Was on my computer earlier looking at grid injection and battery backup for PV, while chatting with a friend about manufacturing an automatic transfer switch for going into standalone mode when the grid goes down (changing to local earth, then synching the local AC sine wave to the grid before rejoining). The cheapest of off the shelf solutions costs over €1,000 so we're looking at a partnership to do it ourselves.
Then the grid went down as we were discussing it. The whole area is affected for at least five hours. Need to get that battery backup sorted out..
Fair enough. If you follow The 8bitGuy on YouTube he's has several episodes on using Solar and batteries as a backup power supply (he's based in Texas).
Not exactly the same as your situation perhaps but it might be interesting 🙂
@davep@simonzerafa I believe at least Victron have this facility built in. Other inverter vendors I have researched seem to offer it as an extra. Also the switchover latency varies enormously. Victron offer 20ms i.e. 1 mains cycle to go to backup. No idea about going to grid tie mode. Tesla and others seemed to vary from 10+ sec to minutes!
HTH
@davep@simonzerafa also Victron advertise that their generator can act as a local grid source for tied inverters.. Depending on how much backup power you need this could be a cheap-ish approved option? Does your SMA system have offline generation capability already or is grid-tie only?
The main modes are off-grid, battery backup and grid-tie. Grid-tie with battery backup is a bit more complicated but doable. Any critical loads should really be on a UPS, but switchover can be about 20ms.
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