Used Solar Panels from Santan Solar--Only 41% of the Rated Power?

MWeiss

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I bought forty 240W panels from Santan Solar in January. Have finally gotten around to deploying them and I'm noting dismal output levels when both 20 panel arrays are in full sunlight around noon-1pm.. I'm at 42° latitude.

I'm getting about 2kW from the southeast facing array and 1.4kW from the southwest facing array at the time when both arrays are in full sun and their outputs peak.

The array that's producing 1.4kW has a bad cell. I found that last night while checking the junction box bypass diodes. One panel has a short and is reading 1.6V instead of 9.8V that the the other two cell groups read. I pulled that diode thinking it was the diode, but no, it's the panel itself. That panel will have to be replaced. So I disconnected that panel and it's series companion for now.

I have the cells wired in series parallel, with ten groups of 2 in series, for a 48V nominal output for each array of 20 panels. These outputs are connected directly across my 48V battery bank's BMS outputs, so the BMS can shut down incoming charge if the voltage exceeds a set value.

I read about MPPT controllers and wonder whether directly connecting the panels to the batteries is creating a mismatch (similar analogy would be like connecting a 4 ohm speaker to the 8 ohm output of a vacuum tube amplifier--power transfer efficiency would be cut by about half) in load resistance to source resistance of the panels. Is it possible that putting a charge controller could double my panel efficiency, or are these used panels degraded to the point where over half their capacity is gone?
 

RCinFLA

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If you connect panels directly to battery the panel voltage will drop to that of battery. You also have no charge managment so may overcharge batteries. Using a BMS for charge cutoff is not a good solution.

When you have panels facing different directions you really should have each group on its own charge controller.
 
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Pyrofx

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Just fyi. I picked up 72 of the 250s. They put out 60%. Kinda sucks but per watt cost is still ok. Just eats up realstate. Especially with the cost of racking steel
 

MWeiss

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RCinFLA, yes, those were concerns of mine, but we never get enough sun here to even full charge a bank 42kWh. My main concern was to do with optimum power point tracking. Like matching the load to the generator for optimal power transfer. Some MPPT charge controllers claim to increase solar power transfer up to 30% this way. I typically see 30-40 amps from each array going into the battery bank. The ammeter shows about 2.5kW at the peak time of day. I was expecting closer to 4kW, given each array is 4.8kW.

Pyrofx, 72 is a lot of panels but now I can see needing 120 of them myself! But I lack the land. I've only a couple of patches of land that get some sun part of the day. If I could lay 400 panels on the ground facing up, they would probably generate enough power regardless of sun, shade or overcast, but that's not realistic on my budget. What I have now just covers baseline household needs. If we turn everything off at night.
 

Bobert

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I have an array of 9 used 240 watt solar panels they have a OCV of 37.2 volts and a VMP of 30.4 and a max current of 7.89 amps. They are wired 3s3p. My MPPT charge controller tends to get stuck at 60v. From the array in full sun I will see 1700watts not to bad considering my panels are essentially mounted flat. But if my controller is holding the panel voltage at 60 volts the output will be around 600 watts under the same conditions. You cannot get the correct wattage out of your panels unless you have a MPPT controller to hold the voltage at max power point.
 

AntronX

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Those panels are 30Vmp so 2 in series need 60V load voltage. You are losing approx. 20% from peak at 48V load. Then there is 15% loss from temperature derating. So with 240W new panels with 1000w/m2 sun you should see 3.2 kW out of 20 of them at 48V. Most likely you are not getting 1kW/m2 sun at your location and not orienting them perfectly perpendicular to the sun. And since those are cracked vinyl modules they may be degraded by 10 - 20%.
 

Bobert

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Those panels are 30Vmp so 2 in series need 60V load voltage. You are losing approx. 20% from peak at 48V load. Then there is 15% loss from temperature derating. So with 240W new panels with 1000w/m2 sun you should see 3.2 kW out of 20 of them at 48V. Most likely you are not getting 1kW/m2 sun at your location and not orienting them perfectly perpendicular to the sun. And since those are cracked vinyl modules they may be degraded by 10 - 20%.
Actually I’m 3s3p so 60 volts is way off the 90 ish I’m supposed to have in full sun so stuck at 60 is way off of max power point. I have the panels mounted flat in an rv application and the panels never get close to optimal angles. I designed the system to give me adequate power in shade or cloudy conditions as these are the prevailing conditions in the area I live. Last week we went to a state campground for 4days and it was overcast 3 of the 4 days and raining 2 of those days and we were parked in full shade the entire stay. We ended up running the generator for 2 hours but probably could have done without it but since the state park has limited generator hours we figured we had better top of the batteries just in case.
 

