Enough Solar for conservative boondocking?

[Mariner14]

Hey Guys, I looked for the "Dumb Questions" thread, but didn't see it, so I'll post my question here.
I want to be able to boondock for 3-4 nights with my family of five on our 28 foot TT. I don't plan to need a lot electricity. I was thinking we would only need the furnace fan, a few lights at night, and water pump. The fridge, water heater and furnace all run on propane, so just their control panels would need some current as I understand it. I was thinking of adding a second battery, but for the same price I could get a small 50-100 watt solar panel to charge the one battery during the day. Wouldn't that be enough to keep us going based on our conservative power usage? What am I not considering?

Also, with just one small solar panel, I could just hook it directly to the battery to charge it, right? I wouldn't need a charge controller or whatever, right?
Thanks

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[2oldman]

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[Almot]

In the OP scenario (and if converted to LED), furnace and fridge circuits will be the biggest items.

With a longer stay, for a family of 5, they might run out of water before 200 AH battery bank drops too low. Still, solar is advisable.

[mike-s]

Crabbypatty wrote:
The water pump is a killer as is heat.

Water pumps don't use much. A common Shurflo 4008 draws about 6.5 A when running at full pressure. At that pressure, it puts out about .5 gallons per minute. So a 42 gallon tank would take about 84 minutes to empty. That's a bit over 9 Ah to empty. Not much really, since that would be over several days for most people.

A Suburban NT20SEQ furnace draws about 2.5 A when running. How much it runs depends on the temperature, but say it's cold and runs 50% for 12 hours (night) and 25% for 12 hours (day). That's 22.5 Ah per day. Still not too bad.

If you've got 200 Ah in dual 6V batteries, you're good for a long weekend with the above.

The common 921 light bulbs draw about 1.25 A each. I see a lot of double fixtures. Having a single bulb porch light, and 3 double bulb interior lights on for 5 hours would use almost 44 Ah in a single evening. There goes that weekend.

That's why people recommend switching to LEDs. They only use 1/6 to 1/3 the power of similar brightness bulbs. For many people, they're the largest consumer.

You can play with the numbers, but I don't think the above is far from common usage.

[Almot]

Mariner - there is a very good chance that Jayco trailer would have "wedge" T10 base. Have no fear, open that double dome light and pull the bulb out. T10 looks like this:
.
LED would have a plastic "wedge".

Agreed with other posters - with 200-300W solar you will rarely, if ever, need a generator. Except for those punished with liquid sunshine 300 days a year - BFL13 knows.

Wintering in dry places like AZ or Baja, running generator is not very smart. There is hardly any rain for weeks, and when it falls, it's not for long. 2*6V batteries or 3*12V, with 300-500W solar is all you need (500W if you are heavy user with coffee maker, MW etc, and December sun is low). Flat, not tilted.

If you stay put for long time and and can go on the roof and tilt it, 300W would work like 400W, more-less. I "could", but don't see why I "should", 490W flat is enough power already. Tilting panels on the roof was popular when they were expensive and people couldn't afford more than 160-200W. Now panels are cheap, especially big 24V panels, it's easier to get more wattage and forget about roof climbing.

[vermilye]

One more example - I dry camped (can't hardly call Quartzsite boondocking) in an Escape 17 all winter, the longest 91 days in a row. LED lighting, 195 watts of solar on the roof & a 160 watt portable. 2 6V 232 amp hour batteries. I usually make a pot of drip coffee each morning, sometimes an electric toaster, run the furnace some nights, and use a power hungry laptop, charge camera & phone batteries, a Cell phone amplifier, rare microwave use, etc. Generally, between 40 - 50 amp hours per day. I don't carry a generator.

Have moved to a Escape 21 with 320 watts of solar on the roof & tilting panels, which provided all I needed last winter.

[BFL13]

How about getting enough (at least 200w) of solar so the trip will go well, and get your dad to sell the used solar set later?

[Crabbypatty]

We have 428 watts of solar (4 panels) feeding 2 Trojan t125 6 volt golf car batteries. We dry camp as much as FHU. The water pump is a killer as is heat. We feed the rig with a 2000 watt Xantrax inverter. I found a single circuit that feeds the entertainment areas and outlets in bedroom. I pulled that from the 110 box and plugged it into the inverter it always runs that way. So if its solar its charging, if its plugged in to FHU its charging. Do your self a favor and do not cheap out on the batteries as you get what you pay for. I sold my other TT with the same batteries going on 10 years. This new to us TT these batteries are going on their 4th season. Never let your deep discharge batteries go below 50%, if you routinely do, you will shorten their life dramatically. So when we wake up we use the water pump first, then it has all day to charge up if need be. We watch tv, dvd's, charge our phones use computers all the time, without worry. Works perfectly.

