Solar Panel Install Ideas - Page 4 - Fiberglass RV


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Old 01-23-2013, 05:04 PM   #43
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Interesting video and I completely agree, you get what you pay for with controllers. I use a Morningstar mppt controller and itís way more robust than the cheapies off ebay. Iíve seen some that donít even have proper heat sink fins, thatís just scary, you could burn down your egg.


Best bet is to buy a good controller and you wonít have to worry about it working properly. With a proper meter you can tell if they actually work. Using my trimetric and a separate meter on my panel I can compare values and see the controller converting the voltage properly and see the amps going in or out of the batteries.
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Old 01-24-2013, 06:15 AM   #44
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Thomas and Drew are right. You get what you pay for. When I buy a product that works, I usually forget the additional cost long before the product disappoints me.
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Old 01-24-2013, 12:33 PM   #45
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Unfortunately I can't watch the video. Videos use too much data. The discussion got me curious so I did a little digging.

I've been to several sites. Lots af smoke and mirrors written by sales folks who were let in the room with the engineers. So far here's as far as I've gotten.

Because each solar panel has it's own unique I-V characteristic, when multiple panels are placed in an array none work at their best. In order to improve the situation and get the most power from each panel, an MPPT controller is paired with each panel.


The Maximum Power Transfer Theorem says that if the load resistance is exactly equal to the internal resistance then maximum power will be delivered to the load. In English, your extension cord has a wire resistance. If you could make your skill saw have a resistance equal to that value then your saw would be at maximum horse power.


The solar panels have an I-V characteristic that looks like a step. The controller uses one of several algorithms to determine this step and adjusts the load such that it is equal to the inverse of the first derivative (di/dv) at the "knee" or corner of the step. Since that point is the maximum power point, by making the load equal to that point you extract the maximum power from that panel. It would be like having a box that would transform the skill saw.

Each solar panel/MPPT controller pair is now at it's peak efficiency for it's current solar condition (sun vs shade). This apparently increases the efficiency of the array. That's as far as I've gotten. I haven't figured how the panels are then configured to take advantage of this peak efficiency. Realizing that any electronics between the panel and your battery will have loses that will subtract from the power delivered by the panel, I'm not sure there is much of a benefit here to a small one or two panel array but since I have never looked at this before, I might be mistaken. Comments would be helpful. . Raz
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Old 01-24-2013, 01:27 PM   #46
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I found this interesting.

Maximum Power Point Tracking Charge Controller

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Maximum Power Point Tracking is electronic tracking - usually digital. The charge controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Most modern MPPT's are around 93-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-15% in summer. Actual gain can vary widely depending weather, temperature, battery state of charge, and other factors.
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Old 01-24-2013, 02:54 PM   #47
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Originally Posted by Thomas G. View Post

That does not sound like what I read about. Reads like a sales brochure. Nobody in the electrical field refers to current as amps. Amps is the unit. Here is where I started. I worked through some of the bibliography as well. The Scientific American article starts well but fizzles at the end. What do you think? Raz

https://en.wikipedia.org/wiki/Maximu...point_tracking
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Old 01-24-2013, 03:23 PM   #48
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Originally Posted by P. Raz View Post
.........What do you think? Raz
I think I'd better stick to your extension cord analogy, that I sort of understood.
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Old 01-24-2013, 05:13 PM   #49
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I think I'd better stick to your extension cord analogy, that I sort of understood.
Well, I may be way off the mark here. This is not an area I am familiar with. But this looks like something folks have applied to large solar arrays. PhD stuff brought to practice. Then someone else sees a chance to cash in and now everyone needs one. When I see Scientific American, and IEEE Spectum and transactions cited I know there's a real technology here. Whether is applies to small panels on our trailers I'm not so sure. Twenty years ago folks bought Green plugs and Mr. Watt. I try to avoid that argument too. I'll read some more. It's damn cold here so I've nothing better to do. My gut tells me at best this is a high price for a few percent gain in efficiency. Kinda like hybid cars. Oops, they closed that thread. Perhaps someone more familiar can shed some light. Raz
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Old 01-24-2013, 08:33 PM   #50
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The real advantage from mppt is when you use a high voltage array to charge a much lower voltage battery bank. An mppt controller will take the higher volts, and give you a gain in amps going into your battery bank. For example, a 200w 42v panel charging a battery at 14.8 volts will give you 13.5 amps (not taking into consideration loss in wire, efficiency, etc.) As someone who uses that setup, I can tell you it works. However when I used a lower voltage panel I saw no difference, and probably would have been better off with a pwm controller because my mppt controller didnít work well below a panel voltage of 15.5v, which occurs quite frequently on cloudy days.

