diy solar

diy solar

The "Meg" Build

Great data, @Lt.Dan

For reference, mind sharing what model AC units you have? Rule of thumb for all HVAC is 2-3% power draw diff per degree lift (approx OAT minus SAT), so that tracks pretty well with your “as high as 1800W” comment. Per AHRI/ASHRAE, design OAT is 95F, aka point where units provide rated capacity.
 
Yes, all 3 are Coleman Mach 15s. Outside temp was 90*, I have it set to 77*, so a 13* Delta. Im guessing when it's 110*, im going to be trying to maintain 82-85*, which will be a considerable difference to now, and I will more than likely be seeing more than 1500 watts based on the info you provided above. Thank you!
 
my 13.5 colmen Mach 3 PS uses 7.5 to 10.5 amps... I was about to say I can't check it with kilowatt meter.. but I guess I can via shore power plug... I will post when I check
 
So im still playing with my panels and such, and I have 12x SanTan 250w panels on the ground mount, and 12x Sunpower E19 240w panels on the roof of my trailer. And consistently every day the Sunpower panels outperform the SanTan panels. Both in early morning/late at night where the sunlight is sub par, the sunpower panels are making way more power. At 8am this morning, the Sunpowers were making over 800watts with some of them shaded! While the SanTan panels were struggling over 150watts. At peak, they both make about the same power, and the sunpowers are mounted flat on the roof, and the SanTan panels are at ~15* angle south (almost perfect for where im at).

The sunpowers were much more expensive, but even they were used, purchased from SanTan, so they definitely were not a bad price.
 
Gotta wonder why. There could be some differences in light absorbed at off-angle, but wouldn't expect 5x difference.
What voltage/current are the SanTan strings delivering?
Could they be outside MPPT range of the charge controller?
Are the SanTan partially shaded, maybe some bad bypass diodes to shaded sections block production of others?
 
I winder why too, but the WatchPower app from MPP is showing the SanTan panels were at 90v at 8am (minimum start up is 80v i think for the LV6548), and the Sunpower panels were at 100v (due to some being shaded by the ACs early in the morning, im sure).

The SanTan panels are in a 6s2p config. SanTan VMP is 30.3v, so 6s should be 181v (which i rarely see it over 150v when in direct sun, but I have seen 175v when I spray with water or later in the day). I think the lower 150v is due to the MPPT pulling it down.

The Sunpowers are in a 3s4p config and a VMP of 40.5v so in 3s, should be 121.5v at full sun, which I see this voltage routinely throughout the day.

Looking at it now, (9:40 AM) the San Tan panels are at 134.2v and the Sunpower panels are at 118.6v. Both are outputting 1000watts +/- 50 watts, so they're starting to level off.
 
In the morning, SunPower is 100V out of 121Vmp. SanTan is 90V out of 150Vtypical.
83% vs. 60% is a big difference.
Any shade on SanTan? Problem with bypass diodes would be an easy to understand issue.

Running half of Vmp is quite low. Low light is less current, not supposed to be that much lower voltage.
Checking Voc and Isc of each panel might show something.
Testing with one 6s string then the other would show if they are similar.
3s ought to be sufficient for operation, certainly 4s or 5s, so could bypass various panels and see if any one as part of a string has different impact from the others.
 
Hedges said:
In the morning, SunPower is 100V out of 121Vmp. SanTan is 90V out of 150Vtypical.
83% vs. 60% is a big difference.
Any shade on SanTan? Problem with bypass diodes would be an easy to understand issue.

Running half of Vmp is quite low. Low light is less current, not supposed to be that much lower voltage.
Checking Voc and Isc of each panel might show something.
Testing with one 6s string then the other would show if they are similar.
3s ought to be sufficient for operation, certainly 4s or 5s, so could bypass various panels and see if any one as part of a string has different impact from the others.
Click to expand...
There should be no shade on the SanTan panels, but im not there to confirm, im at work lol

This was the VOC and ISC of the 12 panels on the ground. All the VOC were a few volts low, but not too bad. The ISC was taken earlier in the morning hence the lower amperage.

