Grid Tied Grief!

[SunEagle]

Out of curiosity, couldn't the utility just dial the voltage back a bit? Here in farm country the POCO can just tweak things a bit to help offset the loads of the grain elevators in the fall, so I'd assume that your POCO would be able to do something similar?

(One time my parents had issues with lightbulbs burning out really quickly, and found that they were getting over 260v(!). Quick call to the POCO cleared that up and took them back down to 240...)

The problem with grid voltage is that the POCO can adjust it by changing out transformer "taps". Unfortunately while this may help someone that had very high voltage near the transformer, someone at the far end now has very low voltage which can cause their appliances to run less efficient or actually burn out. It can happen the other way as well by raising up the voltage at the far end a little, now makes it too high for the customers closer to the transformer.

It becomes a balancing act to keep the voltage up and down a "feeder" between a "High and Low" specification allowed so that the customers do not have problems on their loads. Otherwise you end up having to install equipment at a customers distribution panel which can get expensive.

[smily03]

Totally makes sense to me I figured that it couldn't hurt to ask anyhow, might save the complexity of him needing to do a buck-boost at his place.

In my folks' case, they were at the very end of a long run...can't imagine what was happening up the line...!

[SunEagle]

Totally makes sense to me I figured that it couldn't hurt to ask anyhow, might save the complexity of him needing to do a buck-boost at his place.

In my folks' case, they were at the very end of a long run...can't imagine what was happening up the line...!

Even if the "line" voltage can be stabilized, what do you think can happen if you have a few customers that are generating power from solar installations on that "line" that suddenly stop producing for any number of reasons and then start producing again 5 minutes later. Kind of causes the voltage and frequency to do some type of undulating dance.

[smily03]

Ha, no kidding, especially with the old anti-islanding rules about the inverters dropping out within a half-cycle...seems like the newer rules might be a bit more lenient to help prevent things like that?

Combine that with the giant loads at a grain elevator kicking on and off (where the giant loads are powered by the same feed as the local residences) and you'd think it could get interesting...

[SunEagle]

Ha, no kidding, especially with the old anti-islanding rules about the inverters dropping out within a half-cycle...seems like the newer rules might be a bit more lenient to help prevent things like that?

Combine that with the giant loads at a grain elevator kicking on and off (where the giant loads are powered by the same feed as the local residences) and you'd think it could get interesting...

The new anti-islanding rules and energy storage for grid stabilization helps a lot to keep the voltage and frequency close to normal.

Unfortunately the higher the % of RE generated power the higher the % of stabilization needed to keep things in check. Again it is a balancing act.

[gtuplin]

Oh I tried believe me but they said because we are on a long dead drop that in order to maintain voltage to the end this is how it is! We are actually up from that today sitting at 255v. Yikes.

[sunnyguy]

Hmm sma inverters say they go up to 264v. Higher voltage should actually be an advantage since your dc/ac ratio is >1. There is no adjustment for the grid voltage range on the inverter or a firmware update?

[gtuplin]

Growatt says it will work in a wide range but as it pulls away from the 220-230 ideal range it becomes less and less efficient. Hydro won't adjust the voltage so easiest to just manage it on site with the transformer.

[sunnyguy]

Less efficient, OK. We're talking a few percent. But you're getting <50% rated output, right? That is non-functional. I am skeptical of the diagnosis and fix especially due to the bucket experiment. Have you repeated that?

[gtuplin]

No. Now that we have added the panel per string things have become much better , it was very random and poor out put but now we are about 25% low.

[gtuplin]

So finally success.First off thank you everyone for your input on this strange matter, everything helps point to a repair directly or indirectly!
So installed a buck boost transformer on one inverter to test that was designed to lower voltage from the line service by 16 volts giving us a 225-232 range, Growatt was right! The inverters will work at almost any reasonable range but they have a sweet spot! by bringing the one inverter down to this voltage it is now out producing the other three by an average 36.4%(each) based on final daily totals. That is a major gain! We would have liked to drop it a bit more but the next size down transformer may have put us well below in the winter and thought this was the best choice.
We will now go ahead and install the other 3 transformers and finally finish up this project!
Thanks again everyone.

[jflorey2]

by bringing the one inverter down to this voltage it is now out producing the other three by an average 36.4%(each) based on final daily totals.

Excellent! Glad you got it figured out; that was a lot of power to be "leaving on the table."

[gtuplin]

Very wasteful indeed.

[sunnyguy]

Interesting. So how common a problem is this with string inverters in general? You don't really see efficiency curves based on grid voltage, just DC voltage.

[DanS26]

Glad also you found the problem........but I am interested why the house inverter is not affected? I know you have two transformers, but are they not supplied by the same distribution line? Same number of windings in a 25 kVa as a 50 kVa.....voltage should be the same.

Is this a case of undersized wire design causing a voltage drop (ie rise)?