Note: Visit the EIA website, to drill down to a specific region/state for the daily electricity demand curve in your area. Canadian electricity demand data is available at IESO.
US peak times of electricity production occur during the hours of 7-9am and 5-7pm pacific time. During these peak times, carbon-intensive fuels such as coal and natural gas will be required to meet peak demand. As a result, charging your EV during peak times will be the most carbon-intensive, and most costly. In contrast, during off-peak hours, not only will you benefit from lower electricity prices, clean sources such as wind, hydro, and nuclear will be in service to meet electricity demand. Therefore, EV charging during off-peak hours will be 1) cheaper, and 2) cleaner.