A heated greenhouse prevents indoor temperatures from dropping below freezing, meaning that a wide variety of produce can be grown yearround. There's a variety of ways to heat your greenhouse, with some being more renewable sources of energy than others. A greenhouse close enough to a main building can be connect to water and electric hook-ups, though this will of course add to your standard utility bill. Solar energy is the driving force behind a greenhouse. Sunlight is trapped inside the greenhouse, where air is heated much quicker than it would outside. Thermal batteries are materials or surfaces that are able to absorb lots of the sun's heat, like dark-colored, dense materials, such as water barrels painted black. At nighttime, as the ambient tempertaure drops, the batteries release the heat they've been storing all day.
Geothermal energy is another very popular option for greenhouses, especially in the winter. Even as the surface temperature drops in the colder seasons, the earth retains a steady internal temperature only a few feet under the surface. Air can be pulled from your greenhouse and passed through piping under the ground. Here, the air is warmed by the surrounding soil, and is then pumped back into the greenhouse. This is referred to as a heat pump, and can be a great way to keep your greenhouse warm even in the coldest parts of winter. If you're unable to keep your greenhouse at summer temperatures all year round, there are lots of cold weather crops that can thrive in cooler temperatures.
