Camp Solar Setup (1 Viewer)
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surfpig
The Anti-Tech
You get a voltage drop as the current passes through the wires. So you're reading what's coming right out of the panel, rather than what's reaching the battery. You'll see a greater drop if you're using smaller gauge wires.
Yep - I agree with that. The effect is quite small in my case as Im only 6 ft from the battery and using heavy gauge wire. All mV count though. I think that the temp compensation would also benefit from being out of direct sunlight too (even though this unit is designed for direct exposure). My main reason for mounting the PWM on the slide is to see the charging state LED without having to delve into the engine bay every time (maybe I'll mount it so its visible through the grille). Having said that, having trialled the set-up over the last 3 month trip I am happy that it works nicely. At the moment the set-up is just clipped to the battery (my IBS dual battery controller handles the switching), for my post-trip upgrade I plan to firm this up with proper permanent connections....should improve the performance some more.
Cable power losses pale into insignificance compared with losses from non optimally positioned panels.....unless you want to add a lot more wattage to overcome the non optimum positioning. In my case I wanted to limit the weight and have only a limited space to mount a panel. I used flexible panels to reduce weight over the folding case/glass variety
Cable power losses pale into insignificance compared with losses from non optimally positioned panels.....unless you want to add a lot more wattage to overcome the non optimum positioning. In my case I wanted to limit the weight and have only a limited space to mount a panel. I used flexible panels to reduce weight over the folding case/glass variety
Cruiserdrew
On the way there
George or @TrickyT can explain it far better than I can, but here goes.
In any wire, there are resistance losses, based on how much current is flowing in the wire and how large physically the wire is. If you remember Ohm's law V = IxR. So assuming a constant voltage(coming out of your charge controller), as R goes up, I (current, the good stuff we want back in our batteries goes down.
Voltage drops, are related.
You can calculate the voltage drop with something like this:
Voltage Drop Calculator
So lets look at your set up. If you assume you have 12 ga wire, and 5 amp current, in a 30 foot run (that's to the battery AND back), you've lost 0.3 of a volt. Doesn't sound like much, but in 12 volt systems you only have 1 volt to work with because full battery is 12.8 volts and electrically empty battery is 11.8 volts. So your 0.3 volt loss causes a couple of things. First, your batteries will charge more slowly-with less voltage, there is less current flow. But also they may never reach a full charge before the controller kicks out of absorb and returns to float, because charging time is much slower.
So there are basically 2 ways to approach the problem. Larger cables, or shorter distance, and preferably, both.
So in a solar system, it makes the most theoretical and practical sense, to have the controller right next to the battery. Yours is 15 feet away, which actually is 30 feet electrically. This will keep the voltage at the battery as high as the charge controller thinks it is. When wiring panels, it is always better to have the long wire runs before the controller. You obviously will still have some resistance loss in the wire, but your charge controller will still regulate the voltage properly to the battery.
Anyway, with your controller that far away, you are giving up significant performance that you have already paid for. Especially with a small low power system like ours, every amp hour and every 0.1 of a volt is precious. Will it still work set up like you have-sure. But you'll never reach the full voltage the CC thinks you need, and you have prolonged charging times by say 20%.
ANd the high temp of the controller is another problem. Higher temps regulate voltage DOWN. Not exactly what you want.
And BTW--Nice job on the slide out panel.
In any wire, there are resistance losses, based on how much current is flowing in the wire and how large physically the wire is. If you remember Ohm's law V = IxR. So assuming a constant voltage(coming out of your charge controller), as R goes up, I (current, the good stuff we want back in our batteries goes down.
Voltage drops, are related.
You can calculate the voltage drop with something like this:
Voltage Drop Calculator
So lets look at your set up. If you assume you have 12 ga wire, and 5 amp current, in a 30 foot run (that's to the battery AND back), you've lost 0.3 of a volt. Doesn't sound like much, but in 12 volt systems you only have 1 volt to work with because full battery is 12.8 volts and electrically empty battery is 11.8 volts. So your 0.3 volt loss causes a couple of things. First, your batteries will charge more slowly-with less voltage, there is less current flow. But also they may never reach a full charge before the controller kicks out of absorb and returns to float, because charging time is much slower.
So there are basically 2 ways to approach the problem. Larger cables, or shorter distance, and preferably, both.
So in a solar system, it makes the most theoretical and practical sense, to have the controller right next to the battery. Yours is 15 feet away, which actually is 30 feet electrically. This will keep the voltage at the battery as high as the charge controller thinks it is. When wiring panels, it is always better to have the long wire runs before the controller. You obviously will still have some resistance loss in the wire, but your charge controller will still regulate the voltage properly to the battery.