Thatís why I went high voltage, in bad sun my panel voltage is still in the mid to high 30ís and even if itís not producing much power I can still get something out of it. The other advantage is the cold, panels sit at a higher voltage the colder it gets, so you should get more bang for your buck with an mppt controller when it converts the higher voltage down.
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Old 01-24-2013, 11:04 PM   #51
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Quote:
Originally Posted by P. Raz View Post
The Maximum Power Transfer Theorem says that if the load resistance is exactly equal to the internal resistance then maximum power will be delivered to the load. In English, your extension cord has a wire resistance. If you could make your skill saw have a resistance equal to that value then your saw would be at maximum horse power.
Okay, an example would be that if you were trying to feed your saw with thin lamp cord, you would choose a higher supply voltage (plug into the 240V socket behind your kitchen stove) so that you had less current for the same power (and thus less power loss to resistance); you would then need a high-voltage/low-current saw (motor wound for use on European 240V power) which is a higher-impedance device.

I would be cautious with that analogy, because neither end of our scenario (the panel or the battery) are simple sources or loads. A common application of this matching idea is in energy transfer from a transmission line (a cable, such as the coax cable bringing signal to your television from the cable company or an antenna) to a load (the television's input circuit) - in this case, it's called impedance matching. The problem is that you need to match the characteristic impedance, which is not the same as the simple resistance. No matter how long your cable to your antenna, it is 75-ohm cable; the power cord's DC resistance is not what you need to match, and in our solar setup the is not a simple source.

Quote:
Originally Posted by P. Raz View Post
The solar panels have an I-V characteristic that looks like a step. The controller uses one of several algorithms to determine this step and adjusts the load such that it is equal to the inverse of the first derivative (di/dv) at the "knee" or corner of the step. Since that point is the maximum power point, by making the load equal to that point you extract the maximum power from that panel. It would be like having a box that would transform the skill saw.
It took me a couple readings but yes, this what the MPPT controller is doing - driving the load on the panel to the point where the panel is most effective, rather than where the actual load (the battery) would take it.

I agree that the value of an MPPT controller is matching the current/voltage relationship of the solar panel to the completely different current/voltage relationship of the battery. In other terms, you are decoupling the panel and battery systems so that each can be operated more optimally instead of accommodating the other system. One might think of that as fixing an impedance mismatch, in a metaphorical rather than literal sense.

While the article which Tom linked is written in somewhat loose terms, I don't see any conflict with the more rigorous treatment of the Wikipedia page - picking the peak of the power curve is the same as picking the "knee" of the I-V curve.

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The real advantage from mppt is when you use a high voltage array to charge a much lower voltage battery bank.
Allowing the panel system to operate at high voltage, and thus low current, and thus low resistive loss in conductors, is one of the two advantages. A controller would have this advantage even if it wasn't a tracking controller, but just had a dumb voltage converter. Think of the utility power distribution system, in which high-voltage power transmission lines carry electricity the long distances with minimal loss, then dumb transformers step the voltage down (and current up) to the level we need to get into our houses.

