Experts have warned that the increased use of battery back-up systems and inverters without installing solar power is massively contributing to the risk of a total blackout.
Research has indicated that this back-up system compromised the grid because when load shedding ends the batteries are quickly recharged, putting extra burden on Eskom in an unpredictable manner.
According to Thinus Booysen, University of Stellenbosch engineering professor and research chair in the Internet of Things, battery back-up systems and inverter systems are actually fighting against load shedding by taking away Eskom’s ability to apply load shedding.
“When you have load shedding your battery is discharged and as soon as power is restored, it recharges. Eskom has its normal load to contend with as people switch on and now the extra burden of the batteries charging,” he explained.
What the numbers say
A study conducted by Booysen, his colleagues Dr Michael Ritchie and Professor Japie Engelbrecht, has assessed the impact of domestic users installing battery backup solutions without solar power and evaluates its impact.
The results show that with a mere 15% penetration, the intended effect of load shedding for domestic load will be curtailed by just over 60% in summer and just over 70% in winter when considering the whole day’s curtailment.
“We conclude that the impact of allowing users to charge at 0.5C (half the battery capacity equivalent) without solar augmentation, will have a dramatic impact on the domestic load, even with only 15% penetration. It is therefore imperative that charging batteries from the grid is restricted to protect the potency of load shedding as a grid balancing tool,” the study concluded.
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The experts from the University of Stellenbosch’s Department Electrical and Electronic Engineering point out that the default charge rate on inverters can be as high as 1C, for example 5kW for a 5kWh battery.
They recommended that the charging rate of battery backup solutions is restricted to 0.15C or 0.75kW for a 5kWh battery to prevent the high curtailment after a zone is switched on.
This lower charge rate should be ample to recharge the battery between bouts of load shedding.
Stage 10 load shedding
It is expected that load shedding will be escalated to stage 8 or 10 during the winter of 2023, meaning those who can afford to do so will increasingly revert to power backup solutions.
Because of the additional cost of solar supply and getting approval, the authors found that many users may opt to install only battery backups and inverters.
The study concluded that the impact of allowing battery users to charge at half the battery capacity equivalent, without solar, will have a dramatic impact on the domestic load.
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The researchers explained that if the power demand exceeds supply, the generators will struggle to keep up and may need to be disconnected.
This results in a further deficit of supply and increasing the risk of grid collapse and a total blackout for an extended period of potentially two weeks.
The authors of the report – titled ‘The impact of the increasing residential battery backup systems on load shedding’ – explain that two solutions to the problem are demand management and increased supply.
While the latter is time-consuming and capital-intensive, planned power cuts or load shedding, are the preferred option to reduce demand and each stage of load shedding reduces the total energy demand by 1GW.
Home inverters and batteries
The authors noted that the installation of home inverters and batteries is an increasingly popular solution to soften the impact of power cuts for South African users.
The report explains that domestic users tend to install hybrid inverters with batteries to keep the lights on during load shedding.
“Although a lithium battery with a capacity of 5kWh can theoretically supply 5kW for an hour, reducing the state of charge below 20% diminishes its capacity and causes it to age faster. Solar panels can augment the electricity supply by generating electricity directly to the household and storing excess energy in batteries, while exporting excess electricity to the grid, if the installation allows it,” the report states.
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