Solar panel design and installation

[Isetech]

Time to design and install my solar system for the workshop.

what is the goal, load solution or save money, this is the most important question, especially if there is a budget

My goal is to save money, I want to produce enough electricity during the day to keep my office and workshop functional.

Before I do anything, I need to look and the roof space available, now that I have the panel template on the roof, I can see that there is not that much space, and it is not high enough to stack 2 rows, that huge problem. I was hoping top get about 20kwp on the roof , instead it is more like 8kwp and even that is pushing it, because the roof is made up of different levels and directions.

I have a north east facing roof which will only see sun after lunch due to massive trees ( no they are not getting cut down) .

The other north east facing roof can only fit 2 panels ( not worth fitting).

I have an east facing roof which will get the majority of panels, its flat and one level.

Then the west facing roof will get 6 panels with a push, multi level, so it is a bit of a challenge and shading will be a challenge if the panels are not centralized.

I have a south west facing roof , the other side of the main building, no trees and the most roof space. I could fit 32 panels, but that will be a last resort.

[Andrew_van_Zyl]

Time to design and install my solar system for the workshop.

what is the goal, load solution or save money, this is the most important question, especially if there is a budget

My goal is to save money, I want to produce enough electricity during the day to keep my office and workshop functional.

Before I do anything, I need to look and the roof space available, now that I have the panel template on the roof, I can see that there is not that much space, and it is not high enough to stack 2 rows, that huge problem. I was hoping top get about 20kwp on the roof , instead it is more like 8kwp and even that is pushing it, because the roof is made up of different levels and directions.

I have a north east facing roof which will only see sun after lunch due to massive trees ( no they are not getting cut down) .

The other north east facing roof can only fit 2 panels ( not worth fitting).

I have an east facing roof which will get the majority of panels, its flat and one level.

Then the west facing roof will get 6 panels with a push, multi level, so it is a bit of a challenge and shading will be a challenge if the panels are not centralized.

I have a south west facing roof , the other side of the main building, no trees and the most roof space. I could fit 32 panels, but that will be a last resort.

Hi. I suggest using http://OpenSolar.com to plan it out. It's free and very accurate

Sent from my SM-A226B using Tapatalk

[Isetech]

What inverter will I need ? An 8 KW should do the job and by looking at all the current projects that we have completed, it is the best bang for your buck, a 3.5 kw is just too small and considering the price is only a few grand less than a 5 kw, its not worth the hassle, a 5 kva is a nice entry level load shedding solution, but not suitable for slightly larger loads. I did consider going bigger to get the higher solar rating, but with my roof space challenge, the 8 KW will be the best value for money.

The next question is which brand, well we all know which brand I use, I think I am on no 15 now after this weekend, not 50 yet, but hey if you look at my projects they would all pass the warranty inspection, the test report and COC, safe guidelines for lithium battery installations and most import, only one recorded fault, due to customer error, which he was warned about prior to the installation, which we have since modified to the way I suggested we split the essential and non essential.

Time to look at the spec sheet,

Max DC input power - 10400 watts
PV input voltage - 370 (125-500)
MPPT range - 150 - 425
Start up voltage - 125 (this is important if you only have a few panels or going to split into 4 strings)
PV input current - 26ADC +26 ADC
Max PV Isc - 44ADC+44ADC
No. of trackers -2
No. of strings 2+2 ( this important and we will go into details)

[Isetech]

By the way, I have been told that I should stick to DIY groups because I ask stupid questions and dont have the skills, knowledge or experience to be installing solar systems. So how does that saying go "dont try this at home' Rather consult with a 50 plus installer

The way I see it, we all have to start somewhere, so if you feel any information shared in this thread is incorrect, please feel free to correct the information.

[Andrew_van_Zyl]

The 8kW Sunsynk is an awesome machine if thats where you're going

[Isetech]

Yip the budget is tight, so it would have been cheaper to go the luxpower, growatt, axpert or one of those units, but I want a long term solution with a company that is growing as fast as the solar industry, always looking at improving the technology.

I did consider solar edge, Sungrow or Victron, but to start trying to find someone to educate me on the product or go sit in classes during week, just doesn't make sense.

