Author Topic: Solar setup problems and inefficencys  (Read 1323 times)

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george65

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Solar setup problems and inefficencys
« on: August 31, 2017, 03:11:00 AM »

I set up my used solar system at my old place and while it worked OK, the output was low. There was a lot of shading from the palm trees around the pool so I didn't think much of it.
Having now arrived at the new Digs, I wanted to check some circuits I wanted to backfeed into and set up the panels on the grass.

I have adjusted all the panels to near optimum tilt ( 1/2 degrees off) and with the correct orientation to the sun. I had 7 panels hooked up today through the inverter which are each rated at 190W.  I have a meter behind the inverter and with perfect alignment to the sun and NO shading what so ever, I was geting constantly fluctuating readings between 70W and 700 odd Watts.  The output is never steady, much like I would expect to see if there was a tee branch waving in the wind changing shadowing.  The capacity of the panels should be 1.7 K nominally and while I didn't expect that, I certainly thought I would have got more than an average of maybe 400W and the output would have been steady not the split second and constant variations.

This was borne out by the Inverter readout and when I went and looked at the power meter on the house, I could see it kind of stepping rather than a smooth rotation.
I thought the wire I was using to hook up the DC side may have been too light. It was ordinary 10A mains cable but I had twisted all 3 Cores together so I thought should have been more than enough to carry the load over the 9ft or so length.  Just the same I changed this to 2.5MM cable with 2 cores twisted together so effectively 5MM of wire.  The variation seems to slow a little but by this time it was getting later in the day and the sun angle was far from optimum.

I have checked every panel for Voltage and amperage and they are all the same although again being later in the day when I checked were down on optimum output as would be expected.  One thing did confuse me was when I shorted the outputs in an amperage test and multiplied the open circuit voltage, ( maybe I should have measured Volts while amp testing?)  i got about 110W per panel at that time. with 7 panels should have been around 700W output but I was never seeing more than about 280 on the meters.

 Maybe that test is flawed measuring unladen voltage but what is disturbing me is the wild see -sawing variation of the output. If it was low that would be one thing but it's going at such a high low spread like the inverter can't find a happy place. Similarly I am concerned about the low output.  1.4 Kw of panels made about 2.2 Kwh.

I want to find the problem or what I'm doing wrong before I go tot the trouble of putting these things up on the shed roof.  Pointless if all I'm going to save is .60C worth of power a day.
Is there something I'm over looking or is this normal for a clear sky in springtime? What about the wild variations? I know they aren't dead steady but this is like an 8-10X constant variation.  I have another inverter I can try but I don't get the feeling this is the problem.  I am also running a 20M extension lead back tot he outlet but its a 10A rated industrial type cable so I can't see that not even carrying half a KW steadily. Can't really bring the setup closer to the outlet with a shorter lead as it will be in shadow.

Any heads up or things to check with this?  As I say, pointless installing it the way it is and I need to know if I have dodgy panels, inverter or my testing is flawed.

Bruce S

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Re: Solar setup problems and inefficencys
« Reply #1 on: August 31, 2017, 07:00:49 AM »
How long have the panels been outside and hooked together?
It sounds similar to the issue I had with a new set of Harbor Freight panels when they were pretty new and still "settling" in.
Even though these are used panels there could be a settling in period.
Maybe try disconnecting or bypassing one at a time to see if the swings in power settle down?

Even though these are a much better grade set of panels that the ones I got, they may be trying to settle in. Other than that I would go looking inside the panel junctions to see if there's a flaky diode in there. Might be okay as a stand-alone but starts to break down internally when subjected to higher power stresses.

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george65

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Re: Solar setup problems and inefficencys
« Reply #2 on: August 31, 2017, 04:13:21 PM »

Thanks Bruce. I was wondering about the Diodes.
On these panels they aren't that easy to access as the covers are glued rather than screwed on.  Might have to bite the Bullet and check them anyway.

Settling in seems odd to me. There are a solid state device, what would need to or could change within the panels to eliminate the problem?

I was hoping to find a Dud panel when I tested, one that was different to the rest but I was surprised when they all came out the same. They were much closer in volts and amps than I even would have expected. When I got the panels many had at least one terminal cut off by the butchers that uninstalled them.  I replaced what I had to so most of them have an MC3 and an MC4 Connector.  Putting them in the right order makes them all connect together.  :0)
I might go through and change all the connectors today to MC4 so I can link them in any order and take panels out of the string to see if I get any different results. That will be a long process as the inverter takes about 5 Min to do it's tests before it kicks in and starts pushing power back.

