Big hidden “batteries” beating load-shedding in South Africa – MyBroadband

Multiple types of energy storage have played a critical role in helping Eskom avoid load-shedding over the past few months, according to EE Business Intelligence head and reputed energy expert Chris Yelland.

However, the potential of this energy storage could only be realised thanks to a significant increase in private rooftop solar adoption over the past two years.

Many South Africans are sceptical about the contribution of solar power in reducing load-shedding.

On its own, solar power is only available when the sun is shining and it cannot provide significant generation during the critical evening and morning peak demand periods.

However, Eskom System Operator Isabel Fick previously explained that solar generation nonetheless played an instrumental role in reducing load-shedding.

Fick said the big increase in private rooftop solar reduced demand for Eskom generation during the day, allowing the utility to refill its emergency generation reserves.

This included water “batteries” at its three pumped storage dam schemes — Drakensberg, Ingula, and Palmiet.

These schemes have a combined capacity of around 2,732MW, making them capable of avoiding between two and three stages of load-shedding.

Yelland explained that pumped storage dams are like big batteries that can store and discharge water to provide electricity, but they are not intended to be used frequently.

A pumped storage scheme comprises upper and lower reservoirs with a power station/pumping plant between the two.

When used as intended, pumped storage schemes only pump water to their upper reservoir during off-peak periods.

In peak demand periods, water is released from the upper reservoir, turning turbines that generate electricity — like in a hydroelectric dam.

Restoring the water levels at these dams requires pumping water uphill, which consumes a lot of power on its own.

However, Yelland pointed out that Eskom’s generation shortfall was so dire in previous years that it had to rely on pumped storage dams to keep the power on during the middle of the day on business days.

That often led to the upper reservoir’s levels depleting completely before the end of the week, requiring that Eskom implement load-shedding over the weekend to “recharge” the dams.

With the significant increase in rooftop solar, Eskom had sufficient electricity at its disposal to avoid depleting its dam “batteries” and was able to shift its recharging periods back to off-peak hours — in the middle of the day when the sun is shining.

Home and business batteries also contributing

In addition to high amounts of solar power making it possible for Eskom to use its pumped storage scheme as designed, Yelland reckons that the battery storage paired with solar power installations has also reduced overall and peak demand.

This has further improved electricity availability.

With load-shedding no longer being a factor, it makes sense for private solar power generators to make extensive use of their stored energy to cut their electricity bills rather than focusing on retaining high battery levels for power outages.

There are currently no reliable estimates for how much backup power capacity is installed in homes or businesses with solar power, but the number has likely surged significantly over the past two years.

One indicator of the available capacity is the amount of batteries coming across South African borders.

According to Trade and Industrial Policy Strategies senior economist Gaylor Montmasson-Clair, South Africa imported $1.75-billion’s worth of lithium-ion batteries in 2023, over double the value imported in 2022.

2023’s imports had an estimated capacity of about 12,500MWh or 12.5GWh of storage.

To put that figure into perspective, Eskom’s two newest and biggest coal power stations — Medupi and Kusile — boast a combined design capacity of 9,600MW.

That means the battery storage imported in one year would be able to provide the same amount of power as Eskom’s two biggest power stations combined — for about an hour and a half.

However, Yelland pointed out not all of the imported capacity was necessarily installed.

Some of it could be sitting with suppliers or retailers, which have dealt with a big decline in backup power sales due to the load-shedding reprieve.

In addition, the import figures exclude all the battery capacity installed in previous years.

MyBroadband estimated the battery capacity installed in households and businesses with solar in South Africa using Eskom data and common specifications for solar installations in the country.

A household with an entry-level 3kWp solar system typically pairs it with a 5kW inverter and 5kWh of battery storage.

Larger 8-,10-, or 12-panel installations with capacities of roughly 4kWp, 5kWp, or 6kWp, respectively, are often combined with 10kWh of storage.

The ratio of peak solar power capacity to battery storage is, therefore, around 3:5 for entry-level household systems, while higher-end systems can have ratios of 2:5, 2.5:5, or 3:5.

The National Transmission Company of South Africa’s latest estimates show that there was around 6,000MW of behind-the-meter solar installations in South Africa.

With a ratio of 3:5 for peak solar to battery storage, there could be about 10,000MWh of battery storage spread across these installations.

According to Eskom’s estimates, the average household consumes about 900kWh per month, working out to 1.25kWh per hour in 30-day month.

Assuming that they use 50% more electricity than that during peak hours, they would consume roughly 2kWh per hour.

In that scenario, the 10,000MWh of battery storage would be able to supply 1,250MW of power continuously over the four hours of peak evening demand before being depleted.

That would reduce load-shedding by roughly one stage.

If the ratios of 2.5:5 or 2:5 were closer to reality, the installed battery storage could be somewhere between 12,000MWh and 15,000MWh and could reduce load-shedding by 1.5 to 2 stages.

Coupled with the effective use of pumped storage dams, energy storage in South Africa could be reducing load-shedding by nearly five stages — but not without the assistance of the rapid private solar uptake.

The table below shows estimates for how much capacity batteries could be contributing between 17:00 and 21:00 every evening, assuming households with solar and backup consume about 2kWh from their batteries every hour during this period.