Experiments with solar panels - Page 3 - Escape Trailer Owners Community

Go Back   Escape Trailer Owners Community > Escape Tech > Escape Systems | Water, Waste, Charging & Propane
Click Here to Login
Reply
 
Thread Tools Display Modes
 
Old 11-05-2014, 05:42 PM   #21
Senior Member
 
Join Date: Feb 2010
Location: ?, Arizona
Trailer: ?
Posts: 736
Quote:
Originally Posted by gbaglo View Post
I have a half dozen large mirrors ( up to 2' x 4' ) mounted on a trellis in my garden. They reflect sunlight back onto the raised bed.
Been there for about six years.
I've noticed no improvement in my tomato crop.
I recommend wiring your tomatoes for 120V using at least a 30 amp RV power cord. That way you'll have fried green tomatoes right off the vine.
__________________

jamman is offline   Reply With Quote
Old 11-05-2014, 06:07 PM   #22
Senior Member
 
Vermilye's Avatar
 
Join Date: Feb 2010
Location: Oswego, New York
Trailer: 2016 Tacoma Off Road, 2017 21
Posts: 2,281
Quote:
Originally Posted by Parker View Post
Hi Jon,

Sometime maybe you could point me to the bulkhead connector you used to connect through the wall.
Parker
Because they were already used on my portable panel & the cables that came with it, I used a flush mount SAE connector. Came from SolarSeller.com (item E)
__________________

__________________
Jon Vermilye My Travel Blog
Travel and Photo Web Page ... My Collection of RV Blogs 2016 Tacoma, 2017 21
Vermilye is offline   Reply With Quote
Old 11-05-2014, 06:35 PM   #23
Senior Member
 
Join Date: Dec 2012
Location: Edmonton, Alberta
Trailer: 1979 Boler B1700
Posts: 9,047
Quote:
Originally Posted by alanmalk View Post
2. What are the drawbacks of using different size (voltage) panels at the same time.
...
I assembled two panels from 18 identical cells, one 6 cell (3v) "auxiliary" panel and one 12 cell (6v) "main" panel. The 2:1 ratio was intentional to match the real world where big panels are typically 18v or 36v.
I think there is some confusion here between size and voltage. The area of a panel (as well as the type of cells, of course) determines its maximum power output. That power can be designed to be a high voltage at a low current, a low voltage at a high current, or whatever you want - just be choosing the series and parallel combination of the cells. Bigger doesn't need to mean higher voltage. I should note that practical panels have a lot of cells (or an area of active semiconductor which can be divided into any desired number of cells), not just the minimum number to reach the design voltage, as used in this experiment.

In very large solar systems there are advantages to operating at a high system voltage, to keep currents lower (lighter gauge wires or less power loss in wires; less expensive controllers) and to minimize paralleling of batteries. They don't really run much at the system voltage, and live with the need to convert from DC at that voltage to what they need to use (such as 120V AC).

In an RV, I see no reason to consider any system voltage other than the nominal 12 volts DC of a six-cell lead-acid battery - that's what everything runs on. Panels sold for RVs are nominally 12V (so, peak power output at close to 18V, peak open-circuit voltage more like 20V) because that's what suits an RV's battery - not because the panels are big.
Brian B-P is offline   Reply With Quote
Old 11-05-2014, 06:42 PM   #24
Senior Member
 
Join Date: Dec 2012
Location: Edmonton, Alberta
Trailer: 1979 Boler B1700
Posts: 9,047
Quote:
Originally Posted by alanmalk View Post
To elaborate, a couple of solar panel dealer web sites stated explicitly that a lower voltage panel in parallel with a higher voltage panel would "pull down the voltage" of the high voltage panel. My own thought process concluded that if the panels in question had the normal blocking diode then it was impossible for any panel to "pull down" another.
I agree that a lower-voltage panel does not pull a higher-voltage panel down - for the reason stated - but the load does...

Quote:
Originally Posted by alanmalk View Post
Observations #1: The two ohm resistor is enough to pull down the horizontal panel voltage from a nominal 6v to 1.66v here in Denver on a sunny day at noon while pulling .84amps. Adding in the output from the tipped 3v panel raised the system voltage to 2.54v and 1.27amps. So much for the small panel pulling down the big one! Pure nonsense. But only pure nonsense when the load is bigger than the output of the bigger panel.

