Taking Your Greenhouse Off The Grid
Want to save money on heating and cooling your greenhouse? Want to become more self sufficient? It is quite possible to take your greenhouse off the grid. But first you should determine if this is what you need. Sometimes you do not need to heat the winter greenhouse, although you will probably need some ventilation.
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How Does A Greenhouse Work?
Greenhouses are covered with glass or translucent materials to let the sun’s rays enter the structure. That is why you will notice that the R value (insulation factor) for a greenhouse is much lower than a wall for your house.
The rays enter the greenhouse and hit a solid surface such as the ground, a pot, leaves etc and they are turned into heat. The shorter wavelength infrared rays that entered will become longer wavelength energy that is absorbed. The greenhouse will stay warm during the day as the light is entering and being transformed into energy faster than the heat can get out.
At night you will lose heat to the outside by radiation cooling. This is because the objects in the greenhouse are much warmer than outside. They will lose heat by emitting infrared radiation through the glazing. But, there are several solar methods you can apply to assist heat retention.
I just read about a huge greenhouse operation that put in ponds and a recirculating system to water their plants. They are using 100% rainwater irrigation. This was at a cost though of 1 Million Dollars. This is not practical for the small grower or backyard hobby greenhouse. And I believe the system required electricity. Although there are several things we can do.
I have talked to people who use ponds and recirculate their water on a smaller scale than the operation mentioned above. But, probably one of the simplest things to do is use rain barrels or cisterns to catch the rain water. If you are going to do this be aware of your local codes. This is illegal in Colorado. I am not aware of any other States at this time, but just check and be sure.
Solar methods of taking your greenhouse off the grid
Of course you can try to “trap” as much heat during the day as possible to be emitted into the greenhouse at night. One way to do this is to place dark containers full of water in the greenhouse. I used to have black 55 gallon drums under my benches filled with water. This will hold the heat that is built up during the day. It will then release it at night to warm the greenhouse.
You can place a solar blanket on the outside of the greenhouse at night. A good heavy blanket will help hold in any escaping heat.
You can ” double up” your glazing by placing smaller cold frames inside your greenhouse. This will give you extra insulation.
Heating the Greenhouse
Once you have determined that your crops need additional heat, you will need to supply a heat source.
A compost pile is a good source of heat. The piles will heat up to 150 degrees F. You will have to set up a heat exchange system with tubes filled with water. Some will keep the compost pile inside their greenhouse. Others will leave the pile outside, to conserve valuable space, and run their tubing through the greenhouse.
Manure can be put in crates and placed inside the greenhouse. You can place plants on the tops of these crates for additional heat.
You can use a wood burning stove, such as a rocket heater. These have a large thermal mass that will hold the heat for a long time even after the fire is out. These are very efficient for heating.
Geothermal heating and cooling can be done in some climates. This utilizes the temperatures in the ground to control your greenhouse. In the winter it takes the heat from the earth. In the summer the ground acts as a heat sink.
Cooling the Greenhouse
The greenhouse will build heat much earlier in the season than some people think. I tell people who are only overwintering plants that they too will need some type of ventilation.
The simplest way to vent air is to use roof and side vents. The roof vents allow the hot air which rises to leave that way. When you use side vents in conjunction with them you get a chimney type affect.
These are simple to control with the solar powered roof vents that are readily available. These have a wax cylinder in them and work on contraction and expansion. When the wax gets warm it expands and pushes the vent open. When the wax cools it contracts and pulls the vent shut.
A shade cloth is a simple way to cool the greenhouse a few degrees. If you think about this it is pretty much the same as standing under a shade tree in the summer.
Roll up side curtains can be placed on any greenhouse with straight sides. These can be motorized, but they are also available with hand cranks. These open up the greenhouse considerably for a fresh air flow.
Solar powered ventilation systems are now available. These include an exhaust fan, intake shutter(s) and a thermostat. They operate the same as electrically powered ventilation systems, but they are powered by solar panels.
If you have water available you can add a misting system on a battery operated timer. These will help cool the inside through evaporation.
A greenhouse is a wonderful addition to your backyard, homestead or farm. But, you must have them set up correctly for your climate and your crops. Even if you are unable to take it completely off the grid, try a couple of these methods to save on your power bills.
Let us know in the comments which of these methods you have tried and how they worked for you. Also, if you have any additional methods you have used that worked, please feel free to share those with us.
I use the idea of a large cold frame idea on top of my largest table. I trim the table with 2 x 2s then cover the whole table with 6 mil black plastic. I fill the table with an inch of water which gets heated by the sun during the day. I close in under the table by stapling black plastic sheeting all the way around the bottom half of the table (tightly closed up) and put a small portable heater inside under the table creating a huge heated table. I run lines above the length of the table and cover it with a sheet of clear plastic plastic. The heat is released into the tent all winter long. Little need to go to the store. If the power goes out I throw old comforters over the top until daylight and the greenhouse has warmed up. We eat lettuce, onions, carrots, beats, turnups, cole crops, and anything else that will tolerate cool and low light. The warm weather crops stay under the tent. We start tomato, pepper, egg plants and cole crops to sell at Farmers Market. That’s how we get seed and heating money.