Portable solar for the RV

System

New to the solar world I have obtained 2 12vdc Northstar telecom batteries that are 170ah. I want to do solar but not wanting to install on the rig. For the cost of two of these 120watt version panels and their portability will they charge these batteries?

http://www.examiner.com/x-25177-Phoenix-Solar-Power-Technology-Examiner~y2009m12d1-RV-Solar--Portable-solar-devices-can-produce-more-energy-than-roof-mounted-panels
Tom G.

Kamala

Re: Portable solar for the RV

These are 12V 80W panels. (Unless I'm missing something.)

Whether they will charge your batteries or not depends on how much charging your batteries need which, in turn, depends on how much you discharge them. Ideally, that should be no more than 20%. So for a 340AH (2*170AH) bank that would be 68AH (170AH*.2) needed to recharge it. Or @ 12V, 816Watt-Hours (68AH*12V.)

With 160W (2*80W) of PV derated to 70% (to account for various system losses and inefficiencies) you have 112W (160W*.7) of effective PV. Assume 4 hours of "good" sun and you have 448WH (112W*4H).

So, if i am correct, you have slightly more than half of what you need. You may get more hours of good sun depending on your location (and the time of year.) If you got 6 hr of sun you would be much closer to what you need. 112W*6H=672WH.

The challenge then becomes to keep you consumption to less than 20% of your battery's capacity.

K

P.S. I designed my system to allow 50% depth of discharge and am right on the edge (teetering :roll:)

BTW, I like the idea of those panels.

Cariboocoot

Re: Portable solar for the RV

You read it right. They're talking about how you can get more power out of properly aimed 80 Watt panels than improperly aimed 120 Watt ones. Perfectly true.

As far as charging 2 * 170 Amp/hr batteries ... 340 Amp/hrs total. Wants about 500 Watts of panel in my opinion. Might get by on 300. 240? Nope. 160? Definitely not. You're looking at one of those 'premature battery death' scenarios there.

System2

Re: Portable solar for the RV

If you look at the link that goes to the distributor of this in the article they have a 120watt version of this same thing. I was thinking about using 2 of these and when it does not get the charge back to full I can kick in with my 3500watt generator. Since the batteries were free tome if they do end up dying sooner than normal I will not be out anything for the batteries. I just have to install some kind of monitor to watch remotely. I have been just using a multimeter on the old pair group 24 75ah ones now with only the genny to recharge.

Kamala

Re: Portable solar for the RV

For full time off grid purposes, I'll go with 'Coot's analysis. However, if the system is only cycled twice per week (as in my case,) things may be different. (I have yet to prove that in the real world, however.)

I have a 374AH battery bank and a 261W PV array. It has only been in operation from August through November of last year. During that time it worked well. I did have to get a generator near the end of this time. I have yet to collect and analyze real time performance data. I'll begin doing that next month after the camper is returned to service. :D8)

In design, I estimate that I end each weekend with a 18AH charge deficit. This is easily recovered during the intervening 5 days prior to the next weekend. Incidentally, at the beginning of each weekend the TriMetric always indicated that the battery was charged to full capacity and the "Days Since Charged" was usually greater than 2. The camper does use about 11AH per day (29 if I leave the fridge vent fan on.)

Even under these conditions, I should get 10 years out of the batteries. 30 weekends per year, 2 cycles per weekend is 60 cycles per year. 10 years = 600 cycles. Well with the AGM's characteristics.

So, depending on how the RV is used and the possibility of topping off the batteries with generator/shore power, these panels might be useful to you.

You will need a charge controller and a battery monitor is very highly recommended. Especially when operating on (or over :roll:) the edge like this.

Good Luck.

K

Kamala

Re: Portable solar for the RV

I was missing something! 120W model.

Well, that improves things. Not enough for old 'Coot, tho. :-)

Cariboocoot

Re: Portable solar for the RV

For free batteries ... hey, why not try 'em?
Just as a future reference, you're 240 Watts of panels would probably do about 256 Amp/hrs without trouble. So a pair of the good ol' golf cart batteries could be your future 'upgrade'.

