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Renewable Energy

All things energy, from solar and wind power to efficiency and off-grid living.


Technological Challenges of Off-Grid Homestead Living, Part 5: Heat

Read Part 1, Resources, of this series here. Read Part 2, Electricity, here. Read Part 3, Water, here. Read Part 4, Food, here.

A happy home warms your heart and the sun warms your home, either way, heart or home, sometimes it can be too hot or too cold. In the Cascade Mountains, where I live, the outside temperature ranges from 100 degrees F in summer down to freezing in winter.

In any climate, the least expensive heat systems are the thermal features of the house itself designed to conserve heat and reduce fuel costs. My affordable small house has six inches of insulation in the walls (R19), ten inches in the ceiling (R30), all the pipes are insulated, the attic is ventilated, and the root cellar under the first floor is exposed to the earth. My shady front porch faces north and stays cool, while the attached greenhouse faces south and stays warm. There are operable vents on each wall of the two floors and a cook vent fan on the first floor and a ceiling fan in the second floor.

Heat energy is constantly flowing from hot to cold areas. Controlling heat flow by slowing it with insulation or increasing it with ventilation, collecting and releasing heat by storing solar energy, and/or burning fuels is how to manage heat for comfort.

Summer and Winter Modes

Renewable energy needs to be optimized for the season and often requires two sets of devices, for example, in summer I run a solar hot water collector and solar electric refrigerator; in winter I run a woodstove for space heat and hot water.

summer-winter modes

In order to see how my heat systems are working I use several thermometers: one placed on each floor, one on the porch, one in the greenhouse, one in the root cellar, two for the refrigerator/freezer, one on the woodstove, and one in the solar oven. Although I don’t need a thermometer to find out my pipes are frozen or that the hot water is cold, the temperature data helps me fine-tune my systems.

Wrestling with the Woodstove

Woodstoves do not have thermostats and do not put out heat unless constantly tended by hand. Pellet woodstoves have automatic hoppers, but purchasing bags of pellets is more expensive than my own silviculture harvest. Costs aside, keeping my woodstove stoked has led to choosing between losing sleep to keep it stoked every hour, or letting it go out overnight and waking up to a cold house and waiting until the woodstove has burned a few hours to bring the house up to a comfortable temperature.

Other issues with woodstoves: Starting the fire may cause smoke to back draft into the house. This is because the heat from the fire has to be great enough push cold air up the stove pipe before it will vent normally. I use a torch to start the fire — first directing the torch up the stove pipe for about 60 seconds, then ignite the wood and close the woodstove and its air inlet vent.

After five to ten minutes, the feeble flames generate lots of warm smoke and build up enough heat to travel up the stove pipe, and then I open the air inlet and add more wood.

If you are connected to city energy, or run a large electric generator and/or a large propane tank, you simply set the thermostat and then pay the cost of the fuel, which is much more expensive than renewable energy heat sources. My expenses are 10 times less compared to a typical utility bill in a nearby town. My annual fuel consumption: 15 gallons of propane (cooking), 20 gallons of gasoline (backup generator), and 2 cords of wood (space heat and hot water), supplemented with free solar energy for cooking, hot water, space heat, and electricity.

Solar Heating Options

There are two types of solar thermal heating for your home’s space heat or hot water:

1. Passive heating—has no moving components; heat is transferred by convection through a thermal mass and into the space or water to be heated.

2. Active heating—uses pumps or fans to transfer heated air or water past a solar collector and into a thermal mass.

There are two types of solar hot water collectors, each optimized for different climates:

1. Evacuated tube collector—are very efficient and most suited to cloudy climates. Evacuated tubes have a ‘heat pipe’ mounted inside which is connected to a manifold with additional tubes.

2. Flat plate collector—works well in sunny climates. Flat plate collectors are lengths of copper tubing connected to a manifold and mounted on the surface of a sheet metal plate, all painted black and enclosed in a flat box with glass to admit the sunlight.

