ECN Forum Forums General Topics of the Trade Alternative Energy RENEWABLE ENERGY: YOUR causes for concern?

That gets back to "how do you stop them"?

I doubt anyone with a 175w collector or two is going to make enough difference in their electric bill to show up on the bill as a red flag. How will the PoCo catch them? This is just a plug and go "appliance" that is U/L listed.
It would be easy to argue that if the meter never actually ran backward you never fed the grid in any way at all. The net flow was always in.

Yeah I agree, but if they SEE them they'll raise the red flag, or they might take a cue from the prop tax/permit regulators are start reviewing googleearth aerials for clues as to who's got PV and who doesn't.

Once they're listed someone will start putting them up and continue adding modules as $$ permits until they ARE backfeeding the grid...

Strictly opinion here.

The units are so small in output that the utility probably won't care unless every house on the street completely replaced all of their daylight power consumption with solar generation.

Numbers: ASSUMPTIONS
1) Full size refrigerator: current draw is 5 Amps when compressor is running.
2) Refrigerator compressor runs 10 % duty cycle = 6 min / Hr.
3) Solar panel output is 200 W for 6 hours a day.

Refrigerator load averages 60 W per hour.

So, one panel will power 3 refigerators for 8 hours or one refrigerator for 24 hours. If EVERY customer plugged in one solar panel to their house, it would be the same as every customer removing there refrigerator from the utility grid. Isn't what they have been asking us to do already?

Plus the odds of EVERY customer installing a panel is a bit extreme.

Agreed, but most of the eastern US grid is lacking reverse flow abilities in their protective relay design and is in danger of a cascading collapse when PV saturation reaches levels that would allow a backfeed of the grid, say on weekends when most commercial and industrial loads are shuttered.

There's been a couple of studies on this which have led to highly detailed monitoring of all grid connected PV systems in some areas and the denial of connection in some.

Just like older GFI relays in older distribution gear the utility relays are burned out by a reverse power feed and are then rendered useless and this will generally not be noticed until an overload or fault event occurs that then starts popping OCP devices upstream.

They are pushing grid tie systems with both hands here in Florida (government and PoCo).
They must have some kind of protection from backfeed problems. In real life I doubt solar backfeed will ever be seen back at the substation unless they sell a buttload of them. A kiloton or more of AC compressors humming all day will pretty much guarantee all of that juice is used.

It's mostly a northeast issue and they're attempting to make equipment upgrades as time and $$ permits, but the entire grid is designed this way, so it will take a considerable amount of time to correct.

The problem is not necessarily confined to substations, for example, lets say the utility equipment at the street is 12kV and the utility protection relays there fail when the warehouse complex it feeds is shut down on the weekend and the 1MW roof mounted PV array backfeeds the grid, then on Monday there's a fault in the U/G 12kV feed to the building and the OCP device at the street fails to open because it can't sense the fault, this would mean the next in line OCP device should open, but it doesn't, and so on.....

Several of the large roof arrays we've done have required the replacement of the buildings main 2500-4000 amp breaker(s) and GFI protection because the GFI relays would burn up if backfed, the breakers themselves were rated for backfeed, but not the older GFI units. That can get VERY pricey very quickly, especially if it wasn't taken into consideration when the job was bid.

Several jurisdictions here have required a letter from the manufacturer stating that not only is the breaker listed for reverse feed, but so it the GFI protection associated with it.

There's no way to know how many installations around the country have burnt up GFI protection since you won't know until an event occurs.

For this reason we make every effort to tap the PV feed in ahead of the main unless that is economically or logistically unfeasible because of space or feeder length issues.

So your experience is with the larger arrays. Do you feel that residential neighborhoods do or will suffer from the same problems?

Yes, most of the arrays I've designed were 500kW and larger and we don't do resi work.

From what I've seen and heard from the resi side though, the problems only get worse with resi work, there are loopholes around using licensed electricians for PV and many are abusing them (the loopholes, in case any of you think the electricians are being abused....).

There are a LOT of hacks doing resi PV work and they're giving the sector a poor image. How many times have you seen a roof with modules on two, three or even four sides of a roof? There are ways to optimize arrays in such situations (except the dreaded north side, which I have seen more than once now), but most of the bad installs predate string optimizers or don't include them.

I see a lot of 5kW DC arrays going through 5kW inverters when they should be going through 4kW inverters, the installer doesn't care, he gets paid either way, but it's a waste of the owner's and govt's money.

Lots of violations and bad design practice in commercial arrays too, one of the most prominent that I've seen is the use of a single 200 amp, 3 pole disconnect to disconnect three 200 amp combiner boxes, there are arrays all across the country like that, but there's not a single disconnect anywhere that's rated/listed to do that.

But back on topic, most utility grids can only handle so much PV contribution, too much and grid stability may be affected so too much resi PV can effect the grid and even a little can if there's a large PV array within the same grid block.

I am by no means an expert, but we have encountered just about every issue known dealing with all of the POCOs we've dealt with in Calif and some of them are clueless, blind leading the blind types that will repeat ridiculous regulations verbatim, but have no idea what any of it means or how it works so they can't form an opinion of their own. Luckily the worst offenders have created their own PV department and they are not involved in other POCO/Public interactions and as such they can't spread their infectious stupidity. Sorry, rant off....

Vindiceptor:

I am not familiar with the industrial commercial GFI units main breaker controls burning up when they were backfed. Can you explain to me what they are and how this happens?

Thanks.

This should explain the issue:

http://www.yosemiteiaei.org/pdfs/backfeed-white-paper.pdf