FAQ:Solar Panel without the Technical Stuff

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Re: FAQ:Solar Panel without the Technical Stuff

Postby jss06 » Tue Mar 17, 2015 11:59 pm

The biggest advantage a MPPT Controller has is when it is used with a high voltage panel. It will charge better in partial shade than a PWM.
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Re: FAQ:Solar Panel without the Technical Stuff

Postby MtnDon » Wed Mar 18, 2015 12:32 am

The Tracer MPPT controllers are probably about the best of all the cheap MPPT's that come from China. That, unfortunately is not actually much of a recommendation. The bulk of the pile of cheap MPPT is junk and that just makes Tracer the best junk, IMO. I know someone who tried a Tracer MPPT 30 amp model recently and after two weeks of iffy performance and worse customer service got a refund and bought the Midnite Kid I told him to buy way back when we first started talking about it. Small off grid situation; 4 x 100 watt panels, a little more than the average TD can use.

As Bruce pointed out MPPT have fewer advantages when designing for a TD or most any RV for that matter. MPPT makes complete sense for PV systems that are larger than what we can fit on a TD or other small trailer; off grid cabins and homes for example. . Some of the advantages only come into play when panels are connected in series or series / parallel or when we raise the battery system voltage from 12 volts to 24 or 48 volts.

Good, reliable MPPT controllers are not cheap. MPPT cost can be countered somewhat by using the cheaper per watt large grid tie style PV panels. Those may be a difficult mounting job on some small trailers. If the goal is to have some PV to keep a battery or two that runs lights and mostly small power uses, small PV panels and PWM controllers are often the way to go, IMO.

When / if I do some solar PV on out CTC it will likely be with a PWM controller.
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Re: FAQ:Solar Panel without the Technical Stuff

Postby bdosborn » Wed Mar 18, 2015 9:15 am

jss06 wrote:The biggest advantage a MPPT Controller has is when it is used with a high voltage panel. It will charge better in partial shade than a PWM.


That' certainly true if you're using a higher-than-12V panel to charge a 12V battery. The Sunsaver PWM is rated for a maximum panel voltage of 30V but you need to be careful with that rating. Panel voltage goes up with lower temperatures and the panel outputs ratings are shown are at STP (77F). You're gambling on letting the smoke out of a PWM controller with a panel Voc higher than around 24V. My MPPT controler is rated for 150V input, which allows a lot of flexibility in panel connections - series, parallel, etc. Finally, the MPPT controller will step down the panel voltage to battery charging voltage pretty efficiently irrespective of the voltage difference whereas most PWM gets less efficient when the difference between the panel voltage and the battery volatge gets higher. Hence the cold weather advantage of MPPT.

It's still a cost benefit analysis in my mind; is the HV panel so much cheaper than a 12V panel that the added cost of MPPT makes sense? Maybe if you happen to have a HV panel already but I certainly wouldn't buy one over a 12V. There are people claiming that the HV panel has better performance in low light conditions but it's usually based on empirical results; I haven't seen any test results that confirm it.

I have both a PWM controller and an MPPT controller in my trailer and haven't noticed any difference in partial shading output; both are crippled by any sort of shade. And I wouldn't by an MPPT controller again, their just too expensive for the benefit they offer on a small system. You're better of buying more panel.

Too be honest though, my rambling is wwwwaaayyyy out in the weeds. Bottom line is that 99% of teardroppers are going to be very happy with a 12V panel and a PWM controller. As usual, I fall into the weirdo 1% group. :roll:

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Re: FAQ:Solar Panel without the Technical Stuff

Postby MtnDon » Wed Mar 18, 2015 6:11 pm

The so called 12 volt PV panels often cost $1.60 or more per watt compared to under a dollar a watt for the larger grid tie panels. I just got a note from SolarBlvd that they have some slightly more reasonable pricing on two "12 volt" panels.

150 watt panel $165 +approx 23 shipping on one, depending on where you are

130 watt panel $143+approx 23 shipping on one, depending on where you are

Good match for a PWM controller :)
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: FAQ:Solar Panel without the Technical Stuff

Postby KennethW » Sun Dec 06, 2015 9:53 am

I would like to tap some knowledge on putting solar on my TD. I need to run 2 CPAP's + some led lights,fantastic fan and 19"led tv. The CPAP's are critical!!
I know I can run the CPAP's 2 1/2 days on a group 27 105 amp hour battery. The plate on the Cpap says 2.5 amps time 2( for 2 cpap's)=5 amps. That is the load :roll:
Now I am thinking of using two 65 watt panel wired in serials.
http://www.ebay.com/itm/130-Watt-Mono-S ... SwT4lWRDbC

And a mppt controller PCM-3012.
http://www.ebay.com/itm/like/1411669032 ... ps&lpid=82

If I am informed right the high volts and a mppt controller will give me more watt into the battery even in low light conditions.
Am I right?
Will I get enough power from the system?
Is there a better control for the money?
I like that the two 65 watt panel will fit better on the curve of the roof of the TD.
But is there better lower cost panels?
Thanks to all that respond as I am a baby in the woods as far as solar voltaic's
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Re: FAQ:Solar Panel without the Technical Stuff

