On a budget - 8 panel wiring options - 1x8panels or 2x4panels?

[flyfisherman]

Hi,

On a budget regarding solar panels. I have 8 panels and need to decide what is best regarding wiring? 1 string of 8 panels in series or 2 strings of 4 panels each in series?

(I think my use of the term string is correct? hahaha)

 

I did go through this link, and was very useful: Solar Panel Array: How to Size An Array - Solar Advice

 

Deye 5kw inverter. Canadian solar 455W panels. I am a very low electricity user.

 

My understanding is that 2 strings of 4 panels each in series provides redundancy, but is not optimal to maximize the panel output as 4xVoC of panels is 4x49=196 is at the bottom end of MPPT range, but should still work as the startup voltage of the inverter is like 150V for PV input?

 

Whereas 1x 8 panel string in series has zero redundancy but maximizes the panel efficiency as 8xVoC of panels is 8x49=392 is at top end of MPPT range, and this is apparently what you want to aim for? 

 

So I guess my questions: 

1. what would be the "best bet" ? redundancy or max power?

2. would 2x strings of 4 panels each be too inefficient or too low voltage?

3. can I string 8x 455W panels in series and use only one of the MPPT string inputs in the Deye 5KW inverter?

4. On a Deye 5kw inverter, it says 6500W max pv input...is this for the MPPT in total? Or does this mean max per string is 6500/2 = 3250W per string input if each MPPT has 1+1 string inputs per MPPT tracker?? (So effectively 7 panels max in series per string possible?)

 

Thanks for any input/advice.

Edited April 11, 2023 by flyfisherman

[WannabeSolarSparky]

12 minutes ago, flyfisherman said:

2. would 2x strings of 4 panels each be too inefficient or too low voltage?

That would work fine if you need to point the 2 strings in different directions, like mine facing east and west.

13 minutes ago, flyfisherman said:

3. can I string 8x 455W panels in series and use only one of the MPPT string inputs in the Deye 5KW inverter?

Yes, if the panels facing same direction this would be the the better option.

 

16 minutes ago, flyfisherman said:

4. On a Deye 5kw inverter, it says 6500W max pv input...is this for the MPPT in total? Or does this mean max per string is 6500/2 = 3250W per string input?? (So effectively 7 panels max in series per string?)

If you can afford it and safely oversize the panels (amps/volts in spec) then that will be good for winter production.

[mzezman]

4 hours ago, flyfisherman said:

4. On a Deye 5kw inverter, it says 6500W max pv input...is this for the MPPT in total? Or does this mean max per string is 6500/2 = 3250W per string input if each MPPT has 1+1 string inputs per MPPT tracker?? (So effectively 7 panels max in series per string possible?)

6500w is max for the inverter as a whole. Just note its the max DC the inverter will take either to charge batteries or power loads or a combo. You can have more than 6500w (to a point) as long s you do not go over the V max per mppt. This is beneficial in winter / cloudy days but you waste production in summer 

I would advocate 1 string of 8 panels on 1 mppt - then add more to the 2nd mppt when you can

[Chris_S]

I also say 1 string of 8 facing the same direction. 

I know you say you are a low electricity user but you going to see how on cloudy days that you are going to want more than 8 panels so keep 1 mppt open. 

[Scorp007]

8 hours ago, WannabeSolarSparky said:

That would work fine if you need to point the 2 strings in different directions, like mine facing east and west.

Yes, if the panels facing same direction this would be the the better option.

 

If you can afford it and safely oversize the panels (amps/volts in spec) then that will be good for winter production.

If using all the power the panels can provide winter is not really that bad in Gauteng. Although shorter day the clear skies make up for it in a big way. 

If my panels were @33+ degrees my winter could be better than my summer yield.

One can over spec for the 30 bad days in the year and have the extra panels doing nothing in the other 330 days? 

I have to add this summer with lots of LS did negatively affect my production. 

Edited April 11, 2023 by Scorp007

[suds7162]

I also suggest 1 string with all 8 panels. It's simpler wiring, and it leaves an MPPT open for future expansion.

What you lose in redundancy on the panels, you gain in redundancy on the inverter. It's much more likely an MPPT will give up the ghost, and then you can just switch over to the other one if you can't send the inverter in for repairs.

Also, I honestly don't see the benefit of having redundancy in having multiple PV strings as you explained. If one panel breaks due to hail or whatever, then you simply plug it out, and connect the two panels either side of the impacted one together. Going from 8 panels to 7 is still fine for the inverter. Going from 4 to 3 is not. So you will essentially lose an entire string if you only have 4 per string, and one panel fails. Also, panels remain functional even after hail damage. They usually have junction/diode boxes on the back that can essentially short out an entire section of the panel that's damaged. So if one section get smashed, 60% of the panel remains functional. 

