cape Town charges its residents the most for electricity at around R3.51 per unit (kWh). At this price, a single recharge of a 1.2kWh battery costs R3.37, while a 5.5kWh battery will cost R15.44 to charge fully.

eThekwini Municipality and the City of Tshwane’s charges are also fairly high at R3.00 and R3.08 per kWh, while City Power charges the lowest tariff at R2.41 per unit. Eskom direct customers pay R2.50 per kWh.

Next, it is essential to take the frequency of load-shedding sessions into consideration, as this determines how often you will need to recharge your battery.

The frequency of load-shedding for Eskom’s lower stages can be summarised as follows:

Stage 1 — five bouts per week or 21 sessions each month.
Stage 2 — 11 bouts per week or 42 sessions each month.
Stage 3 — 16 bouts per week or 63 sessions each month.
Stage 4 — 21 bouts per week or 84 each month.

While a single recharge may not seem like a big deal, with prices ranging from R2.31 to R15.44 per cycle depending on the power provider, the cost increases significantly when multiplied by the total monthly recharges.

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Although the calculations below assume a worst-case where the battery depletes fully between load-shedding sessions, they are intended to be indicative and illustrate how quickly these costs can escalate.

Taking the smallest and largest battery capacities from our calculations — the 1.2kWh and 5.5kWh units — we calculated the monthly cost of recharging each under load-shedding from Stage 1 to Stage 4.

The results are summarised in the table below.