Solar panel size question

TerryV6

When we bought our camper, the sales guy told us we really could use a solar panel as an alternative charging for our camper battery.  That sounded good to me, and when he put it on the final tally, we were good to go.  Now, I haven't used it yet and decided to do more info gathering on what we bought.  (What do we know about solar really?)  Anyway, we had purchase a Zamp Solar ZS-M-20-P and it says 20 watts output.  So, I went to the Zamp website and the smallest one they have is a 40 watt.  Hmmm....  Did we buy something too small and also outdated?  I suppose I really should have given a friend of ours a call.  She is living by herself on 80 acres, completely off the grid on wind and solar power.  But hey, you are in the showroom and the man says this will work.  Will it?

Nomad

Traveling full time, I live off solar 90% of the time. I have the Zamp 120.
My limiting factor is really more my battery - I have a dinky Group-24, the standard T@B battery.
A 20-40 will keep your battery charged while being stored, or sitting inactive, but not sure it would keep up if you're actively camping.

Verna

@TerryV6, I believe you are reading the numbers from the Zamp controller with the digital display. If you look for a sticker on the rear of the solar panel, it will tell you how many watts each panel provides.  The solar controller does ontrol the amount of power allowed to be stored in your battery and it stores it in the most efficient mode for the amount of power you have in your battery. 

I have a Zamp 200 watt suitcase that has two 100 watt panels. PXLated has a suitcase with twp 60 watt panels. 

Take a picture and we can help a bit better. 

Nomad

Verna's 200s are the traveling persons version of a weight lifting gym :-)

TerryV6

Thanks Verna...  Here is the picture...  I don't know if a lightbulb just went on, but I maybe looking at this sticker and thinking it is for the whole unit, when actually it is for the one connected panel, of which I have two.  In which case, I have a 40 watt system... And... according to PXLated, this is probably still inadequate...

Nomad

Yep, it's for each, you have a 40.

Verna

TerryV6 said:

Thanks Verna...  Here is the picture...  I don't know if a lightbulb just went on, but I maybe looking at this sticker and thinking it is for the whole unit, when actually it is for the one connected panel, of which I have two.  In which case, I have a 40 watt system... And... according to PXLated, this is probably still inadequate...

Yes, I stand corrected. I have an 80 watt from my Silver Shadow teardrop camping, with two 40 watt panels. I need to get in gear and get rid of the teardrop stuff--tents, etc. 

I agree with PXLated that 120 watts in sufficient to camp without electricity. 40 watts would be a trickle charger for your battery, sorry to say. Too bad you can do some trading with your dealer for a 120 watt. 

Ratkity

A very general rule of thumb is for every amp hr of deep cycle battery have 1 W of solar panel (like if you have a group 24, 80 Ah battery, you should have a minimum of 80W in solar panels). Note I said "Very General" rule of thumb. I have a 20W panel that barely keeps the battery topped off if I don't pull the fuse to stop phantom power pulls when the T@B isn't in use. 

I think giving your off-grid friend a call would be a good idea. She can explain energy needs and appliance demands, then you can scale her information back for the little T@B. Sometimes, speaking with someone and being able to ask questions as they come to mind is easier to grasp how solar works than trying to read the reams of solar threads that this site has (and many other sites). 

Best of luck! 

RollingLagrima

Verna said:

TerryV6 said:

Thanks Verna...  Here is the picture...  I don't know if a lightbulb just went on, but I maybe looking at this sticker and thinking it is for the whole unit, when actually it is for the one connected panel, of which I have two.  In which case, I have a 40 watt system... And... according to PXLated, this is probably still inadequate...

Yes, I stand corrected. I have an 80 watt from my Silver Shadow teardrop camping, with two 40 watt panels. I need to get in gear and get rid of the teardrop stuff--tents, etc. 

I agree with PXLated that 120 watts in sufficient to camp without electricity. 40 watts would be a trickle charger for your battery, sorry to say. Too bad you can do some trading with your dealer for a 120 watt. 

I "third" Verna and PXLated's 120 vote. It was sufficient to power everything I needed at Joshua Tree in March, using common sense as far as not needlessly running fan or lights.

TinMT

Very helpful post. Thanks much! I've been wondering the same thing.

mash2

I fourth 120+ watts.

T@Balong

How about a "fifth"?   Very happy with my Zamp 120w.

ScottG

I did some analysis before buying my 100W setup. The specifics escape me, but I know it involved jkjenn's excellent power use spreadsheet, and some online calculators. From that I determined 100 watts would be sufficient with a good margin for cloudy days, etc. We are also pretty conservative with our power use.

