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| | |-+  A Down Side to String Inverters
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Author Topic: A Down Side to String Inverters  (Read 164 times)
LowGear
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« on: January 22, 2018, 11:53:48 AM »

Wow!  My electric bill jumped up above $300 again.  Running the pool pump too much?  Too many hot showers?  No, a couple of trips out to the SMA inverter and it's obvious that one of two panel strings is not working. 

I've cleaned all the rats nests out but still three KW at noon prevails.  The inverter has two three KW strings so no math majors required.  One of the strings is down.

So I'm sure three KW at about 270 volts is pretty dang dangerous.  You're advice - warnings - heads-ups would be appreciated.

Casey
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mike90045
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« Reply #1 on: January 22, 2018, 04:19:44 PM »

a clamp on DC ampmeter is handy for cases like this.
be sure the one you get has DC amps for the clamp.
http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P
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glort
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« Reply #2 on: January 23, 2018, 06:45:23 AM »


Going out and checking the meter once a week isn't a bad idea either.

I used to screw with the mongeral neighbour at my last place.  The isolator switch for his solar was just over the fence on his wall. It was a rotary type so I cut slots in a piece of PVC pipe that would engage them  and used to just stand on my side of the fence and turn it off.  I only did it about twice in 14 months because he never checked it and being a new house, probably had no idea what his bill should be. I know one time it was turned back on was by a sparky who came to do some work and turned the power off then turned the solar back on . It was off again that night.
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LowGear
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« Reply #3 on: January 24, 2018, 02:08:36 AM »

I have one of those but upon checking I see it's AC only.

Yes, checking it each morning is the new routine.
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David Baillie
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« Reply #4 on: February 10, 2018, 08:26:33 PM »

When you do figure out the bad string maybe look into optimizers for the panels. They will give you panel by panel readings and a heads up if one or more go bad. We use them for partially shaded locations where we have to use the central inverter. More and more we are switching over to micro inverters due to all the rapid shut down requirements and the inherent dangers of high voltage DC strings. Not sure what you have installed forgive the intrusion if its too obvious.
Cheers, David
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glort
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« Reply #5 on: February 11, 2018, 03:01:37 AM »


I have a set of Micros and frankly find them to be a pain in the backside. I also think Casey would not enjoy installing them onto an existing system. More cabling, have to mount the things under the panels or close by, need other connectors, end up with a whole load more wiring and the things are not cheap either.

The thing about High voltage DC strings I find a little bit of a moot point when you are going to have high voltage AC cables as soon as the things leave the panels.  Running a DC string for me has been a lot easier than Hooking up each and every panel to a DC and an AC connection. Mounting the inverters is a whole other issue and you multiply the failure points of the AC connectors as well.

I actually have my micros for sale right now and a couple of regular string inverters on order to replace them.
I don't have any shading issues so to me the positives are nil but the drawbacks are several.

Casey,

I have a few of these watt hour meters.

http://www.ebay.com.au/itm/100A-AC-Digital-LED-Power-Meter-Monitor-Voltage-KWh-Watt-Voltmeter-Ammeter-OK/261671605849?hash=item3cecd7d659:g:U3kAAOSwkNZUcFnP

You would just run the active of your inverter going back to the grid through the little torrid so it does not interfere with the wiring itself.  You tap to the AC just to power the meter which only takes a couple of watts.
They tell you the voltage of the line, the instant power in volts and watts and keep a total of the KWH which is re settable.  There are a few other functions like setting power factor and other things I don't bother with but are there.

You could run some light wire from the torrid back to the meter so you could see all the output the inverter was doing at a glance. You soon get an idea of what is normal and can spot any anomalies in the power produced.
I find scrolling through some of the inverter menus tedious and annoying when you have to look at screen that tells you the brand and then the make of the inverter, the date and timeyearly total and other things in about 10 screens when you only want one. Some of my inverters go back to the start screen after a period of tinme so there is no just leaving them at the screen you want. Pain in the arse!
With these little meters,  you have all the info at a glance.

I have a couple built into small project boxes that I wired up with a short extension cord I cut in half and wired in.  I can plug in any appliance and see what the thing draws.  I can be an interesting experiment to see what that little bar fridge pulls over the course of a day or even just what the total power consumption is to boil the kettle. 

I'm building a diversion box atm to run the hot water heater off the solar feed. I have a PWM controller incorporated so I can regulate the amount of power I send to the heater. One of these little meters tells me exactly how much power that is which is useful to balance the load with the output of the solar.  Without the meter I wouldn't be able to tell if I was feeding 200W or 2 KW.
They make the meters in a straight though setup with no induction coil which is fine for low amperage uses like the test power meter but for something like your solar feed which is going to be heavy wire you don't want to be diverting through tiny little terminals, these meters with the torrid are great because you are not interfering with the cable in any way. Just disconnect the wire, slip the inductor over it and re connect.

