technology

Here in the UK if I had £8000 in panels and batteries I would replace 100% of my electricity usage for a household that has VERY high usage and 6 people in it. Excess can be sold back to the national grid, but if I was doing a coop then it would be many houses operating together to share load and further drive up the efficiency of that.

I don't know why you think "it hasn't been done". Individual households have been doing it for years and groups can do it more efficiently.

These costs are made back in savings within a decade.

I know you're probably not British but you might want to see a calculator just out of curiosity: https://www.spiritenergy.co.uk/solar-pv-calculator

To do this in a coop fashion you'd just be taking the debt burden of installation into the coop, locking people into a contract within the coop for payments at cost for x number of years and then running the installation, panel and battery costs through loans with the bank. You could start with your own house, then link up with your neighbour, then add their neighbours, and so on and so forth. The "grid" is you wiring up between neighbours among yourselves. There is nothing stopping you from running a cable between houses over fence boundaries if both neighbours agree to it. All you're doing is linking up the battery network. The advantage here is that households that already have full batteries would still be producing power that's filling up the batteries of other households. The larger the surface area of your solar network the more efficient you can make it so the more households added, the better.

Oh and if I could order Chinese panels at their prices (I can't) the cost of this would go down by 70%. The biggest barrier to going solar is tariffs that exist for energy industry protectionism.