Portable Solar

I have done some more testing on this, so that OP's 280 on 740AH may work after all depending. And PT's work better understood maybe. New thread on that.

Hi BFL,

No, it is really about designing a solar system that will properly maintain the battery bank including equalization. If that is done there is no need for extreme desulphation at the end of the trip.

There is no "one size" fits all. A full timer can justify a whole passel of solar particularly if they boondock a lot. They should lean towards "supplying daily needs" plus about 60 watts per 100 amp-hours.

A weekend warrior needs far less, so long as there is enough to equalize. When they get home the system will take care of itself.

BTW my rv is in getting a new master cylinder for the brakes. (must have been your mountains? *grin*) and the solar system is putting out 1.1 amps.

It is really about how long can you go with batts part down before desulfation back home is no longer possible, compared with how long your trip is away.

Probably? with vacation time length RVing, the big battery bank with "some solar" is fine to still be able to desulfate as needed back home. When retired with longer times away is when you need a new plan.

I still like the gradual approach using portables that you can nail down later if that then seems like a good idea and you will be keeping that rig

BFL13 wrote:
Right the panels stay sunny or not, but you can leave half your batts behind if that works better by season for being able to reach full most days.

We camp at or near the beach mostly where the mornings can be completely overcast but the sun typically comes out before noon and stays that way for the rest of the day. Depends on the time of year though, sometimes the clouds come back in the evening. I bet I'd get a lot of edge of cloud effect (probably need to over do the controller). Our CG's aren't solar reliable so the best it could do is put back a decent amount of what we use. Inland has far more sun but we don't boondock there (much warmer, mostly urban). A smaller bank that could be charged in a couple of afternoons with lots of solar would probably work best. Or a larger bank with bank switching (solar on offline bank). This is interesting!!!

Right the panels stay sunny or not, but you can leave half your batts behind if that works better by season for being able to reach full most days.

Hi,

I can see no reason to leave panels behind, especially on a fixed installation.

My scenario is quite a contrast between summer and winter. In Kit Carson land this may not be so. We do only long weekends in winter with no solar, so lots of battery is good with recharge at home possible.

Five months off grid in a row in summer with much less daily AH usage than in winter, batts are more in capacity in warm weather, and we use solar too. So we could do the same lifestyle wrt inverter use in summer as in winter with half the battery bank plus some solar.

It is VERY scenario dependent. The thing is, it is easy to leave half your batteries at home on a float charge, but not so easy to double or halve your solar once you nail them down on the roof.

BFL13 wrote:
Mena, beware of having so much battery while camping for a long time.

Some good questions BFL. I have only started to think about this very scenario. Since our trips are short, I get no sulfation while camping (at least none that I notice). I may have to perform more experiments to prove this happens everytime but it seems that staying above ~85% SOC doesn't even require an overcharge to get to 100% on my batts (looked at an old spreadsheet). Maybe there's no sulfation with that shallow discharge too. Maybe you can try this on your bank to see if this was a fluke or not. I'll try this again sometime to see if it happens again. Maybe getting enough solar to keep discharges shallow is the trick to preventing sulfation on trips. Or maybe one long cycle opposed to multiple cycles. I sized the bank to keep from having to charge while camping. The solar is just for replenishing some convection oven use and more than likely that will use up most of the energy I'll get from the panels.

If I were going to start 2-3 week trips I'd have to come up with a different game plan. My next bank may indeed be smaller (with more solar) in anticipation of these issues you've found.

Hi,

280 watts would work with bank switching--but I agree with smk--plan for worst case--450 watts of solar would be enough.

I am suggesting that the Op's idea of 280w may be good in summer if he leaves two batts at home taking the half ( 370AH) with him, but 280w may not be enough if he takes all four (740AH) and stays out two or three weeks. I don't find 130w is enough for 715AH and usage of 70AH/day, where most days are half cloudy.

I am still getting experience with all this, but have enough now to issue the warning I did. YMMV of course. Perhaps others will be able to report their real life examples.