String 1
1 - 36.1v - 5.2a
2 - 35.3v - 5.2a
3 - 35.6v - 5.9a
4 - 35.6v - 5.5a
5 - 34.5v - 5.6a
6 - 35.1v - 5.6a
String 2
1 - 35.1v - 5.4a
2 - 34.9v - 5.4a
3 - 35.1v - 5.5a
4 - 34.4v - 5.9a
5 - 35.4v - 5.5a
6 - 35.4v - 5.9a

Do you think I should still check VOC of the complete 6s strings?
 
Lt.Dan said:
There should be no shade on the SanTan panels, but im not there to confirm, im at work lol

This was the VOC and ISC of the 12 panels on the ground. All the VOC were a few volts low, but not too bad. The ISC was taken earlier in the morning hence the lower amperage.

String 1
1 - 36.1v - 5.2a
2 - 35.3v - 5.2a
3 - 35.6v - 5.9a
4 - 35.6v - 5.5a
5 - 34.5v - 5.6a
6 - 35.1v - 5.6a
String 2
1 - 35.1v - 5.4a
2 - 34.9v - 5.4a
3 - 35.1v - 5.5a
4 - 34.4v - 5.9a
5 - 35.4v - 5.5a
6 - 35.4v - 5.9a

Do you think I should still check VOC of the complete 6s strings?
Click to expand...

If you multiply those two numbers together you get power. For the panels where voltage is a bit lower you likely should have a bit higher current and vice versa. But power should be similar.

This is what the MPPT optimizes for to get peak power possible based on sun, panel temps, etc, etc.

The VOC of the string should be the 6 panels added; by joining them and taking a reading you can tell if any connectors are messed up or possible the bypass diodes if these panels have them. I like to block each panel one at a time to see the impact on the string voltage to make sure the bypass diodes are doing their thing - you should loose a panels voltage but not more.

Just be careful as two of those panels in series is enough to hurt; 6 would be "do you smell the bacon?"
 
Currently have all 3 ACs on and this is what I'm seeing. The MPPT is definitely pulling down voltage on both PV inputs (PV1 is Santan Ground mount and PV2 is Sunpower Roof mounts).

Kinda sad that the PV1 is rated at 3000w and PV2 is rated at 2880w and this is all im seeing.

Screenshot_20210514-152227_WatchPower.jpg
 
Lt.Dan said:
There should be no shade on the SanTan panels, but im not there to confirm, im at work lol

This was the VOC and ISC of the 12 panels on the ground. All the VOC were a few volts low, but not too bad. The ISC was taken earlier in the morning hence the lower amperage.

String 1
1 - 36.1v - 5.2a
2 - 35.3v - 5.2a
3 - 35.6v - 5.9a
4 - 35.6v - 5.5a
5 - 34.5v - 5.6a
6 - 35.1v - 5.6a
String 2
1 - 35.1v - 5.4a
2 - 34.9v - 5.4a
3 - 35.1v - 5.5a
4 - 34.4v - 5.9a
5 - 35.4v - 5.5a
6 - 35.4v - 5.9a

Do you think I should still check VOC of the complete 6s strings?
Click to expand...

If no shade on any panels, nothing jumps out at me. Even if a bypass diode was open, wouldn't matter without shade. If shorted, you'd see a lower voltage.
Can you disconnect one string at a time, see if each is similar Vmp and wattage on the charge controller?

We've heard that Trina panels (which is what SanTan reportedly are) had a problem with leakage to frame. I would think that would be a degradation issue and shock hazard, but wouldn't expect enough current flow to pull down voltage of the array. (one point in cell string leaking to panel wouldn't affect individual panel measurements, but multiple with frames bonded together or a single one plus circuit wired to chassis somewhere would.)

Otherwise, it is either poor light capture off-angle, or watts vs. illumination doesn't follow the curve expected for some reason.

