Load-shedding batteries on wheels — How much power electric cars can add to the grid

If 5% of South African motorists adopted electric vehicles (EVs) with vehicle-to-grid (V2G) capability, they could help alleviate load-shedding by at least two stages during peak demand periods.

One of the common criticisms against EV adoption in South Africa is that charging these cars could put additional strain on the grid, something South Africa cannot afford amid a severe generation shortage.

EVs require a lot of power to fully charge their batteries, with the typical charging speed on a home-fitted charger with a single-phase connection being 7kW.

That is the same amount of power four to five kettles will draw when running concurrently.

The difference is that an EV needs that power for much longer than a kettle needs to boil water.

That is because they have large battery packs to store enough energy to travel hundreds of kilometres.

Electric car battery assembly

Smaller electric vehicles (EVs) have batteries with capacities of around 50kWh, medium-sized models have around 70kWh, and models with the best range feature 90kWh packs or greater.

Those numbers are substantially higher than the typical 5kWh or 10kWh load-shedding backup battery.

In this way, EVs offer a possible answer to the big problem of using renewable power like solar or wind to provide power to the grid.

These technologies have less predictable generation trends, making them more challenging to use as baseload.

Solar power can sometimes generate so much energy during the day that plant operators must curb output.

Unless paired with battery storage, this excess solar is useless during evening peak periods.

By using V2G, a power utility could leverage the storage capabilities of EV battery packs to hold valuable power generated by solar or wind in peak production periods so that it can be dispatched during peak demand times.

V2G vs V2L vs V2H

V2G is one of three commonly distinguished bidirectional charging technologies available in certain EVs.

The other two — vehicle-to-load (V2L) and vehicle-to-home (V2H) — allow EV owners to power up appliances or their entire home, respectively.

V2G can push power from an EV’s battery into the grid so that it can be used by homes, businesses, and other entities kilometres away from the owner’s household.

Several vehicle manufacturers support V2G in some electric cars, including models from Ford, Hyundai, Kia, Mitsubishi, Nissan, and Volkswagen.

Swedish firm Volvo has launched an entire energy solutions business tapping into the potential of bidirectional charging.

The company already offers several electric cars in South Africa, including the C40 Recharge and XC40 Recharge. It is also launching the EX30 and EX90 locally in 2024.

Volvo has estimated that the battery capacity of its global electric fleet will reach 50GWh by 2030. That is nearly equivalent to Eskom’s entire generating capacity.

It is already running a V2G pilot programme in Gothenburg, which leverages the EX90’s bi-directional charging technology to give back extra battery power to a compatible grid.

Volvo EX90

A grid supported by V2G can use excess energy stored in EV batteries while they are parked at home.

For many households, their cars are typically at home in the evening when Eskom experiences peak demand.

Ideally speaking, drivers will be able to charge their cars at work during the day.

That power can come from an employer’s solar installation or Eskom’s grid.

Even without a self-generating source, using Eskom’s power during the day can often be better for the environment as the utility generates and procures more solar energy.

With the typical South African motorist’s commute being 44km both ways, most EVs will have 70% or more of their capacity remaining when they arrive home, even if they are not charged at a workplace.

Assuming that roughly 70% of the battery’s capacity is available after the owner’s daily commute, a small EV will have about 35kWh of charge remaining.

In a single-phase installation, V2G should be able to output up to 7kW peak power through a bidirectional inverter.

With the remaining charge in its battery, it should be able to keep feeding power for five hours before its battery is depleted.

However, V2G currently has efficiency limitations, with the actual power transferred only between 50% and 70%.

Thousands of megawatts to unlock

There are currently roughly 12 million registered cars on South Africa’s roads.

If only 5% of these were small EVs with 35kWh capacity remaining at the end of the day, they could deliver between 2,100MW and 2,940MW of power for five hours, covering the highest demand period from 16:00 to 21:00.

Once the peak period has passed, the car can be charged up sufficiently overnight for the next day’s commute.

While this will increase the amount of power Eskom needs to use at night, demand during this period is already lower than during business hours.

The table below illustrates how much power EVs with 50kWh batteries could theoretically contribute to the grid at four adoption rates.

Reaching this level of adoption will take several years and require that EVs be substantially more affordable.

The V2G ecosystem must also be well thought out, with connectivity integration necessary to operate efficiently and safely.

Eskom or other power distributors will need to be able to curb excess power being pushed into the grid, and consumers will need to be notified when there are shortfalls or excesses in power.

In addition, Eskom will have to make it attractive for EV owners to push power back into the grid during peak periods.

The utility could take a carrot-and-stick approach, with higher electricity feed-in and consumption tariffs over peak periods.

This will encourage EV owners to rather sell their excess energy during peak demand and buy during periods of lower demand.