Matching Panels and Inverter - Page 1
Forum section: electronics / general

author: fastbike
author_rank: Regular Contributor
timestamp: August 20, 2024, 12:53:31 am
content: The final part of the design is starting to firm up having found a local supply of 440W panels at a good price and a suitable 3 phase hybrid inverter.The layout on my roof requires two strings: 13 in one and 10 in the other. This is due to a variable pitch/heading.The initial design used Longi panels, the final design will use Trina.I'm figuring out if the Trina panels are going to work, here's the relevant specs.TrinaLongiPanel Voc52.2v39.8v13 string Voc678.6v517.4v10 string Voc522v398vPanel Vmp44.033.613 string Vmp572436.810 string Vmp440336And here's the inverter specs:Max. PV Input Voltage (V) 800Start-up Voltage (V) 160MPPT Voltage Range (V) 200-650Rated PV Input Voltage (V) 550Is the 13 string max output voltage (572v) too high for the inverter rated voltage of 550V. What about the MPPT range, how does this compare ?

author: fastbike
author_rank: Regular Contributor
timestamp: August 20, 2024, 06:46:34 am
content: To answer my own questions I've just watchedWill Prowse explain the basics.He says the open circuit voltage (Voc) for the string has to be less than the max MPPT voltage for the inverter, or bang !So my 13 panel string has a Vocof 678V which exceeds the inverter's VMPPT_maxof 650V by 29 volts.Maybe time to remove a panel or see if another physical configuration of the panels on the roof works !

author: Siwastaja
author_rank: Super Contributor
timestamp: August 20, 2024, 08:11:02 am
content: You need to temperature compensate the Voc:Find the record low temperature of your region (so usually something between -20 to -50 degC based on where you live)Find the Voc temperature coeff from the panel datasheetCalculate Voc at that low temperature. It is usually significantly more than Voc at +25degC, maybe by 20%.Even though exceeding the max MPPT voltageshouldnot be a safety problem, you are likely to find that you are nearly exceeding even that 800V max rating with 13 panels. So use fewer panels (or lower voltage panels). Or get an inverter which can handle this. 1000V max is not uncommon, and you can still get 200V minimum MPPT voltage, so more range.Range (relative difference between maximum and minimum MPPT voltage) is important if you have potential partial shading, which causes some panels to run through their bypass diodes. If temporarily losing production from 1-2 panels causes the whole string to drop significantly below minimum MPPT voltage, then you lose the production from the whole string (basically making the usually false claims of microinverter/optimizer sales folks true in this corner case).

author: fastbike
author_rank: Regular Contributor
timestamp: August 20, 2024, 08:39:33 am
content: Quote from: Siwastaja on August 20, 2024, 08:11:02 amWe're in a coastal zone so record low is -5 Celcius. This typically occurs in July just around dawn when the sun does not come onto the panels until another hour. At this time they will be running above zero. However even 25 degrees difference at -0.230%/℃ makes the Voc55v, so definitely something to factor in.I'll consider the shading factor although I'm lucky that it is a large section with no other buildings close by, and trees can be managed.

author: fastbike
author_rank: Regular Contributor
timestamp: August 29, 2024, 06:51:55 pm
content: Of interest, local standards applicable in New Zealand (and Australia) limit the DC voltage to 600 in residential installations (but see below), so that is a hard limit that needs to be complied with in order to get certification so we can connect to the grid.I'm sure it would also have insurance implications if exceeded and something went awrySo at Vocof 55v that implies a maximum of 11 panels per string which is a shame as my roof has a slightly irregular shape and I can physically and aesthetically fit 13 on the lower part and 10 on the upper. The lower part is angled at 26 degrees tilt, the upper at around 13 degrees so without individual optimisers they should be on separate MPPT inputs.Time to look at panels with a lower Voc.P.S.Voltage limits in residential installations are covered by two conflicting standards.AS/NZS 5033:2021 sets out general installation and safety requirements for electrical installations of PV arrays, including d.c. array wiring. The revision in 2021 increased the maximum PV array voltage from 600 V.d.c. to 1000 V.d.c. for domestic systems (clause 3.1)However there is another standard, AS/NZS 4777.1:2016, which specifies the lower voltage of 600 V dc for "domestic dwellings" (clause 2.3). This is deemed to override the other standard, so the limit as it stands is 600V.

