Solar Edge, anyone?

Status
Not open for further replies.
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
I am in the midst of designing my first PV system with Solar Edge. It's around 28kW STC DC for a 208V 3 phase system. The Solar Edge design tool says I need two 10000W and one 5000W single phase inverters. Cool; I'm thinking I put them phase to phase with a neutral, a little unbalanced, but I work out the phase currents, figure my OCPD. So far, so good.

Then I go to the Solar Edge single phase inverter installation guide, scroll down to the AC connection page, and I find... what? One Line connector, one Neutral connector, one Ground. L1 only??? How can that be??? 208V L to N won't work!

Can one of you guys 'splain that to me? What am I missing?
 
C

Carultch

Senior Member
Location
Massachusetts
ggunn said:
I am in the midst of designing my first PV system with Solar Edge. It's around 28kW STC DC for a 208V 3 phase system. The Solar Edge design tool says I need two 10000W and one 5000W single phase inverters. Cool; I'm thinking I put them phase to phase with a neutral, a little unbalanced, but I work out the phase currents, figure my OCPD. So far, so good.

Then I go to the Solar Edge single phase inverter installation guide, scroll down to the AC connection page, and I find... what? One Line connector, one Neutral connector, one Ground. L1 only??? How can that be??? 208V L to N won't work!

Can one of you guys 'splain that to me? What am I missing?
Click to expand...

You are probably better off using 3 qty 9kW inverters. They are 3-phase connected by default.


Nevertheless, the easiest way to calculate the maximum line current in a situation like this is as follows:
1. Add up all phase-to-phase currents on each pair of phases.
2. Select the maximum of the above
3. Multiply by square root of 3


Essentially what you are doing, is assuming all possible phase-to-phase connections are of the worst-case kilowatts. And then calculating the corresponding current.
What would the current be if you had all three of your phase-to-phase inverters as 10 kW inverters? Well, it would be your total 30 kW, divided by 120V and 3, or 208V and sqrt(3), which is 83 Amps.

So even though you have the 5kW runt-of-the-litter on phases C&A, the maximum current among all possible lines is calculated by ignoring the imbalance and calculating only the maximum combinations.

More formally, there is a formula for converting phase-to-phase currents into per line currents.
Ia = sqrt(Iab^2 + Ica^2 + Iab*Ica) + Ia0
Ib = sqrt(Iab^2 + Ibc^2 + Iab*Ibc) + Ib0
Ib = sqrt(Ibc^2 + Ica^2 + Ibc*Ica) + Ic0

Where:
Iab refers to total current from all single phase sources connected from line A to line B
Ia0 refers to total current on line A, before you consider the effects of single phase sources connected phase-to-phase
Ia refers to the combined of the above

Continue the naming pattern for the remaining phases.
 
Last edited:
E

electro7

Senior Member
Location
Northern CA, US
Occupation
Electrician, Solar and Electrical Contractor
I had the same problem with their design tool. I would suggest the three phase 208v 9k inverters to keep it simple. Unless you wanted to add a 208/480V transformer and go with the 10k or 20k:)
 
C

Carultch

Senior Member
Location
Massachusetts
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Carultch said:
You are probably better off using 3 qty 9kW inverters. They are 3-phase connected by default.


Nevertheless, the easiest way to calculate the maximum line current in a situation like this is as follows:
1. Add up all phase-to-phase currents on each pair of phases.
2. Select the maximum of the above
3. Multiply by square root of 3


Essentially what you are doing, is assuming all possible phase-to-phase connections are of the worst-case kilowatts. And then calculating the corresponding current.
What would the current be if you had all three of your phase-to-phase inverters as 10 kW inverters? Well, it would be your total 30 kW, divided by 120V and 3, or 208V and sqrt(3), which is 83 Amps.

So even though you have the 5kW runt-of-the-litter on phases C&A, the maximum current among all possible lines is calculated by ignoring the imbalance and calculating only the maximum combinations.

More formally, there is a formula for converting phase-to-phase currents into per line currents.
Ia = sqrt(Iab^2 + Ica^2 + Iab*Ica) + Ia0
Ib = sqrt(Iab^2 + Ibc^2 + Iab*Ibc) + Ib0
Ib = sqrt(Ibc^2 + Ica^2 + Ibc*Ica) + Ic0

Where:
Iab refers to total current from all single phase sources connected from line A to line B
Ia0 refers to total current on line A, before you consider the effects of single phase sources connected phase-to-phase
Ia refers to the combined of the above
is (was, actually
Continue the naming pattern for the remaining phases.
Click to expand...
Thanks, but I know all that, did all that. My issue is (was, actually, since I have solved it) that the installation manual showed only L, N, and PE terminals for a single phase inverter.
 
Status
Not open for further replies.
Top