Cost of Partially Heating Trailer with Solar Power

[Canine]

This should help give people an idea of what it would take to electrically heat a small, highly insulated, off grid trailer.

WalMart had a 250 watt heater on sale for $10, so I thought this could be an affordable experiment. I also picked up a programmable timer so the heater doesn't run too long while I'm gone/sleeping. I'm into this for $23. It's hard to say how much it will run on average because in the middle of winter when I need it the most, it won't work at all due to lack of sun. Then in the summer it will be so warm, there will be no need to use the heater.

So I'm going to throw out a generous average electric heater usage of 4 hours a day. I can run the heater for 5 hours at night without taking the battery down too far. It could run longer, but then I won't be able to use my other electrical stuff. I won't bore you with the math, but after converting electric watts to BTUs then using the BTUs in a 20 pound propane tank at $12 per tank, it would take me almost 8 months to break even.

I have 570 watts of panels and put my other battery back in for 560 a/h of batteries. My 6X12, highly insulated trailer is a great candidate for testing this because it is so efficient at staying warm. I'm in a much better position than most to be able to heat with electric, but even with all of that solar electricity and insulation, I can supplement my heat only in a very small way.

For comparison, we had a cold winter with lots of snow; over the last 6 months (September to February) I used 17 tanks of propane costing me an average of $34 month in propane. I did use the electric heater the last two weeks, but that is such a small factor that I didn't factor the usage in.

The 250 watt heater will warm my trailer to about 65F with outside temp at 30F if it isn't windy.

It is nice to turn it on in the morning to help warm up it up before I shower. I like to keep the propane heater down when I'm sleeping, so there is a savings in propane there. How much savings? Not much, but it helps and I'm still in my comfort zone.

 

[tx2sturgis]

Recently I've seen a couple of videos about these little 200w heaters....if you can heat a trailer with one, you have a well insulated trailer, because the heat output is very little. I think one guy hooked his up to shore power and barely kept a truck topper/camper heated. 

About a foot away, you can't feel much heat at all. I have 2 of them, one under my desk and one in the bathroom...they work, but barely. I consider them as 'spot heaters'....

Based on wattage, they put put out about the same heat as 2, 100 watt light bulbs...yours is 250 watts, so add in another 50 watt bulb.

I wonder why you are staying where it is cold enough to go thru that much propane each month...I tend to assume just about everyone on this forum BUT me can move with the seasons...

If only.....if only.....

 

[Canine]

I live in Central Montana born and raised. The trailer is very well insulated. If it gets cold in here, it takes a good while to warm up with just the 250 watt heater. My foray into actually living the vandwelling type of lifestyle is only about 22 months old with 11 months of that in my current trailer. The idea of a snowbird type of lifestyle is more appealing than it ever has been. I'm semi-retired so I don't have absolute flexibility to what I can do, but I do have a lot of flexibility. We'll see if I can find a place where a 250 watt heater will keep me warm.

 

[jonyjoe303]

how well insulated? In my van I thought I use to be well insulated but I was letting too much cold inside my van. I added foam to all my doors/windows, I had a sliding door dividing front and back of van but there were gaps where cold was coming in, I added foam to those areas. I made van as airtight as possible.

This winter I was able to go without my mr heater, I didnt even have to sleep inside a sleeping bag. Every inch in the back of my van is covered in rtech insulation. In my situation even running my little netbook and lights keeps the back of my van from getting too cold. Even with all the insulation I have, I think I can still add more. 

The 250 watt heater would definitely work in my van but it might work a little too well, but if you can heat with solar thats better then spending on propane. 
You insulate to the extreme (where I am headed but not even close) and that 250 watt will easily keep you warm, I saw firsthand this winter how well insulation works.

 

[John61CT]

Any good heat source should be able to scale up and down as needed.

The ideal of course is a thermostatic controlled one, set it and forget it.

Personally I would not run any heat source from my batteries "in production" day to day, but yes interesting as a science project.

 

[Canine]

The trailer has 2 inches of XPS on the floor, 3 inches of polyiso (same stuff as R-tech) in the walls, and 4 inches of polyiso in the roof. I minimized any thermal breaks and overlapped the sheets of insulation. Instead of piecing in leftover pieces of insulation, I used the largest sheets possible to minimize the seams. The two, 18X24 windows are single pane. The 30 inch by 72 inch door is one inch of EPS. Then one 4 inch by 10 inch vent and one MaxxFan with some foam padding stuffed in it. There is some room for improvement, but overall it is well done.

The electric heater doesn't have a thermostat but it was only $10.

If the trailer had the standard (lower) height, heating it would take less energy. Whenever space is added (like adding a high top onto a van) it takes a surprising more amount of energy to keep it warm.

 

[tx2sturgis]

2 inches of XPS on the floor, 3 inches of polyiso in the walls, and 4 inches of polyiso in the roof.....

{snip}

There is some room for improvement, but overall it is well done.

I'll say.

I think you built the equivalent of a refrigerated trailer. 

 

[frater secessus]

The other day I ran a little $10 200w heater off solar. It did make some difference and was nice to sit by. It also doesn't create water vapor the way propane does.

I have read that watts of electric heat x 3.41 = BTU, so your 250w would put out about 850 BTU and my 200W about 680. 200W of heater should put out more heat than 200W of light bulb because less energy is converted into visible light. Dunno if it's a measurable difference.

I've heated many a dog's house with a lightbulb.

 

[tx2sturgis]

 200W of heater should put out more heat than 200W of light bulb because less energy is converted into visible light. Dunno if it's a measurable difference.

I've heated many a dog's house with a lightbulb.  

Yeah I said 'about' the same heat....I think normal incandescent light bulbs put out about 10% of the energy used as visible light...

That's one reason that the normal, everyday, 60 to 100 watt household lightbulbs have disappeared from the store shelves.

Congress, yada yada...(not political, it's just the law now) 

Really, my point was that the OP's trailer is very well insulated. We used to say dwellings like that, super efficient houses, etc, very air-tight and super-insulated, can almost be heated with a candle, and cooled with an ice cube.

Again...'almost'.

 

[Riverman]

In a super insulated cargo trailer or a van, 200 watts may heat them pretty well.

In my travel trailer, 200 watts might heat just the bathroom on a warmer night.

 

[John61CT]

Yes done right that amount of insulation is sufficient for boondocking in the snow.

A thousand dollar hydronic heater setup with thermostat and timer controls would then use a very tiny amount of fuel per day, keep you toasty camping in ski area parking lots with the kids.

I'd match the floor and ceiling if boondocking with A/C in hot desert as well, go to 4" all around if space allowed, but just 3" for the walls should be enough if the extra inches are required for the sideways bed.

 

[Canine]

AC may be in the future. Evaporative cooling will come first. But that's another thread.

 

[John61CT]

Then make just as sure coolth doesn't drop through the floor, as carefully as you keep heat from floating out the top.

 

[tripper]

I have 2 of those little heaters. One has dual power 175watt/250 watt setting and the other is straight 200watt. I use it to keep my cats warm in the daytime. I have the bed area isolated from the rest of the trailer and the one 250 watt heater keeps that are fairly warm during the daytime. At night I use an electric blanket set on low and my pets sleep with me under the blankets. I like that the heater is so low power I can run it in the daytime all I want. The electric blanket on low is about 1/5 the power consumption of the heater.