Optimal string sizing for a given inverter can improve your return on investment.
As an example, I will use my system as an example. The PVI-5000-OUTD-AU efficiency plot is given below.
The important panel parameters are:
It can be seen from the inverter efficiency diagram that the sweet spot is at 50% full power and 345V string voltage. Note that it has 2 MPPTs. These may be independently specified.
Now the 28 panels for 4.9kW need to be split between the MPPTs such that the Pmax string voltages are near the optimal 345V. This gives us 2 optimal and a symterical choices:
- 2 x 9 Panels in parallel + 1 x 10 panels. This gives string voltages of 325.8V and 362V.
- 2 x 10 panels in parallel + 1 x 8 panels. This gives string voltages of 362V and 289.6V.
- 2 x 7 panels in parallel + 2 x 7 panels in parallel. This gives string voltages of 253.4V
The open circuit string voltage for this inverter must be less than 600V. This is 439V for 10 panels, so this parameter is ok.
By inspection of the efficiency plot, configuration 1 is the best. In fact is it 0.3% better than the symmetrical configuration, which would result in about $10 per year more income/power at 68c/kWh.
The MPPT which has 2 strings in parallel has a greater weight attributed when choosing panel configuration as it supplies more power.
The panels are up but the Aurora inverter is still coming due to supply issues in mid May.
I have opted not to obtain an alternative GCI due to the excellent efficiency of the powerone aurora. It is generally 2% or more better than others currently able to be supplied at short notice so worth waiting. 2% is worth 98W at full power, and derated, works out to about $100 per year.
All things going well, we should be generating power and income in June some time, fingers crossed. Hopefully AGL wont stuff us around like others I know when we apply for the premium rate tarrif too.
Curt Blank has written an Aurora GCI data interfacing program and written a web interface around it.
I’ll be using this one.
I just need to get a linux supported USB to RS485 interface (ebay) and run some cable up the wall from the server patch panel.