The tracking feature of MPPT controllers is beneficial even when the nominal voltage of the panels and the battery are the same, which is the typical case for small panels on our little trailers.
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Old 01-25-2013, 08:19 AM   #52
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Brian, thanks for coming. I like your impedance matching analogy. A bit like an automatic transmatch.

As I said, I'm skeptical of the value here at low power levels. On large multi kilowatt arrays a few percent increase in efficiency justifies the overhead. But at 100 watts, a warm box might be a deal breaker. It is difficult for most to be an informed consumer, thus salesmanship will rule. Once purchased, it's easier to agree to disagree than argue. Much like smart chargers I think this will be another topic I will avoid on the forum.

I'm going to read some more and see if I can get a better handle on the circuits involved. How they match currents in series and voltages in parallel interests me. Take care, Raz
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Old 01-25-2013, 08:59 AM   #53
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Now most of this conversation has been beyond me lol...How about some product comparisons of high powered panels and lower paneled panels? If Im buying a single 85-100 watt panel just to keep my batteries ( I have 2 Optima BlueTop D34M's) Topped off, and honestly I have no idea if Im driving how long it takes to charge my batteries...I did order a 12v battery monitor so I can keep track of power consumption...namely the heater fan. I also ordered led light bulbs, waiting on the last 2 which should be here soon... next weekend I can install them and not worry about them draining my batteries.

But how efficient of panels and a controller do I really need? Obviously I do not want to cook my batteries, but Im thinking "if" I did a weekend of winter camping, my heater isdrawing 2.7amps I don't think I would be getting enough juice to keep the batteries toped off, but to keep it from goin dead.

The day I bought my ParkLiner, I made it to my friends place around 9pm and fired up the heater because the trailer wasn't winterized and temps were dropping down as a storm front was moveing in. I realized after making a little boo-boo I needed more antifreeze on saturday, but had to go home for something and was coming back on sunday morning... around noon on sunday the battery must have gotten low enough the heater wouldn't come on.... hooked it up to my truck and it came right back on.

Im almost 20 years till retirement so the idea of seriously being concerned about maximum power out of a cell isn't as important to me... a high level of efficiency is a plus...Im sure if 10 amps or so of power per day was dumping into my batteries on saturday and sunday it might have survived a weekend...going longer then that I would need a larger and or much more efficient setup but wouldn't really make sense for a "maybe" once a winter trip... my generator in that situation would fill the gap.

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Old 01-25-2013, 09:27 AM   #54
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Originally Posted by deryk View Post
..........
But how efficient of panels and a controller do I really need? Obviously I do not want to cook my batteries, but I'm thinking "if" I did a weekend of winter camping, my heater is drawing 2.7amps I don't think I would be getting enough juice to keep the batteries topped off, but to keep it from going dead.
......
deryk
I think that you'd be happy with a 100 watt panel and a PWM controller. You mentioned not mounting it permanently, so a conventional glass covered panel would probably work just fine. If you want to get fancy you could tape a flexible panel to your roof like Norm did.

Solar Cell, Solar Panel, Solar PV, Solar Products, Charge Controllers, Solar Trackers

Solar Cell, Solar Panel, Solar PV, Solar Products, Charge Controllers, Solar Trackers

Amazon.com: Uni-Solar PVL-68 PowerBond PVL 68 Watt 12 Volt 112-Inch x 15.5-Inch Flexible Solar Panel: Patio, Lawn & Garden

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Old 01-25-2013, 10:41 AM   #55
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While this website speaks more to non-mobile setups, it does have a few articles which explain panel efficiency.

Solar Panel Efficiency Comparison | SRoeCo Solar

I read recently the efficiency record was broken by a lab working on soft portable panels for the US military, for soldiers to deploy out of their packs. That's good news for all of us in the future I'm sure.
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Old 01-28-2013, 05:55 PM   #56
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A downside to the VHB tape method

Solar panels and 3M VHB tape - Escape Trailer Owners Community
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