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diy solar

Should I buy this panel?

B

bry

New Member
Joined
Oct 22, 2024
Messages
7
Location
Dominican Republic
Hey. I’m on a sailboat in the third world and am desperate to replace my solar panel. I’ve got two 50 Ah batteries wired to a Midnight Brat. Power requirements are light, just cabin fans, computer and phone charging.

Local junk dealer has a used 160 W panel for $124 USD that is visually in good shape. Serial number: JPM160M616120127. If anyone has information as to the quality of these panels, please chime in.

The VOC listed on the label is 21.6V. The ISC- 9.47 A. The VPM- 12.9.

I can drag the panel out onto the street and orient it as best I can into the sun and check the actual output. But what should I be expecting from a panel that is maybe 6 to 10 years old. And please don’t muddy the waters with percentages. Hard numbers, please.

Bottom line: Should I buy this panel?

Much thanks, guys… Bry
 
bry said:
Hey. I’m on a sailboat in the third world and am desperate to replace my solar panel. I’ve got two 50 Ah batteries wired to a Midnight Brat. Power requirements are light, just cabin fans, computer and phone charging.

Local junk dealer has a used 160 W panel for $124 USD that is visually in good shape. Serial number: JPM160M616120127. If anyone has information as to the quality of these panels, please chime in.

The VOC listed on the label is 21.6V. The ISC- 9.47 A. The VPM- 12.9.

I can drag the panel out onto the street and orient it as best I can into the sun and check the actual output. But what should I be expecting from a panel that is maybe 6 to 10 years old. And please don’t muddy the waters with percentages. Hard numbers, please.

Bottom line: Should I buy this panel?

Much thanks, guys… Bry
Click to expand...
That Vmp looks too low. Please check it again and don't buy it if that is the actual Vmp.
 
Thanks guys. Really appreciate your responses. I’m going back this morning to look at the VPM again. There wasn’t a lot of light in the store and I didn’t have a flashlight. What VPM range should I be looking for in a 160 watt panel?

Thanks again… Bry
 
Also measure the panel. How big is it? A 10 year old 160 wat panel should be close to 1 square meter. That would be 16% STC efficiency. I just looked up a couple more panels on Amazon, and the decent 200 watt panels all are just over 1 square meter. Mine came in at just under 1.5 meters long and .75 meters wide. That is 1.125 square meters. 160 watts would be a little smaller, but it depends on the efficiency as well. Figure 0.9 meters is a fair size for 160 watt panels. If it is much smaller than that, it is not a 160 watt panel.

With just a simple meter, the VOC voltage out in the sun should be close to the rated 21.6 volts.
If your meter also has am amp scale that can measure to 10 amps, connect the meter across the panel output and when faced directly at the sun, the ISC current should be close to the rated 9.47 amps, but being the real world, clouds, not ideal angle, 10 year old panel, if it makes 7 amps, it is probably still okay. When you go to disconnect the current meter, try to block the sun from the panel to reduce the current first. It can strike a bit of an arc and burn the leads as you open the current on a panel producing power. Even a single 160 watt panel can make a reasonable arc like this. Pull the lead off fast if you can.

If you don't have a current meter, do you have access to old incandescent light bulbs? For example, connecting two 50 watt 12 volt car headlight bulbs in series can make a decent test load for a "12 volt" solar panel. It's not a full power test, but if the panels can push their VMP voltage into that load, you know all the cells are good. A hot 50 watt 12 volt bulb is about a 3 ohm load. Two in series is 6 ohms. At 17 volts, it would pull about 2.8 amps. This is only asking for 50 watts from the panel, so it is not a stress test. In just decent light conditions, it should have no problem pushing the voltage into that load.

The VMP voltage of a typical silicon solar panel is about 80% of the VOC voltage. My "12 volt" 200 watt panels are 22 volt VOC and 18 volts VMP. But this voltage is difficult to measure as it will be the voltage an MPPT charge controller will find while in operation. I would expect this older panel to run about 17 volts, which should work fine on a 12 volt battery system. What are you using for a charge controller? Going with a decent MPPT controller can get you 30% more energy from the panel than a PWM charge controller.
 
Vmp...Vmp...Vmp…

Okay, think I got it. I’m blaming it on dyslexia.

I apologize for the delay in responding, but this is taking longer than I thought. And I did not buy the panel but did test it.

First off, it is a little over a square meter in size, so that’s good. I pulled it out onto the sidewalk and set it in strong sunlight and checked the sticker for the Vmp. And I did get it wrong. The correct number is 17.9. I read the 7 as a 2. When I put the meter on it, the VOC came in at 19.2V and the ISC at 6.3A. This compared to the specs of 21.6V and 9.47A respectively.

Those numbers didn’t seem too awful but I balked when I discovered the cover plate for the junction box was missing. The store own suggested I wrap a plastic bag around it. I told him I would have to think about it.

Anyway, that’s how we left it. And my controller is a Midnight Brat, PWM. At the time, it was the only waterproof controller I could find. My previous unit died when water dripped on it. Life on a boat, I’m afraid.

Any comments are much appreciated.

Bry
 
Wow, too bad you arent near me...
I have tons of 240W used panels for $60 each...
 
Last edited:
Two things.
1, A panel sitting in the sun will warm up and the Voc. will drop from the STC voltage. STC = Standard test conditions of 1000 watts per sq. meter illumination @ 25 degrees Celsius.
2, When testing the Isc. you can aim the panel directly at the sun for peak current. As you tilt the panel away from the sun you will see the current drop.
 
Mmm… sixty bucks each sure sounds like a deal.

Loss of output due to heat is, I guess, a concern in a tropical climate. Not to mention the boat swinging at anchor. You can never get an ideal angle on the sun for more than a minute or two. That seems a good reason to over-size the panels. And yes, currently on the north coast of the DR and might have to travel to the city of Santiago to find an appropriate panel. That’s going to add to the cost.

Thanks again, Bry
 
bry said:
Mmm… sixty bucks each sure sounds like a deal.

Loss of output due to heat is, I guess, a concern in a tropical climate. Not to mention the boat swinging at anchor. You can never get an ideal angle on the sun for more than a minute or two. That seems a good reason to over-size the panels. And yes, currently on the north coast of the DR and might have to travel to the city of Santiago to find an appropriate panel. That’s going to add to the cost.

Thanks again, Bry
Click to expand...
That's the nature of PV on a boat. At least you have ocean breezes to help cool your panels, especially if they are mounted in free air as opposed to down on a hard surface.
 
Yes. Have them mounted on an arch with free circulation. But not much wind this year. Trades are down and it’s really hot. Unusual for the coast when even in the mid-nineties it is quite enjoyable.
 
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