With something like this, throwing in solar makes a lot of sense (IMO). There are already batteries involved so you could use solar as the primary recharge mechanism with the grid as a backup.
That's the neat thing, it doesn't have to. Every kWh that goes into these batteries is a kWh not purchased from the grid. The payback for the solar panels would very quickly add up.
In fact, trying to 100% charge the batteries via solar would not be the most economical way to operate as then you are just wasting money sending power back to the grid.
