Solar or Generator for Boondocking

[Ace_]

This is for a truck camper, no a/c. This would be to keep batteries charged. I was putting together a solar kit (on paper, for purchase at a later date) and started thinking about a generator and whether that is a more efficient/effective solution.

I live in the PNW and some of the solar mfg./retailers state there is less sunlight, so the solar panels will be less efficient than in other parts of the country. I was going to put together a 200watt system, probably roof mounted.

Then I got to thinking that a 2kw generator would cost (maybe) less than the solar panel set up and put out probably close to 1500 watts, 12 amps. So, will the generator recharge my batteries (two deep cycle) in an hour where the solar would take a full day of full sun (realizing the amps used per day is unknown, just wondering about the efficiency between the two)?

When boondocking, especially when no one else is around, I don't mind running a quiet generator for an hour or two.

Solar panel specs:

Max System Voltage (IEC/UL): 600V
Voltage at Maximum Power Point: 18.0V
Maximum Power: 100 W (0%, +6%)
Current at Maximum Power Point: 5.56 A

Seems to me with the panels in full sun I could get 3-5 amps (per 100 watt panel). With the generator I'm guessing 12-15 amps (1.5-2 times what the solar would give me, assuming two 100 watt panels). Does that seem right?

Thanks.

[Fisherguy]

JiminDenver wrote:
You want to know a downside to too much solar and battery, it weighs a lot.

That and your face cramps up from grinning all the time. 😉

lol
Ya, and adding 1 panel is pretty cheap, pretty sure I'll be adding another 120 in the spring.

[JiminDenver]

You want to know a downside to too much solar and battery, it weighs a lot.

That and your face cramps up from grinning all the time. 😉

[pianotuna]

No, but for battery charging only there is not much point in more than 150 watts per 100 amp-hours.

If you run an inverter lots then there is no upper limit to the solar except for roof space.

Ace! wrote:
Is there a downside to too much solar? If it's on the roof, not in the way, why not over-engineer? Is there a chance of overloading a battery bank with a good, adequately-sized controller?

[pnichols]

I really like the complete stop to charging that AGM batteries come to when they're at what I'm calling a "fully charged" condition, as this seems like a solid and unambiguous indicator of state of charge.

However, I have some self doubts about my view above, as several experts in these forums would probably say that AGM batteries may, or may not, be "fully charged" just because they don't accept any more current after X hours at too low of a voltage. I say "too low of a voltage" because I often charge our 230 amp hour AGM batttery bank all the way to a hard stop using only the stock 13.6 volt RV converter. Even on the engine alternator, they only see, maybe, 14.4 volts for a few minutes. There's an awful lot of discussion in the forums centered around the concept that "ya gotta have at least 14.XX or 15.XX volts boost voltage values to ever fully charge lead acid batteries. I'm wondering if this isn't referring to liquid lead acid batteries ... not dry cell lead acid battteries.

I got about 8 years (and probably they weren't done, even then) out of our last RV AGM battery bank using mostly the 13.6 volt low and slow converter approach to their charging. (They were also floated year after year on that same 13.6 volt converter.)

[NinerBikes]

pnichols wrote:
I'm not sure what type of batteries you have, but our AGM ("dry cell") RV batteries will not accept any more current when they're full - regardless of the value of the charge voltage still on their terminals. I call it a "hard stop" to their charging. I've verified this time and time again with an ammeter in the charging cable for the batteries.

Wet cell RV batteries may not act this way, so perhaps a solar system and it's controller that continue to apply charging voltage to wet cell RV batteries may boil away the battery liquid hour after hour because of current flow through the liquid in their cells that never completely stops.

I'm not sure what would happen with any size solar system sitting in the sun when/if the RV batteries become fully charged and stop accepting any more - or only a very small - current. I assume the solar controller is designed to protect itself under all current flow conditions. I don't know what the solar panels themselves do sitting in the bright sun do when current is shut off by a controller (or by AGM batteries) from being able to flow out of them ... I don't think that they burn themselves up.

This hard stop is certainly what I am observing with my AGM Telecom battery also. There comes a point where it just acts like a sealed container, once it's full, it's full, can't put any more amps into it, so don't force it.

[pnichols]

I'm not sure what type of batteries you have, but our AGM ("dry cell") RV batteries will not accept any more current when they're full - regardless of the value of the charge voltage still on their terminals. I call it a "hard stop" to their charging. I've verified this time and time again with an ammeter in the charging cable for the batteries.

Wet cell RV batteries may not act this way, so perhaps a solar system and it's controller that continue to apply charging voltage to wet cell RV batteries may boil away the battery liquid hour after hour because of current flow through the liquid in their cells that never completely stops.

I'm not sure what would happen with any size solar system sitting in the sun when/if the RV batteries become fully charged and stop accepting any more - or only a very small - current. I assume the solar controller is designed to protect itself under all current flow conditions. I don't know what the solar panels themselves do sitting in the bright sun when current is shut off by a controller (or by AGM batteries) from being able to flow out of them ... I don't think that the solar panels would burn themselves up.

[Ace_]

Thanks. I wonder how efficient my Hawk will really be. The lights are LED. I really only worry about the furnace and refrig (AC/DC), and I may purchase an efficient television.

Is there a downside to too much solar? If it's on the roof, not in the way, why not over-engineer? Is there a chance of overloading a battery bank with a good, adequately-sized controller?

[Fisherguy]

Salvo wrote:
Not sure you need that much solar. I've been using 130W for 8 years. It's adequate for us. The 2 x 6Vs (220Ah) are in absorption by 1 pm.

It's important to have a balanced system. 400W solar and 220AH battery capacity is not balanced. There will be a lot of wasted solar energy. You'll need 440 AH.

