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EV load management at homes with solar

04/10/2019

If your utility is considering an off-peak EV charging program, don’t forget about your customers with photovoltaic solar panels.

Homeowners with EVs are more than twice as likely to have rooftop solar as those without EVs, according to a recent report. They are also likely boosters of town or utility programs that support electrification. However, they are often misinformed about the combined benefits of driving an EV and having rooftop solar. The truth is, the carbon savings delivered by solar panels are not increased by using them to charge an electric vehicle. The reverse is also true - the carbon savings from driving electric are independent of whether or not solar panels happen to be producing power when charging.

This truth cuts against peoples’ intuition that they should try to use their panels to charge their EV. This can create communication problems for EV programs that seek to shift charging to overnight hours. It is important to mitigate these concerns effectively.

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Residents displace fuels such as natural gas and oil by allowing panels to push clean power into the grid during the daytime. Driving an electric vehicle replaces gasoline with electricity from the grid, reducing carbon emissions and increasing a utility’s kWh sales. This is a double carbon benefit, since electricity generation is not always carbon producing (e.g. nuclear and renewables), and electric motors use energy more efficiently than combustion engines. Importantly, even if charging coincides with solar generation, gasoline is only being replaced with grid power, since the solar energy that would have gone onto the grid is now charging the vehicle. The net carbon result is exactly the same if charging at night. Concerned EV/solar drivers can rest easy knowing that no matter what they do, they achieve the same carbon savings.


From an overall system cost perspective, it is best to encourage charging overnight. At times of the day when the power demand is highest, peaker plants are often required to supplement power generation, increasing costs and carbon output. Your utility, particularly if you are in a region with mandatory capacity markets, might pay a monthly and yearly fee based on the total electric demand at peak times, and residential solar systems can help mitigate those costs, but only if those customers aren’t using all of their solar production to charge their EV.


Additionally, the infrastructure that carries electricity from the generation source to the end user is built for your maximum load period, meaning there is extra room for growth at night. By shifting EV charging (and other electrical use) to the night time hours, your utility may be able to avoid costly upgrades.


Many EV/solar customers want to be able to use their solar production to charge their car, so it is important when designing overnight charging programs for EV drivers to consider that desire. Sagewell has experience balancing customer satisfaction with utility costs, and it’s Bring Your Own ChargerⓇ (BYOC) program can be designed to fit these needs accordingly. BYOC has an industry-leading load-shifting success rate of over 95%.

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