You can also get DC versions which use a shunt but from what I have seen they only are good to 100V which is probably going to be way too low for your string voltage. They would probably be fine for measuring input in to a battery bank however.
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LowGear
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« Reply #6 on: February 11, 2018, 11:30:31 AM »

Hi David and glort,

Way back in 2010 when we designed the array and system micro inverters were around $200 each and I knew eventually we would need 30 of them.  Yeah, that's $6000 in inverters alone vs 1 SMA Sunnyboy for about $1500.  Not a tough decision.  I'm still good with the decision.  Being about to track each panels output would be nice, espectially today, and I'll look into the individual panel reporter systems.

The unpleasant mother of my situation at this time is access.  I'll take some photos as my helper, that's a person with long arms and a strong back, pulls the panels off as we look for the problem.  I'm thinking rats chewing through a connector somewhere.  I'll report back.

And never worry about intruding on my knowledge base.  If I don't know what you're talking about I'm gonna learn something and if it's basic even to me I really like reinforcement.

The Sunnyboy does report - line voltage - string voltage (up to four strings) - string current (up to four strings) and accumulated production.  About 2 megawatts at this time.  A very nice cast aluminum housing well built unit.  Some person, names withheld to protect the guilty, put a lot of panels on a rather small roof.  In fact, besides a two foot path up the center there is only about one foot on one end that is not covered by panels.

Aloha
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glort
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« Reply #7 on: February 11, 2018, 05:11:08 PM »

  Some person, names withheld to protect the guilty, put a lot of panels on a rather small roof.  In fact, besides a two foot path up the center there is only about one foot on one end that is not covered by panels.

Aloha

How Did you Know? Google earth?
And let me tell you, that's not a 2 foot path up the middle that's only one foot. as in one foot width so I can get one foot in front of the other and that's it. Not sure where you got the foot at the end either, I have over hang there!
Oh, wait, You're talking about your roof not mine..... Oops!   Grin
Nothing wrong with efficiency I say.

I got the micros I have with a set of used panels I bought along with all the rail and fittings.  I have set them up on the lawn to test it all but I personally found that hooking the micros up even like that was a pain and as I mount the panels I have straight to the tin roof, Fitting the micros would be a huge pain. Bad enough I think when one would have rails to put them on.  They are still available here but not sure how they get round regulations which state that the DC and AC sides must be able to be isolated from a position that a normal person could access without aid. IE, not on the roof.

I might re do my panel layout yet.  As I learn more and understand the possibilities better I come up with more ideas.
Riht now I have hit a brick wall. I can't run the potential power I can generate down the wiring I have and need to significantly upgrade it.  My plan is to put in 3 dedicated Solar circuits. One for the shed on one phase, one for the main house array on another phase and a the 3rd on the house on the 3rd phase.  This will allow me to run the house as well as have the 3 phases needed for the AC and the Hot water.
I have built a control box for diverting power to the hot water over the weekend and will hook it up today or tomorrow.

I had to turn my solar setups off yesterday. We are due a meter reading this week and I was in credit on my useage.  I found out that what I'm doing in back feeding is not illegal but the power company would Not want to miss out on revenue and would change my meters if they thought something was wrong with them. I have the old spinny mrers I can rewind with my input and they would give me these smart arse meters which I don't want apart from the fact they can't back feed.
Terrible thing to have that power going to waste but I just have too much atm.  Come winter when the solar radiation drops off may well be a very different story.  My meter reads will put all the winter low generation months together which is less than ideal but guess I have to look at the annual cost and be very happy with that.


Really funny you mention rats.  I picked up a huge one  right out the front of the shed yesterday morning.  First one I have seen since we have been here.  Not a good idea for rodents to hang around a place with 6 cats. Mind you, 4 of them probably wouldn't know what to do if they saw one but 2 of them would be really interested and one is just deadly with them. Shes not a young cat at all now but still looks like a kitten.
Like a 70 Yo woman that looks like a teenager and does not seem to have slowed one bit. I I have seen that cat with one rat or mouse over the years I must have seen her with 100.
Easy to see her with them. She brings them to the backdoor and crys till you come see them usually. 

When she cleaned them all up round our old place she went and cleaned them up at the neighbors. I was out the front one day and she came wandering up the road with a 4 legged catch in her mouth half as big as she was.  A lady that lived well down the next block was sitting at the bus stop and told me that was the cat that had been coming to her place and catching all the mice.  She said she had seen she had a collar and tag but was leaving out a saucer of milk in the hope he would come back and catch more.  I said no worry about that, she will keep coming back whenever she thinks there are any there and won't need the milk to bring her back.
Lady from the street behind knew her too and told us she had wiped out all the rats in her place and she was happy to see her around her yard as well.

I think they would have a hard time getting onto my roof where the panels are and lying flat and screwed down onto the roof. Not much room for them up there and it would get way too hot during the day. Still, they are vile little creatures and I hope to heck my  super mouser Puss gets them before they get up there.
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