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Solar panel layout

8-ball

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Hi quick question. I’m trying to figure out the best way to design my solar panel ground mount. I came up with 3 designs but then figured out that the design in the middle isn’t going to work because of the length and area I have on my property. So I was thinking about going with the design on the bottom. Also by doing 5 across and 4 high I was thinking of doing each across leg as a series and then each string in parallel. So that would be 5S4P. This is assuming I can find 15’ superstruts. I’m doing 2x 5k growatt inverters. The inverts can handle 100A each and Max Voc 450. I’m not exactly sure how it works when you connect this way. I know when you connect in series you add the VOC and in parallel you add the amps. Each solar panel is 460 watts and VOC 50.8 with 10.86 amps. The problem I see in this is if I connect 2 strings in each inverter it’s technically 108A which is a little over. So can I do it this way? Am I missing something?
 

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Each 5S string will be 5x voltage and single panel amps
Combining 2 strings in parallel adds the amps of the strings (10.86 + 10.86).

So each 5S2P array will be 254V and 21.72A
 
Each 5S string will be 5x voltage and single panel amps
Combining 2 strings in parallel adds the amps of the strings (10.86 + 10.86).

So each 5S2P array will be 254V and 21.72A
Ok awesome. I was wondering if that’s how it works but I wasn’t totally sure.
Thank you
 
If your using a commercial style mount you'll likely need to stick to "landscape" layout vs portrait. You'll also find it difficult to mix the 2 on a standard rack build.

my vote is always landscape. Over panel by enough to come out with "full" array of pannels.
 
Someone on a FB said this. And I am totally confused by what he is saying.

“Not enough, but your math is likely not correct. The V and I do not jive with the 460W, so you're likely using Voc and Isc.

Use Voc only to calculate the max system voltage. 5x50.8 cannot be greater than the lower system voltage of either the PV or controller, not just the controller.

In operation, the voltage will be closer to 5xVmp and 2xImp.

Similarly, 450V x 100A is 45kW, nine times the 5kW rating. The V and I are not operational numbers. If the controller is rated at 100Amps, it implies that its lower input voltage limit is around 50V.”
 
Similarly, 450V x 100A is 45kW, nine times the 5kW rating. The V and I are not operational numbers. If the controller is rated at 100Amps, it implies that its lower input voltage limit is around 50V.”
The inverts can handle 100A each and Max Voc 450. I
Where are you getting the "can handle 100A each"? Are you referring to an SCC that can charge at 100A?

If the controller is rated at 100Amps, it implies that its lower input voltage limit is around 50V.”
You are confusing input amps and charging amps. Similarly confusing max input volts and charging volts.

Don't worry about input amps, just worry about input volts (Voc when dealing with the limit). The MPPT will pull the number of amps it can handle from the panels, that's what MPPT is all about.

You have not mentioned your battery voltage so i will use numbers for a "24V" system which is 25.6V nominal. The charging volts for this will be roughly 28V so i will use that number.

If you have a 5S2P array will be 254V and 21.72A, that represents (254 x 21.72 =) 5517W array.

Your MPPT massages the voltage and amps of the array to find the maximum mix of amps and volts. And, it then turns this power into your charging volts (we're using 28V as mentioned above, insert your charge volts for your battery bank).

So you have 5517W coming in and lets just us 100% efficiency for simplicity. So your 100A SCC can charge at a max of 100A. So, the most it can pull from your array is 28V x 100A = 2800W (roughly half of your array). So half of your array is "clipped" to the 2800W. This is not awful because your array will be maxed out early in the day, later in the day and will produce more (up to 2800W) on cloudy days. Its a fairly common strategy though not often to this extent.

If your battery bank is "48V" your charging volts may be more like 56V in which case your 100A SCC can use 5600W.

So distinguishing between input volts and amp vs output volts and amps is important. Hopefully this helps.
 
“Not enough, but your math is likely not correct. The V and I do not jive with the 460W, so you're likely using Voc and Isc.
- old dude who hasn't seen the new panels on the market...

Use Voc only to calculate the max system voltage. 5x50.8 cannot be greater than the lower system voltage of either the PV or controller, not just the controller.
- "...greater than the lower system voltage of either the VP or controller, not just the controller" makes no sense

In operation, the voltage will be closer to 5xVmp and 2xImp.
- this is pretty much true... but why even bring Vmp and Imp into the conversation except to make a point about how panel manufactures rate the wattage of their panels.

