Portable Solar

Hi bfl13,

I've explained it before. But 60 watts per 100 amp-hours is enough to equalize the bank. I came up with that number independently by doing a LOT of online research (two years and at least an hour a day) and reading everything under the sun. Then Mex came along and said "5 amps" is enough--which happens to be 60 watts.

The other number I often quote is 150 watts per 100 amp-hours. That number corresponds to 12.5 amps of charging @ 85% state of charge on a lead acid battery. More amps forced into a battery by higher voltage mostly cause it to "gas". There are times when gassing is desirable--but mostly it is not so good. I believe Mex quotes one bubble per second.

To some extent the larger the bank the more the 60 watt figure can be favored. A 750 amp-hour bank @ 60 watts = 450 watts of solar. That is quite a lot of "ready energy" to directly power items from the panels. It also probably results in about 6 amps of charging when it is raining. It is often enough to cover parasitic loads.

When I purchased my panels the cost was $5.50 per watt, so I went with lower number based on 375 amp-hours of bank.

Of course, both those numbers require (especially the 60 watts) good solar conditions. Fortunately, where I live that is most often the case.

Any "extra" opportunity charging is great, and a "bonus".

BFL13 wrote:
PT, how can you come up with these magic numbers?

I design for the worst case scenario. All my batteries and solar go with me even if I will be plugged in. Nothing is adjusted. Nothing wrong with going to float before noon. If I use more battery power then solar produces more. Many days the solar produces very little. The controller adjusts accordingly.

This may not apply to the OP topic of "portable solar"

smk, when you "design to some amount" how do you allow for summer vs winter?" What do you think of having the same solar but half the batts for summer than for winter? Assuming your summer trips are the longer ones and you can do a long weekend in winter anyway with no solar.

Panels are cheep. When the roof is full you have enough.
If you design to the minimum... at some point you will be short.
Should be no reason to plug in at home to recover any sulfation.
(unless you have covered parking)

PT, how can you come up with these magic numbers? You need to know how many gen hours and when during the day they are allowed, how sunny it is, how much usage there is, and even when during the day that usage is (breakfast or supper?) Then apply the solar needed.

Also how long you can go, at how incomplete, before it is too late to "recover" the batts at home with your various desulfation/100% means?

I don't find the usual quoted amounts of solar watts needed per AH at all useful in real life without more "background info."

Hi,

60 watts per 100 amp-hours of storage if you have a large bank. Or a way to switch the banks. Or both.

Mena, beware of having so much battery while camping for a long time. Now that I have over 700AH of battery like you do, and less solar we are back in the soup as far as keeping them charged. 2Oldman went down to four from six batts for this reason ISTR.

You really have to figure it out for your scenario. Camping with no solar, no gen, in winter with lots of AH usage means you need lots of battery to do it all for a long weekend and then recharge at home. You have that.

Now in summer with less usage (no furnace less lights-on time) you take days or weeks to run down to 50% to need a recharge. But by then, how sulfated are you? You could run the gen more, but that is such a waste at the high SOC-low amps range and campground gen time limits can stop you getting full enough too.

So with "some solar" it takes even longer to get down to 50%. More sulfated. So the full- time off- grid guys say to have so much solar per AH capacity so you can get to full every day and not sulfate.

But is there any way to calculate how much solar you would need to do say two weeks off grid and get home in time to do your 100% recharge and not lose anything to sulfation?

I don't know (yet) but I am having a difficult time since getting more battery and less solar, trying to figure out how to last another month without sulfation. I seem to be in neutral buoyancy above 60% and below 90% SOC and can't break out above that with so little solar. OTOH we could do our usage easily with two batts instead of six right now and then the 130w would be enough to get near full every day with some gen kick start as required.

It may be that you should take only two batts along in summer with enough solar and leave the other two at home on a float for a two-weeker, then use all four in winter as before and not count on much solar in that season.

Right now, I am thinking I should take some batts home and put them on the Float charger until this summer session is over or else I could end up with six sulfated batts. I was fine with the solar I had (330w)and just four batts though.

It is an interesting problem and very scenario dependent what to do. Anyway you might want to do some more math on this whole thing.

Fishbreath wrote:
I've been using a portable 185 watt panel for three years now. I love it. I always park in the shade and move my panels about 3-4 times per day. I am frugal with electricity and never run my generator, even on two week trips.
Design it, build it and report back.
Good luck

Bill

Thanks much and will do!

I've been using a portable 185 watt panel for three years now. I love it. I always park in the shade and move my panels about 3-4 times per day. I am frugal with electricity and never run my generator, even on two week trips.
Design it, build it and report back.
Good luck

Bill

Yeah, setting on the roof would probably get old after two trips. As mentioned, putting them on the ground would enable me to keep the rig in the shade. The prop rod is a good idea and is simple to implement. I'll save the complexity for the permanent install. :) KJ, yes, two A/C units, sat dish, two vent shrouds, plus the other stuff. Smk, that's in front of my house. My CG's have much better surroundings. :) O&S, I really don't need much for solar. It's main purpose will be to replenish some convection oven use (whenever I get that big inverter). Thanks all.