The best time to charge your electric vehicle depends on your goal: Financial (save money), Environmental (least amount of pollution) or Good Citizen (least load on the grid)

The best time to charge your Electric Car when you have solar panels depends on what you want to achieve. Do you want to save money, save your planet or reduce your load on the grid infrastructure.

Ipsun Solar installs solar panels in Virginia, Maryland and Washington DC. We’re lucky that all 3 States have netmetering rules 1:1. This means that each electron produced by the solar panels can either be used in the building or pushed onto the grid and one gets a credit for that electron. The credit is on a one-to-one ratio, so you get paid the exact same to push the electron onto the grid as it would have cost you to get it from the grid.

Financial optimization: Save the most money?

Net Metering:

If you have a 1:1 netmetering setup for your solar panels, then it doesn’t really matter if you consume the power you produce with your solar panels right away, or if you push that power onto the grid and use it later on.

If you charge your car during the day directly from your solar panels, you use the solar power directly and reduces the amount pushed onto the grid.

You get charged by the utility for the difference between what you consumed and what you put onto the grid. It’s not related to when you did that.

Time Of Use (TOU)

Many utilities developed a Time Of Use billing system, where the price of the electricity varies depending on when you consume the power. The power is typically cheaper during the night, increases in the morning, is the most expensive during the day when most people and businesses consume the power and reduces back in the evening. Each utility can calculate these TOU rates in different intervals and they can set chunks of time periods to specific rates. It gets complicated really fast. One of the goals of the utility is to change the behavior of their consumers so the consumers consume power when it’s the cheapest. This allows an utility to avoid having to build peaker plants that are more expensive to operate.

If you have a TOU setup with Solar (and this is not always allowed by utilities), then you would save the most money by pushing your solar power onto the grid during the day when you get the most money for your power, and consume your power by charging your car when the power is the cheapest, meaning at night.

Some utilities don’t allow this setup. They have sometimes a special utility rate for solar, they have another one for EV chargers, but don’t allow both at the same time, meaning you can’t interconnect solar to the grid if you are on an EV billing rate with the utility.

Environmental (least amount of pollution)

To minimize the pollution of charging your car, you should use the clean power locally. You minimize the production of other power sources that need to get pushed on the grid, transported and go through transformers which has power losses during each step. Each loss, even a small percentage, is pollution that can get avoided by using a local clean power source (your solar panels) without transmission losses. So the best way to minimize your pollution is to charge your car when the sun is out.

Good Citizen (least stress on the grid)

The U.S. grid is aging and avoiding to use it all together is the best option. You would then charge your car during the day directly from your solar panels. I assume your solar panels produce more power than your car needs. If your car needs more power than your panels can produce, then I would suggest you charge at night. The power being generated at night is usually coming from a baseload generation facility, in Virginia that’s mainly coal, nuclear and fossil gas. By charging at night you’re part of the baseload and not the peak load during the day when the grid is the most stressed.