You also see Vmp lower than expected. Series resistance would do that. I think it's impact on Isc would be minor.
 
Hedges said:
If no shade on any panels, nothing jumps out at me. Even if a bypass diode was open, wouldn't matter without shade. If shorted, you'd see a lower voltage.
Can you disconnect one string at a time, see if each is similar Vmp and wattage on the charge controller?

We've heard that Trina panels (which is what SanTan reportedly are) had a problem with leakage to frame. I would think that would be a degradation issue and shock hazard, but wouldn't expect enough current flow to pull down voltage of the array. (one point in cell string leaking to panel wouldn't affect individual panel measurements, but multiple with frames bonded together or a single one plus circuit wired to chassis somewhere would.)

Otherwise, it is either poor light capture off-angle, or watts vs. illumination doesn't follow the curve expected for some reason.

You also see Vmp lower than expected. Series resistance would do that. I think it's impact on Isc would be minor.
Click to expand...
Yes, I will have more time on Sunday, and I can unplug 1 string at a time and take note of the voltage/amperage of each.

I do have a 100ft 10 ga lead, but I did the math and should see very little loss at the voltage I should be getting (180v).

I wonder what santan would say if I contacted them about these solar panels peaking at less than 70% of their output?

I know they say they test them and they "have good output" but what is "good" to them? Wills latest video showed the exact same panels peaking at 240 watts each, but I can't get more than 166 each?
 
I'm starting to think... I have 36 panels total (12 on the roof, 12 on the ground, and 12 im not using). And I'm wondering if I can somehow wire in more of these panels to get full usage of this LV6548. I have a max 8000 watt input, and I rarely see over 4000 watts and have never seen over 4200 watts.

How can I do this safely?

Edit: im doing the math now, my current array is 205VOC (measure with a multimeter), which means each panel is 34.16v, and 7 panels would be 239v, which is less than 250v max. I know it's dangerous to get close to that limit, but its doing nothing but getting hotter here, and soon we will be seeing 80-85* at 3 am. It gets very hot here, so I think I'll be safe until later in the year.

Also, I see im never pulling more than 14-14.5amps continously, and after talking with Ian, these units can safely be overpanneled to 23a (instead of the advertised 18a max). Well, 14.5a/2 (because of the 2 parallel strings = 7.25a each string, and 7.25x3 = 21.75a.

So with this little math I've done, I have proved i can safely hook up a 7s3p system and use 21 of the 24 panels total? To check my math and also not go over the 4000watt limit per PV input, 21 panels x 166 watts (which is what I'm currently averaging per panel) = 3486 watts. So as long as I don't get over 190 watts per panel (which so far has been unattainable), then im good.
 
Last edited:
Lt.Dan said:
I'm starting to think... I have 36 panels total (12 on the roof, 12 on the ground, and 12 im not using). And I'm wondering if I can somehow wire in more of these panels to get full usage of this LV6548. I have a max 8000 watt input, and I rarely see over 4000 watts and have never seen over 4200 watts.

How can I do this safely?

Edit: im doing the math now, my current array is 205VOC (measure with a multimeter), which means each panel is 34.16v, and 7 panels would be 239v, which is less than 250v max. I know it's dangerous to get close to that limit, but its doing nothing but getting hotter here, and soon we will be seeing 80-85* at 3 am. It gets very hot here, so I think I'll be safe until later in the year.

Also, I see im never pulling more than 14-14.5amps continously, and after talking with Ian, these units can safely be overpanneled to 23a (instead of the advertised 18a max). Well, 14.5a/2 (because of the 2 parallel strings = 7.25a each string, and 7.25x3 = 21.75a.

So with this little math I've done, I have proved i can safely hook up a 7s3p system and use 21 of the 24 panels total? To check my math and also not go over the 4000watt limit per PV input, 21 panels x 166 watts (which is what I'm currently averaging per panel) = 3486 watts. So as long as I don't get over 190 watts per panel (which so far has been unattainable), then im good.
Click to expand...