Solar Cooking Options

Solar cooking is accomplished by using reflectors or lenses to concentrate the sunlight, thereby producing elevated temperatures where the food is placed for cooking. 300+ degrees F can be achieved in a box style solar cooker. One caution is that since the food must be loaded on the reflector side, eye protection must be worn.

You can re-purpose a conventional oven into a solar oven by cutting off the back top edge of the oven and adding a glass window and reflectors to admit sunlight into the oven. The food is loaded through the existing oven door, opposite the reflector side. You can make this as a built-in oven on the south wall of your home, so the oven door opens into the kitchen and the reflector and bulk of the oven is outside.

More detailed information on solar and fossil fuel heating and cooking methods are available in my book, Hut-Topia.

Christopher James Marshall is the author of the do-it-yourself small house book Hut-Topia and is a modern-day off-grid mountain man. After weathering recessions and lay-offs every decade since the 70s through the “Great Recession,” he became semi-retired by making plans to live sustainably and then built his 500-square-foot off-grid home. Read all of his MOTHER EARTH NEWS posts here.


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chris
12/11/2015 3:34:40 PM

Hi Dave, Your grid-tie system, unless you made it yourself, is code compliant and will force itself to shut off in power outages on the grid. You can't get around this for safety reasons (the code). What you can do is have elect generator + inverter/charger + battery bank, independent of the grid-tie system, Then shut-off the grid-tie when you want to use the other system. The Tripp-Lite inverter-charger has a built-in transfer switch to work with the generator(get this--it must be a 'clean' power generator). Then, connect your PV or wind or hydro conroller to both the battery bank and the grid-tie hardware (no switch needed). It'll work, but it's a bit out-of-scope because usually grid-tie's advantage is no battery bank, but sounds like you want a battery bank for gird out conditions. The only way you can skip the battery bank is if your loads can run intermittently as the PV and wind are intermittent. Hydro is continuous and is ideal if you have it. Hope that helps! Good luck, don't shock yourself or short out the hardware, and good work on using renewable energy. Chris.


dave
12/11/2015 1:15:37 PM

Chris, I currently have a grid - tied PV system. I want to add options for main, off-grid, gen, and battery but I cannot find a 4 position transfer switch. Do you know where I might find a 4 position manual transfer switch? Thanks, Dave


chris
12/9/2015 10:26:27 AM

Thanks Doug. I'm solving the backdraft problem by getting a swiveling wind cap for the stovepipe, the kind you often see on homes at the Oregon coast where the wind seems to always be present. It has a vane on the top that directs it to shield from downdraft and actually helps create the correct updraft in the woodstove. If you've seen the videos on YouTube of my small house, you'll probably notice that the stovepipe is at an angle--I'll fix that with one more elbow before I put the wind cap on. Just waiting for the snow to diminish so I can get out to the hardware store to get the new stovepipe components.


doug
12/4/2015 10:11:55 AM

A tip on the stove lighting. If you have a downdraft in the chimney (warmer outside than inside) or just no flow at all like you describe, lightly crumple a sheet of newspaper and lay it on top of your wood by the stove pipe (if the fire box is full) or half-jam it into the stove pipe (if you don't fill the fire box). Lighting that will force hot air up the chimney almost immediately. If you have a chronic no-flow situation you may need to check your chimney design. It may not be tall enough above the roof or there are close-by trees, etc. that impede its flow. What you describe isn't normal. It also sounds like you need a bigger fire box to hold enough wood, then coals, to last the night. Mine stays hot enough all night to keep the blower on - next morning add more wood and it lasts all day while I'm gone. Often the blower is still on when I get home. Also a suggestion for lighting - collect lint, rags, cotton balls, etc, old candles, and cardboard egg cartons. Some lint/rags/cotton in each divot, a good dose of melted wax, and cut them up. Best fire starters I've found (better than commercial wax-and-sawdust starters which I used for years). The starter lights instantly, no need for kindling, and it lights the wood 99% of the time w/o touching it again.