combiner boxes

[hhsting]

I have 3 strings that uses Solaredge optimizers. The optimizer max output current is 15A. The 3 strings with optimizers input to Solaredge combiner box with fuses.

Combiner box fuse size is 15A. Should not the fuse size be 20A not 15A or should it be 15A?

 

[hhsting]

I have 3 strings that uses Solaredge optimizers. The optimizer max output current is 15A. The 3 strings with optimizers input to Solaredge combiner box with fuses.

Combiner box fuse size is 15A. Should not the fuse size be 20A not 15A or should it be 15A?

Ok so would NEC 2014 section 690.9(b) apply post #1?

 

[Carultch]

Ok so would NEC 2014 section 690.9(b) apply post #1?

SolarEdge has a white paper about fusing not being needed, when connecting up to 3 strings to their inverters. At one point, they had fusing built in to the inverters for the models where 3-strings were anticipated, but they've since replaced them with ordinary terminals that parallel strings directly.

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

If you do decide to use string fusing, it is 1.25*Imax that governs the sizing of the fuses. Imax being the maximum continuous current on the optimizer datasheet. Unlike uncontrolled source circuits that require the first 1.25 safety factor for irradiance enhancement, optimizer output current is limited by design. This means a 15A output optimizer would need a 20A fuse, and an 18A output optimizer would need a 25A fuse. Fuses are generally not rated for continuous use, and therefore require a 125% continuous load factor when sizing for continuous current.

Imax for optimizer strings takes the place of 1.25*Isc for uncontrolled source circuits.
1.25*Imax for optimizer strings takes the place of 1.56*Isc for uncontrolled source circuits.

 

[RumRunner]

. . . This means a 15A output optimizer would need a 20A fuse, and an 18A output optimizer would need a 25A fuse. Fuses are generally not rated for continuous use, and therefore require a 125% continuous load factor when sizing for continuous current.

SOLAR EDGE may have its own way of installation scheme--which is (as you proclaim) but the power cells are only limited to their design output-- e.g. solar cells that will put out 165 WATTS for example will only deliver 165 WATTS Max.

It doesn’t matter whether they are connected in series or parallel. And yes, they are all connected after the solar cells.

Traditional string inverters with SOLAR EDGE power optimizers --don’t increase the power output. They are designed to provide improved efficiency--in cases--where reduced sunlight energy (cloudy days) or shades or shadows that could affect the full exposure of the cells to sunlight--and therefore reduced energy that is received by the PHOTO VOLTAIC CELLS .

IF you monitor the arrays over the course of the day...you will be surprised how efficiency is reduced even for a partial cloudy day. This is one reason why PV is so low in terms of efficiency--around 29 % compared to wind power or other renewable source.

Windmills can turn night and day. . . while PVs take a break at night.

Laws of PHYSICS is at play here.

 

[Carultch]

SOLAR EDGE may have its own way of installation scheme--which is (as you proclaim) but the power cells are only limited to their design output-- e.g. solar cells that will put out 165 WATTS for example will only deliver 165 WATTS Max.

It doesn’t matter whether they are connected in series or parallel. And yes, they are all connected after the solar cells.

Traditional string inverters with SOLAR EDGE power optimizers --don’t increase the power output. They are designed to provide improved efficiency--in cases--where reduced sunlight energy (cloudy days) or shades or shadows that could affect the full exposure of the cells to sunlight--and therefore reduced energy that is received by the PHOTO VOLTAIC CELLS .

A 165 Watt panel will not deliver 165 Watts max. Its power depends on temperature and sunlight intensity, and no part of its design will stop it from producing more than its nominal rating in abnormal conditions. The nominal ratings of panels are based on performance at standard test conditions, which is the nice round number of 1 kW/m^2 representative of typical peak sunlight, and 25 Celsius cell temperature. If you have a glare-assist for the sunlight, you could get intensity in excess of 1 kW/m^2, which is why the NEC prescribes the first 125% safety factor on source circuits derived from the panels directly. Current-limited devices, like optimizers and inverters, don't require the first 125% factor, because the device would limit its output if there were a "super sun" of irradiance available. These devices can steer module voltage away from the sweetspot, and leave "sun on the roof", to avoid exceeding their limits.

SolarEdge's power optimizers are devices that reformat the mix of voltage and current, so that they can be connected in series, all produce according to what is available at the module level, and localize the losses to only the shaded panel. I.e. prevent it from hindering performance of the fully lit portions of the string.

The second 125% factor is the continuous load factor. It has to do with the fact that heating is part of the mechanism for tripping a fuse or breaker. Carrying full load for extended time (3 hours as the NEC specifies) heats up the fuse/breaker, making it more likely to nuisance trip before it gets to its rating of current. The continuous load factor applies, to mitigate this risk.

 

[RumRunner]

A 165 Watt panel will not deliver 165 Watts max. Its power depends on temperature and sunlight intensity, and no part of its design will stop it from producing more than its nominal rating in abnormal conditions. The nominal ratings of panels are based on performance at standard test conditions, which is the nice round number of 1 kW/m^2 representative of typical peak sunlight, and 25 Celsius cell temperature. If you have a glare-assist for the sunlight, you could get intensity in excess of 1 kW/m^2, which is why the NEC prescribes the first 125% safety factor on source circuits derived from the panels directly. Current-limited devices, like optimizers and inverters, don't require the first 125% factor, because the device would limit its output if there were a "super sun" of irradiance available. These devices can steer module voltage away from the sweetspot, and leave "sun on the roof", to avoid exceeding their limits.

SolarEdge's power optimizers are devices that reformat the mix of voltage and current, so that they can be connected in series, all produce according to what is available at the module level, and localize the losses to only the shaded panel. I.e. prevent it from hindering performance of the fully lit portions of the string.

The second 125% factor is the continuous load factor. It has to do with the fact that heating is part of the mechanism for tripping a fuse or breaker. Carrying full load for extended time (3 hours as the NEC specifies) heats up the fuse/breaker, making it more likely to nuisance trip before it gets to its rating of current. The continuous load factor applies, to mitigate this risk.

OK.

When I referred to the 165 Watts output. . .I was referring to the expected energy that a PV panel would be able to provide. It is the rating of current limit on how much current would flow.

Nominal current is what can be expected from regular use. It is the lowest measurement that is observed (expected) from statistical point of view.

And this nuance becomes observable (as you stated) that is caused by thermal influence and other factors.
Thank you for your response.