Unusual wiring arrangement for solar panels. - Page 1
Forum section: electronics / projects

author: tmd63
author_rank: Contributor
timestamp: April 02, 2021, 11:34:17 am
content: I have a solar inverter that has 2 inputs wired to it.Each input requires the same voltage from the solar panels just similar currents!Each solar panel gives the same Voltage and current for the same light hitting it!I have 15 solar panels on my roof!How can 15 panels be wired into 2 inputs to give the same voltage with similar currents? No serial or parallel combination works?

author: tunk
author_rank: Super Contributor
timestamp: April 02, 2021, 11:52:20 am
content: Don't know the answer, but it might help if you say which inverter and panels you have.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 02, 2021, 01:06:29 pm
content: That sounds like an odd requirement. Even if your panels produce the same output in full sun, it only takes a shadow at some time of day to reduce the output from a panel - and the string it's part of - to a tiny fraction of that.My inverter has two DC inputs, each of which can independently accept anything from zero up to the full rated output of the inverter. We have a series string of 10 panels on one input, and 6 on the other, and it's all working just fine.Are you completely sure you've understood the inverter's spec correctly?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 02, 2021, 01:25:58 pm
content: Use a multimeter to check if the two inputs are in fact connected in parallel. Most of the time, they're independent MPPT inputs and only one side will be tied together.

author: Renate
author_rank: Super Contributor
timestamp: April 02, 2021, 11:33:35 pm
content: I'm not familiar with these inverters that have two inputs.Do they use two switches and one inductor or are there two independent sections?I'm familiar with the smaller scale solar controllers for 12 V.I'm running two 300 W panels in series for ~70 V.My controller has a limit of 100 V?If you are running 10 panels in series, what kind of voltage is that and what's the limit?

author: bdunham7
author_rank: Super Contributor
timestamp: April 03, 2021, 12:12:26 am
content: Quote from: tmd63 on April 02, 2021, 11:34:17 amI've never heard of a dual-input inverter that had any such requirement. What model is it?

author: tautech
author_rank: Super Contributor
timestamp: April 03, 2021, 12:56:48 am
content: 2 input inverters are not uncommon and mainly used when one roof area is insufficient for the whole array.Need to have the model and install instructions to safely give further advice.

author: AndyC_772
author_rank: Super Contributor
timestamp: April 03, 2021, 07:42:39 am
content: Quote from: Renate on April 02, 2021, 11:33:35 pmIn my case, each panel is between 30-40V depending on illumination and load, so 300-400V. The inverter is rated to work from 80 to 800V, and to survive up to 1000V.

author: tmd63
author_rank: Contributor
timestamp: December 20, 2023, 10:29:16 pm
content: The inverter is a Samil Solar River It may be a 3300TL (550V Max V, 17.5A Max I, Convention Cooling)

author: tszaboo
author_rank: Super Contributor
timestamp: December 20, 2023, 10:54:22 pm
content: Your inverter has two MPPT string inputs. It doesn't have to be the same voltage and current. One will get 7 panels, the other 8, but even 6+9 will work. It's very useful if the panels are facing different way, you get more efficiency overall. Of course follow instructions, and have it installed by a professional.

author: Jwillis
author_rank: Super Contributor
timestamp: December 21, 2023, 01:22:33 am
content: Read the manuals.https://gold-coast-solar-power-solutions.com.au/wp-content/uploads/2016/07/Samil-SolarRiver-user-manual.pdfYours has1MPPT tracker and can accommodate 2 strings.Those 2 strings must be thesame voltagebut can have different currents. Look at 3.2 Electrical block diagram on page 9. The DC input strings are connected in parallel. Each string will only provide as much current as they are rated for. But the total current to the inverter will be the combination of both strings.Think of the panels as being like batteries. You can connect 2 different 12 volt batteries in parallel to increase current. You cannot connect a 12Vbattery and a 6V battery in parallel because bad things will happen.Another way of thinking is Current is "Drawn" or "Pulled" from a source. A circuit will only draw as much from a source as it requires or as much as the source can provide. Voltage is "Pumped" from a source.If 2 different voltages are put in parallel they will try to equalize the 2 different potentials. Usually in a very destructive manner.