The only case where you should split your panels, is if you are unable to put all 8 of them on the same roof, looking in the same direction. You MUST split to separate MPPTs if you have one batch facing north and another east/west. If the fit is tight, see if it's possible to fit all 8, even if you need to have some overhang here or there. 

For my installation I initially planned to go 6 north and 6 east. Then the installer managed to fit 10 on my north roof. 10 panels facing north will give you better yield than 6 east and 6 north. 

To answer your last question, about the 6.5kW max rating. Nobody has been able to give me that answer. I interpret it as 6.5kW overall, split whichever way between the MPPTs. So you can in theory have 6.5kW PER MPPT, but you will only ever get 6.5kW out of your PV as a whole. This helps to greatly increase your "solar day", but it's a waste in SA as we have tons of sun here. Overspeccing is great for the maybe 30 days of crap weather we have. Rest of the time those panels are just going to sit and bake in the sun and do nothing.

[WannabeSolarSparky]

1 hour ago, Scorp007 said:

If using all the power the panels can provide winter is not really that bad in Gauteng. Although shorter day the clear skies make up for it in a big way. 

If my panels were @33+ degrees my winter could be better than my summer yield.

One can over spec for the 30 bad days in the year and have the extra panels doing nothing in the other 330 days? 

I have to add this summer with lots of LS did negatively affect my production. 

Can I assume the right side (ZAR) is your daily spend on or indicating zero feedback bucks to the eskom grid ?

Edited April 11, 2023 by WannabeSolarSparky

[Scorp007]

It won't be easy to connect up to 6.5kw per MPPT and stay within the voltage levels. 

[Nexuss]

I also run 8 panels per string and it works wonderfully. I started with 5 panels per MPPT and could see a noticeable wattage per panel increase from the higher voltage of 8 panels . These inverters really like high voltage strings for maximum efficiency .

Edited April 11, 2023 by Nexuss

[Scorp007]

11 minutes ago, Nexuss said:

I also run 8 panels per string and it works wonderfully. I started with 5 panels per MPPT and could see a noticeable wattage per panel increase from the higher voltage of 8 panels . These inverters really like high voltage strings for maximum efficiency .

My reply was for @suds7162

That indicated 6.5kw per MPPT. That could mean 11+ panels in series.? 

[Nexuss]

10 minutes ago, Scorp007 said:

My reply was for @suds7162

That indicated 6.5kw per MPPT. That could mean 11+ panels in series.? 

Yea that would struggle lol . The absolute most i would go safely is 9 panels per string 455wx9 so about 4,1kw . The JA 540w panels can also work but you will experience some clipping, so 9x540w =4,86Kw on a string in theory. I would not go larger than 455W canadian panels on the 5kw Sunsynk/deye inverter as they are very amp heavy panels and overshoot their specsheet numbers by a fair margin.

[WannabeSolarSparky]

2 minutes ago, Nexuss said:

The JA 540w panels can also work but you will experience some clipping

Yip in summer it clips quite a bit. Though works out well for cloudy days and of course winter.

[GreenFields]

So what's the answer? Over-spec if you've got a bank of 3 or more batteries that you charge at around mid-day, and the rest of the time export power to the grid?

[Scorp007]

1 hour ago, GreenFields said:

So what's the answer? Over-spec if you've got a bank of 3 or more batteries that you charge at around mid-day, and the rest of the time export power to the grid?

Not easy to give an answer. Some points. 

What is a low user. 250kwh or 450kwh a month? 

When during the day is it used? 

You might want the best solution and gain 20min in the morning and afternoon with 8 in series vs 2 x 4 in series just to have a low daily load and panels standing idle after 12h00 with excess power like a lot of people have to cover a few bad days. 

Does the OP mind to buy some power from the grid if available instead of doing the above. I fit in the group that don't mind buying. 

Some more questions for later.

Edited April 11, 2023 by Scorp007

[flyfisherman]

8 hours ago, Scorp007 said:

What is a low user. 250kwh or 450kwh a month? 

When during the day is it used? 

My total electricity bill is around R800-R1000 per month prepaid - use one of those funny plug-into-the-socket type chargers to charge with electricity directly from eskom - no pre-paid meter or anything at my house...

This is including my pool pump running 3 hrs in AM and 3 hrs in PM as well as a geyser running not on a timer.

The rest of the time the house is idling as everything is energy saver ++ kinda ratings.

I don't mind buying power from the grid at all, but I think according to my rudimentary calculations 8x 455W panels, 2x 5kwh batteries and a 5kw inverter should take me pretty close to off grid, at least in the daytime, but maybe not all the way. I am OK with this and might even prefer to buy power from grid at night in favor of cycling batteries, and only use battery at night during load shedding, although my house uses hardly anything at night so might as well run it off batteries at night too?

