Hybrid Inverter or Inverter with ATS for small scale installation

[philvfl]

I have been reading a lot about solar power and lithium iron phosphate batteries and decided to take the plunge into this adventure. Small info I'm from Europe (Germany).

What I have already done:

• built my own 24V battery out of eight 100Ah cells with BMS, top balanced, tested the capacity with a battery tester and got around ~2kWh (those cells sadly were not as advertised and didn't reach 100Ah, but for the price I paid I won't complain)
• bought a solar charger (Tracer3210AN) that would charge the battery with two JA Solar 345Wp Black Frame panels

Now my idea was to get a Grid Tie Inverter with limiter like a Soyosource and call it a day.

This is going into my small garden hut that only has one phase and a base load of around ~100 Watts 24/7 (IT stuff is running there).

Anyway it's a small installation and now comes my dilemma. I got the info that I'm not allowed to install anything that is on-grid with the existing utility grid. That leaves me no other choice, but to either:

1. Get a hybrid inverter, that supports lithium 24V and has as little power as possible and sell my Tracer3210AN
2. Get an standalone inverter that would be switched with an automatic transfer switch

For option 1 I just can't find something that ticks all the boxes: Have MPPT and 24V Lithium support. I saw one from Growatt, but the 24V one only supports lead acid and I saw another one from PowMr that seems to be fine, but most of these are made for bigger installations and thus cost more. I saw people running those lead acid made ones with LIFEPO4 batteries, but that doesn't seem to be a good idea.

I would love to be as cheap as possible here. Would getting a normal pure sine wave inverter, hook that up to the battery and have an ATS switch (my IT stuff is behind an UPS so the switch taking more than x ms is fine) when the battery voltage gets too low be the easiest way or does anyone know a hybrid inverter that supports 24V lithium with an actual MPP tracker (and not PWM) that doesn't cost let's say more than 500€? (I don't need much power anything above 1KW is already enough)

I saw someone in this forum link an inverter with automatic transfer switch already built in, but that seems to be us stock only and I didn't find anything similar for Europe.

Any help on how to proceed is appreciated, I know this is a kinda strange requirement and small scale installation.

Have a good day.

 

[Shimmy]

You actually have a third option-- charge from grid and use an off-grid inverter. If you want to be fully compliant that is going to be the lowest cost option. The hybrid inverter works best for isolating from the grid when grid is down, rather than switching to grid when battery/solar are down (but many of them can work in that mode).

 

[philvfl]

Yeah, that would be the best option. Now I found an Off-Grid Inverter that has an ATS built in and switches to mains from the grid if the battery runs out. It will use my island until it runs out and switch. I'll go that route.

To make it more efficient I would completely ditch the DC -> AC -> DC chain that I have and power the IT-System through DC directly (the small computer uses a laptop charger and the POE-Switch, too) and have less conversation losses.
I wouldn't know how to make that "failover" though so that let's say 20% is always left in the battery as backup for missing mains and the system doesn't have a blackout when transfering from battery to DC from charger connect to grid.

 

[Shimmy]

...(the small computer uses a laptop charger and the POE-Switch, too) and have less conversation losses.
I wouldn't know how to make that "failover" though so that let's say 20% is always left in the battery as backup for missing mains and the system doesn't have a blackout when transfering from battery to DC from charger connect to grid.

The product offerings have changed here since I last used their products, but check out the offerings at Mini-Box. There used to be something that would switch up to 12V to an alternate source. The other option is to go with blocking diodes on the DC side, but you will need a suitable operating range for them to work properly.