Benefits of Solaredge vs. string inverter for non-shaded

[foo1bar]

I am part of group reviewing proposals for a ~50kW system.

2 of the reasonable proposals are using Solaredge (For one of them the sales guy says the 20kW inverter - but I don't think that works for a 208V 3-phase system)
The other slightly cheaper proposal uses a string inverter (HiQ inverter - will be mounted on roof)

I would like to use Solaredge - I like the per-panel monitoring. And I like the benefits from per-panel MPPT.
But I'm not sure I could justify the additional cost.
If you were doing the cost-benefit analysis, what benefits would you say there are for a Solaredge system vs. string inverter?
I'm not sure whether it's a 2% additional kwh produced because of per-panel MPPT - or a 5% benefit.
BTW - this will be ~25kW facing East, ~25kW facing West.

[solarix]

On my house I run 2 identical arrays, one with a Solaredge system, one with my old Xantrex inverter. There is no shading. The Xantrex inverter consistently outproduces the SolarEdge by a slight amount every day. I was a big enthusiast of SolarEdge early on until I did this head to head comparison and discovered that their "up to 2%" here and "up to 2%" there claims did not pan out. Plus I had a horrendous failure rate (this was on their earlier model). My advice with inverters is: Like in real estate, what matters is Reliability, Reliability, Reliability. All the shade mitigation, per-panel-optimization, and panel monitoring is minor compared to getting the expected life out of your equipment. String inverters give good performance, are a lot more serviceable, and are more reliable than electronics on your roof. SMA is the only brand I haven't had reliability problems from.

[azdave]

Totally agree on the "reliability vs efficiency" cautions.

Reminds me of the newer A/C units that use variable speed (ECM) motors to reach the last few tidbits of efficiency.
After having three expensive motor/controller failures in 8 years I've spent far more in repairs than I could have ever expected to save in electricity costs. I should have bought the "inefficient" single speed motor units and saved over $1000 and many nights of sweating it out waiting for repair parts to arrive.

[J.P.M.]

Who's going to maintain and service the equipment ? Will it happen ?

[sensij]

I'm a big fan of SolarEdge; I've learned a lot about PV from studying the data that the system provides. I am skeptical of Solarix's claim that the Xantrex inverter actually outproduces the SolarEdge system... the numbers are close enough to be within measurement error of each other, and at that level, there are lots of other factors that could be contributing to the results. Despite that, the point still stands; the difference between the system types in an unshaded array is very small.

Even though I enjoy having my SolarEdge system at home, I am also involved with designing what may be a several hundred kilowatt system for work. It is unshaded, and I've strongly advocated against SolarEdge or any other panel level electronics. At that scale, any data needed to troubleshoot that is not provided by the inverter itself can be inexpensively added by a 3rd party monitoring system. It won't narrow it down to the panel, but in the rare event that a panel or circuit does fail, the problem can be isolated to a small enough area that it can be tracked down quickly.

[rsilvers]

On my house I run 2 identical arrays, one with a Solaredge system, one with my old Xantrex inverter. There is no shading. The Xantrex inverter consistently outproduces the SolarEdge by a slight amount every day.

It would be interested to swap the arrays to the inverters and see how identical your two arrays are. How do you know they are identical? Modules generally are -0, +5%. Can you post a photo of your arrays?

[wes@SH]

Solarix, uou have two identical arrays on the same roof face? If you found identical panels as your original array connected to the xantrex, the older panels would have degraded and not be efficient as the newer ones hooked up to the solaredge inverter. Possibly, you have installed something incorrectly on the newer system, or your original system took the best south facing roof and your newer array is pointed in a different direction.

There is always shading, even if it is only from the sky. If it was a residence, I would want SE even without tree shading. You are looking at $12,200 just in optimizers; a rough comparison might be $kWH x 50,000 x .001 x .02 x 4.5 x 365 x 25, even at .05 it probably doesn't add up with risk of failed components and lost time. Also, are you choosing to do a 160 panel E/W split on flat roof over pure south, or is this a very large gable?

[foo1bar]

Who's going to maintain and service the equipment ? Will it happen ?

I'm not anticipating much in maintenance and service.
Any issues that are related to warranty (ex. inverter fails) I expect the installer to handle.
I would guess with 10+ inverters that there will be one infant mortality in the first 2 years.

The only other thing I expect is that occasionally the panels may benefit from being washed. (It often won't rain from May until Oct.)
I expect that to be done by facility staff. (Probably will use a hose and something like the "Mr. Clean AutoDry Car Wash System" for the final rinse)
And at that time I'd expect they'd look for any wires that had slipped out of the cable management.

What other things do you think we should anticipate?

[sensij]

It would be interested to swap the arrays to the inverters and see how identical your two arrays are. How do you know they are identical? Modules generally are -0, +5%. Can you post a photo of your arrays?

Great idea, except you can't swap a SolarEdge inverter with a standard string inverter without handling every panel to remove the optimizers from one array and install them on the other. Solarix has demonstrated a lot of knowledge and experience in this forum... I'd take him at his word that the arrays are identical in the most obvious ways.

[rsilvers]

I'd take him at his word that the arrays are identical in the most obvious ways.

His word has nothing to do with it. Panels are +5% -0%. One array could be 5% more output than the other even if they are all brand new and identical.

[sensij]

His word has nothing to do with it. Panels are +5% -0%. One array could be 5% more output than the other even if they are all brand new and identical.