I have 3 New 260W panels I was given when they were ordered but there was not enough roof space to fit them. Might put them together and couple each of the other panels individually to see what happens. Sure wish I had a 4th of these panels as they are just not enough to  start the minimum inverter voltage and would be a Kw on their own. Been looking for another the same to buy but can't find them. I have a 3 way connector so might put 2 of the smaller panels together and see hat happens with that. If I still get the variation would mean nothing but if the inverter stabilises it's probably a good indication I have a dodgy panel.  or more.

Until I work out what's wrong with this setup I don't want to go any further. Might look at some other panels anyway just to try and have a comparison set. There are some 175's nearby the guy is prepared to sell for $30 ea. May be worth grabbing the dozen and see how they go. Spose I can always sell them if I need.

Should I expect near capacity outputs on a clear spring day or is that only in the intensity of summer sun or???
IF I have 1.4Kw of panels I was thinking I should get 1 Kw+ at least when the things are at the right tilt in the middle of the day and the sun is straight on.

frackers

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Re: Solar setup problems and inefficencys
« Reply #3 on: August 31, 2017, 05:32:57 PM »
Keep an eye on the mains voltage. It could be that the inverter output is pushing it above the value the inverter is happy with so it starts to shut down, recovers and hence cycles.

Could be the new locale has higher grid, could be a high impedance cable or bad connection between the grid transformer (sub-station or on a pole outside?) and inverter.

Also check that the inverter is set up for your country e.g. set for 230v rather than 240v or whatever your national system uses.
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george65

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Re: Solar setup problems and inefficencys
« Reply #4 on: August 31, 2017, 09:58:36 PM »

Swapped out inverters and everything seems OK now. Must have a dodgy Inverter. Bugger!
Still only getting 1.6Kw from 2.6 Kw worth of panels.

Another problem has come up which Frackers pointed out.
The inverter is dropping out which I think I due to high mains voltage. Seems to be pushing it from about 247 to 264. I suspect when it hits 265 it's cutting out.  I noticed on other parts of the same phase the voltage is around 258. I was thinking the higher voltage at the inverter may have something to do with the 20M extension cable I'm using. 

Not sure what I can do about the high voltage on the phase if anything. My other place was pretty consistent at 230V but it was single phase.  The other phases here seem lower but that's generally the case, never all the same.
I want to do at least 3Kw on that phase which could be a problem. Must be a way around it though.

frackers

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Re: Solar setup problems and inefficencys
« Reply #5 on: September 01, 2017, 12:54:34 AM »
AS/NZ4777  has maximum grid voltage as 255 volts so if the inverter is compliant it's doing exactly as it should ;(

Do you have multiple phases on site? If so, you could push the neutral centre point about a bit by banging some oommph into another phase with another GTI.
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george65

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Re: Solar setup problems and inefficencys
« Reply #6 on: September 01, 2017, 02:11:13 AM »

I suspected that's what it was.  I was surprised to see the voltage that high. I want to move the connections on the phases around anyway. I have an electronic meter I can't spin backwards so I want to move everything bar the hot water ( for the time being) and the one leg of the AC off that and have everything else across the other 2 phases.  I noticed today that one phase seems to only have the AC, stove and oven and bathroom heater lights on it.
All very intermittent loads so definitely can put on some more there.

Had way more potential at the old house and that was only single phase so no problem moving things around here.
I also want to try and pull through a 3 phase cable to the garage. That would allow me to split the phases where I want to put a fair amount of panels and be able to pump more than 3.6 Kw back down the line.

Bruce S

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Re: Solar setup problems and inefficencys
« Reply #7 on: September 01, 2017, 08:12:28 AM »
Glad to see you got it sorted out.
Since I'm not connecting my stuff the the grid, I don't see those type of problems.

My settling in comes from working with these harbor freight panels. I'm still not totally convinced that solid state stuff doesn't need a settling in period. My entertainment system seems to sound nicer and louder once it's been on for ~5mins.

Would be nice to find 175W panels around here for those prices :-).

I've just started working with semi flexible 30W panels again. Acquiring a Velo-mobile that uses a 36Vac motor so and there's just no plug-in for the charger at HQ. Fun part is I built the 36V 20Ah NiCd pack 8 years ago (picks are here somewhere) and they're still working.
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Mary B

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Re: Solar setup problems and inefficencys
« Reply #8 on: September 01, 2017, 05:35:11 PM »
You could use a long cable from the inverter to the AC source, voltage drop on it might bring you back in line...

