Why would they plug them in the evening though? If you're using the car, you're likely to be parking it at a place with a high car density (e.g. a large parking

Why would they plug them in the evening though? If you're using the car, you're likely to be parking it at a place with a high car density (e.g. a large parking garage or an employer's parking lot), where chargers can be deployed cheaply. If you have a short commute, you might also not care how fully charged your car is as long as it is enough. So you may specify that you want a state of charge of 50-80% at the end of the day, and the grid can decide when to charge your car. It won't be enough to smooth out all the fluctuations in renewable generation, but it surely will help. 10 million cars (~20% of the cars existing in Germany) attempting to charge is at least 10 GW of load that can be shed when necessary, and significantly more than that in load that you can sink when there is excess power (I'm assuming each car needs to charge e.g. 10 kWh over 10 hours). Wikipedia says the total Regelleistung (operating reserve?) in Germany is 12.5 GW (7 GW in one direction, 5.5 in the other) and that this is responsible for 40% of the cost of the grid fees.