WITH MOST ELECTRIC vehicles parked at work or home all day, you may wonder whether you’ll save that much by having one. But what if someone told you they are actually big batteries on wheels that could earn you some money? Surplus energy in electric vehicles (EVs) can be sold back to the grid instead of being stored, and this could be used to power millions of households when they need it most, which makes particular sense amid a global energy crisis. With cars and vans parked for an average of 23 hours a day, the potential is great.

By 2030, when no new diesel and petrol vehicles will be allowed to be sold in the UK, there will be around 14 million EVs on British roads and 84 million across Europe according to estimates by the energy consultancy firm Delta-EE. That’s plenty of batteries on wheels to tap into.

All people need is, simply put, a charger that works both ways. This kind of technology already exists: Bidirectional chargers allow users to store cheap off-peak or solar-generated electricity in a vehicle battery and then export it to the grid or directly into a home during the hours when electricity costs the most. However there are a few hurdles to overcome before bidirectional charging can go mainstream and convince users of its advantages. 

Harnessing unused electricity from EVs is not a new concept, at least not outside Europe. In March 2011 the Fukushima nuclear power plant in Japan was damaged by an earthquake and tsunami, causing widespread power outages. Car makers Nissan and Mitsubishi sent dozens of electric cars into the worst-hit areas to drive relief workers and supplies around, keep appliances and phones charged, and provide heating. It also marked the beginning of a new technology that would allow the electricity stored in batteries to be shared with buildings and households.

There are essentially two ways to channel electricity from an EV into a household and save money in the process. With vehicle-to-home (V2H) technology, a stationary vehicle can be used in a similar way to a home battery system. Solar energy generated during the day can be stored in the EV and used to power home appliances when the sun has set. “This is aimed at self-sufficiency, and people can save on buying electricity from the grid,” says Markus Kramis, CEO of EVTEC, a Swiss company that builds bidirectional charging stations. The company has installed 110 such systems across Europe so far.

The other option is to sell electricity back to the grid at a higher price than when it was purchased at off-peak times; this concept is called vehicle-to-grid (V2G). A 2018 analysis by OVO Energy and Imperial College London suggested that V2G had the potential to save the UK energy system £3.5 billion per year.

A number of energy companies are trying to figure out how bidirectional charging could work commercially. There are more than 100 V2G trials worldwide, most of which are taking place in Europe in collaboration with grid providers and electric vehicle and charger manufacturers. “The electricity grid fluctuates, especially in the UK as it is not connected to the mainland. That’s why there is more interest and funding from the government to push trials and gain experience with systems that can support the grid,” says Kramis.

In 2020, EVTEC installed five charging stations outside Islington Town Hall in London, and the company will launch another trial with Swiss car-sharing provider Mobility later this year using 50 Honda electric cars. Since the cars are reserved or used via a booking system, the software developers can clearly define and control when a charging station taps the surplus electricity and when not.

It has already been proven that bidirectional chargers can save users money. A consortium including energy company OVO Energy and Nissan ran a three-year trial and installed 330 bidirectional chargers across UK homes. They found that participants could save up to £725 a year in electricity bills by leaving their cars plugged in when not in use and supplying the grid during peak evening hours. These are additional savings to switching from a conventional to an electric car: It costs on average a little more than £500 a year to charge an electric car compared with £1,435 a year for petrol or diesel. Charging an electric car at home is usually cheaper than using public charging stations, and on university campuses and at workplaces it is sometimes even offered for free.

The biggest sticking point, however, remains the high installation costs for bidirectional chargers, says John Murray, head of EVs at the energy consultancy Delta-EE—even though prices have dropped by up to 50 percent in the last two to three years. “Putting an exact price on a V2G charger is challenging because they are not widely available to purchase.” In the case of the OVO Energy-Nissan trial, the V2G charger was £3,700 more expensive than a unidirectional smart charger that can automatically top up a car at the cheapest times and thus save money. Installation costs would have to drop to £1,000, the project group said, to make the new technology worth investing in.

Apart from the models from Nissan, Honda, and Mitsubishi, there are currently relatively few vehicles that support bidirectional charging. The American car manufacturer Ford is launching a pickup truck this spring capable of storing 131 kWh of energy and fully powering a house for three days on a single charge. “The energy crisis and associated price increases could potentially accelerate the adoption of V2H, as customers seek to optimize energy self-consumption and shield themselves from rising electricity costs,” says Murray.

Bidirectional chargers are expected to become cheaper in the next few years as they become more common and the necessary infrastructure is developed. However, EV owners will still need to be convinced that recurrent charging and discharging will not degrade their batteries faster, says Ying Xie, a professor of supply chain management at Anglia Ruskin University. Xie studies consumer acceptance and knowledge of V2G systems and has learned from EV owners that battery degradation is a major concern for them. Their concern is justified and has been subject of scientific debate, but some researchers suggest that letting batteries sit fully charged can also wear them out. Xie says that many owners of EVs do not know exactly how the batteries work. “And that will obviously lead to a relatively low engagement.”

Bidirectional charging and the prospect of lower electricity bills are unlikely to persuade people to buy an electric vehicle, she says. Drivers are more likely to buy one because of environmental concerns, lower running costs in the long term, and the impending regulations. When petrol and diesel vehicles are phased out in the 2030s, they will have no choice but to go all electric. “But promoting V2G to consumers, especially those who already own an electric vehicle, is a way to maximize the use of those batteries.”