Full off-grid system

TheChamp

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Yes, so why 3 and not 4?
2 strings on the right side and one on the not so right side? If it allows it would be more advantageous to have most of your panels on the north facing roof.

Just a guess.
 

wingnut771

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2 strings on the right side and one on the not so right side? If it allows it would be more advantageous to have most of your panels on the north facing roof.

Just a guess.
Yeah, I would have 2 strings on mppt 1 and 2 strings on mppt 2.
 

B-1

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If you have 300K to spend I really dont think you will have any issues.

I would put enough panels up to run all the machines and charge the batteries at the same time. You should then be able to run for about 5 hours a day when its sunny. For cloudy days and early/late work I would get a 10kw diesel generator. (Assuming this will be the exception not the norm)

Then battery wise you can get a decent lithium battery bank this will let you do the odd quick job with bigger tools and plenty with smaller ones (sanders, drills etc) and also carry the house no problem etc.

If you buy a 5kw inverter just make sure you get one that can parallel and has enough mppt capacity for all the panels. Then you can always add another if you are running it near its Max capacity often.
 

B-1

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Something like this:
______________________
thepowerstore.co.za
______________________
1X

24X

1X


_____________________
www.adendorff.co.za
_____________________

1X

That will leave you with +- 65K for cabling, fitment and hardware etc which should be doable for a new install.
 

itareanlnotani

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Why 3 strings when there are 2 MPPT's?
there are 4 inputs., 2 on mppt1, 2 on mppt2

For 9.5kw like I have, they recommend splitting 2 on mppt1, and 1 on mppt2.

You need to keep voltages and amps under the limits (amps will be clipped, but voltage absolutely must stay under the limits)
 

wingnut771

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there are 4 inputs., 2 on mppt1, 2 on mppt2

For 9.5kw like I have, they recommend splitting 2 on mppt1, and 1 on mppt2.

You need to keep voltages and amps under the limits (amps will be clipped, but voltage absolutely must stay under the limits)
Yes, so voltages on all 3 strings are the same (8 panels), but you're doubling the amps on mppt1 (2 strings parallel) and not on mppt2. Why not parallel the strings on mppt2 like on mppt1? AFAIK, it's the volts one has to be careful of, not the amps. So, 4 strings of 6 panels, still 24 panels.
 

itareanlnotani

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Yes, so voltages on all 3 strings are the same (8 panels), but you're doubling the amps on mppt1 (2 strings parallel) and not on mppt2. Why not parallel the strings on mppt2 like on mppt1? AFAIK, it's the volts one has to be careful of, not the amps. So, 4 strings of 6 panels, still 24 panels.

You want to keep the voltage optimal for the inverter - i.e. in a range where it works well. Too low is not good either as its inefficient. Too high is no good, as the inverter will let out the magic smoke.
You also want to make sure the strings are the same size on an MPPT.
i.e if MPPT1 input 1 is 8 panels, input 2 needs to be matched to 8 panels. MPPT2 could be different though.
Note - Max amps don't matter as much as the inverter will only draw what it needs i.e. it won't go over the amps if too high.

The manual says:

If the voltage is too high on the MPPT, you can burn out the front-end. DC to DC converter damage also invalidates your warranty.
Keep your Voc below 450V. Regardless of the power of the solar panel, the inverter will only draw what it needs (basic ohms law). Please refer to our training manual part one.
When wiring to string-inverters in parallel, please make sure the string inverters have identical power, identical size, and identical manufacturer. Do not mix panels if one string is only eight panels and the other nine. This will create an imbalance and cause major efficiency losses. However, you can mix panels between the MPPTs since both inputs work independently.


The Sunsynk 8.8KW has a max of per 450v @ 18.8A MPPT.
I've planned the panels sizes to fit within those specs.
For this inverter, you absolutely need to keep under 450V max on any MPPT input (actually 500v, but 450v is recommended as max). Min voltage is recommended as over 350v. Lower than that and its less efficient.

For the 395W panels - OC voltage is 49.64v MPV is 40.48v / Amps 9.7A (STC)
OC voltage (open circuit is the highest they'll go to) - 49.6 x 8 panels = 400v @ 9.7A odd. This is <450max. So all good.

MPPT1
- Input 1 will have 400v @ 9.7A
- Input 2 will have 400v @ 9.7A

MPPT2
- Input 1 will have 400v * 9.7A

Total - 400v @ 19.4A (midday). This is slightly over the rated 18.8A max, but realistically unlikely to reach that except for cold cloudy days.


Now to answer your question - why not 6 x 4? or even something else.

MPPT1
- Input 1 will have 297v @ 9.7A
- Input 2 will have 297v @ 9.7A

MPPT2
- Input 1 will have 297v @ 9.7A
- Input 2 will have 297v @ 9.7A

Those voltages are a little low for this inverter, and it won't work as efficiently. Its minor but still a design decision I made.

The actual sweet spot for this inverter is at 350v i.e. 7 panels, but I like a little headroom for winter months - more panels = more generation, and winter is the key time, summer I can lose some efficiency points + have a little clipping, as I'll have more power than I know what to do with. Thats fine, and something I'm used to in my other builds.

There are obviously other panels available for sale here - > 500w are on the market for sale, but they don't fit as nicely into the inverter specs. The 395w panels seem to be the best fit for my needs (I want over 9kw of panels total)


Hope that answers your question.
 

