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UC Irvine study concludes intelligent PEV charging can minimize scale of stationary energy storage needed to meet renewable targets

A new study by a team at the University of California Irvine highlights the importance of intelligent plug-in vehicle (PEV) charging for minimizing the scale of infrastructure required to meet renewable utilization targets.

In the study, published in the Journal of Power Sources, the UC Irvine team examined how the intelligence of plug-in electric vehicle (PEV) integration impacted the required capacity of energy storage systems to meet renewable utilization targets for a large-scale energy system, using California as an example for meeting a 50% and 80% renewable portfolio standard (RPS) in 2030 and 2050.

They found that for an 80% RPS in 2050, immediate charging of PEVs requires the installation of an aggregate energy storage system with a power capacity of 60% of the installed renewable capacity and an energy capacity of 2.3% of annual renewable generation.

However, with smart charging of PEVs, required power capacity drops to 16% and required energy capacity drops to 0.6%. With vehicle-to-grid (V2G) charging, non-vehicle energy storage systems are no longer required.

The electrification of the light-duty vehicle fleet through PEV deployment will increase the electric load demand and alter the shape of the demand profile. The first effect poses an obstacle for meeting renewable energy utilization targets, since more renewable generation will be needed to meet a targeted percentage of the total electricity load demand with renewable energy. The second effect, however, can potentially provide a benefit for reaching renewable utilization targets depending on the intelligence of vehicle charging management.

If vehicle charging loads can be shifted to more closely align with renewable generation, it can allow the system to capture otherwise curtailed renewable generation. Additionally, intelligent charging can reduce the amount of renewable generation that needs to be shifted to meet electricity demand, which can reduce the required capacity of energy storage systems need to meet a renewable energy utilization target.

… Currently, almost all public and private charging in the US is immediate, the exception being select pilot projects for smart and V2G. However, the coordinated charging of electric vehicles through smart or V2G charging has the potential to increase renewable utilization, by optimizing the timing and intensity of vehicle charging to maximize capture of otherwise curtailed renewable energy. Smart charging allows for planned charging based on load and time of use (TOU) market signals, and can, therefore, be applied to improve renewable integration. Vehicle to grid (V2G) charging incorporates the functionality of smart charging with the added ability to discharge to the grid.

—Forrest et al.

The UC Irvine researchers used load profiles used were extrapolated from CAISO load data, assuming the historical trend of a steady per capita electricity use, and adjusted for population growth to roughly 44.1 million people in 2030 and 49.1 million in 2050.

The vehicle miles traveled (VMT) demand was also assumed to scale with population and implying a constant per capita VMT demand. For the year 2030, they used a target of a 50% RPS to correspond with existing goals set by SB 350. For the year 2050, they used a hypothetical target of an 80% RPS.

The study assumed a maximum charging (and discharging for V2G) rate of 10 kW, equivalent to a Tesla battery. Under smart and V2G charging strategies, the rate is flexible to accommodate grid generation and load fluctuations.

Charging infrastructure was assumed to be available at home and work. This placement provides a wide availability of charging stations with potential for long dwell periods.

BEV fleet size was based on the percentage of vehicle miles trav-eled. The 2030 level of BEVs is based on significant, but feasible, growth of BEV ownership in response to the ZEV mandate. By 2050, the California Air Resources Board projects 87% of the light-duty fleet being ZEVs, a combination of FCVs and PEVs.

The US Irvine team considered a high adoption case of BEVs (80% of LDVs) and a moderate adoption case (50% of LDVs).

The team chose Vanadium Redox Flow Batteries (VFBs) as the representative stationary energy storage (SES) technology.

The main conclusions from the study were:

  • Installing stationary energy storage systems does not provide benefits for increasing renewable penetration if excess renewable generation is low or non-existent.

  • Increasing charging intelligence reduces the need for energy storage to reach high renewable penetration levels. Switching from immediate to intelligent PEV charging allowed for better alignment of renewable generation and load profiles, decreasing both the power and energy capacity of SES required to reach the RPS target. Shifting to smart charging of PEVs decreases the required power capacity of SES by nearly 75%. Increasing charging intelligence is more efficient at increasing renewable integration than deploying SES.

  • V2G potentially eliminates the need for stationary storage at high BEV deployment.

  • Sizing of stationary energy storage is directly tied to the scale and temporal profile of excess renewable generation. The power capacity of the stationary energy storage corresponds to the peak power level of renewable curtailment. Smart charging reduces the power difference between load and generation during peak curtailment, therefore reducing the power capacity of SES required compared to immediate charging.


  • Kate E. Forrest, Brian Tarroja, Li Zhang, Brendan Shaffer, Scott Samuelsen (2016) “Charging a renewable future: The impact of electric vehicle charging intelligence on energy storage requirements to meet renewable portfolio standards,” Journal of Power Sources, Volume 336, Pages 63-74 doi: 10.1016/j.jpowsour.2016.10.048



I've been saying this for years.
a: You need to be able to charge at work as well as at home (so you can charge during the daily solar maximum).
b: You need a charger where you say "I need X% by time Y" (say I need 100% by 5.30pm today).
or, I want X by Y and I Need Xn by Tn
Thus, you might want 100% by 5.30, but you might only need 60% by then.
Similarly, you might need to be charged by 7am the next morning, but you have till 4.30 am to start a charge.

If you have a "2 day battery" (i.e. enough to charge for 2 day's use, you could go further and try to synch up with future wind (1 day hence).
But maybe that is too complex.

The key thing is to define when you need the power by, not to start charging as soon as you get in.


All those cars in work parking lots can be V2G.


V2G is an end goal, but simple "smart charging" is still very valuable.
For v2g, you want to be able to sell back a small amount of your energy so as not to degrade your battery by much.
It probably depends on when you have the car plugged in.
If it is plugged in during the daily peak (5.30-6 in Ireland), it could usefully sell back some power when the price spikes. Otherwise, the trick is simply not to charge at busy times.

A question is how do you signal these price changes: internet or some less hackable medium, and then, how real time are they - are they day in advance, hour in advance, 15 minutes in advance?
And how do you bill for it?

It is all easy to say, but trickier to implement and make hard to hack / unhackable.


The AC Propulsion test of V2G regulation services required real-time data.

The Green dream of vehicles providing the buffer for unreliable generation is going to be a long time coming.  Suppose we have a balls-to-the-wall shift to BEVs starting now (yeah, right!) and in 2030 the average vehicle has a Leaf-class pack of 24 kWh.  If 1/3 of it is available for large-scale RE buffering, that's 8 kWh * 250 million vehicles = 2000 GWh.  Average load on the US grid is ~450 GW, so this buffer would be about 4.5 hours of load, less than a day of a 20% surplus or deficit.  Wind and sun can go away for days or weeks.

Ironically for the Greens, this plays really well with nuclear.  Adding 20% of average load during the minimum hours and substracting it from the peak hours makes big, steady base-load generation much more economic.


Many future BEVs will have 100+ kWh battery pack. Assuming that 50% (50 kWh) could be made available to share with the grid, it could become a smart way to store enough REs for low production/peak demand periods.

Another complementary method would be to use excess REs to produce and stock clean H2 for FCEVs and for fixed FCs to produce electricity for the grid during peak demand periods.

Some 200,000,000 BEV batteries and H2 depots could eventually store most of the excess REs and relatively low cost. REs with low cost storage could become the clean affordable energy of the future. Good bye, coal and other fossil and bio fuels.

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