To ensure his plans were based on historic originals, Gareth purchased over 1,700 survey drawings of the Bourn Windmill in Cambridgeshire, approximated the measurements, and then reconstructed a quarter-size copy in his garden.
Gareth relied on his skills and education as a classical boat builder at the Falmouth Marine School, which also serves him at his day job repairing furniture. The windmill is built mainly of green oak and can rotate to be directed at the wind. He sewed the sails himself from a curtain he bought in a thrift store.
The mill’s generator produces 100 amps at 12 volts when spinning at its optimum speed.
https://www.goodnewsnetwork.org/man-builds-an-electricity-generating-windmill-in-his-own-garden/
That would be the 25mm2 stuff, about 9mm diameter. Pretty standard for electric ovens.
The joy of producing electricity from renewables at 12Vdc is that you can run it straight into a whole bank of car and truck batteries for storage. Can then either use it directly for powering things - there's a lot of things like portable tellies for use in a caravan that are 12V for this reason - or feed it to an inverter to get 240Vac for 'normal' usage. Again, large outdoor stores will have them, because they're intended for this usage.
Stay on top of maintenance, I’ve seen a large datacenter UPS powered by these batteries catch fire.