Postby jss06 » Sun Dec 06, 2015 11:38 am

That will give you 130 watts. So after conversion loss probably about 100 to 110 watts. That would be around 8.5 amps at 12 volts during sunlight hours to recharge the battery and run your other loads. Should be enough for what you have listed.
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Re: FAQ:Solar Panel without the Technical Stuff

Postby MtnDon » Sun Dec 06, 2015 12:46 pm

know I can run the CPAP's 2 1/2 days on a group 27 105 amp hour battery. The plate on the Cpap says 2.5 amps time 2( for 2 cpap's)=5 amps.


How far does that draw down the battery? 5 amps x 12 volts for 8 hours a night (a guess) = 480 watt hours

the 105 AH battery x 12 volts = 1260 watt hours

So it seems the load would draw the batteries down 480 /1260 = 38% in one night. Two days on just CPAP would draw the battery down to less than 25%. Not good for the battery.

~~~~~~~~~~~~~~~

To replace the CPAP used energy of 480 watt hours with panels that would provide a useful 100 watts all the time would need 480 / 100 = 4.8 hours of "perfect" sunshine. That's not possible in many places.


How much space have you available on the TD roof for solar panels? Could you fit a larger, so called 24 volt or grid tie panel? You could get a brand new panel of around 250 watts from solarblvd.com delivered to most places in the US for about the same cost per watt price as the used panels. You might even be able to buy a single panel locally from some solar dealer / installer who specializes in grid tie solar. Some of them don't mind selling a single panel. That would save the high freight on a single panel.


I'm not a big fan of the "no name" Chinese charge controllers. A Morningstar SunSaver SS-MPPT-15L will cost you more but it is a recognized name with a service network available if needed. Also available at solarblvd but a little cheaper at solar-electric.com.
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: FAQ:Solar Panel without the Technical Stuff

Postby bdosborn » Sun Dec 06, 2015 12:50 pm

KennethW wrote:If I am informed right the high volts and a mppt controller will give me more watt into the battery even in low light conditions.
Am I right?


There's one member here that swears by it. However, when I posed the question to the solar forum, the answer was probably not . The panels you linked are *barely* usable for 12V system with a Vmp of 14V. A better number would be somewhere around 17V. So if you do plan on buying them, I would plan on running them in series to get the voltage up to a better charging level. Of course you'll need an MPPT controller or a high voltage PWM controller if you do.

MPPT controllers are so spendy that any money you save on the eBay panel is more than eaten up by the controller cost. I have an MPPT and a PWM controller on my setup and haven't noticed much of an advantage of one over the other. If it was me, I would buy different panels that are more suitable for 12V battery charging and use a PWM controller. Then you can spend the money you saved from buying the PWM controller on bigger panels. A PWM controller based system gets you the most watts/$. Just make sure you can set your system up so that you can put one on the ground, in the sun, and run a cord back to the controller for the times you're camped in the shade. I get the most amp-hrs/watt from my portable panel as compared to the roof mounted panels since I move it to track the sun whenever I walk by it.

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Re: FAQ:Solar Panel without the Technical Stuff

Postby MtnDon » Sun Dec 06, 2015 2:23 pm

More.... I finally bit the bullet and bought two of the 140 watt 12 volt panels from solarblvd on Black Friday. Those along with the PWM charge controller I already had Midnight Soar Brat) will go a long ways to maintaining the battery charge in our CTC. Bruce is right about PWM vs MPPT in a small system. The 12 volt panels cost more per watt than the grid tie 24+ volt panels, but there are a number of good USA serviced PWM controllers at very good pricing. It's a wash when you add the cheaper per watt panels & more expensive controller and the more expensive per watt panels with the cheaper controller. For a bigger system MPPT is almost a no brainer.
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: FAQ:Solar Panel without the Technical Stuff

Postby KennethW » Sun Dec 06, 2015 6:25 pm

Thank's for the reply's.

MtnDon wrote:
know I can run the CPAP's 2 1/2 days on a group 27 105 amp hour battery. The plate on the Cpap says 2.5 amps time 2( for 2 cpap's)=5 amps.

How far does that draw down the battery? 5 amps x 12 volts for 8 hours a night (a guess) = 480 watt hours
the 105 AH battery x 12 volts = 1260 watt hours
So it seems the load would draw the batteries down 480 /1260 = 38% in one night. Two days on just CPAP would draw the battery down to less than 25%. Not good for the battery.
To replace the CPAP used energy of 480 watt hours with panels that would provide a useful 100 watts all the time would need 480 / 100 = 4.8 hours of "perfect" sunshine. That's not possible in many places.
How much space have you available on the TD roof for solar panels? Could you fit a larger, so called 24 volt or grid tie panel? You could get a brand new panel of around 250 watts from solarblvd.com delivered to most places in the US for about the same cost per watt price as the used panels. You might even be able to buy a single panel locally from some solar dealer / installer who specializes in grid tie solar. Some of them don't mind selling a single panel. That would save the high freight on a single panel.


