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Assistance with building first Solar Array

nexusjosh

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Jul 30, 2021
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This is a continuation of This post. I'm going with a 48 volt system, and have purchased my first MPPT/Inverter.

I'm going to purchase These panels.

The question is, how many do I need, and what configuration do they need to be in. I'm going to Attempt to go over the math, and any help you guys can give is awesome, you guys have been helpful thus far.

So, using the guidelines laid out in This video, looking over the manual, (Data Sheet on Manual pg53) along with an email I've gotten from the manufacturer; I'm getting the following:

1: Battery Bank Nominal
48 Vdc

2: Max PV Input Voltage
250Vdc of PV at each MPPT port. Minimum of 90Vdc

3: Max PV Input Wattage
3000 Wp per MPPT

I want to use These panels, if I can. Hopefully I can. They're both good panels, and cheap!

Rated Power: 250W
Open circuit voltage (VOC): 37.6 V

1 Series String+1 parallel string
2 in Series = 75.2 VOC | 500W2 additional panels; 4 total; 2S2P = 75.2 VOC | 1,000W
3 in Series = 112.8 VOC | 750W3 additional panels; 6 total; 3S2P = 112.8 VOC | 1,500W
4 in Series = 150.4 VOC | 1000W4 additional panels; 8 total; 4S2P = 150.4 VOC | 2000W
5 in Series = 188 VOC | 1,250W5 additional panels; 10 total; 5S2P = 188 VOC | 2,500W
6 in Series = 225.6 VOC | 1,500W6 additional panels; 12 total; 6S2P = 225.6 VOC | 3000W

So 2 questions at this point
1: Is my understanding/math correct?
2: Is a cushion of the 24 VOC enough to account for the winter increase in Northern California, where historically the winter temperature is typically 28°F (-2.22C), but doesn't go below 18°F (-7.77C)? According to This Website anyway.
 
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1: Is my understanding/math correct?
May did not include temp compensation as outage goes up. Do this for record cold.
2: Is a cushion of the 24 VOC enough to account for the winter increase in Northern California, where historically the winter temperature is typically 28°F (-2.22C), but doesn't go below 18°F (-7.77C)? According to This Website anyway.
What does the panels say for extra volts per degrees C? I remember along the lines of .3 volts per degrees celcius cooler. I think the starting point was 25 C. Needs to be off your panel spec sheet. I would not use typical temps. I’d go with record temps of the month you plan to use it in. I’d imagine this is year round unless its a cabin you lock up in the winter.
 
May did not include temp compensation as outage goes up. Do this for record cold.

What does the panels say for extra volts per degrees C? I remember along the lines of .3 volts per degrees celcius cooler. I think the starting point was 25 C. Needs to be off your panel spec sheet. I would not use typical temps. I’d go with record temps of the month you plan to use it in. I’d imagine this is year round unless its a cabin you lock up in the winter.

Yes, this setup will be year around. It will be connected to the grid as backup.

Unfortunately the panels I want to get don't have the temp specs on the website. What I think I'll do, is start with 3 panels, 3 in series with an additional 3 string, 112.8 VOC | 1,500W, and monitor it this winter, and see what the extra volts comes out to.

Other than not accounting for Temp Compensation, is my math correct?
 
The math is fine. How many amps out max on the MPPT? I’m guessing around 60 amps.
 
5 in Series = 188 VOC | 1,250W +1 parallel string (5 additional panels; 10 total) = 188 VOC | 2,500W
6 in Series = 225.6 VOC | 1,500W +1 parallel string (6 additional panels; 12 total) = 225.6 VOC | 3000W
Other than not accounting for Temp Compensation, is my math correct?
Yes.

Temp coefficient for voltage for panels like that is going to be in the vicinity of 0.15V/K give or take.

Depending on how cold it gets where you are I'd suggest 6 panels will be cutting it fine.

In a mild/hot climate like mine where temps don't go below freezing (but 0°C can happen), I'd allow a 10% margin for inverter / charge controller safety. 10% for 6 panels in series takes you to 248V and that's a bit close for comfort.