People tend not to realize there's three basic factors in recharging:
1). You have to have more Volts going in than the battery is at (a 12V battery charging at 14.4V)
2). You need to replace the Amp/hrs used which can be done over any period of time, but for;
3). Sufficient current rate to 'stir' the electrolyte.

This is for FLA's, of course. AGM's and gel batteries have their own charging requirements.

BTW, Craig; you use AGM's which are different. Stirring electrolyte isn't such an issue in an 'acid-starved' battery, but you have to watch the Voltage more closely (typically it is also lower than an FLA). Gel's are even more picky about over Voltage or current. Did I ever tell you about the time I had one explode?

Kamala

Re: Portable solar for the RV

Cariboocoot wrote: »

... This is for FLA's, of course. AGM's and gel batteries have their own charging requirements.

Good point. Hey, tgourley! What type are these free batteries?

Cariboocoot wrote: »

BTW, Craig; you use AGM's which are different. Stirring electrolyte isn't such an issue in an 'acid-starved' battery, but you have to watch the Voltage more closely (typically it is also lower than an FLA). Gel's are even more picky about over Voltage or current.

All of which I am well aware and that is the reason that I got detailed specs from the battery mfg and adjusted the charge set points for the Morningstar and ProSine accordingly.

At one point I thought it might be a good idea to plan an escape route in case of catastrophic battery failure (go to the door and step outside :roll: ) But then I realized that if that ever happened, a route would quickly be provided and I wouldn't even have to move a muscle.:-):-):-)

Cariboocoot wrote: »

Did I ever tell you about the time I had one explode?

If you did, I forgot (or ignored:roll: it.)

Windsun

Re: Portable solar for the RV

Kamala wrote: »

I was missing something! 120W model.

Well, that improves things. Not enough for old 'Coot, tho. :-)

And they only charge twice as much as we do for basically the same thing. 8)

Kamala

Re: Portable solar for the RV

Windsun wrote: »

And they only charge twice as much as we do for basically the same thing. 8)

With the padded storage bag?! :roll:

Actually, NAWS makes a great point. Someone with a mere modicum of DIY skill could easily fix up the mounts, hinges and carrying case for much less than the difference in cost. Heck, it could probably even be out sourced for less than that!

Windsun

Re: Portable solar for the RV

Cariboocoot wrote: »

You read it right. They're talking about how you can get more power out of properly aimed 80 Watt panels than improperly aimed 120 Watt ones. Perfectly true.

True, but not as critical as it might seem. At 45 degrees angle to the sun you lose around 30%. The loss curve steepens beyond 45 degrees (it is basically the cosine of the sun angle). At 60 degrees you are running at about 1/2 power.

Windsun

Re: Portable solar for the RV

Kamala wrote: »

With the padded storage bag?! :roll:

True, we don't provide the padded bag

Kamala

Re: Portable solar for the RV

Windsun wrote: »

... At 45 degrees angle to the sun you lose around 30%. The loss curve steepens beyond 45 degrees (it is basically the cosine of the sun angle). At 60 degrees you are running at about 1/2 power.

As I am sure you are aware, this depends on the zenith of the noon sun at a given latitude. I'm at 45°N so the angle of my camper roof will be perfect twice a year... except it's still in storage, so I missed yesterday.

If I tilt the array (to be roof mounted this season) more towards 40° or 35°, I might get optimal twice per season (April to October.)

System2

Re: Portable solar for the RV

Good point. Hey, tgourley! What type are these free batteries?

They are Northstar NSB170FT.

Those panels do come with a 10amp PWM charge controller mounted to the back. The cost does seem high even with all that and they fold in half for easy carry. It would be one more thing to set up though when I get where I want. I just have to stop the wife from watching so much TV burning the battery juice.

niel

Re: Portable solar for the RV

simply put 340ah of battery capacity needs at least a 5% rate of charge to it or 17a in the case of your 2 batteries. if you don't have the pvs optimally placed or you have loads on while charging or even the resistive losses and efficiency factors these things will make the pv outputs to be less.
my guess would be, no, they are not going to charge those batteries very well with about at least 350w of pv needed with no loads on with good overall efficiencies and aiming done well.
they might serve to top off the batteries and float them.

