Re: I've been pointing this out for years.
Not at all obviously. I'm an electrical engineer, and (respectfully) you're confusing power and energy.
Energy is the potential to do work, such as moving a car. The "power company" sells, and the battery stores, energy measured in kilowatt-hours (kWh).
Power is the instant motive force that actually stores energy into the battery or accelerates the car, measured in kilowatts (kW).
The grid isn't the Internet, routing power instantaneously from the wind farm to your house. Power is added to and consumed from the aggregate grid minute by minute in careful balance. So the power feeding my EV battery is "obviously" from a mix of fuels. You're right as rain about that.
But the energy for which I pay is 100% wind energy. That is, if my EV uses 150 kWh this month, the local wind farm adds 150 kWh to the grid during the month, and I pay them $9. This is what EV owners mean when they say their EV runs on 100% wind energy.
So, I can power my EV with 100% wind energy without any grid instability at my house at all.
The UK has actually reached 100% renewable power inputs at slack times, btw. Managing a grid with a large portion of renewable energy requires care, but solving technical challenges is what engineers do. Trust me, it's doable, as is continuing to upgrade grid capacity to continue to track increasing demand. We've been doing it successfully for over a century, and the slow transition from petrol to electricity allows ample time to manage the grid properly.