Anyway, with your controller that far away, you are giving up significant performance that you have already paid for. Especially with a small low power system like ours, every amp hour and every 0.1 of a volt is precious. Will it still work set up like you have-sure. But you'll never reach the full voltage the CC thinks you need, and you have prolonged charging times by say 20%.
ANd the high temp of the controller is another problem. Higher temps regulate voltage DOWN. Not exactly what you want.
And BTW--Nice job on the slide out panel.
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^ pretty well described, if you get bored of cutting and slashing you can look to engineering as a new career 
Though it's not quite as bad as it seems since as the controller sees the voltage rise to the float state it will then reduce the current, the voltage drop on the wiring becomes less and the controller then sees that the battery isn't quite up to full (less voltage drop on the wiring) so it will start increasing the current (pwm duty cycle increases). So, really what happens is that it takes longer to get that last bit of charge into the battery. For the rest of the time (battery fairly discharged or fridge etc actually running) the controller will be pushing out everything that the panel can provide anyway.
Heat is more an issue, if the PWM controller is 'decent' and using the ambient temperature to adjust the charge voltage then if it is in the sun it will think things are a heck of a lot hotter than what the actual battery temperature and lower the voltage thresholds accordingly. End result is that the battery will take longer to fully top up.
Ideally the controller wants to be near the battery (a couple of feet max of cable) and also thermally at the same temperature. Things will still work if these two points aren't met, but just not as 'optimally'... With most panels being in the 100 - 120W range and relatively inexpensive and most of us with relatively high capacity batteries, it's not too much of an issue to loose a bit of charging efficiency. Of course as an engineer I'm always trying to optimise each and every electron so my controller is right next to the battery
cheers,
george.
Though it's not quite as bad as it seems since as the controller sees the voltage rise to the float state it will then reduce the current, the voltage drop on the wiring becomes less and the controller then sees that the battery isn't quite up to full (less voltage drop on the wiring) so it will start increasing the current (pwm duty cycle increases). So, really what happens is that it takes longer to get that last bit of charge into the battery. For the rest of the time (battery fairly discharged or fridge etc actually running) the controller will be pushing out everything that the panel can provide anyway.
Heat is more an issue, if the PWM controller is 'decent' and using the ambient temperature to adjust the charge voltage then if it is in the sun it will think things are a heck of a lot hotter than what the actual battery temperature and lower the voltage thresholds accordingly. End result is that the battery will take longer to fully top up.
Ideally the controller wants to be near the battery (a couple of feet max of cable) and also thermally at the same temperature. Things will still work if these two points aren't met, but just not as 'optimally'... With most panels being in the 100 - 120W range and relatively inexpensive and most of us with relatively high capacity batteries, it's not too much of an issue to loose a bit of charging efficiency. Of course as an engineer I'm always trying to optimise each and every electron so my controller is right next to the battery
cheers,
george.
Renogy rocks man!
I have the rigid 100W Renogy in the link and yesterday around 2-3PM, December 11 (winter) and totally cloudy, my panel was putting out 20 volts! I didn't check amps but it was probably at least 5A if not 6 or 7. That's a lot of juice with the sun closer to the horizon than overhead, AND totally cloudy about two hours before sunset. In fact it's about 90% of what I get in the summer!
I had been using the charge controller it came with but then I began seeing that my monster 2150A battery wasn't getting enough charge for a couple of reasons, probably including the charge controller putting out too little voltage and stopping too soon. So recently I got a Battery-Minder SCC-180 16 amp charge controller with desulfator and temperature sensor. If nothing else the sensor and full time desulfator are an improvement, and the higher charge voltage and higher charge limit should take better care of the battery.
Yes, I'm sold on solar battery maintenance, but if you have a big battery and regularly deep cycle it to say 12.4V you'll still need regular home charging from a high amp charger (20A-40A).
surfpig
The Anti-Tech
I used a lot fewer words.
I use a sunforce 8 controller and 3 15W panels. Engle 45 with 2 batteries and misc. other duties, temp. use of inverter for tools etc., charge phones, ipads, movie players, and never have run a battery dead. The only time it ran low was when I refused to replace a 15 year old optima until it was just done. The panels are cheap and currently hard mounted up top. I will be changing the mount so I can move the panels around to best location once camp is reached. The advancements in panels has me curious as to a better panel that may be lighter and higher output but the cheap as heck 15W units have been reliable for me. I think the system keeps up but needs movable panels in order to achieve effective recharge. Right now I can not always park in the sun or it's not always sunny where rig is parked.
Cruiserdrew
On the way there
Alright then. Time for science. Today was the day to answer this question once and for all. Very good solar conditions here today-perfectly clear, cool, minimal wind and 1030am BTW. @TrickyT ,@e9999 ,@george_tlc , @PabloVTA
I set up my 100 watt folding panel on the roof rack of my 80 sitting in front of my house. Admittedly, we are near the winter solstice and the sun is lower in the sky and less intense. So this would tend to magnify the following differences.