DamonHD

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Re: Solar setup problems and inefficencys
« Reply #9 on: September 02, 2017, 07:46:08 AM »
Many inverters will cut out if they see too high an impedance to the grid.

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george65

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Re: Solar setup problems and inefficencys
« Reply #10 on: September 06, 2017, 03:08:32 AM »


Last 4 days I have made 37 Kwh from my 2.6 Kw of panels.  As the panels are just propped up on the ground for testing purposes, on 2 days some panels blew over. I day they were still working, yesterday at some time they fell over and were open circuit.
Still, seems to be a worthwhile result.

Today I Swapped out the inverter again to see if I could bring the line voltage down.  It ramped it up to within a volt of the other inverter so not a problem on the equipment side.  I think it's because that phase during the day is lightly loaded but could be something else.

Yesterday while out at the meter box I observed something strange that may be related.  I was watching the meter on the phase I have connected spin happily backwards when I noticed the other meter moving backwards as well. It was barely perceptible and at first I thought it was my eyes playing tricks but after watching a while, like a clock, I could see that the wheel was 3 marks from zero then it eventually went past zero.  Obviously something in the order of just a few watts but none the less, moving backwards.

I was wondering if this is some sort of backfeed through the neutral and could be linked to the high voltage the inverter is seeing?

DamonHD

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Re: Solar setup problems and inefficencys
« Reply #11 on: September 06, 2017, 11:13:43 AM »
What's the earthing scheme used at your property, and in particular is the neutral tied to earth locally for example?

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george65

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Re: Solar setup problems and inefficencys
« Reply #12 on: September 07, 2017, 01:04:38 AM »

The earth here and typicaly for everything I have seen in this country is a rod in the ground a minimum distance.
Pretty sure it used to be tied to the water pipes but I believe thay did away with that many years back.

Far as I'm aware, at least at the individual household, earth is not allowed to be tied to the neutral.  I was looking at the back of my meter box yesterday and they are certainly separate. each phase seems to have it's own neutral point and the earth is separate to that.

Due to being crook last night I was up at daybreak this morning and reset the counter on the power meter.  Went out about 4:30 pm and I'd done over 9 Kwh for the day which seems great.  Going out now and going to set up some scaffold and reposition the panels so they get the full sun sooner and avoid shading.  Probably be a cloudy day tomorrow and stuff up my comparison readings.

I was reading earlier about the current trend of putting more panels than the inverters rating. Here the regulations allow for 33 % over wattage of the inverter on the AC side.  tests show this to be very worthwhile.  The inverters will just clip any extra power ( cannont excede voltage) but obviously develop the full power of the inverter earlier and later in the day as well as doing much better in overcast conditions.

The big plus here is that authorities are limiting the amount of power you can generate. Obviously they don't want you saving too much power and their share prices dropping or the CEO's multi million dollar annual bonuses being reduced because you aren't buying enough power from them!
By putting on a " legal" 5 Kw inverter with 6.5 kw of panels, you can have the thing pumping the full 5kw a lot longer in the day than maybe the 4.5 kw output you would get with 5Kw of panels. Test also showed that putting 6.5 Kw of panels on a 6.5 Kw inverter only resulted in a .4% increase over the over clocked 5Kw inverter.

When reading this I realised I had 2.6 Kw of panels on my 2Kw inverter. Still only seen a max output of 1800W so maybe room for another panel or 2 on the string. Might have to swap over some more loads to that phase first though to pull the voltage down.

george65

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Re: Solar setup problems and inefficencys
« Reply #13 on: September 07, 2017, 02:58:27 AM »

9625 Wh for the day which seems great for a 2600w system.
 I moved the panels to a less shaded location so I should be making more power earlier and later. If it's sunny might crack 10 Kwh for the day.  See If I can hit the full 2Kw output on the inverter. Spring here so I have set the panels between the normal and winter tilt angle. Have them facing slightly northwest as true north has shading I can't do anything about so i'll aim to make more power through the peak and later in the day.

george65

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Re: Solar setup problems and inefficencys
« Reply #14 on: September 29, 2017, 08:00:52 AM »

Been fiddling around and learning more with the panels.

I bought 5KW of 250W panels the other week and have tested them and set them up as an array.  I have 2 arrays set up now, one with 2.5Kw of panels tilted on the scaffold in the right orientation  and degree and the other with a total of 3250W lying flat on the lawn.
This has been interesting in itself.

