South Africa’s solar energy boom is a double-edged sword — on the one hand, it will insulate those who can afford it from load shedding and higher tariffs, and partially fill the electricity supply gap. On the other hand, it poses a real risk to the stability of the national grid.
However, a recent study shows that the humble household geyser can be smartened up to mitigate those risks and open up the solar floodgates.
In response to South Africa’s 15-year-long power crisis, as well as steep annual electricity tariff increases, households and businesses are installing solar systems at a blistering pace.
The country imported roughly $4 billion (R74 billion) worth of solar panels, lithium-ion batteries and inverters in 2023, according to some preliminary estimates. That is as much as the preceding five-and-a-half years combined. Eskom estimates that 2.6GW of solar was added to the country’s rooftops in the 12 months to end-November, bringing total installations to 5GW.
As the private sector reduces its reliance on Eskom, this helps to bring demand for grid power back in line with what Eskom is capable of supplying.
But the catch is that South Africa will soon face a deepening “duck curve” — a phenomenon where demand for electricity from the grid plummets toward the middle of the day as homes and businesses make the most of the sun’s energy. That’s followed by a steep increase in demand for grid power into the evening. Plotted on a graph, the electricity demand curve increasingly resembles a duck.
In some markets where solar is already ubiquitous, such as California and South Australia, there is often zero net demand for power from the grid during the middle of the day.
This creates serious challenges for grid operators, who need to constantly maintain the balance between supply and demand across the network.
Traditional baseload-type power plants were not designed to quickly ramp up and down their output every day, and most take too long to reach full capacity.
Peaking plants – in South Africa, this refers to dirty and expensive diesel facilities – are better suited to ramp up their output fast, but they drive up Eskom’s generation costs, making the utility even less competitive relative to ever-cheaper solar. This, in turn, could accelerate the “utility death spiral”.
Meanwhile, municipalities have a slightly different problem. They buy electricity from Eskom at variable rates, depending on the time of day, and then typically resell it to homes at a fixed rate, or a tariff based on total consumption.
Municipalities typically get the best margins on day-time residential electricity sales. On the other hand, peak-time electricity – in the mornings and evenings – is expensive and often has to be sold by municipalities to homes at below cost.
So, as more solar comes online, municipalities will find themselves in a position where much of the electricity they distribute is sold at times when it is uneconomical for them to do so.
That will put serious strain on municipal finances, considering that electricity sales account for roughly a third of Cape Town’s revenues and a quarter of Johannesburg’s.
But there is a proven solution for this challenge, and it lies in the country’s huge fleet of energy-hungry geysers.
Project Smart Geyser, a 30-month study in the Western Cape found that smart geyser management systems can play a major role in taming the duck curve.
Cape Town-based energy tech company Plentify worked with the City of Cape Town and the Hessequa Local Municipality to deploy geyser management devices in 500 homes, with support from seven European countries via Germany’s GIZ and financing facility EEP Africa, and with oversight of the methodology and results by the University of Cape Town.
The artificial intelligence-enabled devices, called HotBots, automatically turn geysers on and off at the most optimal times, with the aim of shifting electricity consumption away from morning and evening peaks, and making the most of periods of strong solar output instead.
The study showed that HotBots slashed each geyser’s electricity use during peak periods by up to 80%, without affecting the supply of hot water to the participating households.
And by synching geysers up with the sun, it was found that geysers could more than double their use of solar energy.
Further, the devices enhanced each geyser’s overall energy efficiency by up to 24%, simply by switching them off when they did not need to be drawing power.
If rolled out on a wider scale, this solution would go a long way towards smoothing the nation’s energy demand curve and increasing the amount of decentralised solar that both Eskom and municipalities can absorb.
The solar revolution is here to stay, and South Africa needs to get prepared.
- Jon Kornik, CEO of Plentify