If your climate goes below freezing then you may need a 15-20% margin for safety. In which case 5 panels in series is a safer bet.
 
The math is fine. How many amps out max on the MPPT? I’m guessing around 60 amps.
For some reason, I don't see the max Amps. But I suspect it is listed on THIS info sheet as a different value? o_O

Yes.

Temp coefficient for voltage for panels like that is going to be in the vicinity of 0.15V/K give or take.

Depending on how cold it gets where you are I'd suggest 6 panels will be cutting it fine.

In a mild/hot climate like mine where temps don't go below freezing (but 0°C can happen), I'd allow a 10% margin for inverter / charge controller safety. 10% for 6 panels in series takes you to 248V and that's a bit close for comfort.

If your climate goes below freezing then you may need a 15-20% margin for safety. In which case 5 panels in series is a safer bet.
I doubt I'll have need for more than the 5S2P for the single MPPT. Unit has 2. I'm thinking, later on when I want to play around with Solar, I'll get the 2nd unit MPPT going with a Solar Tracking setup.
 
I'm guessing this is a MPP PIP LV6548? There's a lady on another thread where we are discussing her problems. Search for "Jamarsarah". I recommended to her that she wire four panels in series to get 120Vmp/150Voc. Using a string calculator, I estimated her winter lows would be ~168 Voc in winter. Each parallel string of 4 panels will put out at most 8A, so you could wire two 4-panel strings in parallel for each solar input circuit.
1628042232636.png
I myself am running at 120Vmp with Midnight controllers, and am finding that I can run power for more than 130' without measurable voltage drop. That lets me carefully position my arrays for maximal sun exposure, rather than worrying about how far away from my system my arrays are sitting.
 

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I guess 4800 useable solar watts @48v = 100a
?

The MPPT string voltage limit is 250V (but you'd keep it well under that to protect the inverter/charge controller) with a max array wattage of 3000W per MPPT (but it can only suck up to 2400W per MPPT).

The 18A per MPPT limit makes perfect sense and is plenty to allow paralleling of two strings of 250W panels. 10 x 250W panels in a 5S2P arrangement at max production will operate at ~150V and 16-17A.
 
?

The MPPT string voltage limit is 250V (but you'd keep it well under that to protect the inverter/charge controller) with a max array wattage of 3000W per MPPT (but it can only suck up to 2400W per MPPT).

The 18A per MPPT limit makes perfect sense and is plenty to allow paralleling of two strings of 250W panels. 10 x 250W panels in a 5S2P arrangement at max production will operate at ~150V and 16-17A.
my mistake. i was thinking output. Now I understand the focus is on input.
 
?

The MPPT string voltage limit is 250V (but you'd keep it well under that to protect the inverter/charge controller) with a max array wattage of 3000W per MPPT (but it can only suck up to 2400W per MPPT).

The 18A per MPPT limit makes perfect sense and is plenty to allow paralleling of two strings of 250W panels. 10 x 250W panels in a 5S2P arrangement at max production will operate at ~150V and 16-17A.
Sweet. I'm going to start ordering the panels soon.

my mistake. i was thinking output. Now I understand the focus is on input.
(y)

----
On the first MPPT controller, I'm going to roof mount the panels. For the 2nd, I think I'm going to make a solar tracker down the road. Will I be able to fit 10 panels on a single tracker... We shall see. :p

This is powering my barn/barn appartment, and I'm using it to learn the ins and outs of Solar, before wiring up the main house and shop on the property.
 
Sweet. I'm going to start ordering the panels soon.
With my project I was originally going to use 10 x 250W panels in a 2S5P arrangement but I ended up getting 6 x 370W panels and have a 2S3P arrangement. I was glad I ended up with the higher rated panels. Putting up fewer panels was a bonus and meant I only needing cabling for 3 strings instead of 5. It cut down my installation requirements by quite a bit.

But I may still get the others as there can always be another project!
 
Sweet. I'm going to start ordering the panels soon.