The Victron has too many bits and pieces, the Solar edge is limited with variety and Sungrow, I have only heard of them never actually seen any installation. A tip for people wanting to get into the SA market, I would suggest you offer lots of free training and not on Monday and Tuesday, when we are busy at work. I would be happy to go sit in a classroom for the weekend to learn about a different product. or better still, with technology today, who needs to sit in a classroom?

The system which will eventually win the race to the top, will be the system with a lithium battery that is safe to install anywhere on the property.

The 8kW Sunsynk is an awesome machine if thats where you're going

[Justloadit]

One thing that the suppliers of PV Combiner boxes, is that to make it cheaper, they leave out the isolating diode.
Effectively if you have each string with an isolating diode, then you can have the same number of panels in each string, and then parallel this into the combiner box and have a single connection to the inverter.

What is important here is that you could have a number of panels facing east, north, west, and which ever string has the most sun radiance, will power the inverter, the other panels will contribute less but are still active. The inverter will see the total power from all the strings and do the MPPT. As the sun changes during the day, so each bank will effectively come into supplying power to the inverter. The diodes ensure that this occurs. Not using the diodes, will cause issues as the panels are of different temperatures and therefor have different internal impedance's, and may affect the total operation of all the panels, and of the MPPT controller.

BUT - using the diodes does have an issue, and that is the reason no one wants to have this in their equipment. The diodes must be able to carry the current of the string, and have the blocking capacity of the total string voltage.
This means that the diodes have to be on a suitable heat sink.

Lets take for instance we use silicon rectifying diodes, and they are rated at say 20A and 1000V, no problem, however, the diode has a 1.7V drop across the junction, so if we take 10A as a value to do comparisons with, then for silicon diode V X I = 1.7V x 10A = 17Watts, this is per string, so it requires a decent heat sink, and you do not want fans as there is a number of issues for that.

Lets take for instance we use a Schotky rectifying diode, they may be rated at 600V at 12A, and has a 1.2V drop across the junction, so using the same formulae, V X I = 1.2V x 10A - 12Watts. A substantial difference since power is a non liner function and falls under the square type of curve. The cost of Schotky is no cheap device, but in no way beaks the bank. But under the right conditions, it makes sense in using it in your application of panels all over the place.

[Isetech]

I have scrapped the idea of installing the panels on the south side of the roof for now, I will be installing a small 3.5 kw inverter which will be grid tied and registered with municipality, which will require a small admin fee, calculated per KW, but more about that later.

The inverter has 2 MPPT trackers which can connect 2 strings per MPPT (2+2)

I will be using JA solar 545 watt panels.

https://solar.co.za/wp-content/uploads/2022/01/JA-Solar-525W-550W.pdf

The kick start is 125-150 VDC, so we need at least 4 panels per sting

The current is 26 amps so 2 strings of 13 amp will be fine

I plan to install 10 panels on the east facing roof, spit into 2 x 5 panels and 6 panels on the west facing roof (thats all I can fit)

I am going to build a carport and fit 10 panels on the carport all facing north

String 2 (1 and 1.1) + 2 (2 and 2.1)

String 1 - 5 panels x 49.75 x 5 = 248 VDC
String 1.1 - 5 panels x 49.75 = 248 VDC

String 2 - 6 panels x 49..75 x 5 = 298.5 VDC
No string 2.1

Once I get the carport built, we will revisit the layout.

[Isetech]

I am busy with another project. The roof is big enough to double stack the panels. The reason I am sharing is because I get asked these questions at least once a week.

"What is the max amount of panels you can connect to an 8 kw Sunsynk inverter"

We plan to install 32 x 545 watt panels,

8 per string on the east facing roof and 8 per string on the west facing roof.

string 1 top row (east) - 8 panels x 49.75 VDC = 398 VDC
String 1.1 bottom row east - 8 panels x 49.75 VDC = 398 VDC

String 2 top row (west) - 8 panels x 49.75 VDC =398 VDC
string 2.1 bottom row (west) - 8 panels x 49.75 = 398 VDC

Optimal voltage 370, so it is just above.

Looking at the STC values which are higher than the NOCT values so it should be ok, max power for a 545 watt panel is 13.04 x 2 = 26.12, border lining the 26 amp for the MPPT.

The short circuit current is 13.93 amps.