I disagree. If you live near the equator or somewhere like sunny California that may be true but with panels mounted flat on the roof and living more north where we don't get as much sun you'd need more watts on the roof. Better to have too much up there than not enough.

I'd get a generator first, a Honda 2000 and make sure your converter is working well, the WFCO in mine was a POC so I installed a PD-9280. You won't be able to drive that converter with a 100 watt generator.

I had a 100 watt panel years ago, used it as a portable for a few seasons, it was a waste of time, even chasing the sun around all day it just didn't put out enough, and that was before we had a tv etc. That was a long time ago though, it was a Siemans panel, maybe panels are better now. I just put 360 watts of panels on, will be heading out in a couple weeks, anxious to see how it works.

Like others have said, changing all the lights to LED's really helps.

[NinerBikes]

ktmrfs wrote:

pnichols wrote:

MEXICOWANDERER wrote:
Prepare for the worst...

I agree 100%.

What this means with regards to electrical power for an RV when not on hookups is:

1) If you cannot afford both initially, or don't want to mess with a permanent solar setup initially ... begin with a good battery and generator setup for your RV. If you have the relatively small amount of extra money required, add plug-and-play portable solar right after a good battery and generator setup.

2) When you have a larger amount of money plus personal knowledge and time, or plus access to a competent RV solar installer ... add permanent solar after doing 1), above.

IMHO, having solar only ... whether with or without a good battery setup .... is non-hookup RV'ing on borrowed time. Eventually you're going to get caught with both your batteries' energy and the sun's energy too low. Our RV has three (3) non-solar ways of keeping it's 230 amp hour battery bank charged up rain or shine, day or night.

P.S. Of course a lot of folks borrow a lot of time. 😉

couldn't have said it better.

Agreed with pnichols, and this is the path I took, quite by accident, only because I had the generator before the TT, and the plug and play solar panel made sense initially, until I got a proper sized battery pack with enough Amp hours, found out about adjustable charge controllers, got a bigger more amp hour battery set up, and got a bigger panel to balance and match the battery pack, as well as getting a Mega Watt and RC battery charger gauge/display. You live, you travel, you dry camp, you gain experience, and hopefully you fine tune as you go. But this is a good start as suggested above.

Above all, it's been fun learning, measuring, experimenting, observing, and in general being fascinated by electrical energy in a jar.

[pianotuna]

Salvo, I thought you ran your generator for 15 minutes each day?

[Ace_]

Deleted.

[ktmrfs]

pnichols wrote:

MEXICOWANDERER wrote:
Prepare for the worst...

I agree 100%.

What this means with regards to electrical power for an RV when not on hookups is:

1) If you cannot afford both initially, or don't want to mess with a permanent solar setup initially ... begin with a good battery and generator setup for your RV. If you have the relatively small amount of extra money required, add plug-and-play portable solar right after a good battery and generator setup.

2) When you have a larger amount of money plus personal knowledge and time, or plus access to a competent RV solar installer ... add permanent solar after doing 1), above.

IMHO, having solar only ... whether with or without a good battery setup .... is non-hookup RV'ing on borrowed time. Eventually you're going to get caught with both your batteries' energy and the sun's energy too low. Our RV has three (3) non-solar ways of keeping it's 230 amp hour battery bank charged up rain or shine, day or night.

P.S. Of course a lot of folks borrow a lot of time. 😉

couldn't have said it better.

[BFL13]

In the 5er, we use about 70AH for normal things including inverter to run MW, toaster, kettle, etc., any time of year. In a provincial park in February we add another 100 AH for just the furnace to heat our barn. (The OP has a TC so easier to heat)

So to get by then, we need about 170AH a day from the batts and then need to recharge before reaching the dreaded 50% SOC. It happens that solar is useless in February in Rathtrevor Park, so it is all generator to power the charger(s) to get the job done. The park says two hour gen limit from 9-11 and then another from 6-8 but by 6 it is dark out so my target is to replace 170 AH in two hours 9-11am every day there. I have the equipment to do that (learning curve involved).

Then in the summer at an off grid place out in the open we still do the 70AH and hardly any furnace and about 230w of solar can do it all most days. Once in a while we still need the gen to do "catch up" if it gets cloudy for a day or two. More solar would not reduce the need for "catch up"

"Catch up" requires that you do the full day's work as usual plus another day or two's work that same day or over several days if you are blessed with several sunny days in a row. Meanwhile the batts are sitting there still not fully charged and the longer that goes on the more sulfated they get.

For any sort of trailer the answer is to always have both gen and solar (if solar is justified at all). With a TC, when the solar is useless, and there is no room for a generator, the guys who say use the truck's alternator with extra fat wires to get enough amps are correct.

An alternative to that is to clamp an inverter to the truck battery outside the engine compartment and plug a battery charger into that clamped to the house batts. This may not be physically convenient, but it works.

I have found with the TC and the truck that you can fit extra batteries in front of the wheel wells to parallel with the batts in the TC's actual battery compartment. You leave the linking wires dangling over the rails, slide in the camper, then connect up. That helps with extra batts, but you still need to recharge them.

Scenario is everything!

[JiminDenver]

A 2-1 ratio of watts to Ah is nice to have in shortened sun hours be it my conditions of cloudy afternoons or short winter hours. A single GT panel portable on a 8-D taken down to 50% can't provide enough amps to do the job in either case. Using the 2-1 system last year could. It's a simple numbers game, 1-1 just doesn't push a bank around.

I haven't taken our generator for years but will on longer trips from now on. No reason to take a chance of damaging the bank if the weather turns bad or the solar goes out.