Is This Solar Panel Useful? - Fiberglass RV


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Old 08-13-2019, 07:21 PM   #1
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Is This Solar Panel Useful?

I was at a local refurbish supply store the other day & saw a bunch of these 10w solar panels for $20 each. The cord has a stripped black & white wire.

I'm not familiar at all with solar but was hoping someone could let me know if I could make use of it..... if anything.

We have a 12v marine battery which we mainly use for the fantastic ceiling fan & a few LEDs.

Thanks for any info. Click image for larger version

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Old 08-13-2019, 07:59 PM   #2
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While quality counts, the primary metric is price per watt. Small panels like this cost more per watt than larger ones, such as 100 watt panels, so if you need more power, a larger panel is likely a better buy. But for a minimal trickle charger, a 10 watt panel might work, assuming its of good enough quality. For most larger solar panels for small campers I would expect to see no more than $1.20 a watt. The ones you are looking at at $2 per watt but like I said.. these smaller ones cost more per watt.

So if you just want to maintain a battery's charge while the battery is not being used, or maybe maintain a battery for a driveway gate opener back-up battery, then one of these panels (with a controller) might be fine. But if you want to run your camper on them then I expect you would need a number of them, and the price would be more than buying larger panel(s). And you should add in the cost of a controller, matched to the total watt output of the panels you will or might use.

What you need to determine is how much power you need to generate.. and thats a much longer discussion....
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Old 08-14-2019, 12:33 AM   #3
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you could charge your cell phone...
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Old 08-14-2019, 01:55 AM   #4
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you'd need a solar charge controller to use that as a battery tender/keeper,,, 10 watts is just way too small to be of any use for actual battery charging.

here's the specs on that panel,
https://www.solartechpower.com/SPM010P-A.html
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Old 08-14-2019, 11:33 AM   #5
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Quote:
Originally Posted by John in Santa Cruz View Post
you'd need a solar charge controller to use that as a battery tender/keeper,,, 10 watts is just way too small to be of any use for actual battery charging.

here's the specs on that panel,
https://www.solartechpower.com/SPM010P-A.html
Hey, thanks! I'm glad I didn't buy any.

What would be a good choice?

I'd like to keep the 12v battery charged & maybe charge a couple phones.
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Old 08-14-2019, 11:39 AM   #6
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I use a Renogy 100W "solar suitcase" to charge the RV battery, and I do my phone charging off the RV battery using automotive phone chargers.
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Old 08-14-2019, 12:17 PM   #7
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Quote:
Originally Posted by barryra View Post
...
What would be a good choice?

I'd like to keep the 12v battery charged & maybe charge a couple phones.
Quote:
Originally Posted by gordon2 View Post
...
What you need to determine is how much power you need to generate.. and thats a much longer discussion....
Do you mean "keep the 12v battery charged" without otherwise using it except to charge a phone or two? Or do you plan to do more than that with your battery and solar? A 100 watt system works very well for many people who use a small camper and its hard to go wrong with a suitcase type since it can be used for other things, but you really need to come up with an energy budget based on usage, expected available sun, size and number of batteries, etc. to properly size a solar system, and thats a longer discussion .
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Old 08-14-2019, 05:36 PM   #8
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Quote:
Originally Posted by John in Santa Cruz View Post
I use a Renogy 100W "solar suitcase" to charge the RV battery, and I do my phone charging off the RV battery using automotive phone chargers.
We're basically wanting to charge the 12v marine battery. We use the fantastic fan & I'll eventually put in some USB chargers.

I saw some on Amazon from $352 to $56. Can you please show a link where you got yours? Thanks
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Old 08-14-2019, 06:02 PM   #9
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i got the older version with the 30A 'Adventure' controller, paid $3something for it in 2017, here is the current version, comes with a waterproof 20A controller. the 100A panel only needs 10A, so a 20A controller would let you slave two panels through one controller...

https://www.amazon.com/gp/product/B079JVBVL3/

I could run my water pump as needed, fantastic fan, furnace when it was cold at night, and all the LED lighting I wanted, and if I left the panel pointed towards the sunrise, by the time I woke up, the 27M in my Casita would be fully charged.
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Old 08-14-2019, 07:23 PM   #10
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Quote:
Originally Posted by barryra View Post

I saw some on Amazon from $352 to $56. Can you please show a link where you got yours? Thanks
Prime Day (July 16th) Amazon had the Renogy 100w suitcase with controller for $210.

I see its $235 right now (link above). Or get the newer model for $8 more. I'd probably go that route. I don't see any Renogy suitcases for $352 US (you are in MN, right?)

20A controller is more than adequate, as one panel puts out about 8 amps max.

+10 Do a survey of what you want to run, for how long, and how many amps each item draws.

