Solar edge inverters voltage drop

[hhsting]

I have solar edge inverters SE9K-US and SE43.4K-US. DC conductors go from the inverter inside to the roof long distance. Designer of the project tells me voltage drop for DC conductors to the inverter is irrelevant since optimizer communicated with the inverter to adjust current.


I cannot find this anywhere in their website. Does anyone know if voltage drop calculation needs to be provided for DC conductors from inverter to the solar panels?

 

[winnie]

The inverters and optimizers will compensate for the voltage drop to get correct operation, but they cannot magically restore the power that is lost. The greater the voltage drop the less efficient the system.

Jon

 

[hhsting]

The inverters and optimizers will compensate for the voltage drop to get correct operation, but they cannot magically restore the power that is lost. The greater the voltage drop the less efficient the system.

Jon

Two questions: Is it required by code to perform voltage drop for solar DC side? Also does it state specifically anywhere in Solaredge instruction voltage drop not required?

 

[hhsting]

The inverters and optimizers will compensate for the voltage drop to get correct operation, but they cannot magically restore the power that is lost. The greater the voltage drop the less efficient the system.

Jon

I don’t follow inverter would draw more power to compensate how does that make system less efficient? Can you please elaborate?

 

[winnie]

I do not know the details of the particular inverters you are working with.

One of the issues faced by inverters is changing sun conditions. It is the job of the inverter to adjust input voltage to get maximum power production in given conditions. While changing sun conditions primarily alter short circuit current, they do change open circuit voltage to some extent.

Changing panel temperature also changes voltage.

Add additional resistance between the PV array and the inverter means lower input voltage at the inverter. But the inverter must have the capability of adjusting for this because it has the capability of adjusting for other voltage variations.

If the output of the PV panels is 200V at 10A, but what gets to the inverter is 190V at 10A, then 100W has been lost heating the wire. The inverter doesn't draw more power to compensate...instead is has less power available to deliver to the AC side.

Same input sun, less output power, less efficient.

Jon

 

[hhsting]

I do not know the details of the particular inverters you are working with.

One of the issues faced by inverters is changing sun conditions. It is the job of the inverter to adjust input voltage to get maximum power production in given conditions. While changing sun conditions primarily alter short circuit current, they do change open circuit voltage to some extent.

Changing panel temperature also changes voltage.

Add additional resistance between the PV array and the inverter means lower input voltage at the inverter. But the inverter must have the capability of adjusting for this because it has the capability of adjusting for other voltage variations.

If the output of the PV panels is 200V at 10A, but what gets to the inverter is 190V at 10A, then 100W has been lost heating the wire. The inverter doesn't draw more power to compensate...instead is has less power available to deliver to the AC side.

Same input sun, less output power, less efficient.

Jon

Ok I don’t follow is if solar panel sees 200V at 10A and if even though resistance between inverter has ability to change voltage then why would it not see 200V instead sees 190V by changing the voltage at the inverter like your saying has the ability to do?

 

[wwhitney]

Pretend for the moment that all the solar panels are one unit, and that the only source of power loss is the voltage drop on the DC conductors from the panel(s) to the inverter.

Say under certain conditions a certain array can produce 4000W DC. And say it has the ability to do that in various ways: 10A @ 400V, 9.5A @ 421V, etc. And say it is connected to an inverter designed to accept 400V DC input, and which can tell the panels (via the optimizer) what combination of Volts and Amps to produce (given the fixed DC power available). If there's no voltage drop between the panels and the inverter, then the inverter will instruct the panels to make 10A @ 400V, the inverter will see 10A @ 400V, and the inverter will make 4000W AC power.

But consider instead the case that under the relevant conditions there will be 21V drop on the DC conductors. The inverter wants to get 400V at its input, so it will instruct the panels to make 9.5A @ 421V (which is still 4000W). With 21V of drop, the inverter will see 9.5A @ 400V, and it will make 3800W AC power. The other 200W of power produced by the panels end up as heat in the DC conductors, due to their resistance (which is causing the voltage drop).

So the system as a whole is less efficient in the second case, converting less of the DC power generated by the panels into AC power at the inverter output.

Cheers, Wayne

 

[hhsting]

Pretend for the moment that all the solar panels are one unit, and that the only source of power loss is the voltage drop on the DC conductors from the panel(s) to the inverter.

Say under certain conditions a certain array can produce 4000W DC. And say it has the ability to do that in various ways: 10A @ 400V, 9.5A @ 421V, etc. And say it is connected to an inverter designed to accept 400V DC input, and which can tell the panels (via the optimizer) what combination of Volts and Amps to produce (given the fixed DC power available). If there's no voltage drop between the panels and the inverter, then the inverter will instruct the panels to make 10A @ 400V, the inverter will see 10A @ 400V, and the inverter will make 4000W AC power.