(y)

----
On the first MPPT controller, I'm going to roof mount the panels. For the 2nd, I think I'm going to make a solar tracker down the road. Will I be able to fit 10 panels on a single tracker... We shall see. :p

This is powering my barn/barn appartment, and I'm using it to learn the ins and outs of Solar, before wiring up the main house and shop on the property.
Do some research on solar trackers. Some people say youre better off investing that money in more panels. Will does, anyway.
 
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Do some research on solar trackers. Some people say youre better off investing that money in more panels. Will does, anyway.
A tracker is just another thing to go wrong. Adding a few extra panels to a strong fixed platform / roof and creating a split orientation array is cheaper and more reliable way to achieve the same outcome.
 
I'd say "it depends". Maximal power production is not so much my goal as it the maximal running of loads. For example, running my well-pump at 2000W is a priority for me. Assuming a fixed array will be at <10% output around 8:00AM, then I'd need 20,000W of panels to run that load at 8am.

With my cheapo, low tech arrays, I can rotate them East at 7am, and have my pump running at 7:30-8:00AM. This lets me get by with 4500W instead of 20,000W.

Take a look at my design. I sunk a schedule 40 pipe in the ground, and slipped a larger pipe over it. The frame is welded to the larger pipe. I'm the tracking mechanism. I go out a 7am and rotate the arrays East. I find I only need to make another azimuth correction mid-morning, and another around 1pm. I call it hillbilly solar tracking.
 

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Hey guys!

I know its been a bit. I ordered and received the MPPT/Inverter. Batteries are on order, and ordered 10 panels.

Now I'm onto the step of figuring out how the wiring of my array should go. I prepared This.

Question: I know there should be fuses between strings. Would it be fine/safest to put a fuse between each panel Or just put a fuse between each strings? I don't mind spending the extra money if it improves safety.

Thanks for all your help so far!

I'd say "it depends". Maximal power production is not so much my goal as it the maximal running of loads. For example, running my well-pump at 2000W is a priority for me. Assuming a fixed array will be at <10% output around 8:00AM, then I'd need 20,000W of panels to run that load at 8am.

With my cheapo, low tech arrays, I can rotate them East at 7am, and have my pump running at 7:30-8:00AM. This lets me get by with 4500W instead of 20,000W.

Take a look at my design. I sunk a schedule 40 pipe in the ground, and slipped a larger pipe over it. The frame is welded to the larger pipe. I'm the tracking mechanism. I go out a 7am and rotate the arrays East. I find I only need to make another azimuth correction mid-morning, and another around 1pm. I call it hillbilly solar tracking.
As for Solar Tracking. I've watched This guy's video. It looks like an easy thing to setup for the most part, you'd just need to build your own mounting bracket, or find one of those old Sat Mounts, which isn't impossible.
 
Hey guys!

I know its been a bit. I ordered and received the MPPT/Inverter. Batteries are on order, and ordered 10 panels.
Can your panel order be updated before it gets shipped? Ten panels is really not the best choice. For MPPT controllers, you can only wire 10 as either 5S2P, or 2S5P. Do you know the voltage/amperage limits of your new controller? You might be better off with either 8 or 12 panels. What are their specifications?
 
Can your panel order be updated before it gets shipped? Ten panels is really not the best choice. For MPPT controllers, you can only wire 10 as either 5S2P, or 2S5P. Do you know the voltage/amperage limits of your new controller? You might be better off with either 8 or 12 panels. What are their specifications?
I went over it on my first post on this thread. Read up.

I've bought 10 panels to eventually go into 5S2P, but I'm going to start with 3S2P, then 4S2P, and if I need the 2 extra, installed the final two for 5S2P.

All of the limits and such are all on the first post of this thread where I did all of the figuring and math.
 
I went over it on my first post on this thread. Read up.

I've bought 10 panels to eventually go into 5S2P, but I'm going to start with 3S2P, then 4S2P, and if I need the 2 extra, installed the final two for 5S2P.

All of the limits and such are all on the first post of this thread where I did all of the figuring and math.
It looks like you've planned it well. 5s2p should work for you. Why wait to install them all? Do the first 5s string, then tie the second one in. Use em!
 
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