The alligator clips to hook up to your battery are pretty stupid IMHO. I added an SAE style pigtail on the battery, making hookup easy.
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Old 08-14-2019, 09:22 PM   #11
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Redarc Dual Battery Charger/Isolator/Solar Controller

This Redarc DC to DC battery charger can take solar and alternator input voltages from 9VDC to 36VDC and transform that into the perfect charge profile for whatever 12V battery chemistry you have. So if you have some strange old PV panels that fall within those limits you can probably make them work for you. If your TV charging system is making at least 9V, you can fully charge the RV battery.



https://redarcelectronics.com/collec...ttery-chargers


It also acts as a battery isolator, and MPPT solar charge controller that will preference the solar input when available.


This unit also allows you to use a smaller wire from the TV battery to the RV battery charger because the charging current is completely managed, and the Redarc will take whatever voltage it gets and make it perfect for the RV battery.


The 25A model I just bought cost $369, but it replaces 3 devices and uses a tiny bit of real estate, and makes for fully charged RV batteries no matter what is wrong upstream. It is waterproof and needs no fan.


Looks like quite a problem-solver.
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Old 08-14-2019, 11:21 PM   #12
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All math is approx. as are amp output of solar panels of assorted wattages. Those are real but your mileage may vary. As might your amount of sun. Arizona and Montana are not going to yield the same amount of solar energy per day. And who knows what you get in the North Wet Coast.

40 watt would be about the minimum size, 50 watt would be better. Note the Current listed for most solar panels. Often on Amazon it will be in the images. Current (Imp) will be in amps. Might also be called Working Current or Operating Current also in amps.

Typical 100 watt solar panel 5.24 amps.
Typical 50 watt solar panel 2.53 amps
Typical 40 watt solar panel 1.78 amps
Typical 20 watt solar panel 1.14 amps

What you care about is how many amp hours of power it puts back into your batter vs how many amp hours you draw down.

Figure 8 hours of sun. 4 hours of full sun and 4 hrs. of angled sun, 2 hours of angled in the AM and 2 in the PM. So a crude rule of thumb calculation would be.

4 hrs x panel amps for full sun.
+
4 hrs. x 1/2 panel amps for angled sun.

You need to use the amp output for how many hours to get amp hours going back into the battery. Take the 40 watt example:
4 x 1.78 = 7.12 amp hours for full sun
4 x 0.89 = 3.56 amp hours for angled sun 1/2 amp output.

Total of 7.12 + 3.56 = 10.68 amp hours back into battery.

Then it is simply a matter of taking the amp draw of you appliances for how many hours they will be drawing those amps to determine how many amp hours you will draw from your battery.

5 amp phone charger running for 2 hours would draw 10 amps. A 2.5 amp phone charger running for 4 hours would also draw 10 amps.

Fantastic fan on low is I think around 1 amp draw give or take. Running for 8 hours would be 8 amp hours from the battery.

I bought this 40 watt suitcase because I figure it was the minimum output that was useful and it fit in a location I wanted to store it. Along one side of the closet. 13 ft. Scamp doesn't have a lot of large flat spots for storing a solar panel Power wise it is on the small side, storage wise it is also on the small side so....

https://www.amazon.com/ECO-WORTHY-Po.../dp/B010WUHW2G

Without repeating the math a 100 watt could give you about 31.44 amp hours a day back into the battery. A 50 watt would be about 15.18 amp hours.

Additional things to consider are how long does your battery need to go before it can be charged from the tow vehicle or you will be someplace with AC power to charge it? You can charge less than you use up to a point.

If you have a 100 amp hour battery you have about 50 amp hours of useable power (going below 50% charge shortens battery life a lot) so let us say you use 15 amp hours a day but only replace 10 amp hours. It would take you 10 days to get down to a 50% state of charge running a 5 amp hour a day charge deficit. Bet you run out of water first.

More charging amps from solar panel means much easier to recover from days with little or no sun. Using that same 15 amp hour a day draw, 3 cloudy days in a row and you are almost at 50% charge, and 40 watt panel giving you 10 amps from a sunny day will only buy you one more day.

Same 3 cloudy days, same 15 amp hours a day draw so down to only 5 amp hours above half discharged and the 100 watt panel on a sunny day puts back in better than two full days worth of charge (over 30 amp hours) Second day of sun and boom back to fully charged. So bigger buys you a good cushion.

If you use your propane furnace and it has a blower it will suck a lot of amps and run often enough to really put a draw on your battery.

You might also consider these connectors for hooking between battery and solar panel if you have one that is portable. I just put one on battery, one on solar panel wire, and one on the clip & lighter plug original connector I cut off. Wasn't going to take battery cover off and on every time I hooked up solar panel suitcase. Can still plug in the original clamps if I wanted them.

https://www.amazon.com/SPARKING-Exte...p/B074VS2DG6/r

Personally I like the suitcases, or portable panel. Not that hard to put some legs on any panel or make a stand. I would rather park in the shade and still be able to place panel in sun, and angle toward sun. That said one can always mount a panel on the roof. People use 3M VHB tape to attach brackets with good success. Then maybe a portable panel as an additional source. In which case you probably want the charge controller on the camper not on the panel so you can feed more than one panel to it.