But consider instead the case that under the relevant conditions there will be 21V drop on the DC conductors. The inverter wants to get 400V at its input, so it will instruct the panels to make 9.5A @ 421V (which is still 4000W). With 21V of drop, the inverter will see 9.5A @ 400V, and it will make 3800W AC power. The other 200W of power produced by the panels end up as heat in the DC conductors, due to their resistance (which is causing the voltage drop).

So the system as a whole is less efficient in the second case, converting less of the DC power generated by the panels into AC power at the inverter output.

Cheers, Wayne

I see. Well I requested voltage drop calculation. If the engineer/ designer doesn’t want to provide voltage drop calculation then why I should interfere. I only enforce code so if it’s not in code then I cannot enforce. Let the owner who paid the engineer have less efficient system. The owner might wonder why his electric bill is same as before even with Solar panels.

Unless of course code enforces solar panel to provide voltage drop

 

[Carultch]

I have solar edge inverters SE9K-US and SE43.4K-US. DC conductors go from the inverter inside to the roof long distance. Designer of the project tells me voltage drop for DC conductors to the inverter is irrelevant since optimizer communicated with the inverter to adjust current.

I cannot find this anywhere in their website. Does anyone know if voltage drop calculation needs to be provided for DC conductors from inverter to the solar panels?

Voltage drop is only irrelevant, if you are using superconductors, which is just not practical today.

What ends up mattering, is the consequence of too much voltage drop. There is always the loss of power associated with the voltage drop, as the power becomes heat within the wiring. There could also be other consequences, depending on the specifics of the circuit that has this voltage drop.

One example is when voltage drop results in a voltage outside the range of the equipment. For inverter output circuits, this would happen if you exceed the voltage window of its internal relay protection, because voltage drop manifests as a voltage rise above the grid voltage at the inverter AC terminals. For array DC circuits without optimizers, this manifests as the inverter's MPPT tracker finding a voltage that is slightly lower than what the array produces, and too much voltage drop would result in a voltage lower than the inverter's MPPT window.

For optimizers, neither of these consequences exist, but you do have practical limits for communication over power-line-carrier signals, that the system uses to communicate. This document specifies 2300 ft as the maximum round-trip circuit length for the optimizer strings, with no way to compensate for it by increasing size. It doesn't indicate whether that is field wiring plus the factory output wiring, or just field wiring. I would assume it is only field-wiring that needs to be below this limit.

https://www.solaredge.com/sites/default/files/design_guidelines_for_three_phase_inverters_na.pdf

 

[jaggedben]

Two questions: Is it required by code to perform voltage drop for solar DC side? Also does it state specifically anywhere in Solaredge instruction voltage drop not required?

No, and no. The second no is because of the first no.

 

[Fred B]

If my understanding is correct, in most cases, voltage drop is a concern on load end of a circuit, a peice of equipment requires specific level of voltage and anything less would negatively impact operation, so you would calculate the voltage drop across a specific set of conductors and adjust up wire size to minimize the drop caused by the load. Knowing voltage drop also useful in troubleshooting and when looking at NEV. Each conductor has a specific known resistance per linear foot, and using that information is how you get to the voltage drop. Now if the solar was a stand alone system powering entire load, then voltage drop may or may not be considered in system designing in view of load demands.
I don't think voltage drop is added into the calculation for Article 690 (2017) requirements as to maximum DC or AC voltages created by a solar system, the primary concern is what is the individual and combined voltages produced by the panel or panel assembly, and not the end of wire resulting voltages. And as previously mentioned, the controller makes some adjustments to voltages produced to maintain optimal perfomance within engineering design specifications. It also appears there are different standards for residential and commercial solar farm applications regarding power production.

 

[ramsy]

..so if it’s not in code then I cannot enforce..

Read John Wiles article in Nov/Dec 2020 IAEI Magazine.
EMS-MID-PCS-DCM-ESS The New Guys In Town

The bottom line is, the person inspecting the systems will have to become intimately familiar with the requirements found in the instruction and operation manuals for these systems.

So inspectors already tasked with mastery of all trades, codes, & listing requirements, must now track emerging Solar tech manuals, which compete with each other, and are obsolete a year later?

I'd rather task tech support for ways installers break their system, then add a temperature probe or thermographic report of wire terminations for over-heated terminals, per NEC 110.14(C).

 

[Carultch]

So inspectors already tasked with mastery of all trades, codes, & listing requirements, must now track emerging Solar tech manuals, which compete with each other, and are obsolete a year later?

Not necessarily "inspectors" as in the AHJ's inspector. The job of the AHJ's inspector is to look for compliance with the NEC and other governing codes. Not all manufacturer's recommendations are necessarily binding, but product-specific requirements that are violated, would be a violation of 110.3(B).

It's the job of the engineers and installers to keep track of the details of the manufacturer's requirements. When engineers inspect/commission the system, that is what John probably meant by "the person inspecting the systems" in that sentence.

 

[ramsy]

It's the job of the engineers and installers to keep track of the details of the manufacturer's requirements. When engineers inspect/commission the system, that is what John probably meant by "the person inspecting the systems" in that sentence.

Thank you sir. That makes more sense.