author: EPAIII
author_rank: Super Contributor
timestamp: December 21, 2023, 09:04:15 am
content: This whole thing does not seem to make much sense. Is this a DIY or did someone install it for you? If DIY, can you go back to the people who sold the system? Or did you buy the parts from different sources?Seems to me you should be asking the supplier or suppliers or installer this question. And they should provide the answer(s) you need.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 21, 2023, 10:23:41 am
content: Quote from: Jwillis on December 21, 2023, 01:22:33 amYeah, so result is the same as paralleling strings - this is what the OP should Google for more information -, which is stupid and worse than having two separate strings, but probably still better than not having the extra panels on the roof at all. In any case, this is like buying a Ferrari and installing a 80km/h speed limit to it; waste of money for the panels, mounts, roof space, and installation work, for saving a few $ worth of parts in inverter.I would return the inverter and buy a real one instead. Price difference can't be that big.

author: bdunham7
author_rank: Super Contributor
timestamp: December 21, 2023, 03:40:51 pm
content: I'm not sure I see a serious problem here, just an inverter with what is really a single input and parallelconnections. That seems odd for such a small power capacity, but the obvious solution seems to be to run all 15 panels in series to one set of connections and just ignore the other set of connectors.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 21, 2023, 03:49:44 pm
content: Quote from: bdunham7 on December 21, 2023, 03:40:51 pmOtherwise yes, but this inverter has maximum DC input voltage limit of just 550V unable to handle 15 panels in series, so either paralleling the strings (through the "handy" connections), or getting a decent inverter for the job are the only choices.

author: rteodor
author_rank: Frequent Contributor
timestamp: December 21, 2023, 03:58:35 pm
content: Quote from: Siwastaja on December 21, 2023, 03:49:44 pmWell, maybe use only 14 panels (and keep one as a spare or sell it) or add one more if there is place for it?

author: Siwastaja
author_rank: Super Contributor
timestamp: December 21, 2023, 05:42:22 pm
content: Quote from: rteodor on December 21, 2023, 03:58:35 pmWell, it's obvious to use 14 or 16 panels if paralleling can't be avoided, to make things a little bit better, but it still doesn't solve the problem - paralleling still sucks. Series connection would be better, and two separate series strings with their own MPPT inputs even better.

author: bdunham7
author_rank: Super Contributor
timestamp: December 21, 2023, 06:24:00 pm
content: Quote from: Siwastaja on December 21, 2023, 03:49:44 pmHe didn't say what solar panels he has, but if they are 60-cell he should be OK. The specs say the MPPT goes all the way to 500V and 15 (60 cell) panels will just maybe touch 550V at the very highest at open circuit. Otherwise he will have to just parallel them and use blocking diodes.I think having one extra panel in one string really wouldn't cause an issue with the MPPT, especially if you knew that one or the other had some shading or directional issues. Of course, the MPPT is probably crappy too, but I don't see anything that would blow up.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 21, 2023, 07:05:27 pm
content: Quote from: bdunham7 on December 21, 2023, 06:24:00 pmThis is not how they are dimensioned. 550V is the maximum rating, and lacking separate absolute maximum, this is something you just don't exceed or you really risk blowing the inverter up, possibly causing a fire in the crappy inverter because solar strings are not (cannot be) fused. A random 60-cell panel pulled from Google search* says Voc=37.7V at Tpanel=25degC, with temp coeff of -0.32%/°C. Then you find the worst case cold record for the intended location, say 100-year lowest, and add a bit of margin, which for the UK could be maybe -30degC**, I don't know, and calculate Voc = 37.7V * (1+(-0.32%/degC * (-30 - 25))degC)) = 44.33V. Times 15 is 665V, over 20% beyond the maximum limit. The thing probably uses 600V rated semiconductors and will probably burst in flames the first time it gets a bit colder than usual during a winter night after which sun rises quickly behind the neighbor's rooftop while the panels are still cold. Maybe this happens a few years from installation.You either calculate it like this, or use a design software with gazillion built-in panel and inverter specifications + conditions based on locations, which is what professionals do to save time.*)https://static.trinasolar.com/sites/default/files/PS-M-0474%20A%20Datasheet_Duomax_PEG5.XX_US_Feb_2017_A.pdf**) Google search "UK record low temperature": "Scotland recorded -27.2°C, the UK's coldest ever temperature, in 1895, 1982 and 1995. The first two times were recorded in the same location, Braemar, Aberdeenshire, whilst in 1995 it was recorded in Altnaharra, Sutherland. In England, the coldest ever temperature recorded was -26.1°C"

author: tmd63
author_rank: Contributor
timestamp: April 24, 2024, 05:51:33 pm
content: It was installed for me as a free install.The inverter wasn't work a while ago and I had to get the installer out to put a new inverter in, but I am concerned about the wiring arrangement. I would have preferred a localised inverter on each panel, but it was a free instal, they just rent the airspace free of charge for 25 years.