author: fastbike
author_rank: Regular Contributor
timestamp: September 01, 2024, 11:40:49 pm
content: Quote from: fastbike on August 29, 2024, 06:51:55 pmFunny how things progress, because the standards applicable to getting my system certified so it can be connected to the grid ( AS/NZS4777.1) has just been revised to AS/NZS4777.1:2024And the good news is that the voltage limit has been raised to 1000 V dc, so the planning is now limited by the specification of the chosen inverter, rather than by confusion within the standards setting bodyOnwards and upwards.

author: nctnico
author_rank: Super Contributor
timestamp: September 02, 2024, 08:44:31 am
content: Still you need to ask yourself whether you want your system to run at 1000V. The higher the voltage, the quicker insulation is deteriorating and thus more chance of electrical problems long term. And it is also not ideal situation for solar panels as well as high voltages do have an effect. I would aim for an operating (= solar panels loaded) voltage of 500V to allow for some margin.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 02, 2024, 10:23:39 am
content: Yeah, if you have a choice, don't go close to maximum voltages, effects like PID degradation are real.But 600V limit by legislation is stupid because nearly every inverter supports more and it's awkward if you have to change your plans because your system voltage would be 600.000001V due to that one extra panel which looks good.In any case, that 1000V limit (if absolute maximum of the inverter, not just MPPT max) must be temperature compensated so is closer to 800Voc in reality.If you have a suitable location where certain number of panels looks aesthetically good, then go for a tad over 600V seeing they have fixed the legislation. Splitting in two strings has a new type of risk of the strings going too low in minimum voltage and in some conditions produce poorly.Anyway, when reading standards be careful if they talk about nominal/average/typical operating voltages, or actual voltage at any point in time (so worst case). There's a big difference here, 500V typical operating is approx. 1000V worst case open circuit or so.

author: fastbike
author_rank: Regular Contributor
timestamp: September 07, 2024, 08:40:41 pm
content: Quote from: nctnico on September 02, 2024, 08:44:31 amThanks for the feedback from some real world experience. I have two firms coming out this week to provide installation quotes - I wanted to be an informed consumer so can ask intelligent questions and see what is realistic.The two preferred layouts I have sketched for our roof can fit either 26 or 27 panels (1762x1134mm 440W, temperature adjusted Vocof 55V and Vmp of 44V). The Fronius Gen24 has a MPPT range to 850V.The first layout which is aesthetically the best would be split into two strings of 13, so would be a max of 715Voc on each input, with an input of 572Vmp when producing the max output.The other layout would be split into a string of 7 panels (385V) and two parallel strings of 10 panels (550Voc, 440Vmp). However due to the nature of the roof it will not appear as integrated.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 08, 2024, 06:30:41 am
content: Don't do parallel strings, if you want three strings then get inverter with three MPPT inputs. With 7-panel string carefully check if minimum MPPT voltage gets satisfied in all conditions. I would probably go for the two 13 panel strings.

author: nctnico
author_rank: Super Contributor
timestamp: September 08, 2024, 09:55:00 am
content: About the 3 input inverters: I looked around but I have not been able to find models with 3 MPPTs. Only 2 MPPTs where one is connected to two string (in parallel I guess) to make for 3 inputs. So if you need to have 3, seperate strings, you'll probably end up with 2 inverters.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 08, 2024, 10:06:24 am
content: E.g. Solis S6 hybrid series has 3 MPPT inputs for the 5kW model and 4 MPPT inputs for the bigger ones. So more than two is getting more common but indeed having exactly two is still the "industry standard" of today (single input inverters have nearly disappeared).

author: fastbike
author_rank: Regular Contributor
timestamp: September 23, 2024, 06:46:56 am
content: Quote from: Siwastaja on September 08, 2024, 10:06:24 amI had an installer here on Friday for my third quote. This time it was the two guys who will do the work (the others have been sales people). The recommended Solis.I've been reading up on the S6-EH3P(3-10)K-H-EU models but can't see them on the approved inverter list - must be new and the paperwork is behind.

author: fastbike
author_rank: Regular Contributor
timestamp: October 13, 2024, 03:23:35 am
content: Quote from: fastbike on September 23, 2024, 06:46:56 amI've put the application into the network operator using the localised version of the 10kW inverter (S6-EH3P10K-H-AU) and it has been approved. I had to supply the testing certificate to show compliance with AS/NZS4777.2 (Grid connection of energy systems via inverters, Part 2: Inverter requirements).Quote from: fastbikeRegarding the maximum allowed d.c. voltage, apparently in Australia it is now 1,000V as revised 4777.1 has taken effect. But here in New Zealand the standard needs to be "cited" in the relevant regulations passed by the government, which have not been updated since 2010 ! So back to a maximum temperature adjusted limited for Voc of 600V.Luckily the panels we're now looking to use (TW) are rated around 40V IIRC, and the inverter has 4 separate MPPT inputs so there is a lot more flexibility. It is likely we will end up with 2 strings of 5, 1 string of 7, and 1 string of 10 due to roof layout.

