Hello. I am hoping that somebody can help me with this conundrum. Our recently installed 4kW PV system comprises six panels positioned on a section of the roof facing south and a further four panels on an adjacent section facing south south east. Our irradiation level is 962, roof pitch 45 degrees and there is no shading. The panels are JA 395W and the inverter is a Solis 3.6. Another system installed approximately 800 metres away from our home, by the same supplier only days after ours, also benefits from similar irradiation levels, has approximately southerly orientation and no shading. In this instance the roof pitch is 35 degrees and two inverters (not Solis 3.6) were used to accommodate the 6.5kW rating of the installed 16 x 405W panels. Clearly, this second larger system is producing a greater daily output than ours and we would expect this to be in direct proportion to the rating of the two systems ie approximately 50-60% more than our system. However, when we account for system size differences, our system consistently produces a daily average of 40-50% less energy than expected. For example, yesterday (which was a sunny day for December) our system produced 5kWh and the second system 14kWh. We have contacted our installer who assures us that our output is acceptable and will monitor our system for 90 days. Please could somebody suggest why our system performance is so dramatically inferior to the second system? Are there any checks we can make, given that we are not qualified electricians? Many thanks.
Relative Low Performance of Domestic PV System
- Thread starter Jena
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Sorry not going to be much help re comparison with your neighbours system but if I was just looking at the figures for yours they look ok to me, I have a south facing 2.4kW system and I generated 2.1kWh of electric yesterday. The winter months my expectations of the systems are low and I have had mine for 12 years.
bladerunnerpv
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Bit of a guess, but I wonder if the behaviour may be connected to the startup voltages of the inverters in the two systems being quite different, or even if they're similar having with less panels at low winter irradiance the smaller system may be struggling make the startup voltage. You might be able to compare the operating times of the two systems, the smaller one might be starting to generate later in the day even if the aspects are very similar?
Thank you for your reply, that’s helpful. Based on my limited data I’m going to have bash at estimating annual production taking into account daylight hours and average monthly irradiation values. May be a waste of time, but might give me an idea whether the system will deliver what was stated in the spec.
As a matter interest, how many kWh do you generate from your system in July?
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With my 2.4 kW system I generated 1.74MWh total for last year, so far this year I have generated 1.72MWh with just less than 3 weeks to go in the year it will end up as almost exactly the same.
During the summer I do get shading from a tree at about 5pm, so right at the end of the day my generated power drops of suddenly rather than gradually reducing.
Last July I generated 247.6 kWH.
Been pleased with the whole solar thing.
During the summer I do get shading from a tree at about 5pm, so right at the end of the day my generated power drops of suddenly rather than gradually reducing.
Last July I generated 247.6 kWH.
Been pleased with the whole solar thing.
Your string voltages should be fine, quick Google says 30v per panel and the Solis is 90v start up. However, the orientation SSE means that string will shut down earlier, and only being 4 panels is going to struggle to get going and keep going in lower light levels. Your panels are also slightly less efficient. So I suspect there is nothing wrong bar the fact that with recent gloomy weather your system struggles more to get going.
Something you could check on the inverter display is the string voltages
Something you could check on the inverter display is the string voltages
The other installation may be close to you but it may simply get “better” sun for longer,
we live in a bit of a dip so our production hours are less than homes up the road
we live in a bit of a dip so our production hours are less than homes up the road
Just a thought as I had faced this issue.
When you only have a limited number of panels facing the same orientation and installed on a string inverter, sometimes the issue is due that that small number of panels don t generate enough to kick off the inverter. There is a calculation that help defining the minimum number of panels.
You can also check on some website how much the pitch of the roof makes for a difference. but in winter the more pitch the better though.
Otherwise, I am in Cheshire, I have 4kWp (16x250W) from 2016 all facing South East. No shade. below the month production
Thank you Bladerunnerpv, that’s interesting. We are good friends with the owners of the larger installation, so comparing start-up times is achievable.
Thank you Binky. There is a bit of a theme developing here regarding start-up. Responses from this forum are helping to make sense of our observation regarding comparative outputs from that of our system and the nearby larger system. I’ll check the string voltages as you suggest. Thanks again.
Thanks Bob. Interesting to compare your output for the month so far. It is higher than ours, but if I recall correctly, we did have two or three days of misty weather at the beginning of the month. As you suggest, the gloomy south-west weather could be delaying start-up.
Once you have done a bit more research you may be able to confirm that the issue is this. The minimum requirements for your inverter to start converting DC into AC.
Once it is confirmed the question is what can you do about it?
Here are my thoughts only:
1) How often does this is occurring? It could be that in the worst-case scenario you are only a few % below the limit and therefore most of the year you'll be fine. ie compare to a more optimal system you'll lose only a few % of generation.
