we are looking for a good option to feed in the power of three separate stands with 1800Wp each. They have roughly the same direction but are affected by shadows differently. Unfortunately, the distance to the batteries is between 60 and 70m, so a direct connection with DC cables does not sound sensible because of the high resistance.
There is a closer AC connection at 5-10m, which we intend to use. That opens the question, of which inverter to use.
Fronius would be the first option, but most of their inverters only have 1 Tracker, and only the bigger ones have two MPPTs. There appears to be none with 3.
The next option is Micro-Inverters, for example, the Hoymiles HM-1600. As we are optimizing for winter, losing some power in the summer is OK for us.
However, the problem here is their use of wireless communication for control and management. Sadly, that’s not an option in that project, only wired communication is possible.
Enphase would require one inverter per panel if we understand that correctly.
Do we have any other options?
We are really looking forward to your ideas, any help and advice are much appreciated.
What is the maximum voltage you can get out of your arrays?
Greater voltage = lower current = lower losses
The distance is not ideal but I’d do the maths on plain resistive losses verus conversion losses by inverting the PV at source then feeding into batteries via another conversion.
You might find spending money on more cross sectional area in your PV cables is just or more cost effective than a standalone inverter long term.
One panel has 37.9Voc and 18.4Isc, so each triple would have 113.7Voc. On 70m, the voltage drop will be 7% if we can pull the 6 DC wires through the existing pipe.
Otherwise, with just 1 pair of DC cables and connecting all the stands in parallel, the current would be 54A, and the loss 21% with maximum current (though that only happens in summer).
Another reason why we were looking for chargers on the AC side is that we would have better efficiency for the direct consumption of the power compared to the diversion through the batteries.
It appears that we should put nevertheless DC wires in (up to 6, but 2 or 4 would also work) and wait potentially for new ideas or products to arise.
Are you physically able to connect the entire array in series? So around 340Voc.
That would put your losses at about 2% using 6mm cable.
If you have options to change the array configuration the I would put you panels into the MPPT calculator and see what it says. MPPT Calculator - Victron Energy
AC coupled PV inverter is of course possible. Either fed directly into the Victron inverter or running parallel.
You can also operate the Hoymiles micro inverters without wireless communication. They run stably out of the box. To integrate them into the GX and monitor the power, you simply connect a VM-3P75CT or EM540 etc. Either one for several HMs or one for each HM. For long cables, the 3-phase HMT-2250-6T may be ideal because the power runs on 3 phases at low currents.
Yes, that’s definitely the backup plan.
The only issue with one string is the different shading from the roof in winter when the sun is low.
Yes, but the existence of the wireless network itself is the issue
Thanks for the hint, we somehow missed that model series completely.
We have now also identified the Kostal Plenticore 5.5 as a potential candidate. It has 3 MPPTs and the power matches the required power. Though not officially supported by Victron, the Kostal Inverter appears to support frequency shifting, which is all we need. And the data could be read with GitHub - schenlap/venus_kostal_pico: plugin for victron venusos for kostal pico
OK, it turns out that these devices need 150V minimum per tracker, so that would still require putting all panels in series. That’s basically the same result (in terms of losses) as connecting them all via DC to Victron with the long cable.