Similarly, 450V x 100A is 45kW, nine times the 5kW rating. The V and I are not operational numbers. If the controller is rated at 100Amps, it implies that its lower input voltage limit is around 50V.”
- all of this confusion because you left out the 6,000 watt max array factor. hmmm

------------

- The 5kW rating on the GroWatt is not how much solar you can put into it... It is how much AC wattage you can get out of the inverter for your loads. I am assuming you are looking at 2 inverters cuz each inverter can only take on a maximum of 6,000 watts of solar and you got 9,000 watts of solar and not because you have that heavy of loads.

- reading the spec sheet for the 5kw GroWatt inverter you are correct that it can take a max of 450Voc and a max of 100amps of solar input which you may think to just multiply those to get 45,000 watts, but the spec sheet specifically says the max solar array wattage supported is 6,000 watts.

- assuming you will tie one 5S-2P array (4,500 watts) to one inverter and the other 5S-2P array (4,500 watts) to the other inverter. This would put you well within the specs of the inverters for solar input, and give you 10kW of rated AC output with buffer above that for surge needs.

- 5 in series sets your array Voc at 254v, well under the max of 450v
- 2 in parallel sets your array Isc at ~22amps, again well under the max of 100a and you can get away with 8awg cables from the arrays to the inverters.

- So you are installing 9,000 watts of solar that will likely produce around 40kWh per day on good days.
(my rule of thumb is total array wattage x 4.5 to give you likely daily watt hours)
 
Where are you getting the "can handle 100A each"? Are you referring to an SCC that can charge at 100A?


You are confusing input amps and charging amps. Similarly confusing max input volts and charging volts.

Don't worry about input amps, just worry about input volts (Voc when dealing with the limit). The MPPT will pull the number of amps it can handle from the panels, that's what MPPT is all about.

You have not mentioned your battery voltage so i will use numbers for a "24V" system which is 25.6V nominal. The charging volts for this will be roughly 28V so i will use that number.

If you have a 5S2P array will be 254V and 21.72A, that represents (254 x 21.72 =) 5517W array.

Your MPPT massages the voltage and amps of the array to find the maximum mix of amps and volts. And, it then turns this power into your charging volts (we're using 28V as mentioned above, insert your charge volts for your battery bank).

So you have 5517W coming in and lets just us 100% efficiency for simplicity. So your 100A SCC can charge at a max of 100A. So, the most it can pull from your array is 28V x 100A = 2800W (roughly half of your array). So half of your array is "clipped" to the 2800W. This is not awful because your array will be maxed out early in the day, later in the day and will produce more (up to 2800W) on cloudy days. Its a fairly common strategy though not often to this extent.

If your battery bank is "48V" your charging volts may be more like 56V in which case your 100A SCC can use 5600W.

So distinguishing between input volts and amp vs output volts and amps is important. Hopefully this helps.
I should have mentioned that I am doing a 48v battery system. In fact they are on back order. So when you say my system is “clipped” is that a bad thing? I basically figured out my usage and appliance load and added about 50% for future needs.
Yes I am doing 2 inverters both 5K inverters.
 
Hey 8-ball,

Pg 36-38 of the user manual ( https://signaturesolar.com/content/documents/GROWATT/1519013-manual.pdf ) have some really great detail specs...

You are no where near clipping on the high side, but I believe the concern is due to the MPPT startup voltage being about 150vdc on the growatt and your array is spec'ed at about 254voc, meaning your array would have to be really pumping out the power before the charger would kick in and start using it to charge the batteries.

If you went to an 8s-2p (16 panels @ 401.6Voc) you may actually get more out of the array than with the 5s-4p (20 panels) due to the 150vdc startup voltage for charging.

Please note that actual panel voltage in the real world is only about 80% of VOC, but we are just going to use VOC here...

in the 5s-4p scenario, the 150v startup voltage means your array would have to be at or above 59% production (150/254) before the growatt would even use your array for charging.

in the 8s-2p scenario, the 150v startup voltage means your array would have to be at or above 37% production (150/401.6) before the growatt would even use your array for charging.
  • PV Input Current 10.86A x 2p = 21.72A which is less than the max of 22A
  • PV Array Open Circuit Voltage 50.8V x 8s = 401.6Vdc which is less than the max of 450Vdc
Giving a total array value of 7200 watts instead of 9000 watts.

...just some thoughts
 
1648782135739.png
actual voltage and current metrics from one of my 325w solar panels for 3 days back in february. You can see that the actual volts peak out around 36v and the current peaks around 10a.

specs for this Suniva Opt325-72-4-100
- power = 325w
- Vmp = 37.5v
- Voc = 45.8v
- Isc = 9.42a
 
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