Tiny Solar Heater

I have a 119 Sq Ft house located at 7500 feet in the Rocky Mountains. The house is inhabited sporadically 1-2 weeks a month. I am looking to add a little heat to:
-Take the chill off when I am not there
-Add capabilities for charging devices and a night light down the road

I wanted to bounce this idea off and hopefully get some feedback!

Take 1 or 2 solar panels, ~200-400 watts @12v $100-200 and mount it on the roof.
Buy an automotive heater with thermostat and hardwire that baby to the panel.
Theory: If there is any sun, it will power the heater and do some form of heating during the day, for ~$100-$200. For 119 Sq Ft, it wont take much to heat the place, it is well insulated so hopefully will need less propane/wood heat. I don't want to wire a heater to the batteries and cycle them unnecessarily.

Questions:
1. Do you think a 12v electric blower motor would burn up in lower than rated voltage situations? If yes, I can just put a resistor type heater and thermostat in there, although I am thinking it might be fine.
2. Does hard wiring a solar panel have any other negative effects?
3. If I wanted to charge a battery separately for lighting(1 12v led light), but not run the heater off of the thermostat, how could I isolate the circuit to power the heater when there is power from the panel, and charge the batteries at the same time? I understand a charge controller would be needed. I have batteries. I am thinking just wiring the + and - in series with the charge controller wouldn't cause any issues other than both devices sucking power, and therefore limiting the power to both.
4. I would place the heater in a fire-safe location in case it did fry. What about other wiring? Any way to make the setup/wiring more fire safe in case of a short? Will a panel shorted long-term fry\pose a safety hazard?
5. Any other safety issues you can think of? Other Ideas?

 

The 12v heaters are so cheap I wouldn't trust them
Plus if you hook it straight up to panels the voltage will go way over normal 14.4vdc charging system voltage.

Cold panels make more voltage. You could see as much as 17 or 18v under load going to that heater.

 

Agreed , cheep heaters will cause a fire .
You need to do this once & well .

7500 feet in the Rocky Mountains , snow level you see ? shading from any trees ? Know your winter sun scape (area of sun beams to hit you ) . Roof mounts are not good for winter cabins . You'll want your panels higher than snow level & almost standing straight up in winter.

Your turn in letting ME/US know more about your area.
Something Like this : https://www.survivalmonkey.com/members/mountainmariner.13585/


Now MM didn't build his system Critter proof , so He has damage .

Sloth

 

I can't speak to whether the system would keep the place warm, but there is a very simple way to make the technical stuff work.

For starters, you will need a battery of some kind. You cannot connect a device directly to a large solar panel.

Electric car heaters top out at 150 watts. That's not much. You're just as well off using a 12 volt/150 watt incandescent lightbulb to heat the place. It's a lot cheaper, less risk of fire during operation, and no risk if the bulb burns out/fails in service.

150 watts at 12.5 volts is about 12.16 amps, so a 15 amp charge controller would be about right. Maybe go a little higher to allow for safety and future expansion. You can have approximately 400 watts of solar panels on a 15 amp controller.

Here is a good one: Morningstar PS-15 Charge Controller

Connect the solar panels to the controller, then connect your batteries to the battery terminals and the light/heater to the load terminals. Yup...just a few wires. It's that easy.

From there the system will literally run itself. The light/heater will run until the batteries get too low, then the controller will automatically disconnect from the load until the batteries are charged, then it will turn the heat back on. This cycle will repeat itself with no human input.

If you go with a different controller than the one I linked, make sure you get one with LVD (low voltage disconnect). Some of the cheaper models do not have this option.

In strong sun you should be able to power the light/heat regardless of the battery state-of-charge. Four hundred watts of solar is enough to run the heat and charge the battery at the same time. As it gets dark and the solar output decreases, the battery will pick up the slack until the controller shuts the system down due to low battery voltage. Then you have no heat until at least sunrise, maybe longer. If you must have heat at all times, then get enough batteries to make the trip (and add more solar accordingly). A 150 watt resistive load will suck a lot of battery.

What you are trying to do is actually quite simple so don't overthink it.

 

A cheap 15 amp charge controller will melt if it' ran at 12 amps continually.

 

Plus Tevins EZ system needs to make sure the Battery is looked after first & in float or @ a set factor the bulbs come on in sequence of Voltage settings.

