Need help sizing a solar array

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veroxious

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Been running in circles for a few months trying (unsuccessfully) to figure it out.

I currently have a Goodwe GW5000-ES-20 inverter with a Hubble AM5 battery. I want to add solar (max the inverter can handle) but need to figure out how many panels. From what I have read you need to work out the max voltage the solar panel will supply on the coldest day of the year. I live in CPT so I assumed 3 degrees celcius which comes to 11 panels (only 4675w) ? I used this excel spreadsheet for the calc https://www.victronenergy.com/upload/software/VE-MPPT-Calc-1_9.xlsx

Specifications:
Inverter -
Max solar supported is 7500W (has 2 MPPTs)
Max Voltage is 600V
Max Input current per MPPT is 16 Amps
Max short circuit current per MPPT is 23 Amps
1696118665284.png
Link https://en.goodwe.com/Ftp/EN/Downloads/Datasheet/GW_ES G2_Datasheet-EN.pdf

Proposed solar panel -
Trina Solar 425w Solar Panel Mono (TSM-425DE09R)
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The north facing roof section is 8.25m wide x at its lowest point and about 8.6m wide at the highest point by 3.2m. I can definitely get 8 of those panels on there and possibly 12 if I have it stand about 300mm beyond the ridge capping and about 400mm pass the one edge of the roof which has a carport next to it. I have West and East facing roofs as well which could easily take 20 panels either side but then I have the issue that comes with West and East facing panels. What configuration would give me the optimal solar production while staying within the max voltage parameters?
1696119596573.png

Thanks in advance
 
OK I stumbled upon this link: https://unboundsolar.com/blog/string-sizing-guide

Very helpful. using their calculations I can add a maximum of 10 of those 425W panels which is disappointing to say the least. Any way I can increase that without buying a 2nd duplicate inverter? Like an inverter just for extra panels as I'm looking to use zero Eskom power during the sunshine hours. I avg 25Kwh in Winter and 20Kwh in summer (daily average).
 
Those 10 panels will majority of the time exceed your use in any case
If you do feel the need to add more daytime power another inverter is what you're after. If you were looking to just charge the battery a standalone MPPT could be used to charge
 
Those panels will provide about 20kWh most days.

Also, the inverter has two MPPTs so you can add two strings to it, which doubles your current calculation.

To further optimise you can go for higher current panels. The ones you're looking at are only about 10A while the MPPTs are rated for 16A. 550V x 16A is 8.8kWp per MPPT.

Given your roof I'd go with 8 high current North facing panels on one MPPT and then about 5 East and 5 West connected in parallel. If you're paralleling the 10A panels are ideal. You'll lose too much if you go with higher current panels on that MPPT.
 
The spec says you have 2 mppt trackers that can take 1 string each. So you can do up to 11 of those panels per mppt controller.

You are looking at 22 Max panels but the watage is limited to 7500w so 2 strings if 9 panels each would probably be the best configuration.

Why don't you put 10 panels on the north facing roof on one mppt and then see how that goes. With 1 battery it will likely be a good match. Then when you get another battery put 8-10 panels on the east roof.
 
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a lot depends on your load

i have a 5 panels which totals 2275WP that can produce on a good day 14kwh
my battery is 7 kwh and my base load is about 1kw while sun is shining so i would have to have the battery totally empty to catch all i produce (with no load shedding backup if weather catches me of guard)

thanks to keeping a reserve i can't fully utilise all the solar i produce with even 5 panels
(i have a geyser as a dump load as soon as production shoots up i run it with a 1kw element to compensate for my small battery bank)

so relax buy some panels populate one mppt with as many panels as you need to cover you base load and recharge the battery , fit the rails for 10 panels or 20 panels while busy and make the wires long enough to where the panels will end, that way you can just plug and play more panels as you expand

you would need to expand the battery bank to use all the panels your inverter can handle

Hence why u suggest only adding enough panels and then expand it as your battery expands

at the max power of 7500w there is a notation marked 2 ? what does it state at the bottom of the page about 2?

but with current inverter you can easily handle almost 18panels if the 7500 is max for both mppt combined if per one you can handle more than 20
 
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The notion of bigger is better baffles me, a higher wattage panel is just bigger panel

With same efficiency you will fill the same amount if space for same combined power

Smaller panels are easier to handle

May be wrong but wont a smaller panel be less likely for glass damage

The only difference that matter from panel to panel, is the cell count which affects voltage

Other than that nothing matters apart from price per watt + guarantee

And if doing phases you want to buy a popular size that you can get again for next phase

Edit what also matters is would a slightly different size panel allow 2 rows while another only one etc ie choose the size of the panel based on what fits best on your roof
 
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If adding panels to north facing i would not put two rows the roof to the left will cut short the late afternoon production on bottom row and place the panels as high as possible not centre

Going east or west or combo on the other string would depend on weather ie if mornings are always clear and afternoons is thunderstorms then east bias

If the inverse west focus

I would go west focus as normally our usage patterns is less early morning and more late afternoon

Your decision should be considering load
 
First off, you're overthinking things.

Second off.
North facing will give you the best bang/buck in terms of panel.

I'd probably mix the east/west and North facing, so you have longer /earlier voltages.
That said, your inverter won't support many panels to do that justice. I'd probably just go with north facing for now, as that

Why the 425W? I'd probably lean towards higher power panels as your main costs here are in labour. Panel costs are marginal really. You have the space for large sized panels.

Max Voltage is 600V
Max Input current per MPPT is 16 Amps
Max short circuit current per MPPT is 23 Amps

Your chosen panels would need to be in series as MPPT input would be exceeded; don't go near Max Voltage. Rough rule of thumb, look at your VoC, add 20%, and don't exceed that.

