We slashed our yearly electricity bill with R11,000 using a small solar power system

We were able to offset roughly 83% of our annual electricity bill — worth about R11,000 — using a small solar power system in Pretoria over the past year.

After enduring plenty of load-shedding from 2020 to 2023 with a portable power station in rented homes, we decided that after buying our first house, an investment in an integrated system made sense.

Our solar power system was installed on 25 March 2024 and features a 6-panel JA Solar array providing 3.27kWp generation, a 5kW Deye hybrid inverter, and a 5.12kWh Dyness battery.

Due to the decline in load-shedding shortly after our installation, we quickly reconfigured the system to maximise savings rather than ensure security of supply.

That primarily meant allowing the battery to deplete up to its minimum recommended state-of-charge of 20% instead of the 50% level the installer had selected.

A year after its installation, the system had generated about 3,920kWh of electricity, working out to an average of 10.73kWh per day.

It should be noted that this figure would have been much higher if we had been able to sell excess power back into the grid or draw the maximum potential during the day.

On days where we made maximum potential use of the system by turning on a large air conditioner or charging an electric car, we regularly recorded solar production over 18kWh.

On the system’s three highest peak production days in the past year, it recorded 21.3kWh, 20.7kWh, and 19.8kWh production.

On the consumption side, we used 4,190kWh since the system was installed.

If we did not have the solar power system, we would have spent about R1,099 per month on electricity from the City of Tshwane.

The difference between the production and consumption works out to roughly 250kWh.

However, due to losses in AC-DC power conversion and battery round-trip efficiencies, not all the electricity generated was consumed or discharged by the battery.

The actual energy purchased in the past year was about 712.2kWh, working out to 59.35kWh per month.

With the amount of electricity produced by our solar system, our average monthly spend is around R185 per month.

That means we are saving over R900 on our monthly electricity bill and have reduced our annual bill by about R11,000.

The table below compares how much we would have paid for electricity on a monthly and annual basis if we did not have the system and how much we are actually paying.

Shifting demand to daytime

It should be noted that we were only able to reduce our bill by more than 80% due to shifting as much of our demand to the day to make the best possible use of sunshine hours.

The most important step in achieving this was installing a geyser timer that would turn on mid-day when solar generation was at its best and battery levels were adequate for supplementing the element’s heavy power demand.

Another factor to consider is that we primarily used an air fryer and gas hob for cooking our food.

We also minimised grid usage by timing our washing machine and dishwasher cycles to run while solar generation was adequate.

On the other hand, our consumption was pushed up significantly on several occasions due to the charging of electric vehicles.

This likely contributed somewhere around 200kWh to 300kWh of the total energy purchased from the grid.

In addition, the inverter was configured to pull a constant 20W trickle feed from the grid to avoid tripping the prepaid meter for incorrect feed-in detection.

That alone contributed roughly 480Wh consumption per day or 175kWh during the entire year.

As a closing thought, it is important to emphasise that our total monthly energy bill is still around R600 greater than it would have been without the system.

We did not have sufficient cash to buy the system outright, so we took out a loan at a reduced interest rate to pay it off over time. Over the five-year loan period, the system will cost R103,938.

Assuming annual electricity tariff hikes of roughly 10% over the coming years, it will have paid for itself and its interest after about seven years in operation.

However, this calculation changes dramatically if Eskom’s grid connection price hikes get passed on to municipal users.