I was very careful that there was no shading of the panel from the edges of the rack.
Results:
-With the panel flat on the roof, the controller at the battery and the power meter between the controller and the battery, the max output into a battery intentionally discharged to 12.5 volts, the maximum out put was 2.34 amps.
-With the panel legs deployed and facing the sun directly, literally a minute later, The maximum output into the battery was 4.9 amps.
This was a much bigger difference than I expected. So I repeated the experiment and this time turned on the headlights to assure at all possible power from the controller would be directed into the battery.
-Flat 2.4 amps
-Pointed optimally at the sun 5.0 amps
Anyway, my conclusion is that tracking the sun makes a huge difference, especially at wintertime sun angles.
I learned a couple other things too...
-At max summer time sun in similar conditions, I get an additional amp out of the panels. I've seen up to 5.9 amps and today even as we got toward noon, I only saw 5 amps
-And most interesting was testing the length of the lead out to the panel and how much that would affect output. Remember, the controller is right next to the battery. All wires (in sections) are 10 gauge and connected with Anderson powerpoles
-10 feet 4.9 amps into the battery
-10 feet+10 feet 4.9 amps into the battery
-30 feet 4.9 amps into the battery
-30 feet+10 feet+10 feet 4.9 amps into the battery
-30 feet +10feet +10feet +25 feet (75 feet!) 4.8 amps into the battery
I thought that was pretty cool, because even out to 75 feet of wire and several connections, the resistance losses were minimal.
So, my conclusion is that well, @LandCruiserPhil is wrong. Sun tracking at least in the winter but in otherwise perfect conditions makes a HUGE difference in panel output. Optimally orienting the panel can as much as double the output vs flat on the roof.
Also, that the panel can be out on a very long lead indeed without hurting the output into the battery--as long as the controller is right next to the battery!
Geek day over.
I concur with the conclusion on angle to the sun. Interestingly check the impact that shading of one or two of the individual solar panel areas has on voltage/current output: seems disproportionate to me...... There are curves of power vs light incidence angle...not quite a cosine function (a complex function) as there is light from the blue sky/clouds even when the panel is 90 degrees to the sun......
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Yep #1, I point my panel at the sun and can measure a reasonable difference via the display on my controller. Given time is spent at camp anyway, it's no big deal to move/re-point the panel a few times a day. Of course well before the end of the day the batteries are fully topped up (assuming sunny day and not too extreme heat to run the fridge more often). Now, if we have some cloud and then sun etc, extracting the most out of the panel becomes more important. Comes down to how much extra solar is being extracted versus output demands. Moving/pointing the panel at the sun is obviously only important if the net power drawn is otherwise more than the net incoming charge power and you have to try and extract more from the panel.
Yep #2, given the panels typically output 18 - 20V, you have quite a bit of headroom in a PWM controller to deal with voltage losses (long leads on the controller to panel side). With a MPPT controller, any voltage losses (due to cable/connector resistance) will reduce your output since it is doing a DC : DC power conversion versus a PWM that just pulses power on/off at varying duty cycles.
cheers,
george.
Yep #2, given the panels typically output 18 - 20V, you have quite a bit of headroom in a PWM controller to deal with voltage losses (long leads on the controller to panel side). With a MPPT controller, any voltage losses (due to cable/connector resistance) will reduce your output since it is doing a DC : DC power conversion versus a PWM that just pulses power on/off at varying duty cycles.
cheers,
george.
TrickyT
Hate that mud...
The efficiency improvement of sun tracking is going to be related to location and time of year, and someone must have an app for a smart phone that would tell you what the available solar flux is for any given latitude and date. Anyone know of one?
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So, my conclusion is that well, @LandCruiserPhil is wrong. Sun tracking at least in the winter but in otherwise perfect conditions makes a HUGE difference in panel output. Optimally orienting the panel can as much as double the output vs flat on the roof.
Also, that the panel can be out on a very long lead indeed without hurting the output into the battery--as long as the controller is right next to the battery!
Geek day over.
Wrong? Reread my post, I agreed with you if you want to move your panel all day long you will optimize output. What I said "I will agree if you want to move your panel several time a day it will help."
I also stand by when I said "Flat verses an angle panel is only good for 10% in AZ." To be crystal clear I should of added in the word accumulative.
My bad for assuming based on my first sentence you would know it was accumulative. If you do not move your fixed panel (at my longitude and latitude) angle throughout the day your data will support what I said.Looks like Sacramento is no different
Read it from the experts - Optimum Tilt of Solar Panels
If you need to change the angle of your panel all day long why leave home?
