So we are currently planning a PV System for a winery building. The PV will have around 27 kWp. Originally we planned to have a Fronius ECO 25 Inverter between the grid and the PV System and leave it to that.
We have a very relyable grid here but now the idea came up to build a backup system with batteries. Also to use the charge of the batteries for winery and private use in the evening/night and to charge an electric car after sunset. We could design the setup simpler (with no or less sophisticated backup) but we figured once we spend the money we might just go for it and be able to run the winery from the batteries in case of a grid failure. This means that we should be able to run the bottling plant (single highest electricity consumer, 32A/380V/3 Phase) for a few hours when we are off grid.
The original plan was that we use 3 Multiplus2/5000 to set up a three phase system. Although the 1.0 rule shows that we might have to get 3 Multiplus2/10000 and a battery that is about 3 times the size of the PV (3 times kWh to kWp). If i understand the 1.0 rule correctly this rule does not apply if we feed the Multiplus with PV from the DC side (?) so we could use the 5000 and smaller batteries (?)
MY MAIN QUESTION now is if we should use the Fronius ECO and convert from the PV DC to AC and then back to DC to go to the batteries (and life with the conversion losses) OR run directly from the PV the 40 to 60 meters to the Multiplus and the batteries and have the hassle of way more cabling.
Since we have only the occasional AC Peak loads when bottling plant, harvest equipment or cooling system is running we do not use very big AC loads all the time. Also since the PV is fairly big in output, PV surplus will be fed into the grid a lot, at least during summer. I need to add that the PV System is about 40 to 60 Meters away from where we plan to install the Multiplus since i do not want to have them and the batteries in the winery where we have the occasional splashing and sometimes high humidity after washing etc.
As i see it (and please correct me if i see things wrong)
PROs (of AC)
- Easier connection from PV Array to Multiplus
- Easier connection with a single Inverter for the whole PV array as opposed to multiple Mppt Tracker and Charge controller (ALSO cheaper)
- Since a big part is fed into the grid most energy is consumed as AC anyway
- Dont need to feed all the energy trough the batteries and the Multiplus constantly, so less wear and tear to the heart of the setup
- Therefore cheaper to replace a single Inverter after failure than batteries and Multiplus
CONs (of AC)
- 1.0 rule -> bigger battery and 3 Multiplus2/10000 instead of Multiplus2/5000 required, therefore a more expensive system is necessary on this side
- If charging forklift and ecar conversion of energy from DC to AC and AC to DC again.
- Cannot run as backup if only AC Setup and battery is flat (But i don't think thats a big issue for now)
I hope i explained my plan well enough. Let me know if not.
THANKS for any input and answers in advance
Martin
