Yesterday we had three ideas we wanted to develop in order to cover the needs of energy of the building. Today we searched for figures of consumption and we eliminated some ideas and find others. Since most of our energy will be weather-dependent (wind + sun), we need to have big capacities of storage, in theory the equivalent of two weeks without energy input (very bad weather without wind). So the capacity we need is in theory almost 300 MWh.
At this stage, the ways to store energy which seem feasible are the two following:
ADELE Project : CAES (Compressed Air Energy Storage) → big plant, high capacity (can store 1000 Mwh/day and feed 300 MW for several hours), actually too high for our needs (20 Mwh/day, 1,5 MW during the highest demands) so we thought about connecting on a regional project, which doesn't exist yet.
Using extra-energy to make electrolysis of water, storing H2 somewhere and using fuel cells to produce electricity during low-production times. The problem is that H2 is not dense at all (90g/m^3) so we need either to compress it at really high pressure (→ energy consumption) or enormous volumes (a rapid calculation of the volume needed to store 30 Mwh gives about 10000 m^3).
We abandonned the idea of pumping up some water. To cover the needs of the building for one day, we would have needed to pump 80000 m^3 of water on 10 m.