Happy trails

[Mariner14]

BFL13,
yes, I expect we will have a great time. I should upload my planned trip calendar. 4 weeks - Yellowstone, Tetons, Utah, Grand Canyon will be the highlights. Only thing is, we don't live in the US and only come back for a few months every few years. So I'm not going to get my own TT especially when dad uses it sparingly and keeps telling us kids to use it or else he is going to sell it (like he did our lakehouse a few years ago 😞 )

Almot,
As for LED lights, our TT is Jayco. Does that use a common "wedge" socket you mentioned?

mike-s,
Bravo on getting the word "pedantic" into the thread.

Everyone, thanks again for all the insight. This was really helpful. As I mentioned, I think there's a good chance we won't really need the furnace much. Utah, 9,000 ft in July. Maybe a little. If there's anything that gets us it will probably one of my kids leaving a light on all day or something.

[dieseltruckdriv]

Almot wrote:
With LEDs there isn't much to look into - just plug them in. If yours are a common "wedge" socket, These are what I bought. Or get it with a different socket if you have to.

The price is for pack of 10. Quite a few people on the forum bought from this guy. Brightness and color are indistinguishable from 18W RV lights. Not all the Ebay LED are same good. Simple unregulated boards can be better than more expensive ones, less radio interference.

Yes, small solar will let you stay longer before batteries drop down too low. Try not depleting them below 50%.

On a bright day and without furnace 100W solar might even keep batteries fully charged, but don't count on it.

EDIT: my mistake, the link is to lights with G4 socket. Same LEDs with T10 "wedge": Here. To match the brightness and color of 18W "old" bulb, use boards with 24 LED, color "warm white".

I use that seller exclusively for my LEDs.

I was also (in my mind) the one that could get by with 100 watts of solar. I can't, but when we are in our 5er, we live in our 5er, not survive. That means what lights she wants to use, she can use. If she wants to watch 4 hours of tv, she can. The furnace gets set to 60 at night, and if it runs, it runs.

That being said, 200 watts of solar will just get us by in the middle of summer, so I have more solar to add to my roof this summer. But I like tinkering with that kind of stuff, so it is fun for me.

[theoldwizard1]

SoundGuy wrote:

Mariner14 wrote:
What am I not considering?

Depending on night time temps especially, your furnace draw could be a lot greater than you anticipate. :E

Concur ! I would start with two 6V golf cart batteries (much more energy storage than two 12V dual purpose "marine" batteries). The key is to make sure they are 100% charged before you go to bed.
If you want to charge the "house batteries" from your vehicle, READ THIS !!

[theoldwizard1]

skipro3 wrote:
A typical incandescent bulb in your RV draws roughly 10 amps.

A typical festoon style (round tube with contacts at each end, used in auto dome lights) incandescent 12VDC bulb will draw between 0.25A and 1.0A.

A single filament 12VDC bulb (1156 - typical "backup" light bulb) uses about 2.1A. A dual filament 12VDC bulb (1157 - typical stop/turn bulb) also uses about 2.1A

LED equivalent use a fraction of this.

[mike-s]

Harvey51 wrote:
Electrical energy is measured in units of watt hours or kilowatt hours (kWH). A KWH on your home electricity bill costs about ten cents. An ordinary RV battery stores about 100 amp hours which is 100 amps x 12 volts x 1 hour = 1200 watt hours or 1.2 kWh. Note that discharging a battery below half charge damages it.

If you want to be pedantic, it's joules, not KWH (sic, it would be kWh anyway).

Discharging a lead-acid battery by any amount reduces its cycle lifetime, but 50% isn't any sort of magic number. In fact, for the vast majority of campers, the batteries die because abuse or their calendar lifetime, not the cycle lifetime. Getting 500 cycles instead of 1000 simply doesn't matter - it's the difference between dry camping every weekend of the year for 5 years vs 10 years, and the vast majority of people simply aren't off-grid that much. Discharging by 80 or 90% a few times a year simply won't make a difference, as long as they're recharged soon, and it's ultimately cheaper than buying more batteries to meet some "50% rule." The 50% thing comes from off-grid daily use, where it does make a difference.

The other thing which kills them is not recharging them shortly after discharge, or not recharging them fully. The latter happens with the cheap converter/chargers most campers come with. Even the $20 from China eBay solar controllers do better in most cases.