As electricity costs are quite high here in Germany (~0.30€/kWh), we had some solar panels and a battery installed last year. As the shape and position of our roof is not optimal, it's only a rather small system with 18 solar panel modules (together 5.76 kWp) and a 6.5kWh battery.
I didn't look that deep into the issue beforehand, but followed the recommendation of a friend who did some investigation. The nice thing about the system is that the battery and electronics etc. are from one company, so they provide an automatic power switch in case of a power failure (not uniterruptible, but within a few seconds. So in case of problems with the power grid, we have at least electricity as long as there is enough sun (or the battery is loaded).
Normally, the system is connected to the grid, so the energy which is not used directly in our house or used to load the battery is sent into the grid and I get some money for it. So in spring, summer and autumn, we mostly use the energy from our roof, only in winter, we still need energy from the grid as the days are too short (and often too grey) to fully supply our needs (not to think of loading the battery).
Here are the statistics from this year:
dark green = load battery
light green = use battery
light blue = send electricity to grid
dark blue = use electricity from grid
yellow = solor production
red = energy consumption in house