A way to heat a cabin without electricity year round?

[OlJarhead]

http://cansolair.com/component/virtuemart/view/productdetails/virtuemart_product_id/2/virtuemart_category_id/1?showall=1#garage-brochure

Check this out!!!  It's expensive but I can see the possibilities!

[Ernest T. Bass]

Seems like if your house was already designed for passive solar gain, then this unit really wouldn't be that beneficial.. But it would be a great addition to a building with little glass, especially a shop or something. I've seen the can idea on a few youtube vids; wouldn't think it would be terribly difficult to diy.

[DaveOrr]

It would be useless where I live as there is only 4 hours of sunlight in the winter and it gets down to -60!!!!   

[MountainDon]

Even here in the SW it would help but doesn't do anything for night time. We have some older, les efficient solar collectors (hot air circulation).

[OlJarhead]

My thought was more along the lines of a way to keep a cabin above freezing when not in use.   After all, a few hours of warming during the middle of the day (they say it works best in winter by the way) would keep the cabin above freezing all night.  It takes a long time to warm the place up from freezing and it takes a long time for it to lose all that heat.

Seems like a viable option to me -- though an expensive one!

[Rob_O]

Like this?

http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

[Squirl]

You mean like this:
http://solar.freeonplate.com/diy-how-to/DIY-solar-panels.htm
DIY solar has about a dozen plans.
About 2 years ago, I believe homepower had an article how to build one for $300.

I've seen these for years.  I can't believe they are selling it for $2800!  You could probably buy $2800 worth of PV panels , wire them to a dump load with thermostat and get more BTUs.

It depends on the mean daytime temperature.  A building with high interior thermal mass, efficient, with good insulation will hover around the mean daily temperature.  For most climates you only have to raise it a few degrees.  I have read and talked with people doing it with dump loads on their off grid systems.  When they aren't there, the power from their PV modules and wind turbines is wasted.  Hook it to a dump load in a house attached to a thermostat and even small systems can raise the temperature a few degrees.  Also the dumpload can be placed near a floor or where pipes are such as in a kitchen or bathroom, unlike solar air collectors which usually heat the ceiling.

Many of the passive space heaters suck without an electric fan to circulate the air.  I know the technical theory is hot air rises so that the hot air will automatically circulate out and draw in cold air.  The holes are small and they are more efficient with active air circulation. 

There is debate whether these "can" style heaters are better than passive solar.  You can fully insulate all the walls.  When the sun comes out, it activates a solar panel that connects directly to a fan.  This circulates the warm air.  When the sun goes down, it shuts down the air circulation losing less heat to glazing.

The downside is that the sun heats the air, then the air has to heat the thermal mass to retain the heat overnight.  That part is less efficient than passive solar, in which the sun directly heats the thermal mass.  Hence the debate, greater gain vs. less loss.

[OlJarhead]

Now you have my interest really peaked!

I'm wondering how complex this is for a system like mine in which I have 615 watts of solar power running to a Morningstar MPPT controller?  Dos this mean I'd have to add a controller configured as a Diversion Controller before the charge controller?  it would seem that as soon as the system goes into float it could divert excess watts to the dump load to warm the cabin (kinda like running a 100 watt light bulb in a root cellar) which in turn would warm the place even if only slightly.

I'd like to be able to arm the cabin in the winter when I'm not there -- more specifically I wonder if I couldn't install something like this into the crawl space near the water lines once I've enclosed it completely and insulated it.  Then with just a little heating capacity I could probably keep the crawl space warmed up.

It would also give me a way to run my heat tape/trace that I keep on my sewage pipe and run in the winter to prevent freezing (and clogging).  I ran it one winter too long without sun when I wasn't there and the batteries took a beating!  I'd like a way to divert power to it to constantly warm the pipes in the winter.

[Dave Sparks]

Even here in the SW it would help but doesn't do anything for night time. We have some older, les efficient solar collectors (hot air circulation).

Yes agree! A fun project that might help, but would not be as reliable as a photovoltaic running a heat pump.
2 days of bad weather and in many places the house will freeze.  A three to five day battery design with a generator back-up is about as reliable as it gets. Next level of reliability is the power utility,  sorry just kidding! hey Don !

[Rob_O]

A three to five day battery design with a generator back-up is about as reliable as it gets. Next level of reliability is the power utility

Aaaaaaaaaand, ya still have to keep a generator around for when a major storm rolls through

[MountainDon]

Aaaaaaaaaand, ya still have to keep a generator around for when a major storm rolls through

For the past few years our generator has only been run every other month or so just to keep it "in shape". "Before solar", during construction of the cabin and in the earlier "RV stage" the generator saw a lot of use as the source of power. We have never run the batteries down into a serious or even semi serious state of charge. As of a few days ago the clock on it read 889.something hours. That's a lot of oil changes.

If it gets cloudy for a few days in a row we may curtail or limit the use of the toaster, crock pot cooker or microwave. We're past the heavy construction stage and find no problem running the few power tools as wanted. I can even run a battery equalization cycle off the PV panels.

I have been giving thought to changing the generator over to propane so I don't have to be concerned about the issues associated with gasoline fuels. Or doing away with it completely as that would be cheaper.       