I have been really killing the battery. That is one of the reason I am looking at doing solar.I just looked at a 24v 230w panel. It seems a little heavy for a foamy at 130# and the size would look funny on a small TD. Shipping is a killer at $45 plus $159 for the panel and the need for a mppt control. makes it out of my price range. But for a enclosed trailer it would give one a lot of power.

bdosborn wrote:There's one member here that swears by it. However, when I posed the question to the solar forum, the answer was probably not . The panels you linked are *barely* usable for 12V system with a Vmp of 14V. A better number would be somewhere around 17V. So if you do plan on buying them, I would plan on running them in series to get the voltage up to a better charging level. Of course you'll need an MPPT controller or a high voltage PWM controller if you do.

MPPT controllers are so spendy that any money you save on the eBay panel is more than eaten up by the controller cost. I have an MPPT and a PWM controller on my setup and haven't noticed much of an advantage of one over the other. If it was me, I would buy different panels that are more suitable for 12V battery charging and use a PWM controller. Then you can spend the money you saved from buying the PWM controller on bigger panels. A PWM controller based system gets you the most watts/$. Just make sure you can set your system up so that you can put one on the ground, in the sun, and run a cord back to the controller for the times you're camped in the shade. I get the most amp-hrs/watt from my portable panel as compared to the roof mounted panels since I move it to track the sun whenever I walk by it.
Bruce


I did not like the ideal of used panels anyway. I am now looking at
https://www.solarblvd.com/product_info. ... ts_id=3020
on ebay they are the same price with free shipping
http://www.ebay.com/itm/New-Mono-Solar- ... SwEeFVFIf4
At 59"x 27" it will fit on the TD and it only weighs #35. with a the lower cost of a PWM control it will be in my cost range.
Would I need a 20 amp control? like this
https://www.solarblvd.com/product_info. ... ts_id=2946
I do more of the road trip thing. So I am looking more of the charging on the go. But I could add a remote panel later if needed. I will have to look at if I can hinge the panel that would be on the roof, when at the camp site. With one 150 watt panel I may be light on power for two CPAP's but it would be a good start.
If the panels don't keep up I can run my HF generator. But I would rather not.

Thank's again all for the information.
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Re: FAQ:Solar Panel without the Technical Stuff

Postby catinmoon » Wed Jan 06, 2016 3:11 pm

Hi, I just saw this post and am wondering if it is still "current" (ha ha) in 2016? That is, I want a robust solar system for my teardrop, and am wondering if there have been any significant changes since this was initially posted.

thanks
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Re: FAQ:Solar Panel without the Technical Stuff

Postby MtnDon » Wed Jan 06, 2016 4:24 pm

Pretty much everything is more or less the same, except today you get more PV panel watts for your money.
Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ... http://countryplans.com/smf/index.php?topic=2335.0
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Re: FAQ:Solar Panel without the Technical Stuff

Postby catinmoon » Wed Jan 06, 2016 4:40 pm

Thanks, good to know. I followed some of the links in the electrical section but many of them were old.

I am a newbie to this so have a few "dumb" questions. I looked online for Class 27 batteries. Is this the same as a Marine battery? Or does Marine just mean Deep Cycle?

thanks
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Re: FAQ:Solar Panel without the Technical Stuff

Postby afreegreek » Wed Jan 06, 2016 9:37 pm

catinmoon wrote:Hi, I just saw this post and am wondering if it is still "current" (ha ha) in 2016? That is, I want a robust solar system for my teardrop, and am wondering if there have been any significant changes since this was initially posted.

thanks
Stephanie



https://www.wholesalesolar.com/

http://www.solarray.com/TechGuides/Batteries_T.php
Last edited by afreegreek on Thu Jan 07, 2016 2:33 am, edited 1 time in total.
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Re: FAQ:Solar Panel without the Technical Stuff

Postby catinmoon » Wed Jan 06, 2016 9:57 pm

afreegreek wrote:
catinmoon wrote:Hi, I just saw this post and am wondering if it is still "current" (ha ha) in 2016? That is, I want a robust solar system for my teardrop, and am wondering if there have been any significant changes since this was initially posted.

thanks
Stephanie


you would be much better off going to solar system company online and learning about, and how to use solar.. the people who think 12 volt group 24, 27, 31, Marine batteries are actual deep cycle batteries suitable to work as a solar power bank don't have any real knowledge about batteries.. solar panels will easily charge those batteries (to start your motor with) but those type of batteries are not designed to supply DC power.. they are starter batteries.. group GC2 are primarily the smallest size of true deep cycle batteries..

https://www.wholesalesolar.com/ this is a good information site to learn from even if you buy elsewhere..

http://www.solarray.com/TechGuides/Batteries_T.php is also good info.. especially "step to success" section..


Thanks, I will check out the links. I'm looking for power, not starting.
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