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2024, 09:56:37 am
content: Given your curved roof shape (as you showed in a different thread), it would make sense to connect panels at the same angle into 1 string in order to maximise output.

author: fastbike
author_rank: Regular Contributor
timestamp: October 13, 2024, 05:46:31 pm
content: Quote from: nctnico on October 13, 2024, 09:56:37 amWe're going with three rows (I started installing rails at the weekend), see the diagram.The tilts (from the bottom row) are 26,17,12 degrees. There is some potential shading late in the afternoon, in the middle of winter at the bottom right.So a 4 MPPT inverter is quite attractive as I will have the top seven on one string, the next middle ten on another, and the then two strings of five each from the left and right of the bottom row. This row will provide the most power in the winter so gets VIP treatment to avoid shading issues.

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2024, 05:48:48 pm
content: Sounds like a planHave fun on the roof. Take some time to enjoy the view as well

author: fastbike
author_rank: Regular Contributor
timestamp: October 16, 2024, 02:58:02 am
content: Quote from: nctnico on October 13, 2024, 05:48:48 pmIt was 23 years ago that my Dad and I installed the roof when I built the house - I'd forgotten the views !I've been doing it after work, starting around 4pm and working through to 7pm. So far I have installed all the pucks/feet for the rails for the bottom two rows and will install those rails after work today. I'm awaiting more pucks (the piece that sits on the top of the corrugation to spread to the load and has an EDPM membrane to seal the screw hole. They should be here on Friday.I have one final installer coming out to quote on Friday, he is very relaxed about letting a home owner provide "sweat equity" to help keep costs affordable.

author: fastbike
author_rank: Regular Contributor
timestamp: October 18, 2024, 04:23:27 am
content: Quote from: fastbike on October 16, 2024, 02:58:02 amGosh, I started this thread 2 months ago, and am finally installing stuff !The installer came today, he's pretty relaxed about allowing me to do work up until we do the actual wiring of the panels into the inverter, so very happy for me to finish the rails, run the earthing, install the actual panels ... we've agreed the layout will be one string for the 7 landscape panels at the top, and the ten panels to the left of the skylight (two rows in portrait) are the second string, with the panels to the right being the third string. This makes wiring a whole lot easier.I've used theexcellent Niwa SolarView toolto check how this impacts the output, as the ten lower panels will be throttled at the output of the ten above them - it looks like I'll lose about 400wH per day, assuming I was exporting all of this, that around $25 per year.I've just ordered apallet of 36 TW panelsas it is much cheaper to buy them wholesale, they should be here later next week so it looks like a weekend job for next week to get them on the roof.The installer will supply the inverter and all switchgear/sub panels etc.Now, back to work, levelling the top horizontal rail and then tomorrow I'll install the 14 short vertical rails for the top row.Edit: added link to panels

author: fastbike
author_rank: Regular Contributor
timestamp: October 20, 2024, 08:14:59 pm
content: Just had an email from the installer (who was to supply the inverter), the one we selected is not available in NZ at the momentRequirements were:- 3 phase- unbalanced loads to 50% of rating- handle 12kW of panels => inverter sized at 10kW- HV DC battery capable- 3 independent MPPTSo I'm looking for any recommendations for an alternative to Solis S6-EH3P10K-H ?

author: fastbike
author_rank: Regular Contributor
timestamp: October 24, 2024, 01:21:47 am
content: Quote from: fastbike on October 20, 2024, 08:14:59 pmFound another local wholesaler who can supply mid November. By the time I get the panels on the roof and the electrician to finish the wiring, it will be about a one week delay.

author: fastbike
author_rank: Regular Contributor
timestamp: October 24, 2024, 01:23:05 am
content: Look what arrived today ....