LVD is one But that is the WORST Voltage & kills cells , unless were using a NiMH type OR Li-Ion , Now were $$$$$$$$ .

Sloth

 

I know it's only a PWM controller. But, I have run the hell out of a little MorningStar SunLight SL-10L-12V for the past oh, three or four years. It is still going strong. (I bought it used, off eBay.)



I use it to provide outside 12vdc LED flood lights at the farm. (The timer settings are great.) What I am getting at here is, I would definitely buy more of MorningStar's products. Unfortunately, their customer service department has not proved to be as good as their products. (They have been rude and short with me in the past.)

Whoops! I forgot.


to the site.

 

For heat, why not go passive solar? If you have enough sun exposure for photovoltaics, this should work without the potential for fire.
Solar Air Heating for Mobile Homes and Metal Outbuildings
Then just set out your panels for charging when you are on site.

 

Morningstar isn't cheap junk. If a Morningstar says it will do 15 amps it will do at least 15 amps.

 

I was agreeing with you. Sorry. Was trying to verify that he could not go wrong with buying MorningStar products.

I know I have pushed mine over the 10 ampere rating it has, many times.

 

MorningStar products are Good & I have a few SS300 toast out , Handled well .
Still need to hear if he is like MM or ME with trees .
Sloth

 

I have a Morningstar TriStar MPPT for my home system and a Morningstar 10 with LVD like @Asia-Off-Grid 's on a portable system.

@oil pan 4 & Asia are absolutely right. Morningstar is not junk and will perform flawlessly as claimed for a very long time. They are an outstanding value for the money.

 

Wow excellent replies thank you! Thanks for the welcome messages as well.

Bruce, I am from Alaska, it doesn't snow like that here (where I am at) in Colorado. I am not worried about snow covering the panel. 7500 is a pretty low mountain elevation for us. If it does snow, it usually melts in a few days. I'm on a south facing slope, with some shading. However pretty damn good sun exposure.

You all talked me out of cheap heaters.

Tevin, Why couldn't I hook a 110V Baseboard, or other heater directly to the solar panel? "You cannot connect a device directly to a large solar panel." I am not questioning you, I am curious why. I love the incandescent bulb idea. If it keeps the chickens warm... why not! Thanks for sharing your charge controller experience, however, a little spendy for me. I took your advice on the low voltage disconnect, I bought a controller with a programmable disconnect.

I'd like a little more control over the temperature. I am looking for a 12v thermostat to keep the temps under 60 degrees. Any ideas? How about this: https://www.amazon.com/dp/B01N035M70/?tag=survivalmonke-20

I bet the cabin heats quickly and holds the heat pretty well. I don't want to cycle the battery unnecessarily. I am also thinking a 50w bulb would work fine, so will start with that.

Asia, I downloaded that manual to check out the lighting functions, if my cheapo controller doesn't meet my needs, I'll likely follow your lead and get a used Sunlight 10 or 20.

Techstar, many thanks! I read the entire article and will definitely integrate this into the cabin... Just have to find the right glass panels! I have a 11'x2' section of the wall south facing that can dump into the loft. Any ideas for glass panels? I am thinking an old window or sliding glass door would be perfect. Does it have to be tempered? Wont this bring a lot of cold air through the bottom vent at night when its cold?

 

When first installed and running, if I recall correctly, it will take a couple / few days for the timer to calibrate dusk to dawn. Afterward, it will work like a champ.

Below is how my controller was originally setup. It energizes the lights 4 hours on (~18:00 - 22:00), off for several hours, then energizes the lights from 2 hours before dawn, to dawn (~04:30 - 06:30).

I have since upgraded this to a single Just Solar 135 watts panel.

 

Sure you can. I have a DC fan that cools one of my greenhouses that runs wired directly ( well, it does run thru a fuse and a thermostat so it doesn't suck 0 degree air in this time of year) to a pair of 100watt panels.

The purpose of a battery in the system is to 'buffer' loads IF that is a requirement of your system....stop lights from dimming off to nothing, etc. IF what you are doing doesn't matter if the power flow varies, you do not need a battery.

In the case of a simple heating element, connecting a panel, or panels, would be the ideal situation for NOT using a battery. You'd simply need to size the heating element so it is greater than the power output of the panel(s). I'd also run it thru a fuse of some kind....shame if mouse chewed thru the line, shorting it and causing your building to burn down. I'd probably also run it thru a thermostat to do what I did in the green house for the opposite reason.....no need to heat the cabin in July.