So max voltage from panels I would safely go with is < 500v.

I'd suggest look at other panels though.
 
Thanks so much for all the replies. Much appreciated. The reason I chose those 425W panels was because (a) I can get them at a great price (R1600 each if I can get some people to share in buying a pallet) and (b) the physical dimensions (1764mm length as opposed to 2200mm) mean I can get more panels on my north facing section of the roof. Also I want to use 2 of those 425w panels to power the Geyserwise PV solution I intend installing in the near future (Edit: those 2 panels will be mounted on the small section of north facing roof closest to my neighbour on the North side as it comes with it's own MPPT controller).
 
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Speedster said:
Those panels will provide about 20kWh most days.

Also, the inverter has two MPPTs so you can add two strings to it, which doubles your current calculation.

To further optimise you can go for higher current panels. The ones you're looking at are only about 10A while the MPPTs are rated for 16A. 550V x 16A is 8.8kWp per MPPT.

Given your roof I'd go with 8 high current North facing panels on one MPPT and then about 5 East and 5 West connected in parallel. If you're paralleling the 10A panels are ideal. You'll lose too much if you go with higher current panels on that MPPT.
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The inverter max is 7500w

So he will lose nothing if using 10a panels

ie 10A on 50v panel will most likely hit a vmp of about 370v with 9 in series meaning 2 mppt
With this config will hit his 7500w max of inverter

All it means is if he uses higher amp panels he will end up with a lower panel count to strike the same watts
 
Speedster said:
Those panels will provide about 20kWh most days.

Also, the inverter has two MPPTs so you can add two strings to it, which doubles your current calculation.

To further optimise you can go for higher current panels. The ones you're looking at are only about 10A while the MPPTs are rated for 16A. 550V x 16A is 8.8kWp per MPPT.

Given your roof I'd go with 8 high current North facing panels on one MPPT and then about 5 East and 5 West connected in parallel. If you're paralleling the 10A panels are ideal. You'll lose too much if you go with higher current panels on that MPPT.
Click to expand...
So say I use 10 x 425W panels on the north facing roof which leaves me with 8 I can split in parallel on east and west as you say. Adding 2 strings of 4 of those 425W 10 amp panels in parallel will give me 20 amps on the 2nd MPPT which is 4 amps above the 16 amp rating of the MPPT. How will that work? Forgive me if my lack of understanding is showing. Being able to safely use 18 panels is compelling for me.
 
Bang for buck is king so if you can get a good price on a specific panel go for it

If you do do double row on north facing do check out the shading on the yellow spot the top row first panel on that side will be affected much later so try and fit most panels on the top row and do the rest on bottom row (fewer panels) further east to try and avoid shade cutting the day short

Can also make this north facing array smaller if you do see it affects it end of day and rather throw the rest of the panels on a west or east facing array on the other mppt
 

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veroxious said:
So say I use 10 x 425W panels on the north facing roof which leaves me with 8 I can split in parallel on east and west as you say. Adding 2 strings of 4 of those 425W 10 amp panels in parallel will give me 20 amps on the 2nd MPPT which is 4 amps above the 16 amp rating of the MPPT. How will that work? Forgive me if my lack of understanding is showing. Being able to safely use 18 panels is compelling for me.
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The inverter will most likely just clip the amps ie you would only get 16amp from your 20A peak time of the day meaning you essentially just lost 20% of your 425w panel meaning at best your panel is now a 340w panel effectively

Sure early morning and late afternoon you won't lose anything as the output is less at those times

So no stay away from higher amp config if you don't have to

Especially since your mppt can handle high voltage

Higher amp panels are more intended for lower voltage mppt imo
 
leon.davibe said:
The inverter will most likely just clip the amps ie you would only get 16amp from your 20A peak time of the day meaning you essentially just lost 20% of your 425w panel meaning at best your panel is now a 340w panel effectively

Sure early morning and late afternoon you won't lose anything as the output is less at those times

So no stay away from higher amp config if you don't have to

Especially since your mppt can handle high voltage

Higher amp panels are more intended for lower voltage mppt imo
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Ok so you essentially recommending I go for 8 panels in series on either East or West facing on the 2nd MPPT?
 
leon.davibe said:
Bang for buck is king so if you can get a good price on a specific panel go for it

If you do do double row on north facing do check out the shading on the yellow spot the top row first panel on that side will be affected much later so try and fit most panels on the top row and do the rest on bottom row (fewer panels) further east to try and avoid shade cutting the day short

Can also make this north facing array smaller if you do see it affects it end of day and rather throw the rest of the panels on a west or east facing array on the other mppt
Click to expand...
I have to do a physical check but there is complete shading in the late afternoon on the North facing section as the East-West section of the roof is higher than the north facing as it is a substantially larger roof.
 
You could
veroxious said:
Ok so you essentially recommending I go for 8 panels in series on either East or West facing on the 2nd MPPT?
Click to expand...
i would stick to one side have seen youtube clips that mix and show that the losses isn't as bad as some make it out , but have also seen clips that state shading kills panels , so would not take a chance to have panels in full production in the same series as panels with low production

yea one of the strings will overwhelm your load /battery

so i would get the installers to fit the rails for both strings , but only do the panels on one
and rather buy an extra battery instead of the second string

on this forum many posts with guys that say they need 20kwh batteries to utilise arrays of that size

but yea it is all about budget and preference
ie if you want the panels to be all fitted in one go, no problem
but the panels will produce a lot less than you expect, since if no load or empty battery to absorb they produce nothing, unless you grid feed naturally

in bad weather it is a plus to be oversized though as you may still be able to produce enough for load and battery charging
 
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