For me the deficit comes from running the inverter to charge camera battery. Those batteries charge slowly, so even though the draw isn't high it is over several hours, and the inverter is not 100% efficient so there is some power loss to running it.

Good luck.
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Old 08-15-2019, 10:18 AM   #13
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RogerDat, That is a terrific presentation of the whole solar/battery design and use situation! Thanks for taking the time to set that out for public use.
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Old 08-15-2019, 10:45 AM   #14
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Quote:
Originally Posted by RogerDat View Post
All math is approx. as are amp output of solar panels of assorted wattages. Those are real but your mileage may vary. As might your amount of sun. Arizona and Montana are not going to yield the same amount of solar energy per day. And who knows what you get in the North Wet Coast.

40 watt would be about the minimum size, 50 watt would be better. Note the Current listed for most solar panels. Often on Amazon it will be in the images. Current (Imp) will be in amps. Might also be called Working Current or Operating Current also in amps.

Typical 100 watt solar panel 5.24 amps.
Typical 50 watt solar panel 2.53 amps
Typical 40 watt solar panel 1.78 amps
Typical 20 watt solar panel 1.14 amps

What you care about is how many amp hours of power it puts back into your batter vs how many amp hours you draw down.

Figure 8 hours of sun. 4 hours of full sun and 4 hrs. of angled sun, 2 hours of angled in the AM and 2 in the PM. So a crude rule of thumb calculation would be.

4 hrs x panel amps for full sun.
+
4 hrs. x 1/2 panel amps for angled sun.

You need to use the amp output for how many hours to get amp hours going back into the battery. Take the 40 watt example:
4 x 1.78 = 7.12 amp hours for full sun
4 x 0.89 = 3.56 amp hours for angled sun 1/2 amp output.

Total of 7.12 + 3.56 = 10.68 amp hours back into battery.

Then it is simply a matter of taking the amp draw of you appliances for how many hours they will be drawing those amps to determine how many amp hours you will draw from your battery.

5 amp phone charger running for 2 hours would draw 10 amps. A 2.5 amp phone charger running for 4 hours would also draw 10 amps.

Fantastic fan on low is I think around 1 amp draw give or take. Running for 8 hours would be 8 amp hours from the battery.

I bought this 40 watt suitcase because I figure it was the minimum output that was useful and it fit in a location I wanted to store it. Along one side of the closet. 13 ft. Scamp doesn't have a lot of large flat spots for storing a solar panel Power wise it is on the small side, storage wise it is also on the small side so....

https://www.amazon.com/ECO-WORTHY-Po.../dp/B010WUHW2G

Without repeating the math a 100 watt could give you about 31.44 amp hours a day back into the battery. A 50 watt would be about 15.18 amp hours.

Additional things to consider are how long does your battery need to go before it can be charged from the tow vehicle or you will be someplace with AC power to charge it? You can charge less than you use up to a point.

If you have a 100 amp hour battery you have about 50 amp hours of useable power (going below 50% charge shortens battery life a lot) so let us say you use 15 amp hours a day but only replace 10 amp hours. It would take you 10 days to get down to a 50% state of charge running a 5 amp hour a day charge deficit. Bet you run out of water first.

More charging amps from solar panel means much easier to recover from days with little or no sun. Using that same 15 amp hour a day draw, 3 cloudy days in a row and you are almost at 50% charge, and 40 watt panel giving you 10 amps from a sunny day will only buy you one more day.

Same 3 cloudy days, same 15 amp hours a day draw so down to only 5 amp hours above half discharged and the 100 watt panel on a sunny day puts back in better than two full days worth of charge (over 30 amp hours) Second day of sun and boom back to fully charged. So bigger buys you a good cushion.

If you use your propane furnace and it has a blower it will suck a lot of amps and run often enough to really put a draw on your battery.

You might also consider these connectors for hooking between battery and solar panel if you have one that is portable. I just put one on battery, one on solar panel wire, and one on the clip & lighter plug original connector I cut off. Wasn't going to take battery cover off and on every time I hooked up solar panel suitcase. Can still plug in the original clamps if I wanted them.

https://www.amazon.com/SPARKING-Exte...p/B074VS2DG6/r

Personally I like the suitcases, or portable panel. Not that hard to put some legs on any panel or make a stand. I would rather park in the shade and still be able to place panel in sun, and angle toward sun. That said one can always mount a panel on the roof. People use 3M VHB tape to attach brackets with good success. Then maybe a portable panel as an additional source. In which case you probably want the charge controller on the camper not on the panel so you can feed more than one panel to it.

For me the deficit comes from running the inverter to charge camera battery. Those batteries charge slowly, so even though the draw isn't high it is over several hours, and the inverter is not 100% efficient so there is some power loss to running it.

Good luck.
Thanks VERY much for putting all that effort into explaining it so well. I really appreciate it.

Are you a rocket scientist or something??
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