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wingnut771

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You want to keep the voltage optimal for the inverter - i.e. in a range where it works well. Too low is not good either as its inefficient. Too high is no good, as the inverter will let out the magic smoke.
You also want to make sure the strings are the same size on an MPPT.
i.e if MPPT1 input 1 is 8 panels, input 2 needs to be matched to 8 panels. MPPT2 could be different though.
Note - Max amps don't matter as much as the inverter will only draw what it needs i.e. it won't go over the amps if too high.

The manual says:




The Sunsynk 8.8KW has a max of per 450v @ 18.8A MPPT.
I've planned the panels sizes to fit within those specs.
For this inverter, you absolutely need to keep under 450V max on any MPPT input (actually 500v, but 450v is recommended as max). Min voltage is recommended as over 350v. Lower than that and its less efficient.

For the 395W panels - OC voltage is 49.64v MPV is 40.48v / Amps 9.7A (STC)
OC voltage (open circuit is the highest they'll go to) - 49.6 x 8 panels = 400v @ 9.7A odd. This is <450max. So all good.

MPPT1
- Input 1 will have 400v @ 9.7A
- Input 2 will have 400v @ 9.7A

MPPT2
- Input 1 will have 400v * 9.7A

Total - 400v @ 19.4A (midday). This is slightly over the rated 18.8A max, but realistically unlikely to reach that except for cold cloudy days.


Now to answer your question - why not 6 x 4? or even something else.

MPPT1
- Input 1 will have 297v @ 9.7A
- Input 2 will have 297v @ 9.7A

MPPT2
- Input 1 will have 297v @ 9.7A
- Input 2 will have 297v @ 9.7A

Those voltages are a little low for this inverter, and it won't work as efficiently. Its minor but still a design decision I made.

The actual sweet spot for this inverter is at 350v i.e. 7 panels, but I like a little headroom for winter months - more panels = more generation, and winter is the key time, summer I can lose some efficiency points + have a little clipping, as I'll have more power than I know what to do with. Thats fine, and something I'm used to in my other builds.

There are obviously other panels available for sale here - > 500w are on the market for sale, but they don't fit as nicely into the inverter specs. The 395w panels seem to be the best fit for my needs (I want over 9kw of panels total)


Hope that answers your question.
Yes, thanks for that answer, but I have another question. If you maxing the amps on mppt1 and only half on mppt2 then aren't you still loosing efficiency? Even at 300V, if your amps are maxed then you're getting the most out of it? Isn't 300V smack bang in the middle of the allowable range? I would have thought that would be OK? It's just my OCD doesn't compute maxing one controller and not both. I suppose it's swings and roundabouts at the end of the day?
 

itareanlnotani

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Messages
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Yes, thanks for that answer, but I have another question. If you maxing the amps on mppt1 and only half on mppt2 then aren't you still loosing efficiency? Even at 300V, if your amps are maxed then you're getting the most out of it? Isn't 300V smack bang in the middle of the allowable range? I would have thought that would be OK? It's just my OCD doesn't compute maxing one controller and not both. I suppose it's swings and roundabouts at the end of the day?
The inverter has a sweet spot for efficiency.

It would prefer voltage to be in that range. Too low, and its less efficient. To high, and the magic smoke leaves.
As explained, its best at 350-400v +-

Their manual says to lay out the strings this way also...
 

Colin62

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Apr 23, 2008
Messages
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If you have 300K to spend I really dont think you will have any issues.
Good point, but ideally I'd like to come in under that - to be honest I got a hell of a surprise when I ran the numbers on the cable size and price.


If you buy a 5kw inverter just make sure you get one that can parallel and has enough mppt capacity for all the panels. Then you can always add another if you are running it near its Max capacity often.

One thing I'm not sure of is how the parallel mode works. Does each inverter have it's own panels and each supply a 5kW load or does one set of panels feed them both and they combine their outputs for a single 10kW load.

In other words do you have two 5kW feeds, or one 10kW feed into the house?
 

TheChamp

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Good point, but ideally I'd like to come in under that - to be honest I got a hell of a surprise when I ran the numbers on the cable size and price.




One thing I'm not sure of is how the parallel mode works. Does each inverter have it's own panels and each supply a 5kW load or does one set of panels feed them both and they combine their outputs for a single 10kW load.

In other words do you have two 5kW feeds, or one 10kW feed into the house?
They say panels should be connected to individual inverters and it's only the battery that's shared.
 

B-1

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Good point, but ideally I'd like to come in under that - to be honest I got a hell of a surprise when I ran the numbers on the cable size and price.




One thing I'm not sure of is how the parallel mode works. Does each inverter have it's own panels and each supply a 5kW load or does one set of panels feed them both and they combine their outputs for a single 10kW load.

In other words do you have two 5kW feeds, or one 10kW feed into the house?

It really depends on how you configure it. You can have one 10kw output or two 5kw. Some can even do 3 phase with 3 or six inverters.
 

Colin62

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They say panels should be connected to individual inverters and it's only the battery that's shared.
Thanks.

And the output? Two separate feeds or one combined feed? Could I run a single 8kW load safely?
 

TheChamp

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Thanks.

And the output? Two separate feeds or one combined feed? Could I run a single 8kW load safely?
As long as your cable is big enough, it wouldn't make practical sense to have multiple outputs unless you have to, so a single one combining everything should be fine.
 

TheChamp

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It gets slightly complicated on the DC side of things because 8kW is massive, maybe you would need to be creative to pull all 166A, the cables looks slightly smaller for that, what do you guys with massive systems do?
 
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