As others suggested, what you have sounds more like a battery maintainer designed to keep a good, minimally-loaded battery at full charge all the time. Assuming you top your battery up and disconnect it when you park the trailer, you probably won't need it.

That said, if I already owned the 40W setup, I'd probably go out and give it a try and see what it can do given your usage patterns. You might be pleasantly surprised--let us know what you find!

Fathand

So I used my T@b first time last weekend running my Norcold 3163 on Propane from Wed night until Sunday morning and my battery was almost dead. Also ran occasional LED interior lights. How much Watts solar would I need to keep the battery Group 24 charged up?

Verna

Not trying to be a smart Alec, but read the above. 

Fathand

I did read the above and some other threads and saw a lot of different answers to a lot of different scenarios but none that seemed to match mine. Thank you for being so helpful to someone new here.

ericnliz

Fathand, I think what Verna was trying to say is that everyone's needs will be different. If I were you, I would START at no less than a 100W panel, and you can add if needed. That would give you more than just a battery "maintainer". Hope this helps.

ScottG

Everyone's scenario is different, and there are no definitive quick answers. Without assessing and monitoring your own usage, you can only make a best guess.

That said, your scenario sounds similar to my typical long weekend. Four days of dry camping (no hookups). We run the fridge full time on propane. The Alde is run on propane, too--typically twice a day to make hot water. We use lights for a bit at night, and the water pump as needed. Overall, our usage is pretty conservative.

Last season I could get four days out of my group 24 battery, but it would be drained to the point of damage. This year I replaced it with a larger group 27 battery and a 100 watt solar suitcase. I deploy the suitcase daily and so far this season my battery has not dipped below 12.5 volts. It's probably a little overkill for what I need, but I like having a bit in reserve for a rainy spell, or in case I feel like gettin' crazy with the vent fan.

Nomad

Fathand - Yep, what ericnliz said ... Needs (perceived or real) are all over the board. I do absolutely fine with my 120s but others feel they need 200s. As with a lot of things, there isn't a difinitive answer. And it's somewhat a solar/battery combo issue.

Tabaz

Fathand - I was in the same boat as you are regarding making a solar decision, so I understand your frustration.  Scott G's response above is spot-on.  You won't go wrong with a Group 27 battery and 100W solar system.  You can always add more solar later if needed.  BTW, Verna and just about everyone else of this forum are here to help.  If a response seems insulting or mean-spirited, it was not intended to be.   

ericnliz

OutbackAZ, Hear, hear on the response comment. Sometimes it comes off a little harsher than was intended. I also took a couple the wrong way, but with a grain of salt, and in the long run, the comments were actually extremely helpful. Hang in there, at times it CAN, and WILL be frustrating.

ScottG

While we are back on this topic... @TerryV6, have you had the opportunity to test that 40 watt panel in the field? If so, did it do anything to keep the battery drain in check?

Tommy

@Fathand, I think Verna was gently making the point that your question had been pretty well addressed multiple times in the various responses above and the basic direction was to make sure you had read all of them. Being sensitive in a public forum is probably not going to work out for you as a long term strategy - especially since this forum is by far the most polite and courteous forum I've ever encountered It's also worth noting if you want the best most focused responses to your specific questions, the best way to accomplish that is by doing a topics search, reading a lot and if your questions haven't been answered yet, start a new topic.

Ratkity

ScottG said:

While we are back on this topic... @TerryV6, have you had the opportunity to test that 40 watt panel in the field? If so, did it do anything to keep the battery drain in check?

I tried with my 30W panel and left the fuse in to see if it kept up with the parasitic draw (keep in mind I added the digital Alde controller and my battery meter draws a small amount - add those draws to the basic list of about 300 mA a day). It couldn't keep up. Also know that I DID wipe the panel off daily of debris (pollen, dried raindrops, etc), but this experiment was done in the winter sun when usable solar daylight hours were weak and minimal. 

Now I just pull the main fuse and use the 30W as a maintainer. Works perfectly.

Verna

Fathand said:

I did read the above and some other threads and saw a lot of different answers to a lot of different scenarios but none that seemed to match mine. Thank you for being so helpful to someone new here.

I do apologize if you were offended by my comment. Many have already said which wattage is best suited for most T@B applications. We need more information from you if you feel 120 watts aren't enough. I know PXLated full times, Pit Pat spent most of last winter with out electrical campsites, and they both have 120 watt solar panels and both have had no problems.

So, why do you feel you need more than 120 watts, please, so you can have your question answered?