To oversize SolarEdge Inverter OR NOT?

[J.P.M.]

I agree, very few people will ever expand their existing array unless they significantly undersized for whatever reason (lack of funds, no space but now there is, inherited array, etc). If you still want to lower the elec bills further it'd probably be the energy efficiency route (insulation, envelope seal, Windows, appliances, etc).

Which, from a cost effectiveness standpoint, after simply turning stuff off, ought to be measures taken before solar, not after.

[cebury]

I agree, very few people will ever expand their existing array unless they significantly undersized for whatever reason (lack of funds, no space but now there is, inherited array, etc). If you still want to lower the elec bills further it'd probably be the energy efficiency route (insulation, envelope seal, Windows, appliances, etc).

[TimeOrMoney]

As is typical for me over analyzing things, and probably going Solaredge, here are my thoughts:
1. We don't have efficiency curves for the inverters. They are probably not that different in the range you are looking at, however.
2. Depending upon your local jurisdiction, watt limits, permitting costs, add-on rules, etc., the whole idea of expansion may be not worth it ever. Probably best to figure what the maximum allowed that covers your power needs and do it all at once. Will you upgrade in the future? Odds are against it, but you may be the exception.

[CoyoteVB]

Thanks sensji. Being new to solar I appreciate all the great advise on this forum

[sensij]

The oversizing they recommend is array size to inverter size... opposite of what the OP was suggesting. Any clipping is more likely to happen in the spring or fall, when temperatures are cooler, and less likely in the summer when it is hot and the array power drops. However, that is to some extent location and orientation specific.

You can use PVwatts to estimate clipping loss... in the Advanced parameters, use the DC:AC ratio. For example, a 4 kW array on a 3 kW inverter would be 4/3 = 1.3333.

[CoyoteVB]

I am curious if you have decided to oversize or not. I have been researching the same question. The SolarEdge design tool documentation and Technical notes encourages oversizing by 125% to 135% depending on the average high temperature. I was not actually able to use the tools since is for Windows. No MAC version. They state better performance in low light. They define oversizing when Pdc (STS) > Pac max. The calculation in the SolarEdge Technical note is Pdc(STC)/Pac max * 100%. I wonder if SolarEdge recommends oversizing since the optimizers/inverter system continuously adjust voltage based on light and shading. I am also wondering if I will clip on the peak summer days.

[thejq]

However, I have heard that there is "startup voltage" for some of the inverters and if I go very oversize then the number of the panels may not be enough to reach the starting operation for a big inverter when the light is low (early morning or late afternoon).

Don't worry about it. If your installer follows the installation instructions correctly, the optimizers will automatically and collectively adjust the voltage so the inverter's input voltage is in the optimal range. There's a minimum of 8/string, so you're over that already.

[sensij]

Hi Sensij,
I see that you are also located in San Diego. Do you know whether we have to put the inverter inside or it can be also placed outside according to the county regulations?
Thanks,

It can go either inside or outside. If you run high DC voltage into the house, there are code requirements about how the conductors are protected and marked that are different from typical household 120/240 VAC.

I have mine outside, on a south facing wall. It has roof overhanging above it, which means it is fairly protected from the sun in the summer when the sun is high, but actually gets much warmer this time of year when the sun is lower and the eve won't shadow it.

[posol]

If you don't follow code, you'll have a hard time getting a permit approved. Without a permit, you won't have much luck convincing the power company to allow net metering. Without net metering, the whole thing is probably a waste of money.

Hi Sensij,
I see that you are also located in San Diego. Do you know whether we have to put the inverter inside or it can be also placed outside according to the county regulations?
Thanks,

[sensij]

Some inverters have adjustable startup voltage.

Oops 20 Amp breaker that trips is what I should have typed. Also, I looked it up the 5000 can be set to limit power anyway, so if you didn't follow code you could limit power.

If you don't follow code, you'll have a hard time getting a permit approved. Without a permit, you won't have much luck convincing the power company to allow net metering. Without net metering, the whole thing is probably a waste of money.

[sensij]

5000W inverter is 30A breaker. 5000/240 *1.25 =26A
6000W inverter can be 35A breaker (probably a special order) 6000/240*1.25 = 31A

Fair enough, but the math around the service panel rating isn't really changed. If you go bigger than 3800A, a 100 A panel is too small. Since the OP already has 200 A, it is moot, but that hadn't been shared.

[FFE]

Thank you all for the insight.

My Panel is 200A, so I am fine with either. However, I have heard that there is "startup voltage" for some of the inverters and if I go very oversize then the number of the panels may not be enough to reach the starting operation for a big inverter when the light is low (early morning or late afternoon). But I cannot find such information for SolarEdge inverters nor their operating range graphs.

Any thought of these?

Some inverters have adjustable startup voltage.

Oops 20 Amp breaker that trips is what I should have typed. Also, I looked it up the 5000 can be set to limit power anyway, so if you didn't follow code you could limit power.

[foo1bar]

So, if it is a 100 Amp panel and the OP installs a 16A breaker, installs the 5000, .

There are no 16A breakers.
But lets assume you meant 20A. (16 * 1.25)
Installing a 5000W inverter with a 20A breaker is not up to code.
Therefore it would not be installed that way.
If it was installed it correctly, it'd be a 30A breaker, with appropriate wire size for 30A. With a correct installation the breaker would not trip even if the inverter reached it's peak output.

[posol]

Thank you all for the insight.

My Panel is 200A, so I am fine with either. However, I have heard that there is "startup voltage" for some of the inverters and if I go very oversize then the number of the panels may not be enough to reach the starting operation for a big inverter when the light is low (early morning or late afternoon). But I cannot find such information for SolarEdge inverters nor their operating range graphs.

Any thought of these?

[foo1bar]

The OP is asking if there is a TECHNICAL reason not to go with the larger inverter. He's not asking if there are REGULATORY considerations (which is what it seems like others on here have defaulted to).

Actually we were discussing ECONOMIC considerations - not regulatory. (or at least I was)

I haven't seen a solaredge efficiency curve for any of their inverters. So really I don't know whether you would gain or lose a little efficiency by running 2kW through their 3800W inverter vs. their 5000W inverter. I have seen curves for Sunnyboy - and on those I think it's pretty flat until you get down below 10% of the rated power. So my best guess is that the effect of upsizing is largely going to be unnoticed in overall power production. That it'll be within 1-2% overall (and that could be either better or worse, since at least some of the graphs have higher efficiency at ~20% than they do when running at 50% or 100%). Quite possibly keeping a nearby tree pruned will make more difference.