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Moving the panel is pretty well given if you are STOPPED in one place for a few days if you want to catch decent rays in the morning, during the middle of the day and in the afternoon. That's 3 times per day, the morning is easy - just repoint the panel when you go to bed and it's waiting for the morning rays and to get the battery charging quickly to make up for the entire night of the fridge running - even if you sleep in. The panel is also more efficient at that time since it is cool.
Tilt angle for fixed mount is simple - set it due south and tilt as per your latitude.
I leave home and the 3 times per day panel reposition hasn't put a strain on my camping experience yet
Anyhow, whatever turns your crank and MOST IMPORTANTLY keeps the beer COLD
cheers,
george.
Tilt angle for fixed mount is simple - set it due south and tilt as per your latitude.
I leave home and the 3 times per day panel reposition hasn't put a strain on my camping experience yet
Anyhow, whatever turns your crank and MOST IMPORTANTLY keeps the beer COLD
cheers,
george.
surfpig
The Anti-Tech
Cruiserdrew
On the way there
Actually, a fixed average tilt works well. You could leave the panel near 45 degrees all year and get decent performance.
For sure it makes a big difference now, and less when the sun is higher above the meridian. It's the always flat I was discussing. In a camp situation assuming no drive day-oriented south, tilted to 30 degrees and you could leave it all day.
I guess you (@LandCruiserPhil ) missed it, but I'm just giving you a hard time in a nice way. From a practical perspective, in the summer, flat on the roof would give adequate performance.
For sure it makes a big difference now, and less when the sun is higher above the meridian. It's the always flat I was discussing. In a camp situation assuming no drive day-oriented south, tilted to 30 degrees and you could leave it all day.
I guess you (@LandCruiserPhil ) missed it, but I'm just giving you a hard time in a nice way. From a practical perspective, in the summer, flat on the roof would give adequate performance.
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I don't know what is so complicated or surprising here...
- the angle effect is almost entirely geometry. Get your trig calculator out and you can figure out how much more or less power you'll get depending on the angle from the sun direction, everything else the same. (Yes, that neglects lower order effect like reflectivity of the panel as a function of angle etc that nobody arguing about the basics here would care about -and I don't either for the sake of this discussion-.)
- if you're gonna leave it in place forever, tilt it at your latitude angle, facing south, and you can't go wrong
- as to whether it's worth bothering to orient the panel or not, I suppose it depends on whether you have a big panel or a small one and whether your ice cream is about to melt or your beer to boil or not and whether you are a geek or not and whether you need exercise or not and whether you have a jump pack or not, like walking or not, and whether you'd rather stay in the tent with your girlfriend engaging in wild
, oh heck never mind that one... IOW, YMMV! 
- the angle effect is almost entirely geometry. Get your trig calculator out and you can figure out how much more or less power you'll get depending on the angle from the sun direction, everything else the same. (Yes, that neglects lower order effect like reflectivity of the panel as a function of angle etc that nobody arguing about the basics here would care about -and I don't either for the sake of this discussion-.)
- if you're gonna leave it in place forever, tilt it at your latitude angle, facing south, and you can't go wrong
- as to whether it's worth bothering to orient the panel or not, I suppose it depends on whether you have a big panel or a small one and whether your ice cream is about to melt or your beer to boil or not and whether you are a geek or not and whether you need exercise or not and whether you have a jump pack or not, like walking or not, and whether you'd rather stay in the tent with your girlfriend engaging in wild
, oh heck never mind that one... IOW, YMMV!
Cruiserdrew
On the way there
So I did just what you said. And, they do not agree with you that flat vs tilted according to latitude makes only 10% difference. They don't seem to discuss flat on the ground or roof top panels. They make the point that some fixed angle near your latitude makes a 5-10% difference when changed a few degrees seasonally. Flat, near the equator would be reasonable, but the further north or south you get, the bigger difference it makes. As e9999 says, this is no surprise.
So to leave "home" or "camp" the smart money would be to face the panel south, and elevate it to the angle of your latitude (a bit less in summer, a bit more in winter) and then forget about it. Leaving it flat on your roof. gives up significant performance, especially in the winter.
This discussion may make me re-think my Baja solar plan, since I was going to just fix flat panels on the roof. It seems smart to be able to tilt them to 20-25 degrees.
this bit about the lat tilt and south is only true if you don't move it at all, of course. If you do adjust the elevation and azimuth during the day you will easily beat the average of the fixed panel, by a lot.
If you want a project, a couple of motors, some gears, a light sensor and an Arduino and you are set to catch every photon coming your way!
If you want a project, a couple of motors, some gears, a light sensor and an Arduino and you are set to catch every photon coming your way!
TrickyT
Hate that mud...
Yeah. For our Baja trip, I'm thinking now what I want is a simple compact light-weight frame to use with my foldable panel. It looks like we'll be 23 or 24* latitude, so it won't have to poke up all that far from horizontal. Maybe I can come up with something simple that attaches to my RTT.