timselectric

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Can you elaborate?
The output of solar panels is a raw power. Without equipment designed to harness the power. You will end up with either an under performing system, or a hazardous condition for all other connected items.
 

iamrich

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I have the cells wired in series parallel, with ten groups of 2 in series, for a 48V nominal output for each array of 20 panels. These outputs are connected directly across my 48V battery bank's BMS outputs, so the BMS can shut down incoming charge if the voltage exceeds a set value.
My 250w used panels put out 80% on a good day. I would definitely invest in a charge controller, preferably one with a 250vdc input so you can rewire the panels 5S4P. I think you will see much better output at higher voltage.
 

Bobert

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We keep mentioning MPPT controllers because they give the best possible performance. With your voltages a 48v pwm controller would give a dramatic improvement in charge rates but the cost savings would probably not be worth it in the long run but pwm will beat direct connect by a long shot.
 

MWeiss

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If I can get 30% more power out of the system, it would probably be worth me spending $500 on a MPPT controller. Rather than buying a lot more panels.
We've been running off the inverter since Sunday morning. Batteries are at about 55% in the morning and make it to 68% or so by evening.
I have three banks of 16S with three JK BMS, the outputs of which are summed at the buss bar. What's odd is that the lowest charge bank is always the one that's discharging the most and getting the least charge. So I have one bank at 71%, another at 58% and another at 49%. The last one is always bank 3, the one bank that has never been charged to 100%. With them all connected in parallel, I would think they'd balance to eachother. So what I'm doing is shutting off charging on banks 1 and 2 and trying to charge up bank 3 to full. If I turn on charging on all three, banks 1 and 2 show 10-30 amps charging and bank 3, with the lowest charge state, shows negative current or discharge. It's exactly the opposite of what should be happening. Right now it's overcast and I've got about 30A going into the batteries, but a long way to go to reach 100%. Not today.
The inverter has an automatic shutoff if the voltage were to go above 64V. So I suspect that the manufacturer accounted for overvoltage.
I've looked at a few controllers, but they seem to max out at 40A. I guess the idea of rewiring the panels for higher voltage, maybe 96V and using the MPPT, might gain me some, but how much is the question.
I do have that one cell that's shorted in the south facing array, so I disconnected it, which took two series panels offline.
If we are very careful with energy use, we can hold the battery level if it's sunny every day. Today I think we're going to start losing charge as the solar input for the day will be less than the 24 hour kWh usage.
My new 18kW LF inverter is on the way and already purchased and it has an MPPT charge controller. But the spec is min voltage 60 and maximum voltage 100, which puts 2S at the minimum and 3S over the maximum. And it's max charging is something like 80A. I was planning to add some new, high efficiency panels to the roof and feed this charge controller from the roof panels, while the back yard panels still feed the battery bank, or through their own dedicated MPPT.
Can you recommend some good MPPT charge controllers I should be looking at?
 

MichaelK

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My new 18kW LF inverter is on the way and already purchased and it has an MPPT charge controller. But the spec is min voltage 60 and maximum voltage 100, which puts 2S at the minimum and 3S over the maximum. And it's max charging is something like 80A. I was planning to add some new, high efficiency panels to the roof and feed this charge controller from the roof panels, while the back yard panels still feed the battery bank, or through their own dedicated MPPT.
Can you recommend some good MPPT charge controllers I should be looking at?
Something sounds very wrong here? An 18kW inverter with a 100V limit? Please provide a link to the inverter you are talking about here. Either there's a mistake with the numbers you are providing, or this is some kind of cheapo imported junk that you shouldn't have spent money on in the first place.

I haven't bought panels from SanTan, but I have made multiple used panel purchases, and each and every one of them so far has had excellent output, some better than my retail purchased Renogy panels. I measured 94% output from some used Astronergy panels, and that was measuring them at 4pm, facing West, exactly perpendicular to the sun.

I suspect that the majority of problems you are having is from utilizing the wrong/improper/absent equipment. I'm worried at this point that the stuff you've already spent money on needs to be junked.

I personally would only consider quality controllers from MorningStar, Midnight, Outback, or Victron, though you might find that the higher end Epever's are a reasonable good value for you.
 