author: fastbike
author_rank: Regular Contributor
timestamp: October 24, 2024, 01:35:28 am
content: Now I'm looking for a home for the remaining 9 panels. I have room for 2 rows of 7 on my stand alone garage (I can buy an additional 5 for about the same per panel cost), so this would add approx 6kW of peak capacity.This roof is not optimal but gets useful afternoon sun. In winter the insolation is about 1kWh/m^2 per day (main roof is approx 1.7), and in summer it is roughly the same as the main roof (6kWh/m^2 per day). It is also subject to seasonal and time of day shading, which is not evenly across the roof.So I'm thinking of going the optimiser or micro inverter route for this part of the install.What are the gotchas I should be aware of. Installer has said we should be connecting to all 3 phases to avoid phase imbalance. I can see that Enphase do a 3 phase combiner cable. Or would I just use optimisers and a cheap 5kW 3phase inverter ?

author: nctnico
author_rank: Super Contributor
timestamp: October 24, 2024, 10:46:21 am
content: The extra panels are a good excuse to build an extra shed in your garden to put them on.

author: fastbike
author_rank: Regular Contributor
timestamp: October 24, 2024, 08:36:54 pm
content: Quote from: nctnico on October 24, 2024, 10:46:21 amThe garage is bigger than the garden shedFor the garage, in theory I could fit 2 rows of 7 in portrait, with another row of 5 in landscape (total 19 panels) but the mounts for the additional 5 would be more effort than justified.By putting 14 on the garage I will have 41 panels in total, tied into my electrical installation: that is 18kW. The local network operator has a limit of 15kW feedin without going to a different contract aimed at commercial installations.

author: fastbike
author_rank: Regular Contributor
timestamp: October 24, 2024, 08:44:45 pm
content: My next issue relates to physical installation of the panels which are 1134 wide. My nephew is going help me on Sunday, he wants $$$ and I want a strong helperI placed one of the panels on the floor inside my house and have tried to lean across to see what access is like for tightening the clamp on the far side. There is no access from the far side (6m above ground) so only access is across the panel (see diagram). I am thinking I will make a small kneeler board that transfers the weight to the frame without putting pressure in the glass (a small wooden "fin" to locate it).The numbers indicate the sequence of placing clamps assuming panel installation moves from left to right, bottom up: for the first panel clamp 1 is accessed from below, clamp 2 from above. 3&4 are unencumbered. For the second panel clamp 5 requires a long reach (the subject of this post), clamp 6 is accessed from above. As the installation moves across, the clamps 3&4 can be accessed for tightening when the third panel is placed, from below and above respectively. However clamp 7 will be hard to reach when the fourth panel is placed.How do installers normally do this (and I'm not walking on the panel !)

author: nctnico
author_rank: Super Contributor
timestamp: October 24, 2024, 09:34:29 pm
content: I reached across the panels when I did my install. However, I had to to use a ladder to tighten the last two bottom clamps because I couldn't access them from the roof.

author: fastbike
author_rank: Regular Contributor
timestamp: October 25, 2024, 07:58:22 pm
content: Quote from: nctnico on October 24, 2024, 09:34:29 pmThanks, are you quite tall ? I've placed a PV panel on the floor and am having trouble reaching across without putting my knee on the frame. I think I will make a small wooden pad that has a "fin" to keep it centred between panels and two fillets to ensure the only point of contact is the frame.Ladders cannot be used due to the height (roof is 6.5m above ground). I have scaffold at the front, and the rear has a working platform about 1.5m below so access from front and back is fine.On another note, I washed the (metal) roof yesterday with a roof cleaner product (probably just expensive detergent LoL) and a soft broom, then hosed it down. This is the first time I've done that since it was installed 23 years ago. It is amazing the dirt and debris that was removed, as the only other maintenance I had done was to spray for lichen about 2 years ago with a product containing Benzalkonium chloride. Once the panels are up access will be more difficult, and the areas underneath will no longer be washed by rain, so time for the bird poo to be gone.It's raining here today but the forecast is for fine weather tomorrow with light winds (<20km/hr) so should be a good productive day for panel installation.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 26, 2024, 07:34:32 am
content: You can put your knee on the frame or even on the glass. Just avoid placing all your weight on a small spot. Many installers do that all the time but there is risk of hidden damage. Leaning over the panel carefully is fine.You can find the load ratings on the datasheet and calculate how much weight is allowed given a certain surface area.

author: nctnico
author_rank: Super Contributor
timestamp: October 26, 2024, 01:00:17 pm
content: I'm quite tall indeed. But I used a socket wrench to tighten the clamps so I didn't need to reach all the way. Just enough to rotate the socket wrench a bit. Being a complete novice where it comes to laying solar panels (*), I didn't want to take any chances with the panels and took my time. I did read some manuals where it was strongly advised not to put any weight on the panels so I followed that advice. There probably is a grey area the professional installers know about intimately but I don't* And already strongly regretting doing the solar panel project so much that I don't want to go onto the roof again to mess with the solar panels.