I also know someone with a solar installation who does not have a fossil fuel consuming generator in their system at all.

Plan well, use wisely and you can be truly off grid.

[Squirl]

It depends on the charge controller.  Some have aux outputs that can be programed to turn on at a certain voltage. So you can set the load to turn onwhen the battery is fully charged and to shut off when the battery is 95%.

Some people use a pwm charge controller hooked directly to the batteries.  It just has to kick on .1 volts before the mppt charger is set to shut off. 

[MountainDon]

I went through this scenario a couple of years back. I wanted heat to reliably keep things from freezing as well as perhaps keeping the cabin interior from deep freezing... being colder than the outside temperature on arrival is common in winter. The hours of being cold are much more numerous than the hours when the sun warms things; more heat loss hours than heat gain hours.

My conclusion was that it was not feasible. Maybe the specifics of our location are unusual, maybe not. Winter in the area of our cabin has enough serially occurring cloudy days that are combined with below freezing temperatures to mess up even the most optimistic calculations I made. I had thought of using hot air as well as liquid recirculating systems for grabbing solar heat and heating the interior. Several below freezing days in a row with no heat had too great a heat loss to guarantee a frost free interior or compartment.

As I mentioned earlier in the thread, we do have a couple hot air collectors here at home dating back to '85. They work fine in daytime. The gas furnace never runs during a normal sunny day. But the furnace does run in the evening and first thing in the morning when we want to bump up from the lower overnight thermostat settings. And on the cloudy and cold winter days the furnace runs as if there was zero solar. It may be possible to keep things inside the insulated envelope from freezing on a sunny day to sunny day basis but the cloudy days mess things up.



Trying to use diverted electrical energy to a dump load heater can run into issues. The incoming voltage from the PV panels varies wildly and you can run into problems with the resistance elements not acting as they were meant to as the voltages change...  resistance changes with big changes in the voltage and things get wacky. I did some research and now forget the exact details but it was a problem.

Using a resistance heater element off the batteries or inverter at a constant voltage makes it easier to make it work but is not terribly efficient use of electricity. Heat pumps can be a better use of the electrical power per BTU benefit.


My sadly arrived at personal opinion is that trying to heat anything with solar derived electrical energy using resistance heaters of any kind, is a waste of time, effort and money. The efficiency level is too low.

[Abbey]

I know some people here in Vermont who have a similar setup and they say it makes a noticeable difference in the winter when the sun is shining, however their house is inefficient and what heat they gain in the day is quickly lost as soon as the sun begins setting. Something like this would, I think, make a great addition to a tight, well insulated house. I'm sure you can find plans to make one yourself far cheaper, although I wonder if it would have the same efficiency.

[tommytebco]

The "Earthship" design will do it.
A guy I met in Silverton, CO lived in one. He is/was a long distance trucker, gone for weeks at a time. He stated that, on return from a long run (weeks) in the dead of winter, his inside temperature was around 50 or 60 degrees. This was with no back up heat

[OlJarhead]

Hmmm... I have a Zantrex C40 just sitting in a box....so I could use that to come on at say 14.4 volts or 13.5 (depending on which portion of the cycle you want to use I guess) and dump excess power into the heating elements while the batteries remain charged?

I'm thinking the draw would have to be matched to the extra amps available on the panels at the time of use which might be tough to predict....

[MountainDon]

I'm thinking the draw would have to be matched to the extra amps available on the panels at the time of use which might be tough to predict....

quite tough, I think. near impossible perhaps.

FWIW, CC like the Outback have a programmable auxiliary that could be used to shunt power from the PV input before it reaches the batteries by using a solid state relay. That was the route I was considering. The aux on the CC is low current, low voltage and could be used to trip the solid state relay. The relay would carry the "extra" power to the load. The relay would have to have high enough voltage tolerance for the highest PV voltage on cold days, as well as carry the expected current.  You still have to figure out the best heating element to use as this voltage can vary wildly depending on sun conditions. Power changes affects how the heating elements work. The resistance of a heating element changes as the temperature of the heating element changes. That is hard to figure.

I gave up when I calculated the likely available extra power on a winter day, and the time it would be available. Take that to get the watt-hours and then convert to BTU's to give an idea of heating power available.   
   
600 watts = 2047 BTU.   

G/L

[Gary O]

Is it possible to stay on topic ('without electricity') and stray off solar, into propane?
If the intent of this thread is solar only, I'll go away and start a new one, but I do have some burning questions;

In less than 2 yrs, my wife and I w/be living at our tiny cabin.
I really don't wish to get involved in wood fired stoves, or solar just yet, as I don't want to do all that until I build my shop and house (all to code and permitted) but will need heat, appliance service, elect tool power, and lights for habitation.
My initial thought is a rather large diesel/propane generator, leaning heavily toward propane.
And one or two 100 lb propane tanks.
I do need to study up on size regulations (set backs etc) of propane tanks, and thoughts of battery storage conversion from generators.
Any suggestions as to where best I can read up on this?

Or maybe there's a thread here somewhere that talks about it?

Gary O'