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.