I see +5W/-0W as the power tolerance a lot more often than i see +5%/-0%. What panels are you looking at? Even with that tolerance, the chance that two entire arrays would be built on opposite ends of the tolerance isn't the most likely explanation for the observed power output difference, in my opinion.

[DanKegel]

http://www.lg.com/us/commercial/sola...lg-LG310N1C-G4 is +3% / 0-%

http://www.sunpreme.com/wp-content/u...le-Rev-1.3.pdf is +5% / -3%.

What's a +5W / -0W example?

[rsilvers]

http://us.sunpower.com/sites/sunpower/files/media-library/data-sheets/ds-e20-series-327-residential-solar-panels.pdf

[J.P.M.]

I'm not anticipating much in maintenance and service.
Any issues that are related to warranty (ex. inverter fails) I expect the installer to handle.
I would guess with 10+ inverters that there will be one infant mortality in the first 2 years.

The only other thing I expect is that occasionally the panels may benefit from being washed. (It often won't rain from May until Oct.)
I expect that to be done by facility staff. (Probably will use a hose and something like the "Mr. Clean AutoDry Car Wash System" for the final rinse)
And at that time I'd expect they'd look for any wires that had slipped out of the cable management.

What other things do you think we should anticipate?

Since you ask:

Vandalism - fenced or not.
Critters chewing on things.
Put some $$ in the budget for roundup and payroll $$ to apply it. It'll help keep things looking pretty.
Keep spares. Keep them locked up.
Keep people informed of performance. They'll bitch less when they see it's reducing the bills.

Monitor input. Even if not required, still a good idea. Check utility requirements (if any) and if allowed, get Davis Pro II+ or a Li-Cor pyranometer, both w/ data logging, and maintain them. The Davis will set you back ~~ $1K +/- some, and comes with enough instrumentation for performance estimates. The Licor costs a bit more to get all the bells/whistles for data logging and only measures irradiance, but it's a bit more professional.

On cleaning, I'd think long/hard about a cleaning schedule and more so about who does it. Without some controls on when and who cleans the array, I'd plan on some well intentioned but solar ignorant person(s) hitting an array with a hose when the panel glass temp. is ~ 60 C. or so. Just sayin'.

The folks at the Furnace Creek Resort ( Death Valley) clean their array (1.23 mW) every other year as a guano wash only. They monitor performance fairly well (Li-cor + Davis) and tell me that fouling does not seem to increase (and thus performance decrease) after a short initiation period of desert dust buildup.The array near me that feeds the pumps for the Valley Center H2O district (1.1 mW) is in plain sight to me as I write this. It has yet to see any cleaning other than rain in the 7+ yrs. it's been on line that I've seen.

Keeping track of my array's output (and input), suggest to me that, without rain, my array fouls at a rate that causes, very approximately, and very non linearly, ~~ 1% performance decrease per week. I suspect that without rain, that rate might becomes asymptotic and level off @ ~ 7 - 8 % or so after about 7 weeks or so, sort of in agreement with the Death Valley observations, but I haven't had longer than a 7 week spell w/ no rain to confirm/refute. A decent rain seems to restore ~~ 1/2 to 2/3 or so of the performance lost to fouling. I usually suggest to people as a practical matter that they add ~ 3% to the array size to account for performance degradation and hit the array with a hose if it hasn't rained in 3 - 4 weeks.

Like most things of a solar utilization nature, this is not an exact science.

[foo1bar]

Vandalism - fenced or not.
Critters chewing on things.
Put some $$ in the budget for roundup and payroll $$ to apply it. It'll help keep things looking pretty.

2nd story roof - so not too worried about vandalism or roundup (if the weeds get that high, I'll be looking around for a guy named Jack)
I'm not expecting much for critters either - I think it's too far from edge of the roof for squirrels to jump to a tree - and wouldn't be a spot I think they'd find attractive nor find reason to be traversing.

Keep spares. Keep them locked up.

Probably won't happen...
$500 for spares just in case two panels fail or live with 1% less output if two panels fail...
I think the choice will be 1% less output.

Monitor input. Even if not required, still a good idea. Check utility requirements (if any) and if allowed, get Davis Pro II+ or a Li-Cor pyranometer, both w/ data logging, and maintain them. The Davis will set you back ~~ $1K +/- some, and comes with enough instrumentation for performance estimates. The Licor costs a bit more to get all the bells/whistles for data logging and only measures irradiance, but it's a bit more professional.

Interesting - but I wouldn't know how we'd use it. Nor how it'd be any better than just comparing different string's outputs or comparing to other installations nearby.

On cleaning, I'd think long/hard about a cleaning schedule and more so about who does it. Without some controls on when and who cleans the array, I'd plan on some well intentioned but solar ignorant person(s) hitting an array with a hose when the panel glass temp. is ~ 60 C. or so. Just sayin'.

Good thing to think about.

I haven't had longer than a 7 week spell w/ no rain to confirm/refute. A decent rain seems to restore ~~ 1/2 to 2/3 or so of the performance lost to fouling. I usually suggest to people as a practical matter that they add ~ 3% to the array size to account for performance degradation and hit the array with a hose if it hasn't rained in 3 - 4 weeks.

5-6 months without rain is fairly common here.
I don't think we'll be cleaning more often than ~3 months... We'll have to see who will go up on the roof.

Thanks for your thoughts.

[J.P.M.]

Thanks for your thoughts.

You're welcome.