Therefore, I would suggest there is nothing to do as what could be done to make improvements would not be cost-effective.
2) If indeed you do lose in generation and that level of loss is not acceptable for you. Do not think that optimizer like Tigo will help because you do not have a shading issue on some panel so with or without optimizer your inverter will still get not enough voltage to kick off
I can only think of micro-inverter. This makes each panel fully independent of each other. This will require a significant design change of your installation and will surely not be cost effective.
Short answer is 'size matters' with solar arrays. You get other affects on performance, like being in a valley can mean you get colder misty air hanging around, more frost cover etc. I never really liked installing solar in winter, despite everything working as it should customers would quite often be disappointed with performance. They kind of expect 4kw from the array even when the weather is poor. I was quite surprised this morning to see my own array, which is south facing but completely shaded this time of year was still outputting 270W with a heavy covering of frost. I would keep an eye on things going into spring/ end of February. The longer days will probably make a big difference.
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270W !! lucky you. Mine is 0 and will be 0 for a while today. We have 15mm of snow
bladerunnerpv
Well-known member
The spec for your inverter says it has has 2 pair of PV inputs and you have two sets of panels. What your installer should not have done is connect all panels as a single string to just one of the PV inputs. Can you please find out from your installer whether 6 panels are stringed to one PV input and the other four are stringed to the other PV input? Alternatively, you can look at the DC Volts and Amps output from each PV input by clicking the enter button twice then down arrow to look at values. You can lock the readings by clicking enter again; a padlock icon then appears.
This reminds me I did have a problem when I got my system in 2016. I bought my system with a friend living about 500 yards. We place the ordered together to get a discount. We got the exact same equipment, The only difference my 16 panels are SE while his are 8 E and 8 West- His roof has a slightly higher pitch than mine. Our systems were commissioned mid of jan 2016.
It was expected that he would generate earlier and later in the day and in winter, because of the pitch, also more. This is what happened.
However, came April and his system could peak at about 3kW while mine did not exceed 2kW. I started to really wonder.
I contacted the installer and they found out only one string was producing. They came and found out one string had not been connected correctly!!
I would have found out eventually but not knowing when would my panels generate the most power, it would have taken longer.
Comparing is good
So maybe as Joules says, maybe another cause is that some panels or string are connected correctly.
It was expected that he would generate earlier and later in the day and in winter, because of the pitch, also more. This is what happened.
However, came April and his system could peak at about 3kW while mine did not exceed 2kW. I started to really wonder.
I contacted the installer and they found out only one string was producing. They came and found out one string had not been connected correctly!!
I would have found out eventually but not knowing when would my panels generate the most power, it would have taken longer.
Comparing is good
So maybe as Joules says, maybe another cause is that some panels or string are connected correctly.
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Thank you for your really useful comments Joules. I interrogated the inverter as you suggested and have attached images of the first two items on the scrolling information list. The first shows a voltage of 167.0V and 0.2A. The second line on the list displayed a voltage of 1.6V and 0.1A. Lines three and four were in a similar format, but both showed voltages of 0.0V and a amperages of 0.1A. There are only two cables entering and then exiting the isolation box located before the inverter (please see image). Forgive my ignorance, but could one cable be from one string and the other from the string located on the adjacent roof? Alternatively, could one cable be from a single string made up of all 10 panels, whilst the second cable just completes the circuit back to the panels? As I wrote earlier, I am no electrician.
Probably not the best day to be looking at the system performance figures given that it is exceptionally gloomy today, with current power output only being a miserly 20W and I guess readings being subject to inaccuracies from baseline noise, perhaps. I’m not sure whether this helps you to comment further on our system, but any additional thoughts would be appreciated. I do possess a clamp voltmeter and wondered whether trying to measure DC current and voltage in the cables entering the inverter might be useful. Yesterday was also overcast and we managed only 0.4 kWh and our nearby friends produced 1.6 kWh. Many thanks.
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Jena,
You should have one DC switch per string. The DC Switch is the black one we see on your photo.
I assume you have a online logging to see what your panels/inverter are doing.
Mine looks like this
This is the two string (PV1 and PV2), right now as you can see they are producing nothing.
From my auntie it looks like this
you can see that the two strings have not performed the same. Her panels are similar to yours. Some facing west (one one string) and the rest facing Est (on the other string)
Check on your online account and see if you can see something similar.
You should have one DC switch per string. The DC Switch is the black one we see on your photo.
I assume you have a online logging to see what your panels/inverter are doing.
Mine looks like this
This is the two string (PV1 and PV2), right now as you can see they are producing nothing.
From my auntie it looks like this
you can see that the two strings have not performed the same. Her panels are similar to yours. Some facing west (one one string) and the rest facing Est (on the other string)
Check on your online account and see if you can see something similar.
