Hi Carlos,
Thanks for getting in touch. Power is not actually ‘sent to grid’. It rather follows the simple formula that in each point in time Consumption = Grid + Production + Storage (where Grid and Storage may also be negative values, meaning ‘sell-to-grid’ or ‘charge battery’ respectively). I posted some slides of my lecture a while ago here (sorry - German): FH Kiel: Pro 9-12 + OpenEMS Potential.
With this formula in mind we can control:
- charge/discharge the battery
- curtail photovoltaics production
- start additional generators
- start/stop/reduce consumption
- …
and as a result the grid exchange power will change. And this is what OpenEMS Controllers do.In our Gidpod Live-Demo you can play with this yourself, using OpenEMS as a simulator:
For your use-case you could write a Controller that evaluates with how much power you would want to charge/discharge any of your storage systems (e.g. stop at 80 %). The rest is solved by physicis 
Regards,
Stefan