Observation #2: Under no load conditions, the small panel pulled down the voltage of the big panel by 0.002v. Essentially nothing
This illustrates that the load pulls the panel voltage down. Whatever the various panels are doing, the load keeps them from running at their ideal output voltage. In the case of the two ohm resistor, the very low resistance of the test load caused the higher-voltage (6V) panel to run far lower than its ideal. This operating voltage is so low that the lower-voltage panel was still able to put out enough voltage to contribute current (and the greater current meant more voltage across the resistor, moving the higher-voltage panel to a higher point on its curve). A greater resistance would radically change the situation... as we see in the "no load" case, which appears to be open circuit, rather than short circuit.

The load in a trailer is a combination of the battery and anything that is turned on, so it is the battery (all of its characteristics, including the state of charge), and to a small extent the other stuff that is running, that "pulls down" the panel voltage.

Panel manufacturers and decent retailers all publish the performance curve for the product. The load pulls the panel operation down to some point along the performance curve.
Brian B-P is offline   Reply With Quote
Old 11-05-2014, 07:11 PM   #25
Senior Member
 
Join Date: Dec 2012
Location: Edmonton, Alberta
Trailer: 1979 Boler B1700
Posts: 9,047
Alan, thanks for doing all the work and reporting the results.

Quote:
Originally Posted by alanmalk View Post
My conclusions (and it sure took me long enough to get here). Mixed size panels in parallel are not an issue. Smaller (or bigger) than the roof mounted ETI panel is not a factor - if the load is "big".
From the same data, I draw somewhat different conclusions.

We can see from the test that panels with two very different nominal voltages can run together. How - and how well - they work depends on the load.

If the load has enough resistance, high enough internal voltage, or any suitable combination, the higher-voltage panel will run up where it should at an effective working voltage; for power output that's ideally the peak power voltage, usually perhaps 85% of the open circuit voltage. Any panel connected in parallel which has a much lower nominal voltage will not be able to push any current into the load, and will just sit idle with its cells (and its blocking diode if so equipped) reverse-biased. The lower-voltage panel may as well be a brick, because it is just useless weight.
For instance, a high enough resistance in this test to force the 12-cell panel to run at 5 V would leave the 6-cell panel doing nothing.

An example might be a normal panel on the roof of an Escape (which of course has a nominally 12-volt battery or battery bank), with a 6-volt portable panel leaning against the side. The normal panel will work normally; the portable panel is pointless.
If the load has less resistance or internal voltage so that it allows the lower-voltage panel to run at any useful point, the higher-voltage panel is just running at a less-than-ideal voltage.
The two-ohm resistor in this test, when both panels are attached, is an example of this: at 2.54 V both panels are working. When only the bigger 12-cell panel is attached, the two ohms is too little so that panel is running very ineffectively at 1.66 V to produce 1.4 watts (compared to 3.2 watts at 2.54 V with only 50% more panel).

An example might be a too-high voltage panel on the roof of an Escape - let's say 36 V peak - with a normal (12 V nominal, 18V ideal, 20V peak) portable panel leaning against the side. The roof panel will work but at far from peak effectiveness; the portable panel will usefully contribute additional power.
If the load has low enough resistance or internal voltage, the two attached panels are both pulled by the load to far below their normal operating voltage, so they are just operating poorly, but to different degrees of badness.
A trailer example would be a 48V panel on the roof and a 24V portable panel against the side. Both panels would work, but both are a waste of money. Two panels of the same areas but constructed for the right operating voltage of up to 18 V (matching the trailer's nominal 12V system) would put out much more power.
To understand these scenarios in the test would require one more ammeter, so that the output of each panel could be separately observed, and a range of resistances. There's still only one voltage to measure, assuming we're still not concerned about voltage drop in connecting wires. It would also help to use the same size of panel, to separate the effect of panel size from the effect of panel voltage.

In the end, the mismatch of panel voltages may not be a fatal issue, but it is just bad for performance.
Brian B-P is offline   Reply With Quote
Old 11-05-2014, 07:47 PM   #26
Senior Member
 
MyronL's Avatar
 
Join Date: May 2013
Location: Edgewood, New Mexico
Trailer: 2013 Esc19/'14 Silvrado
Posts: 2,063
Alan, your info much appreciated. Tested my solar kit today while running the television playing a DVD disk off my Xantrex 600 Watt inverter. Conclusions are what you would expect.

1.) Solar more than kept pace with the load.
2.) Morningstar converter display indicated roughly .5 less power in the batteries.
3.) Biggest irritant, having to run extension cord from the inverter to the bed while the two (shore power) duplexes beside bed remained unused.

