Energize Weekly, October 23, 2019
Turning electric vehicle (EV) batteries into a source of electricity during peak demand hours – making them “virtual power plants” – can shave load and save money, according to an analysis by energy consultant Jackson Associates.
The study took customer data – hourly loads, commuting and household data – and used that to model the impact of EVs as both a user and provider of electricity.
A sample of 5,000 individual residential-owner single family homes Southern California Edison (SCE) customers was used.
Households with more than $125,000 in income and with total daily automobile commutes of less than 120 miles were selected to represent future EV owners. EV ownership was randomly assigned to households in this subset who used private automobiles to commute.
The study assumed that the utility would access battery reserves after the afternoon commute, with a 20 percent reverse being left in the battery for EV driving. It also assumed that each home had a Level 2 charger capable of recharging the battery in nine hours for a 300-mile drive range.
The study found that even at a 10 percent market share, the use of batteries to meet load was sufficient enough to shift the peak load with the recharging of the batteries taking place in the middle of the night, a period of low demand.
Using the utility’s time-of-use rates, shifting from the 4 p.m. to 9 p.m. peak rate to the lower nighttime rate saved SCE 25 cents a kilowatt-hour in the summer and 23 cents a kilowatt-hour in the winter.
Over the course of a year, each EV generated $560 in actual net cost of service savings, according to the study. The savings include the cost of recharging for the daily commute.
“We were surprised both at the relatively small 10 percent EV market saturation required to completely clip the SCE residential peak and the large annual savings of $560/EV per customer even after paying for nighttime recharging,” Jerry Jackson, president of Jackson Associates and author of the study, said in a statement. “These results suggest that utilities should shift from defensive ‘managed charging’ strategies to an offense strategy that draws on EV battery storage during peak hours with overnight recharging.”
The study noted that its analysis was limited to potential cost savings in the SCE service area and that the result may vary from utility to utility.
Two broader issues to be addressed are how such a system is managed and the impact on battery life, which is measured in its cycles (charging and discharging). Battery manufacturers are currently offering warranties averaging eight years or 100,000 miles, stationary cycling isn’t covered.
The Jackson study calculated that the average weekly battery discharge to the grid in its modeling was 43 kilowatt-hours (kWh) a week. “At 15,000 miles driven per year with the 43 kWh grid discharge each week, the VPP [virtual power plant] program reflects 52 percent of total charging cycles and an expected battery lifetime of 19.6 years so battery degradation is not likely to pose a problem for most EV owners,” the study concludes.
A Japanese study linked 60 EVs to a “virtual power plant system” manager that connected to the vehicle owner’s smart phone to test the management of the EVs on the grid.
The study concluded that “the key to establishing a VPP as a business is how we can control a high number of the EVs that are owned by electricity users scattered across different locations as a single resource in order to manage the electricity demand. To promote the practical usage of VPPs, it would be important to attain a more accurate estimate of controllable demand and optimize the control mechanism.”
