The hardware for a 50Kw CCS unit is nearly $20K (US), not counting the land and installation costs. SOmebody has to pay for it, even if the power was free. Do you think that the windmills or solar cells come for free, too? They need to be bought, installed, and maintained, even if the energy itself is 'free'. For rough numbers, 40p is about $0.50 US, so if the thing costs $20K, that's 40,000Kwhr assuming the electricity was 'free'...that's recharging 40,000/18 (for an i3 to full, probably less on a single charge) or over 2200 charging sessions. Considering the thing isn't 100% efficient, probably more like 2500 sessions.
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)