Your math sounds correct. You can also sneak up on it doing a 6s3p and if the "actuals" are where expected just add the extra panels to each string.
 
Your individual panel measurements x 6 came close to 215V, so the string measurement of 205V was either less light or hotter. Individual x 7 comes to 250V, the max allowed.
On a cold day, Voc would go higher. I wouldn't recommend doing 7s.
Spec for the SanTan panels is "Open circuit voltage (VOC): 37.6 V", so 6x gives 225V and 250V would be 10.8% over, OK for relatively cool ...

If this is the data sheet:


it shows temperature coefficient of Voc = -0.32%/degree C
10.8% voltage headroom with 6s configuration means OK for 34 degrees below 25C nominal, so as low as -9 degrees C. I would be OK with that for my San Jose location.
I wouldn't use 7s.

If you want to go with your measurements for degraded panels being lower you can, but would be best if you had accurate panel temperature to use in calculations, and you were sure it was close enough to full sun to get Voc.
But I still wouldn't use 7s, since your measurements put that at 250V without being cold.

SunPower panel ratings are higher wattage per area than SanTan (older Trina), and your experience show larger spread because the SanTan are further below their rating. Getting more of the high efficiency panels would be the way to get the most watts.
 
Hedges said:
Your individual panel measurements x 6 came close to 215V, so the string measurement of 205V was either less light or hotter. Individual x 7 comes to 250V, the max allowed.
On a cold day, Voc would go higher. I wouldn't recommend doing 7s.
Spec for the SanTan panels is "Open circuit voltage (VOC): 37.6 V", so 6x gives 225V and 250V would be 10.8% over, OK for relatively cool ...

If this is the data sheet:


it shows temperature coefficient of Voc = -0.32%/degree C
10.8% voltage headroom with 6s configuration means OK for 34 degrees below 25C nominal, so as low as -9 degrees C. I would be OK with that for my San Jose location.
I wouldn't use 7s.

If you want to go with your measurements for degraded panels being lower you can, but would be best if you had accurate panel temperature to use in calculations, and you were sure it was close enough to full sun to get Voc.
But I still wouldn't use 7s, since your measurements put that at 250V without being cold.

SunPower panel ratings are higher wattage per area than SanTan (older Trina), and your experience show larger spread because the SanTan are further below their rating. Getting more of the high efficiency panels would be the way to get the most watts.
Click to expand...
You are right, adding them up makes them a little higher. I will check again and probably decide on 6s3p.

Right now my batteries are fully charged and there's very little load. And the voltage is at 201v.

Screenshot_20210515-170627_WatchPower.jpg

Current setup attached to unistrut. Tilted with some jack stands ? pic taken around 7:30 last night

20210514_190517.jpg
 
how did you end up supplying and charging the 12v side of your system?
 
GSXR1000 said:
how did you end up supplying and charging the 12v side of your system?
Click to expand...
I still have 2x Battleborn Batteries and my Progressive Dynamics converter to keep them charged. I am thinking about removing the generator to get rid of the need of a high amp draw and adding another inverter/48v battery. The only other high amp draw i have is the leveling system which draws 80a.

I'm wondering if I can get the hydraulic pump "rewound" or something to make it compatible with 48v. After that, a simple 48v to 12v buck converter can power the rest of the 12v appliances.
 
Lt.Dan said:
I still have 2x Battleborn Batteries and my Progressive Dynamics converter to keep them charged. I am thinking about removing the generator to get rid of the need of a high amp draw and adding another inverter/48v battery. The only other high amp draw i have is the leveling system which draws 80a.

I'm wondering if I can get the hydraulic pump "rewound" or something to make it compatible with 48v. After that, a simple 48v to 12v buck converter can power the rest of the 12v appliances.
Click to expand...

Should be able to get a 48V hydro pump no problems. It might even be much more compact for same pressure/flow.
 
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