- Daytime EV charging wastes less solar and wind power
- If EV owners charge at night more batteries will be required
- California has oodles of sunlight, and this solar energy
An all-electric Karma Revero charging at a Tritium fast charger in Pasadena, California. Supplied
Charging electric vehicles from home at night is not the way to go, according to a new study from Stanford University. Instead, it says that we should be charging during the day at work or at public charging stations.
A Stanford University research team published the paper which modelled EV charging demand for the whole of the Western United States. It examined the stress the region’s electric grid may be subjected to by 2035 as the electric vehicle market grows.
The researchers found peak electricity demand will increase by up to 25% if EV charging continues to take place mostly from home at night.
But they concluded that increased costs of electricity demand caused by EVs could be limited. Drivers can help achieve this by charge at work or public charging stations during the daytime.
Such a move would also help to reduce greenhouse gas emissions from all the new capacity for generating and storing electricity.
Ampcharge. Supplied
Daytime EV charging wastes less solar and wind power
“We considered the entire Western U.S. region, because California depends heavily on electricity imports from the other Western states. EV charging plus all other electricity uses have consequences for the whole Western region given the interconnected nature of our electric grid,” said Siobhan Powell, a Stanford mechanical engineering PhD candidate and lead author of the study.
“We were able to show that with less home charging and more daytime charging, the Western US would need less generating capacity and storage, and it would not waste as much solar and wind power.
“And it’s not just California and Western states. All states may need to rethink electricity pricing structures as their EV charging needs increase and their grid changes.”
Cumulative EV sales in California reached one million in February, accounting for around 6% of cars and light trucks. However, California has targeted five million EVs on the road by 2030.
But when the level of EV penetration reaches 30% to 40%, the grid will experience significant stress.
Major investments and changes in charging habits can help avoid this. Decisions about infrastructure investment must be made now to avoid this, as development requires significant lead time.
If EV owners charge at night more batteries will be required
Stanford researchers say more than 5.4GWh energy storage will be needed when 50% cars on the road are EVs. This is the case if night-time charging habits remain as they are now.
However, if habits change to begin charging at work during the daytime, the need for storage would only be only 4.2GW.
“We encourage policymakers to consider utility rates that encourage day charging and incentivize investment in charging infrastructure to shift drivers from home to work for charging,” said Ram Rajagopal, the study’s co-senior author and an associate professor of civil and environmental engineering at Stanford.
Time-of-use electricity rates encourage consumers to switch electricity use to nighttime whenever possible. This is true in California as well as other places.
But these rates are a reflection of a time before the widespread deployment of wind and solar when demand threatened to exceed supply during the day – especially in the late afternoon during summer.
California has oodles of sunlight, and this solar energy
However, today, California has excess electricity during the late morning and early afternoon thanks in large part to its huge solar capacity.
Drivers can put cheaper solar-generated electricity to better use if most EVs were to charge during these times.
“The findings from this paper have two profound implications: the first is that the price signals are not aligned with what would be best for the grid – and for ratepayers,” said Ines Azevedo, the new paper’s other co-senior author and associate professor of energy science and engineering in the Stanford Doerr School of Sustainability.
“The second is that it calls for considering investments in a charging infrastructure for where people work.
“We need to move quickly toward decarbonizing the transportation sector, which accounts for the bulk of emissions in California. This work provides insight on how to get there. Let’s ensure that we pursue policies and investment strategies that allow us to do so in a way that is sustainable.”
Citation:
Siobhan Powell, Gustavo Vianna Cezar, Ram Rajagopal, Scalable probabilistic estimates of electric vehicle charging given observed driver behavior, Applied Energy, Volume 309, 2022, 118382, ISSN 0306-2619,
https://doi.org/10.1016/j.apenergy.2021.118382
Keyword: Study finds charging EVs in daytime better for grid