Which brings me to another very common question asked all the time "what size fuse must you install? " If the panel has a short circuit current of 13.93 amp, why do people fit 30 amp fuses, the answer because they use a 6 mm sq solar double insulated wire. Is the fuse the panels or the wire, according to any electrician to speak to, it is protect the wire. What do you think?

Back to the panel:

So we have 17440 kwp on the roof, you cant do that, actually you can, your voltages are within the VOC rating which is the most important factor when designing installations and your currents are within the limits.

If these panel were all north facing, I probably wouldnt suggest this many panels, however there are a few things to consider, the east west facing roof, the angle of the roof and the losses in winter (which could be as much as 40 %) which means you can only produce a total of around 11kwp in june/july. If you are registered and feeding back into the grid to maximize ROI, best you push as much power as you can.

Considering the price of panels, I am looking at only installing 1 x 5.1 kwh battery for now, just to keep the lights on and the rest of the money will be pushed into panels and inverter.

There is talk that the load shedding will be done by the end of the year, I know I heard that back in 2008, so I wont be holding my breathe, however even if they do fix the load shedding. my goal is not to install a system for load shedding but rather saving money on my bill.

Our utility charges a fee per kw which is around R143.75 per kw x 8 kw (hence the small grid tied) = R1150.00 per month.

So you need to push as much power back into the grid to recover these cost. Having 6 panels on the roof with an 8 kw unit was a nice load shedding solutions, to top up your batteries without using the grid power, but will become a waste of money once they force you to register your system.

Just think if you install a 16 kw unit x R143.75 = R2300 monthly charge, with a feed back tarriff of only around R1.40 , you gonna need a lot of panels.

[Justloadit]

String 2 (1 and 1.1) + 2 (2 and 2.1)

String 1 - 5 panels x 49.75 x 5 = 248 VDC
String 1.1 - 5 panels x 49.75 = 248 VDC

String 2 - 6 panels x 49..75 x 5 = 298.5 VDC
No string 2.1

Just I note, and I stand to be corrected here, I am not sure if you can use 2 different voltages on each MPPT input on the inverter.

[Isetech]

My understanding is that is reason for 2 MPPT's, is MPPT1 and MPPT2 work independent of each other.

It is better to keep the 2 strings on the MPPT 1 as close as possible, but string 2 and 2.1 on MPPT 2 can be completely different from MPPT 1.

This is what makes those home made DC control boxes so dangerous when connected to Sunsynk inverters with dual MPPT's.

There should be a separate DC control box for each MPPT and there should be a 4 pole DC isolator in each DC control box, isolating both strings, which should also be a metal box, considering they have been identified as a fire risk.

There should never be power on the bottom of an main switch/ isolator, ever. I leant the hard way.

The 8 kw Sunsynk 2+2 in the Sunsynk manual identifies as MPPT 1 (with 2 strings) + MPPT2 (with 2 strings)

The 12 kw 3 phase unit has 2+1 MPPT 1 2 strings and MPPT 2 (only 1 string)

I am sure this confuses a lot of people, like the 50 amp pass through current, very few people understand what the pass through current is all about.

Just I note, and I stand to be corrected here, I am not sure if you can use 2 different voltages on each MPPT input on the inverter.

[Andrew_van_Zyl]

Perfectly fine - just don't exceed the maximum.

[Isetech]

You cant exceed the max power, the Sunsynk inverter automatically caps the power as a default setting. we normally adjust cap to suit the plant.

I dont know about the 26 amp current rating, but I do know that you must never exceed the VOC, in fact I make sure we never go over the 450 absolute max.

Perfectly fine - just don't exceed the maximum.

[Isetech]

Reading the 8 kw installer manual I found this rather interesting ... page 76 "Inverter commissioning info" under solar ... ensure both MPPT's are balanced.

Just I note, and I stand to be corrected here, I am not sure if you can use 2 different voltages on each MPPT input on the inverter.

[Andrew_van_Zyl]

Not sure what they mean by "balanced" but in my experience inputs to MPPT's are rarely exactly the same as so many factors come into play like roof design, module layout, orientation, old vs new modules, shading, etc.

Only on my own roof do I have EXACTLY the same inputs into my 2 mppt's but that's only because I am blessed with a vast north facing roof.

In my humble opinion the mere fact that (Sunsynk) inverters have 2 mppt's is to deal with precisely the above inconsistent roof issues.