Some intermediate results from today, calculated to make The Reef a 20-person household with solarpunk 
heating:
Let’s put a 5.66 m diameter and 6 m high water tank into the center of the building, insulate it with 40 cm styrofoam and connect it with heat pumps powered by 27 m² of solar panels during the summer – then we have a zero-emission space and water heating system for the inhabitant’s heat requirements during all winter in central Europe. What’s more, operation costs are 46% lower than burning natural gas (!), which means there will be no economic reason for burning fossil fuels for heat anymore.
This assumes that compact living, heated clothing, small heated spaces and other ideas from the document above lower heat requirements to 20% of current average values already – which is actually easy. The detailed calculations are in section “3.16. Seasonal heat storage with ASHP charging”.
Since this sounds a bit too good to be true, @trythis is invited to poke holes into the idea 