The Bigger problem I see with running a panel to an air exchange heating element is that as sun as the sun begins to wane in the afternoon, your heat production stops. You'd be better off putting a water heating tank in with a DC heating element (or 2 elements) (Like this: https://www.amazon.com/dp/B00KLKGJ1I/?tag=survivalmonke-20 ) in an uninsulated tank (take a regular WH tank and strip the insulation off) and let the panels heat a glycol-water mix (mix made to withstand the lowest possible temp you'd experience) and let the panels simply heat water. Water is a great storage medium, and the tank would act as a buffer, giving off heat long after the sun went down.

 

The notion of using solar panels to harvest solar energy to then heat a cabin with resistance heating elements is inefficient both thermally and economically. Depending on the panel, you harvest roughly 14-18% of the solar energy. If you used a solar collector that heats water or air directly you can increase that efficiency by a factor of 4-5 up into the range of 80% or more and you can do it at a lower cost. You can also DIY many very effective solutions quite easily as well.

The primary exceptions allowing for using solar panels for this might be because the cabin is not in direct sunlight and you need to move the energy a fair distance. Possibly space constraints inside the cabin, etc. Collection of solar energy (in radiant form) thru the photovoltaic conversation to electricity is about the least efficient collection method so generally only use it if their aren’t viable alternatives which in this case of cabin heating there likely are.

If I was wanting to solar heat the cabin, I’d likely build one or a few 4x8 flat panel collectors to heat water. There are many plans on the net. One I saw several years ago could be built in a day for under $200 ( bulk of cost was copper pipe) and it was measured at 94% of the capability of a $1200 commercial unit. There are much cheaper less efficient designs now that use PEX tubing instead of copper. To store heat for night, you just need a well insulated tank. You can build a 200 gallon tank (strong wood box lined with a rubber membrane or IBC tote surrounded with extruded polystyrene foam insulation panels) for a hundred bucks or so. Add a battery, small charge controller, solar panel, small 12 volt pump, a small car radiator from junk yard (or do floor radiant heat with PEX in the floor), a couple valves, a few bits of plumbing and PEX and you can stay warm all night for years.

I suggested a water based system as you could bury or locate a water tank outside the small cabin whereas a direct to air system generally needs thermal mass for heat storage inside or adjacent to the cabin. Water also facilitates a bit more effective control of the heat a bit easier.

AT

 

I must interject here. You will need a battery for most applications. and a charge controller and inverter. You cant run a 110v appliance straight from a panel as the voltage will vary vastly and be insufficient. your fan is 12v and will just spin slower with low voltage (direct vs alternating)., Your likely to burn something down trying to tie a heater straight to panels.

Airtime is spot on. This is a problem prime for Ma nature IE solar mass. Too many ways to skin this cat in one post but youtube has a million different solar heater DIY videos. In my opinion I would leave nothing lit or plugged in while gone. These things I have learned living off grid....thank god for fuses! Even if I just go into town, which a 4 hour round trip, I turn off my inverter, and make sure my fire is under 50% burnt, etc.

 

Thanks again guys, great perspectives.

I happen to have a 40gal water heater lying around, and have saved my pex and copper scraps for years. I will definitely start with the heat sink idea, I can spare a couple square feet inside for the tank, I will see if it will dissipate heat naturally. Costs would likely be close to free, and a few hours of work. I cant help but wonder if I could use this heated water to bathe, heating water manually gets old. Just worried about freeze breaks in the collector at night... Im guessing Ma typically means ethelene glycol for freeze protection?

I will be doing PV solar also, I am just waiting for a great deal to pop up, I see panels for $.70/watt, waiting for a deal closer to $.50. My total cost to add a baseboard or tank heater will be about $10, mostly for the thermostat. Proper fusing, and conduit with firestop for fire protection will eliminate most fire danger. If my batteries are charged, even 10% efficiency doesnt seem like a bad deal. Heating the tank/cabin with the surplus PV energy seems like a cheap bonus, even if highly inefficient.

TnAndy, would you mind sharing details of your thermostat? 12v? Digital or mechanical?

Thanks again guys, great to see differing opinions!