EG4 18k, MPPT Range, and PV Array Design

[Brooklyndodger]

I have a newbie question about MPPT range. I am planning an off-grid solar power system using an EG4 18K. I was thinking of installing a 10-panel array of Blue Sun Bi-Facial panels, model BSM460M-72HBD. The ground mount array will be approximately 100 yards from the inverter, so I am looking to maximize voltage to minimize voltage drop over that distance. The Voc of that array in series would be 502V under SOT, and 582V at -40C (what I am using as the theoretical max) based on the listed temp coefficient Voc.

While the EG4 18K is capable of taking 600V from a PV array, its MPPT range tops out at 500V.

I honestly don’t know how much that matters. Should I rethink my array to get the max Voc below 500V? In order to do that while keeping my voltage as high as possible it seems like I would actually have to increase the size of my array to 2 strings of 8 panels each, so 16 panels total. This would get the max voltage per string in the 400-500 range, depending on temperature, but would also mean more expense in panels, racking, etc. On the other hand, I also know that many people eventually upsize their array anyway...

I would appreciate thoughts from the very knowledgeable members of this forum. Thanks in advance!

 

[EastTexCowboy]

You didn't give us any info on what your anticipated kwh usage would be, but since you're going with the 18k I'm thinking you're going to be happier to go with the 16 panels in two strings rather than pushing the limit with 10 panels. 10 panels isn't a lot to feed that big ole AIO. Actually 16 panels isn't a lot either but it all depends on your needs.

 

[Brooklyndodger]

You didn't give us any info on what your anticipated kwh usage would be, but since you're going with the 18k I'm thinking you're going to be happier to go with the 16 panels in two strings rather than pushing the limit with 10 panels. 10 panels isn't a lot to feed that big ole AIO. Actually 16 panels isn't a lot either but it all depends on your needs.

Understood, thanks. I will probably end up upsizing the array. My needs are pretty modest at the present — maybe 4-5kwh a day -- but I anticipate them growing as I eventually convert propane appliances to electric, and the 18K unit gives me some future headroom. Also it‘s quiet and seems to actually work! I could get away with a 6k max load unit currently, but one with 12k output should future proof it for me. I just don’t know the downside of exceeding the MPPT range of an inverter…

 

[EastTexCowboy]

Understood, thanks. I will probably end up upsizing the array. My needs are pretty modest at the present — maybe 4-5kwh a day -- but I anticipate them growing as I eventually convert propane appliances to electric, and the 18K unit gives me some future headroom. Also it‘s quiet and seems to actually work! I could get away with a 6k max load unit currently, but one with 12k output should future proof it for me. I just don’t know the downside of exceeding the MPPT range of an inverter…

Exceeding amp max shouldn't cause any problems - the inverter will just clip the excess. You're nowhere close to that with either of your configurations. Exceeding the max voltage can damage the inverter. I would avoid that scenario.

 

[crossy]

You should have the total of the Max-power voltages within the MPPT voltage range, preferably towards the top for best low-light performance.

And of course, the total worst case Voc well within the max permitted voltage.

 

[hnchen]

I have a similar question as OP.

There is usually a big difference between the max MPPT voltage and the top end of the MPPT range.

For example (made up numbers) -
MPP voltage max - 600V
MPPT Range - 120V to 450V

What happens if the solar array is sized in between 450 and 600?

 

[timselectric]

Less efficiency

 

[SignatureSolarJames]

I have a similar question as OP.

There is usually a big difference between the max MPPT voltage and the top end of the MPPT range.

For example (made up numbers) -
MPP voltage max - 600V
MPPT Range - 120V to 450V

What happens if the solar array is sized in between 450 and 600?

the key here is MPP voltage vs VOC

VOC is not relevant to MPP efficiency calcs.

Basically, I think of VOC ceiling first, so for instance I want the string total VOC to be 40 or more volts under 600v on an 18k depending on climate
if you do that you can check the MPP string voltage, which will always be at least 20% lower and typically right in the range needed for efficiency.

 

[SolarSamAK]

May I ask if you are mounting your EG4 18k outside? I saw you set -40C as your low temperature extreme and the EG4 18k is only rated to -25C.