Kamala

Re: Portable solar for the RV

Google search yields this pdf: Northstar NSB170FT.

Doesn't make it clear whether they are "starved electrolyte" or not. Meaning AGM or FLA. I'm pretty sure they are not GEL (mission critical, anyone?) In my research (non-scientific) and experience (ground transportation management,) when I see this statement:

Approved as non-hazardous cargo for ground, sea and air transportation.

I think AGM, which is appropriate for a telecom application. Also note the lack of filler caps.

Still, one can't be sure. No warranties provided or implied on my part. :roll:

I have since found this: NSB170FT_SES-542-06.pdf

So we can be sure! They are AGMs.

tgourley wrote: »

I just have to stop the wife from watching so much TV burning the battery juice.

Or stop the universe from expanding.:p

At home, my wife watches plenty of TV. Still does more work at home than I. But I got her a very nice pair of binoculars for the camp. And now she watches turtles! Go figure. That's right! You can't. ;)

Kamala

Re: Portable solar for the RV

niel wrote: »

simply put 340ah of battery capacity needs at least a 5% rate of charge to it or 17a in the case of your 2 batteries. if you don't have the pvs optimally placed or you have loads on while charging or even the resistive losses and efficiency factors these things will make the pv outputs to be less.
my guess would be, no, they are not going to charge those batteries very well with about at least 350w of pv needed with no loads on with good overall efficiencies and aiming done well.
they might serve to top off the batteries and float them.

But what if the batteries are not cycled daily, as I suggested in an earlier post on this thread?

At one time, I seem to recall that 3% of total AH was offered as minimum charge rate.

Neil, I'd like your thoughts on this matter.

Also, maybe this should be moved to the Off-Grid Forum.

Thanks,
Craig

niel

Re: Portable solar for the RV

Kamala wrote: »

But what if the batteries are not cycled daily, as I suggested in an earlier post on this thread?

At one time, I seem to recall that 3% of total AH was offered as minimum charge rate.

Neil, I'd like your thoughts on this matter.

Also, maybe this should be moved to the Off-Grid Forum.

Thanks,
Craig

that could possibly lower the requirement to say as low as 3% or so as they would be allowed a bit more time to recover. 3% x 340ah = 10.2a. it may depend on how much he depletes his batteries in this case that he would be allowing enough time until the next usage. remember that this 10.2a is what is delivered to the batteries and not the imp rating of the pvs and does not account for any other losses due to efficiency or bad aiming, clouds, resistances, dirt, etc..
even a 5% rate may be too low for some as it does vary to the circumstances involved to some degree. 3% is pushing the envelope, so to speak, and 5-13% as you know is what is generally recommended.

System2

Re: Portable solar for the RV

Hopefully I will get this all connected up soon if I go through with the purchase. They are not available yet in the 120watt version. I am going to do a comparison of the cost of similar setup of perm mounted panels from NAWS and then see if it just makes more since that way.
Thanks for all the insight. I will continue reading the forum for more knowledge. It appears I already see I need a shunt and a monitor of some sort to start.

Cariboocoot

Re: Portable solar for the RV

Windsun wrote: »

True, but not as critical as it might seem. At 45 degrees angle to the sun you lose around 30%. The loss curve steepens beyond 45 degrees (it is basically the cosine of the sun angle). At 60 degrees you are running at about 1/2 power.

Except in this case we're not talking about just angle, but the difference between panels fixed on the roof of an RV which it may not be possible to park in an ideal location vs. portable panels that can be moved around on-site even several times during the day so as to maximize the potential solar 'harvest'.

Cariboocoot

Re: Portable solar for the RV

Kamala wrote: »

At home, my wife watches plenty of TV. Still does more work at home than I. But I got her a very nice pair of binoculars for the camp. And now she watches turtles! Go figure. That's right! You can't. ;)

Careful! You know what turtle-watching leads to? Yep: SLOTH!