Re: Great looking but...
"we can wait for a point when there is little demand but a big gust happens to be passing the wind farm."
Ok, let's have a look at the National Grid generation history and see how often we have low demand and an excess of wind power then.
So, we use 30GW worth of power overnight. We nominally have 8GW worth of installed wind capacity. This installed capacity has generated peaks of over 2GW but under 5.5GW for generously 20% of the year and has never, ever generated the nominally installed capacity. The remaining 80% of the year has been delivering under 2GW.
So, it looks roughly like the times that the times that your wind farms are going to be generating sufficant power to charge car batteries overnight from an excess of power generated from wind farms is going to be approximately "never".
Over the last week wind has produced less power than coal plants converted to burn trees (sorry, biomass) for the "green" renewable handouts this results in precisely twice. Burning biomass generates less than half what coal plants burning coal produce, which is turn is less than half what nuclear provides 24/7, which is less than half of what is produced by burning gas since gas and gas plants are cheap to build and everybody accepts them to "back up varying outputs from wind farms".
Usually backups are understood to be secondary fallbacks, rather than generating over fifteen times(!) the output of the supposedly primary wind plants.