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Owners of electric vehicles (EVs) are used to plugging into charging stations at home and at work and charging their batteries with power from the grid. But one day soon, when these drivers plug in, their cars will also have the capacity to reverse the flow and send electrons back into the grid. As the number of electric vehicles increases, fleet batteries could serve as a cost-effective large-scale energy source, with potentially dramatic impacts on the energy transition, according to a new paper published by an MIT team in the journal Energy Advances.
“At scale, vehicle-to-grid (V2G) can drive the growth of renewable energy, replacing the need for stationary energy storage and reducing reliance on utilities [always-on] generators, such as natural gas, that are traditionally used to balance wind and solar,” says Jim Owens, lead author and PhD student in MIT’s Department of Chemical Engineering. Additional authors are Emre Gencer, principal investigator at the MIT Energy Initiative (MITEI), and Ian Miller, research specialist for MITEI at the time of the study.
The group’s work is the first comprehensive, systems-based analysis of future power systems, relying on a new mix of computational models that integrate factors such as carbon emission targets, variable renewable energy (VRE) generation and storage costs, energy generation in buildings, and transmission infrastructure .
“We explored not only how electric vehicles can provide service back to the grid – thinking of these vehicles almost as energy storage on wheels – but also the value of V2G applications to the entire energy system and whether EVs could reduce the cost of decarbonizing the power system “, says Gencher. “The results were surprising; I personally did not believe that we have such potential here.”
Relocation of new infrastructure
As the United States and other nations pursue strict goals to limit carbon emissions, the electrification of transportation has taken off, with electric vehicle adoption accelerating. (Some projections show that electric vehicles will replace internal combustion vehicles within the next 30 years.) However, as zero-emission driving increases, so will the demand for energy. “The challenge is to make sure that there is enough electricity to charge the vehicles and that that electricity comes from renewable sources,” says Gencher.
But solar and wind energy is intermittent. Without adequate support for these sources, such as stationary energy storage using lithium-ion batteries, for example, or large-scale natural gas or hydrogen power plants, achieving clean energy goals will prove elusive. Even more disturbing, the cost of building the necessary new energy infrastructure runs into the hundreds of billions.
That’s where V2G can play a critical and welcome role, the researchers reported. In their case study of a theoretical New England power system meeting strict carbon limits, for example, the team found that only 13.9 percent of the region’s 8 million light-duty (passenger) electric vehicles moved 14.7 gigawatts of stationary energy storage. This contributed to savings of $700 million — the expected cost of building new storage capacity.
Their work also described the role of the EV battery during times of peak demand, such as hot summer days. “V2G technology has the ability to inject electricity back into the system to cover these episodes, so we don’t have to install or invest in additional natural gas turbines,” Owens says. “How EVs and V2G can affect the future of our energy systems is one of the most exciting and novel aspects of our study.”
The power of modeling
To investigate the impacts of V2G on their hypothetical New England power system, the researchers integrated their EV travel and V2G service models with two existing MITEI modeling tools: the Sustainable Energy System Analysis Modeling Environment (SESAME) for fleet design and demand growth for electricity. and GenX, which models the investment and operation costs of electricity generation, storage and transmission systems. They included such inputs as varying EV participation rates, production costs for conventional and renewable energy providers, charging infrastructure upgrades, road vehicle demand, changes in electricity demand, and EV battery costs.
Their analysis revealed benefits from V2G applications in power systems (in terms of shifting energy storage and solid generation) at all levels of carbon emission constraints, including no emission constraints at all. However, their models suggest that V2G provides the most value to the power system when carbon constraints are most aggressive – at 10 grams of carbon dioxide per kilowatt hour of load. Total system savings from V2G ranged from $183 million to $1,326 million, reflecting EV participation rates between 5 and 80 percent.
“Our study began to reveal the inherent value that V2G has for the future power system, showing that there is a lot of money that we can save that would otherwise be spent on storage and solid generation,” says Owens.
Exploiting V2G
For scientists looking for ways to decarbonize the economy, the vision of millions of electric vehicles parked in garages or office spaces and plugged into the grid for 90 percent of their working lives is proving an irresistible provocation. “All this storage is sitting right there, a huge amount of available capacity that’s only going to grow, and it’s wasted if we don’t fully utilize it,” Gencher says.
This is not a distant prospect. Startup companies are currently testing software that would enable two-way communication between electric vehicles and grid operators or other entities. With the right algorithms, electric vehicles would charge and send energy to the grid according to profiles tailored to each car owner’s needs, never draining the battery and jeopardizing the commute.
“We don’t assume that all vehicles will be available to send power back to the grid at the same time, say at 6 p.m., when most commuters return home in the early evening,” says Gencher. He believes that the highly varied schedules of electric vehicle drivers will allow enough battery power to cover spikes in electricity consumption over an average 24-hour period. And there are other potential sources of battery power down the road, such as electric school buses that are only used for short distances during the day and then idle.
The MIT team acknowledges the challenges of purchasing V2G consumers. While electric vehicle owners enjoy a clean, green drive, they may not be so enthusiastic about handing over access to their car’s battery to a utility company or aggregator that works with power system operators. Policies and incentives would help.
“Because you’re providing a service to the grid, just like solar panel customers do, you could get paid for your participation, and get paid at a premium when electricity prices are very high,” Gencher says.
“People may not be willing to participate 24 hours a day, but if we have blackout scenarios like in Texas last year, or hot day congestion on power lines, we may be able to turn these vehicles on for 24 to 48 hours, sending energy back into the system,” he adds. Owens. “If there’s a blackout and people are waving wads of money at you, you might be willing to talk.”
“Basically, I think it comes back to we’re all in this together, right?” Gencher says. “As you contribute to society by providing this service to the grid, you will get the full benefit of reducing the costs of the system, and you will also help to decarbonize the system faster and to a greater extent.”
Actionable insights
Owens, who is building his dissertation on V2G research, is now investigating the potential impact of heavy-duty electric vehicles on the decarbonization of the power system. “Last-mile delivery trucks from companies like Amazon and FedEx are likely to be the first to adopt electric vehicles,” says Owen. “They are attractive because they have regular routes during the day and return to the depot at night, which makes them very useful for providing electricity and balancing services in the power system.
Owens is committed to “providing actionable insights for system planners, operators and to some extent investors,” he says. His work could come into play in determining the type of charging infrastructure and where.
“Our analysis is really timely because the electric vehicle market is not yet developed,” says Gencher. “This means we can share our insights with vehicle manufacturers and system operators — potentially influencing them to invest in V2G technologies, avoiding the cost of building utility storage facilities and enabling the transition to a cleaner future.” It’s a big win, within reach.”
Research for this study was funded by MITEI’s Center for Future Energy Systems.
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