Why the 9.6 kW Limit for EV Home Charging Rebates?

Ever wonder why the PowerMIDrive residential program offers rebates for Level 2 home chargers capped at 50-amps (40-amp continuous)? As an electric vehicle (EV) driver, we understand how it could seem confusing to turn down your charging limit from 48-amps continuous (11.5 kW) to 40 amps (9.6 kW), because on an individual basis it might not seem like a big deal. But the limitation provides reliable energy for all.

Benefits of the 9.6 kW Limit

Limiting Level 2 charging to 9.6 kW or less is a good thing for everyone in your neighborhood. It’s also a good thing for every customer in the Consumers Energy electric territory whether they drive an EV or not. The 9.6 kW requirement reduces infrastructure costs and increases system reliability. 9.6 kW will put plenty of miles back into your battery overnight between 11 p.m. and 6 a.m.– probably 200 or more miles to be exact.

Why It’s a Reasonable Standard

The typical home in Michigan utilizes about 10 kW during the heaviest use times of the year, called on-peak or peak time periods. Peak energy use time periods typically occur between 2 p.m. and 7 p.m. during weekdays in the summer. The 10 kW standard is how most residential distribution lines and transformers were constructed, and of course most neighborhood powerlines and transformers weren’t designed with EVs in mind. While Level 1 chargers use minimal power (about 1 kW) and pose no risk to the energy grid, some Level 2 chargers can use up to 19 kW—as much energy as it takes to power three homes combined when charging during peak time periods. A 9.6 kW charger limitation is a good balance because it adds enough range overnight and avoids overloading the system.

This is why we’re a big proponent of EV load management programs like PowerMIDrive as EV adoption ramps up. A single 11.5 kW (48 amp) may not be a big deal now if you’re the only home charging an EV on your transformer, but if every house on your block starts charging above 9.6 kW and other large loads also occur coincidently (i.e. a summer hot tub party at the same time), then distribution reliability risks increase. Plus, if we can manage EV load and shift charging times to off-peak time periods, not only can we avoid expensive upgrades to neighborhood distribution infrastructure, but we can also offer rebates and incentives for our EV driving customers due to the avoided costs.