I will soon receive a Backup-Kit to use for some home server systems.
The system will consist of a single Pytes V5a Battery (to be extended later) and a Multiplus-II 48/3000 with a Cerbo GX for control.
I have a SMA Inverter (with some storage) and Sunny Home Manager which I will add to the Cerbo (SMA Inverter with the native sunspec integration and SHM via Speedwire, which I do parse with Nodered. I already implemented this on a raspberry to test it.) There will be no PV on the DC at the time, and even if I add it later it should not feed any power back to the grid.
Grid Code for an ESS system would be Germany VDE.
Primary function of the system is to use excess solar power during the day and provide it to the home servers at night, while keeping 20% SoC for UPS purposes.
My fear now is, that an ESS system may be too slow for providing uninterrupted power to the servers due to the LOM configuration. I think it would be easily possible to implement my desired control loop with a non-ESS system, but I don’t know if it is worth the effort.
Can anybody give me any insights what would be the ideal way to proceed?
ESS uses the grid as an “endless storage” with a small battery, offgrid uses a big battery to overcome bad weather.
It is just your consumption you have to calculate, and then size the battery to your needs.
Both ESS and off grid can be used as UPS, ESS is of course safer as that is your back-up when the battery is empty.
Blackouts in Europe are rare, and when they occur, they last a very short time.
ESS is the cheapest when installed, but of course will cost you more overtime due to the grid supplier contract bi-directional, lost money.
Off grid, you have to invest in a bigger battery when installed, overtime no extra costs.
So, an offgrid is cheaper overtime.
There is however an option, off grid with grid, meaning, you do not deliver to the grid and take a “poor man” connection, just enough to keep your batteries full when needed.
That will reduce your grid supplier connection costs drastically and having the best of 2 worlds for an UPS installation.
Hospitals, Police, fire brigade, telcom centres, etc, have that as well, sometimes also a generator of course for really bad times.
I generate about 8-10 MW (2100-2600 euro solar) a year and pay 250 euro to my grid supplier, as I only use it as a “generator” to keep my batteries (24V @ 4200Ah) from becoming empty.
thanks for clarifying on the differences between ESS and off-grid in terms of economy.
I’d indeed prefer to go with an ESS system, as the necessary prerequisites are already in place at the installation site.
The only question remaining would be, if there is any noticable difference (e.g. in switchover time) between using ESS with grid-code for UPS functionality, or off-grid with the UPS function enabled.
Yes, offgrid, you can switch UPS on, but really, you only have your battery then, so no use, unless you have a generator of course which then starts on low SOC.
And again yes, ESS, UPS on of course, battery is then always full, or at a maintain SOC (80% for example) to save money and with solar priority to charge.
If you’re worried about the switchover time when grid tied (ESS), an old fashioned server/pc UPS that can handle a few seconds of server load is an idea.
The inverter while it has a ups function is not fully ups certified.
If (following a theorerical scenario - experienced in real life) it follows a brownout condition since it synchronises to the grid, sometimes it doesn’t switch over fast enough. If it is very critical have a properly rated UPS in place even if it can only handle 5 minutes of run.
I just received and installed the system, and I can report that the ESS with correct GridCode config is fast enough for my servers, and I am quite impressed
