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

[Almot]

Measuring voltage is a proven method to tell battery state of charge. Trailer OEM panel with indicators Full/Half/Empty is about as useful as Christmas lights.

But you need to measure a NO-LOAD VOLTAGE ON RESTED BATTERY. In your scenario this would be early in the morning before solar kicks in, and with lights off and furnace and fridge not cycling at that moment.

[BFL13]

This is a one-off this time, but what if you have a good time?

Will your dad go for a next time? If you get more solar now (like 200w which is more like what you will need even with the second battery) for your one time trip, would your dad want it for his use after that?

IMO talk to your dad about where this is all going. You might even get your own RV and then what? 🙂 (Speaking as a dad )

[Harvey51]

Kudos to Mr Wizard for pointing out confusing misuse of electrical units. Pardon this old school teacher for repetition.

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.

Electric power is the rate of energy use; energy per hour. The unit is watt hour per hour or just Watt. It is never correct to say “watts per hour” because the watt is already a watt hour per hour.

I ruined our first pair of RV batteries by relying on engine charging and the voltage method of measuring the per cent of full charge: 12.6 volts means 100 %, 12.0 means 50%. This method is tricky because the battery voltage indicated is charging voltage while charging ... and for some time after charging ceases, depending on the power drawn. So a 50% charged battery can be at 13 volts a few hours after charging which lights up all the indicator lights on the RV panel making you think all is well.

After installing a 100 watt solar panel, we find we can camp without hookups indefinitely in summer. We don’t use electricity hungry appliances like incandescent lights, microwave, TV or coffee pot and we don’t run the furnace at night. We cannot camp now (March in northern Alberta) when it is -10 C, 15 F most of the day.

[Almot]

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".

[Boon_Docker]

A 100 watt portable kit is going to run around $225-$300. If you shop around you can get a 200 watt portable kit for about $350. Includes panels, charge controller and the cable to connect to the batteries.

[Lwiddis]

Mariner14, a properly sized solar system will recharge your battery/batteries daily....one solar watt per batter amp hour should be good for Texas. It is for Southern California.

[Mariner14]

OK everyone, I promise to look into LED lights!!
So we have a second battery now. If I put a 100 watt solar on to two batteries I realize that might not fill them back up everyday, but it would delay their running down completely and let us stay out an extra day or two, right? I have a hunch water will begin to be our limiter after day 4 anyway what with 5 people and such.

[Almot]

Mariner14 wrote:
I could get a small 50-100 watt solar panel to charge the one battery during the day. Wouldn't that be enough ...

Also, with just one small solar panel, I could just hook it directly to the battery to charge it, right?

1) At least 100W, if your lights are LED and furnace isn't used often.

Another battery is not "or", but "and". This will be your insurance against non-stop rain when even 300W won't do much.

2) I would not use any panel over 20W without controller.

Agreed with 2oldman - if this is just one trip ever, - get another battery.

Lights should better be Led. It DOES make a big difference in your scenario.

[2oldman]

crosscheck wrote:
As this is going to be a one off sort of trip, could you buy a 100-200W suitcase solar kit with controller that clips to the batteries and because solar is so popular, sell it on Craigs List etc. when you get back?

No. Bring another battery - unless you really like dealing with CL's customers.

[crosscheck]

Lota good advise from those that boondock with solar on this excellent thread. As this is going to be a one off sort of trip, could you buy a 100-200W suitcase solar kit with controller that clips to the batteries and because solar is so popular, sell it on Craigs List etc. when you get back?
Dave

[ksg5000]

Mariner14 wrote:
I am not going to do LED lights as I don't think we'll use lights enough to make a difference.

As others have pointed out - it makes a big difference. You just have to change the bulbs and not the fixtures - it's a inexpensive/effective move.

[time2roll]

100 watts into one battery is fine. You do need a controller. For the effort I would go 100 watts minimum on solar. You can use flashlights if the voltage starts dipping below 12.2 and to run the furnace moderately all night you really should have 12.4+ volts as you turn in. If conservation is too much effort then get a second battery and another 100 watts solar.

Sounds like you really want to do the minimum and that is fine. Be mindful that overly discharging a battery will significantly shorten it's life and capacity.

The 12 Volt Side of Life

[profdant139]

For whatever it is worth, we do a lot of boondocking. We are just two people, not five. We are very conservative in our use of power. We have two group 31 batteries with 110 amp hours in each. We have a 120 watt portable solar panel.

That setup can keep us topped off for weeks at a time. But we camp in the West, with lots of sunshine most of the year.

It is not hard to do an energy audit of each of your devices, to come up with a cumulative total. You then multiply the data for each device by the number of hours you will use it.

For example, we use our LED lights a lot, but they draw very little. We seldom use our furnace (except at shower time), but it draws a lot.

The other trick is to keep careful track of the state of charge of your battery -- you can then calculate how much of your reserve you use each day. Remember that with an ordinary 12v deep cycle battery, you can only use about half of the capacity. So our 110 a/h batteries really only give us 55 a/h.

[MrWizard]

A little clarification
Some members are not specifiying 'watt hours'
A fridge drawling 800ma aka approx 10watts, will use 240 watt hours of power in 24 hours
Your furnace using 8 amps for the blower will use 100w while running if total run time is 4 hours out of 12hrs, 30% duty cycle for the night
It will use 400 watt hours aka 0.4kwHr

A 100watt solar panel might produce 400 watt hours per day
It varies with each person's install and camping location etc
My 600+Watts of solar never produced more that 2200 watt hours in one day
So that is less that 400 watt hours total per 100 Watts of solar
Usually much less

100w is good for extending the week end into a three day affair

I don't think it's enough for a family of five for five days

I think you will be operating at deficit, use more each day than the 100 watt solar creates

I think 200 Watts and the second battery would be a better choice

This is not really an either/or situation, it is a use both for the desired results situation

[ppine]

Add a sceond battery and minimize the use of your furnace. Add LED bulbs and you can make it without solar. With solar you should able to go out for quite awhile.