 

I think I have settled on 8x panels in series into 1 MPPT...this is called 8S in solar terms i think?

 

I do have one more question  I did some calculations based on zero-degree Celsius days in Riebeek Kasteel (little dorpie in western cape)...then the Voc can apparently be like 54,55V per panel based on stc? So, am I correct in saying 8x55=440V worst case is ok as it's under the inverter 500V limit and when operating even in cold then the Vmpx8 will be like roughly 8x46=368 so that is all still perfect and does not overload the inverter or MPPT even in icy cold days? Warm days is not a problem it wont blow up anything as voltage drops 

 

Thanks again for all the input - completely wasted 2 days at work reading about solar and inverters and doing some calculations and hardly did any work  And I have not even connected the app or remote monitoring yet ... I dread that day as I can see how it can become rather addictive

Edited April 12, 2023 by flyfisherman

[Chris_S]

6 hours ago, flyfisherman said:

My total electricity bill is around R800-R1000 per month prepaid - use one of those funny plug-into-the-socket type chargers to charge with electricity directly from eskom - no pre-paid meter or anything at my house...

This is including my pool pump running 3 hrs in AM and 3 hrs in PM as well as a geyser running not on a timer.

The rest of the time the house is idling as everything is energy saver ++ kinda ratings.

I don't mind buying power from the grid at all, but I think according to my rudimentary calculations 8x 455W panels, 2x 5kwh batteries and a 5kw inverter should take me pretty close to off grid, at least in the daytime, but maybe not all the way. I am OK with this and might even prefer to buy power from grid at night in favor of cycling batteries, and only use battery at night during load shedding, although my house uses hardly anything at night so might as well run it off batteries at night too?

 

I think I have settled on 8x panels in series into 1 MPPT...this is called 8S in solar terms i think?

 

I do have one more question  I did some calculations based on zero-degree Celsius days in Riebeek Kasteel (little dorpie in western cape)...then the Voc can apparently be like 54,55V per panel based on stc? So, am I correct in saying 8x55=440V worst case is ok as it's under the inverter 500V limit and when operating even in cold then the Vmpx8 will be like roughly 8x46=368 so that is all still perfect and does not overload the inverter or MPPT even in icy cold days? Warm days is not a problem it wont blow up anything as voltage drops 

 

Thanks again for all the input - completely wasted 2 days at work reading about solar and inverters and doing some calculations and hardly did any work  And I have not even connected the app or remote monitoring yet ... I dread that day as I can see how it can become rather addictive

Run off of batteries the whole night so you can store and use more PV during the day. This will save you a lot more money on electricity. Use the grid only when you really have to. 

I think of Eskom as my generator for occasional use only. It's still cheaper to charge batteries from Eskom than it is from a generator. 

[Scorp007]

Due to the marginal difference in a lot of cases between 4S per MPPT and 8S for the Cape 8S is by far the better option due to the winter period. 

Little info makes a huge difference

Edited April 12, 2023 by Scorp007

[Inverter]

On 2023/04/12 at 1:56 AM, flyfisherman said:

My total electricity bill is around R800-R1000 per month prepaid - use one of those funny plug-into-the-socket type chargers to charge with electricity directly from eskom - no pre-paid meter or anything at my house...

This is including my pool pump running 3 hrs in AM and 3 hrs in PM as well as a geyser running not on a timer.

The rest of the time the house is idling as everything is energy saver ++ kinda ratings.

I don't mind buying power from the grid at all, but I think according to my rudimentary calculations 8x 455W panels, 2x 5kwh batteries and a 5kw inverter should take me pretty close to off grid, at least in the daytime, but maybe not all the way. I am OK with this and might even prefer to buy power from grid at night in favor of cycling batteries, and only use battery at night during load shedding, although my house uses hardly anything at night so might as well run it off batteries at night too?

 

I think I have settled on 8x panels in series into 1 MPPT...this is called 8S in solar terms i think?

 

I do have one more question  I did some calculations based on zero-degree Celsius days in Riebeek Kasteel (little dorpie in western cape)...then the Voc can apparently be like 54,55V per panel based on stc? So, am I correct in saying 8x55=440V worst case is ok as it's under the inverter 500V limit and when operating even in cold then the Vmpx8 will be like roughly 8x46=368 so that is all still perfect and does not overload the inverter or MPPT even in icy cold days? Warm days is not a problem it wont blow up anything as voltage drops 

 

Thanks again for all the input - completely wasted 2 days at work reading about solar and inverters and doing some calculations and hardly did any work  And I have not even connected the app or remote monitoring yet ... I dread that day as I can see how it can become rather addictive

@flyfisherman Do have any screen print results of the 8 panels in series please?