We slashed our electricity bill by R900 using a small solar power system

We reduced our monthly electricity bill by more than 92% using an entry-level solar power system.

In late March 2024, we installed six solar panels with a peak output of 3.3kW, a 5kW hybrid inverter, and a 5.12kWh battery at our 3-bedroom townhouse in Pretoria.

The initial intent of the system was primarily to provide backup power during load-shedding and unscheduled outages, while also saving on grid electricity usage to help make up the system’s cost over time.

However, we were only able to benefit from the system once during load-shedding and for a few hours of unscheduled outages in the City of Tshwane.

We initially set the system to use grid energy for our demand or charge up the battery from the grid during certain periods to ensure we had sufficient battery charge for two to four hours of load-shedding or power cuts.

That included a top-up to around 50% charge between 02:00 and 05:00 to ensure that we would have backup power capacity for the early morning routine if load-shedding kicked in.

Due to power outages becoming less of a concern, we reconfigured the inverter to focus on electricity savings.

The main change was setting the minimum battery charge level to 20% at all times instead of 50% during certain periods.

The Dyness battery we installed has an excellent depth-of-discharge rating of 90%, which means we could theoretically take the minimum charge level even lower without voiding the warranty .

However, we figured sparing that 10% capacity each day over the long term would help the battery last longer.

That said, even if we consumed two full charging and discharging battery cycles per day, the battery would last over eight years before its maximum capacity dropped to 80% of what it initially was.

We also installed a geyser timer so our water was primarily heated during the day with the solar and battery and set the electric geyser to a maximum of 70°C.

The latter ensures the water stays as hot as possible for as long as possible, allowing for hot showers in the late mornings, even after one or two showers in the evenings.

The six solar panels on our roof

Less than 10% grid usage and cost

Our household consists of just two people with relatively small power consumption, thanks to the use of a gas hob and air fryer for cooking.

During June 2024, we consumed around 321.94kWh of energy, over 91% of which came either directly from the solar panels or the energy stored in the battery, produced only by solar power.

Without the system, that energy would have cost R998.53 on the City of Tshwane’s prepaid tariff schedule, excluding the service fees of the platform from which we bought our electricity.

Thanks to solar and battery power, we only consumed around 28.2kWh of electricity from the grid, 91.2% less than without the system.

Around half of this was due to a 20W trickle feed from the grid that prevents the prepaid meter from incorrectly detecting disallowed feed-in and tripping the grid connection.

The remaining grid consumption was primarily for a handful of periods early in the morning, when we sometimes made extensive use of an 800W electric heater or turned on the geyser for about half an hour if we consumed water at above-average levels in the previous afternoon or evening.

Where we would have paid R998.53 for the energy without our own generation and battery storage, we only paid R78.28.

The saving of R920.25 works out to around 92.2% of our hypothetical bill without the system.

The table below shows the differences in energy consumption and costs with and without our entry-level solar system.

Return on investment is still years away

While the savings are significant, it should be noted that we are still paying an effective additional cost per month for the load-shedding protection.

The system cost roughly R74,000 with installation, but it is being financed with a 60-month personal loan at a prime plus 1% interest rate.

With all additional admin, life and credit cover fees included, the monthly loan repayment is currently R2,035.56.

Deducting the R920.25 savings means that we were paying roughly R1,115.31 per month for the benefit of having backup power during the previous municipal financial year.

However, the annual electricity hikes are expected to reduce that effective cost significantly over the remaining loan term.

With just the latest increase of 12% from July 2024, the monthly saving would increase to R1,030.68 using the same energy consumption as in June 2024. That brings down the monthly effective cost of the system to R1,004.88.

If another 12% hike followed in July 2025, the saving would increase to R1,154.36 and the monthly effective cost of the system would drop to R881 during that year.

However, Eskom is reportedly eyeing an astounding increase of 43.55% for municipalities from July 2025.

While it is unlikely that the National Energy Regulator of South Africa would grant such a significant increase, even half that hike would see the savings increase signficantly.

Assuming Nersa granted an increase of 21.78%, the monthly saving would increase to R1,255.11 and the effective cost of the system would drop down to R780.45 per month.

In addition, the repo rate is currently at its highest level since the 2008 financial crisis.

With expectations that it will come down in the second half of 2024 or early in 2025, the monthly loan repayment will also decline, further reducing the system’s effective cost.