author: fastbike
author_rank: Regular Contributor
timestamp: October 27, 2024, 06:22:48 pm
content: Quote from: Siwastaja on October 26, 2024, 07:34:32 amWasn't going to risk it (panel is rated at 5400Pa, I'm 100kg/1kN, spread that over 10cmx10cm, and you're at a loading way over what the panels can withstand) , so I made a small "kneeler", just a piece of 4x2 timber a bit longer than the width of the panel with two equal angle 20x20x3 alloy pieces screwed to it at each end and some tape to stop it scratching/slipping. I could place it across the panel to reach the tricky clamp and get it torqued down.Where there's a will there's a way

author: fastbike
author_rank: Regular Contributor
timestamp: October 27, 2024, 06:44:02 pm
content: Quote from: nctnico on October 26, 2024, 01:00:17 pmWe got all 27 panels installed, mainly following the plan I'd drawn up for the sequence to avoid issues trying to get access. I had a 22 nephew help me and he got the hang of attaching cable clips and routing the 1200mm long leads. For the row in portrait mode at the bottom we ran the leads down to the bottom so they could be connected after all panels were installed. For the upper portrait row the leads ran up the panel so could be connected at the top after placement. The panels at the outside of each 5x2 "block" had one lead up and one down so they could connect to the other row. The terminations to the home run cables for each block are at the inside edge (adjacent to roof window), with all leads running up.I left a small (~25cm) access gap between the middle and top row which is 7 panels running in landscape mode so we alternated the panels here (+ve up, then +ve down) so the connections either ran along the bottom or the top, keeping the +ve lead always pointing left so this took a bit more figuring out.The installer said to attach clips before we got on the roof so we did this on the scaffold where we could eyeball the location.I'd preinstalled conduit with draw wires so this is now ready for the installer to come and do his magic sometime this week ready for the inverter which is two weeks away.This is what it looks like on the house ...And of course because I ordered a pallet of 36 and only used 27 on the house, I now have a "problem" of 9 spare panels. I've checked in with my wife and will order another 5 panels so I can fit 14 to the garage. This gets some shade which moves across the panels depending on time and season which would wreck the output of a string inverter so will look at optimisers or micro inverters for this.Quote from: nctnico on October 26, 2024, 01:00:17 pmSorry to hear that, I've quite enjoyed it so far. A bit frustrated at times but a good opportunity to learn something new, and a challenge to get my fitness/upper body strength up a bit. It's 23 years since I was up on the roof when we built (I put the roof on with my Dad and father -in-law). Also I'm luck that the steepest part of the roof is less than 30 degrees and because it is curved it is only about 10 at the top so relatively easy to work on.My nephew asked why we did not install solar PV when we built the house LoL. I had to explain that this system would have cost approx $100k back then so would never have been economic as power prices were 50% of current, so would have taken about 60 years for cash break even ignoring ROI. For comparison the full cost (excl garage) will be approx $15k, which I've modelled has a 5 year cash payback period, slightly longer if time value of money is included.

author: nctnico
author_rank: Super Contributor
timestamp: October 27, 2024, 06:51:41 pm
content: The scaffolding is nice. Makes access easier! I have two big windows on the roof (35 degree slope) and I used those for roof access as I found using my ladder would be a bit iffy.

author: fastbike
author_rank: Regular Contributor
timestamp: October 27, 2024, 09:04:47 pm
content: Quote from: nctnico on October 27, 2024, 06:51:41 pmIt would be very hard without the scaffold. I erected it myself using 3 "H" frames and then tube/clip style stuff. We have rules here that anything with a working platform over 5m has to be installed by certified installers, I am under that limit so could do the work myself which saves a heap as the weekly hire is very cheap - the delivery/install/remove is the expensive part.Yes, ladders are not good for carrying stuff up, you probably can't see but the ladder for the scaffold is attached at the top and then tied in at the bottom to make it super stable.As an aside, I was up on the roof and a neighbour called out to talk. Her husband had been up on their (steel) roof the previous week, water blasting the lichen off - which by the way does not fix the problem as the roots will still be there and it regrows. I asked if he had a harness, the answer was no. So I asked if he had life insurance, and the answer was still no. Crikey, sounds like a widow making activity