Solar + Hydropower + Inductive diversion load
I've been asked by a neighbour to help with designing/setting up his new off-grid setup. The main power source will be solar through an MPPT controller into a decent sized battery bank. In addition he has a small wind turbine which has it's own controller and he has also been given a "Stream Engine" micro-hydro turbine.
He has an intermittently refilled large water storage reservoir up the hill (topped up once a week in the summer) from which he can bring down water for hydro + then irrigation. Since there's a finite supply of water at some times of year, the idea occurred to us that the ideal diversion load would be a pump to send water back up the hill during the later part of summer days so that the turbine could run at night to generate power once the sun went in. There are some large scale hydro plants that act as giant batteries on this basis, so it would be cool to do something similar.
The issue I've hit is that almost everything I've read suggests that the only really effective way to co-ordinate such a diversion load with an MPPT solar controller is to use a 100% resistive load that is progressively phased in with PWM via an SSR in order to maintain desired voltages. My Outback FM80 could do this, for example. That's obviously not going to work for a pump, however.
Is there a better way of approaching this that won't fall foul of the problems involved with suddenly cutting in a large load and pulling the rest of the system out of the desired charge stage?
Thanks in advance for any suggestions!