MWeiss

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iamrich,
thanks for the link. I wonder if I need a separate MPPT for each array, given that they are facing different directions to catch morning and afternoon sun?

MichaelK,
Yes, it's in the owner's manual, but I mis remembered it.. it's 60-145VDC and 80A rated charge current.
I presently am using the small SunGold Power 6kW LF inverter and, aside from massive RF interference it causes on HAM radio bands, it's been perfect. Runs quiet, reliable and handles high surge loads better than our 13kW generator. I reckon I'll be just as happy with their 18kW model.

If you're getting 94% of rated panel output, you must be near the equator. I'm way up north near Canada and the sun is a lot weaker here.
The way I tested a couple of panels back in January and again in April, was to set on up against my truck, facing perpendicular to the sun. Then I put a 4 ohm power resistor across the output and measured the voltage. I calculated 80W in January. When I repeated the test in April, I got 186W. That was at 12:30pm both times. I also experimented with shading. If I put my hand over half of one cell, total output of the panel dropped by about 40%!
But the thing is, I'm not sure that a 4 ohm load gets the optimum power out of the panel. As is the case with going direct to the batteries, it's probably not optimal either. So if a MPPT controller can help match the "impedance" (for lack of a better term, because impedance only refers to alternating current) to the load, I can get better transfer of power.

I'm looking at the websites for the companies you listed. Seems that several of them do not sell to end users and others do not have dealers in my area. All of them do not list prices and require filling out forms for a quote, which I am doing.

I need one shorted cell/panel replaced to get the south array working at full capacity again. The rest of the gear is fine.

This is the inverter that I ordered last week. It's the larger version of what I now have, but includes MPPT charge controller.
 
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MichaelK

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iamrich,
thanks for the link. I wonder if I need a separate MPPT for each array, given that they are facing different directions to catch morning and afternoon sun?

MichaelK,
Yes, it's in the owner's manual, but I mis remembered it.. it's 60-145VDC and 80A rated charge current.


If you're getting 94% of rated panel output, you must be near the equator.

I'm looking at the websites for the companies you listed. Seems that several of them do not sell to end users and others do not have dealers in my area.
I don't think so. What I've found is that I can have different arrays facing 90 degrees to each other, and voltage doesn't vary much, just amperage. I myself think that overpaneling by facing in different directions is an excellent way to make extra power on cloudy days, without overloading the controller. I'm in California. I've measured the output of my panels looking at the total watts coming into the charge controller.

Looking at the specs for your new unit, a few of the numbers don't seem to quite match up.
1654631044179.png

It seems to be rated at 80A, but to get 80A at 50V, you'd need 4000W of panels, so I am a bit surprised their watt limit is 3200W? Their overcharge disconnect also seems quite low at 59.2. I'm charging my Rolls batteries at 59.6V?

Assuming you never see more then 85%, that would work out to be 4000W/85%= 4700W of solar.

Assuming you have panels with a Vmp of 30.0V and a Voc of 37.5V, then it would be safe to wire three in series. Looks like you could safely handle six parallel three-panel arrays. Midnight's 6-breaker combiner box would pair well with this wiring strategy. Since your area might get cold enough, plug your panel specs into Midnight's string calculator to make sure you won't exceed the Voc limit at your winter low.

Here is the company I like to do business with that carries most of the brands I've mentioned.
 
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iamrich

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iamrich,
thanks for the link. I wonder if I need a separate MPPT for each array, given that they are facing different directions to catch morning and afternoon sun?
I was going to say you could probably run both strings on one, but I just don't know enough about your setup and output.

Specs say 5700w (7000w over paneled) and you have 9600w of panels, but with your setup I wonder if you would ever see more than 5000w of output at any point? You could hook the unit (or something similar) to one array for a week and monitor how much output you get (I think that unit will graph), and then switch to the other array, and then combine the data to get a rough estimate. If it is under 5700w you are golden. My assumption is the next couple of months will be your peak production.
 

iamrich

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I was going to say you could probably run both strings on one, but I just don't know enough about your setup and output.

Specs say 5700w (7000w over paneled) and you have 9600w of panels, but with your setup I wonder if you would ever see more than 5000w of output at any point? You could hook the unit (or something similar) to one array for a week and monitor how much output you get (I think that unit will graph), and then switch to the other array, and then combine the data to get a rough estimate. If it is under 5700w you are golden. My assumption is the next couple of months will be your peak production.
You likely would get more output out of two MPPT's, but at $400 a piece, not sure it is worth it?
 
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