On sunny days the tilted panels will tend to make more than the flat panels. On cloudy days the flat panels do a fair bit better.  The 2.5Kw aray is on a 2Kw inverter and the other setup is on a 3Kw inverter.  best I have seen so far is 1980W out of the 2.5 array. The other tends to sit around 1.8 quite consistently in full sunlight for several hours of the day.  Biggest shading problem has been the cat siting on a panel on the cooler days for the warmth. On the hotter days he sits under them getting the shade but the radiated heat at the same time.

I have been battling the phase going high once the power levels go up. tried a few things with that but nothing worked. once I added the second array I could only run one at a time through the middle hours otherwise the inverters would trip out. I thought I'd just let them do that but it killed output. they would take about 3 min to reset then run for 5 sec then default and go into test mode to rest again. Sometimes one would trip and the other would hold but often they would both trip and the power losses during the down time really knocked the daily KWH figures.

I am running long extension leads and always was concerned about that. I was reading things and learned what should have been obvious, Voltage drop works both ways.  You loose when you are trying to pull through but you get a bottle neck when you are trying to push.  the resistance of the wire rather than dropping the voltage at the outlet end was causing the inverters to see a higher voltage at their end.  I had seen this with testing the circuit at another point and at the inverter end but thought that may have been because of local loads taking the edge off at the connection side.

Thinking of the resistance, I got out a 1.5mm extention lead to replace the standard 1mm cabled conductors and I re wired the plug from the inverter in 2,5MM cable.
On the other inverter i did the same to the plug and also made a 25M extension cable from 2.5mm.  It certainly helped but didn't cure the problem. I figured the feed in points were just too close together and the circuit didn't have enough load and that was all I could do in this testing setup.  Each array was working well and delivering good output for it's limitations and I'd have to wait to get them on the roof and wired properly to see them really working hard.

I have been turning one set of panels off during the middle of the day and back on about 3PM.  this works well as something else I have concluded along the lines of over paneling the inveters is it's not the peak output that makes the difference to the days total generation, it's the mornings and afternoons.
Having the 2 arrays running in the ramp up and down would allow the same output as the middle of the day for much longer and because the total was the same, the line voltage wouldn't go high and trip one inverter out.  having a peak output for 2-3 hours a day longer made a big difference to the much faster fall off of either arrays singularly.  Although a bit difficult to test as the light changes faster than one would normally realise, the output total of both inverters seemed to be greater than the sum of the outputs individually.
Not sure how that works, maybe the higher line voltage made for greater efficiency in converting the high volt, lower amp output of the panels.?  About the only thing I can think of to explain it? Seemed a case of 2+2 = 4.5

Today while wanting to add in some more power outlets to the house , I was studying the circuit breakers and saw that there were 2 circuits sharing the phase I am back feeding. I ran a lead from one of the inverters to the other circuit  and although on the same phase, resulted in a MUCH lower combined voltage. I measured the phase at a 3rd point and it was much lower as was the voltage the inverters were reading.  It was well past peak sun but the 2 arrays were producing the max output I can get before either inverter trips out which is about 2KW. I had over 4 Kw of panels on the 3 Kw inverter at one stage but as soon as it went over the 2kw output, the line voltage went high and it tripped out. I had to remove some panels to keep the output down so the thing wouldn't reset constantly even though it was under the inverter and the circuits rating by a long shot.

I'm hoping tomorrow that I will be able to run both arrays flat out all day.  If I can get around 3.5 Kw max, maybe 4, it will certainly make a big difference over the 1.8 Kw peak I have been seeing as an average out of either inverter. I still have some panels spare doing nothing so I may be able to splice them back in and run nearer the inverter max and get even more output.

What I can see would be useful is a device that would allow one to severely over clock the inverter and dump control output.
the controller would monitor the array output and being oversize would allow a lot closer to full output morning and afternoon. In the middle of the day when the array got to the inverters max, instead of the inverter just clipping and wasting the power, it fed it to the dump load. once the output dropped back town to full inverter level, it would send the power back to the main circuit.  Sounds like something else I have read about and probably could be adapted from some other controller.

Tomorrow is forecast to be mostly clear but I'll be happy to get a clear hour around midday so I can see if both arrays can sustain full power output without the line voltage going too high.  I have around 23V rise to play with and was well short of that this afternoon at normal max power so see how I go.

If I get the interfering tree " Pruned"  ( about 12 ft lower) this weekend I'll have the shed roof clear and I'll start on building my framework to hold the 5 Kw of panels I want to put up there next week.

Mucking around with this really has been a fun and profitable learning experience. Just hope I can remember most of what I have learned once I have it in place and aren't fiddling with it and watching what happens every day.