2 ea. 50 watt panels, 10 g. wire
(One) Morningstar controller inches from the batteries
Attached Images
File Type: jpg DVD1.jpg (94.2 KB, 11 views)
__________________
Myron
"A billion here, a billion there...add it all up and before you know it you're talking real money." Everett Dirkson
MyronL is offline   Reply With Quote
Old 11-05-2014, 10:02 PM   #27
Senior Member
 
Join Date: Mar 2013
Location: Yellow Springs, Ohio
Trailer: 2013 Escape 19
Posts: 544
Quote:
Originally Posted by Vermilye View Post
Because they were already used on my portable panel & the cables that came with it, I used a flush mount SAE connector. Came from SolarSeller.com (item E)
Oh, that's right.....you posted this a few days ago. Thanks again.
Parker is offline   Reply With Quote
Old 11-05-2014, 11:14 PM   #28
Senior Member
 
alanmalk's Avatar
 
Join Date: Apr 2014
Location: Arvada, Colorado
Trailer: '21 - 'Velocity'. Tow: Toyota Tacoma V6, 4X4, manual.
Posts: 546
Quote:
Originally Posted by alanmalk
The 2:1 ratio was intentional to match the real world where big panels are typically 18v or 36v.

Quote:
Originally Posted by Brian B-P View Post
I think there is some confusion here between size and voltage. The area of a panel (as well as the type of cells, of course) determines its maximum power output. That power can be designed to be a high voltage at a low current, a low voltage at a high current, or whatever you want - just be choosing the series and parallel combination of the cells. Bigger doesn't need to mean higher voltage. ...

...because that's what suits an RV's battery - not because the panels are big.
I probably should not have used the word "big panel" in this discussion. What I should have said was "...real world retail panels..." as opposed to my home-made low voltage panels.

Another point I should have emphasized is that I was not trying to measure "power" or wattage produced or consumed by a load. I'm strictly trying to measure a solar panel's behavior under a few specific conditions and debunk a myth or two in the process. A 2 ohm resistor gives me repeatable results and I don't have to locate a partially discharged 12v battery.

Finally, trying to optimize a given panel's output seems to me to be an exercise best left to the obsessive-compulsive. (Reminds me of trying to optimize a marginal refrigerator. ) Yes, it can be done, but all I am interested in is how to best replace a substantial amount of battery power quickly when the sun is on the "wrong" side of the equinox.

Your points are all valid - I just didn't want to get quite so deep into the subject.

--
Alan
alanmalk is offline   Reply With Quote
Old 11-05-2014, 11:34 PM   #29
Senior Member
 
alanmalk's Avatar
 
Join Date: Apr 2014
Location: Arvada, Colorado
Trailer: '21 - 'Velocity'. Tow: Toyota Tacoma V6, 4X4, manual.
Posts: 546
Quote:
Originally Posted by Brian B-P View Post
...
In very large solar systems there are advantages to operating at a high system voltage...
I shouldn't mention this but I can't help myself. One of the test I envision is to send the output of the smaller of my two home-made panels into a DC-DC boost converter. Maybe go up from 3v to 6v to match the larger panel. Then use two amp meters to measure actual efficiency of each system. Conversely, use a buck converter to drop the voltage of the bigger panel - similar to the action of a ($$$) MPPT device. (A reminder, I'm using 3 dollar parts to mimic 300 dollars worth of real-world equipment.)

And in case anyone is getting ideas - remember, this is just an experiment, not a suggestion that I have found a magic solution to a problem - that may not even exist.

All in good fun while I await my '21.
--
Alan
alanmalk is offline   Reply With Quote
Old 11-05-2014, 11:47 PM   #30
Senior Member
 
Join Date: Feb 2014
Location: Port Angeles, Washington
Trailer: 2014 19'
Posts: 532
Originally Posted by alanmalk
I'm strictly trying to measure a solar panel's behavior under a few specific conditions and debunk a myth or two in the process. A 2 ohm resistor gives me repeatable results and I don't have to locate a partially discharged 12v battery.

FYI - in a DC circuit a resistor is a fixed load. A battery is a reservoir. I'd suggest using a battery, testing both voltage and specific gravity, and use an auto light bulb shining on a white sheet of paper to observe charge/discharge. (looking at the filament is much more accurate, especially as it gets dim)

The light bulb can draw more or less depending on your choice. You can glance at the white sheet hanging on the wall and see 1. the load is connected. 2. you will see the color change which will give you a visual prompt to take measurements.

Battery specific gravity is much more accurate then voltage, you'll see if you test with the 'real thing' (a reservoir). Voltage moves much quicker then specific gravity.

Interesting tests, I enjoy reading your findings.

Mel
__________________

Klem is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off






» Virginia Campgrounds

Reviews provided by



All times are GMT -5. The time now is 05:58 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright 2012 Social Knowledge, LLC All Rights Reserved.