I haven't been talking much PV the past two months but I've been busy.
I bought 16 (I think is the number) 6kw Delta string inverters with the intention of that being a several year supply. The first thing I did with them is hooked two or more up with reverse polarity and probably fried them. Not realizing what I had done wrong, I fried at least two SMA 4kw inverters the same way. FINALLY realizing my mistake, I expected smooth sailing. Just eat my loss of 4-5 ~$500 inverters and get the show back on the road. The sailing was NOT smooth. After weeks of testing and experimentation, I now believe that "transformerless" inverters were spawned in hell. They are highly prone to "isolation faults". Older string inverters that contain transformers have no "isolation fault" possibility or risk. I've used some old transformer inverters with very good results. Well, maybe the problem is only with the Delta transformerless inverters? So, I order three different other brands of transformerless inverters for testing. The first one, a 7kw SMA (but more modern than the 4kw transformer SMAs I've used) worked quite a bit better than any of the Deltas. But, for me, it is not "production grade" since it shuts down and refuses to produce for about a day following a rain. Two others are in the queue for testing.
But, I expect to be shopping for old transformer inverters.
Meanwhile, I've completed two rails "across the road" and have been testing one with a 4kw transformer SMA and one with the 7kw transformerless SMA. The 4kw works continuously without complaint.
I've decided to rework two old (only about a year old) low slope single face rails into a steeply sloped two faced rail. Orientation is not very important on the single face rails but two faced need to be oriented N/S. So the new two face needed to be repositioned/oriented compared to the old ones. Those in the "south field" near the house. The primary reason is to make use of the big wire I've recently run to the old greenhouse which was part of the "new garage". Depending on what inverter I settle on, I could produce up to about 8kw from that new rail.
All recent rails have been 24E + 24W with each 24 divided into 2 strings of 12. That's an attractive setup for string inverters, especially those with 2 or more MPT trackers. The new south field rail is longer and could support up to 56 panels.
Plans for a new transformer with meter (new electric service) proceed. The cost is discouraging, maybe $8k-$10k. I think I've estimated my current cost for PV to be about $.30/watt. For 50kw, the new service would add up to about $.20/watt. My recent upgrade from a 15kva transformer to a 50kva cost about $5k. Nearly as much per watt.
Probably more elaboration later.
6/4/2020
I received two inverters yesterday, a 6kw Aurora and a 5KW Growatt. Both transformerless. This morning, I had them both installed. Both failed to start, diagnosing "low isolation". The 7KW transformerless SMA continues to work whenever we've had dry weather for a day or longer. A 6KW Delta continues to mostly work except after wet periods. I'll leave the new inverters attempting to start for a few days.
I hope to return my 9 virginal Deltas next week and buy some more transformer inverters.
Have I mentioned that I believe "transformerless" inverters were spawned in hell?
The reworked two face rail in the south field is complete and accepting panels. Currently, I have 9E + 9W installed. Heading for at least 24E + 24W. The new Aurora is currently trying to use it. As soon as I give up on the Aurora, I'll try a 4KW transformer SMA on that array.
6/6/2020
This is of the rail being lifted into place about 6/4/20. Current situation is that 11E and 11W panels are in place. A 4kw SMA transformer inverter is accepting their power. Mid day production is about 2.4kw which indicates 20E + 20W panels will be sufficient should I decide to use that inverter. If I find a good larger inverter I might use up to about 26E + 26W panels on that rail to produce up to about 6kw.
ONE of my projects is cutting back brush to left of the rail and in the distance; they are casting morning shade on the E panels.
6/11/2020
The rail completed:
The rail is 3 33' joints of oil well pipe. At about the same site were two single face rails with one remaining and ready to be taken down. The new, higher, two face rail is mounted on five lengthened posts.
Installed and working on 44 panels, two strings of 11 on each side. The four strings feed a good, reliable, old, transformer SMA 4kw inverter and produces about 4kw for about 9 hours each day. The rail has space for three more panels on each end on each side. So, I could easily go to four strings of 14 panels. Though I believe 14 panels will have too high voltage. With the right inverter, I can probably produce 6+ kw from that rail for up to nine hours per day.
If I decide I should/could produce more power in this south field, I can make another two face rail to the right. That would necessitate taking down the two single face rails that are currently in that area.
6/14/2020
The new rail with 44 panels has been working with the transformer SMA 4kw for a few days. This morning, I decided to swap inverters. One of the few transformerless Delta 6kw that works is in the greenhouse so I hooked the new rail up to it. So far, it is working. I'll let it go a few days and, if there is no trouble, I'll start adding panels to the rail; the SMA would not benefit much from more panels. The transformer SMA is now working on the temporary test array that had been feeding the Delta: 13 panels in a single string laying flat on the ground.
