Greenhouse Solar Water Heating Systems
Another agricultural application of solar energy is greenhouse heating. Commercial greenhouses typically rely on the sun to supply their lighting needs but are not designed to use the sun for heating.
They rely on gas or oil heaters to maintain the temperatures necessary to grow plants in the colder months. Solar greenhouse, however, are designed to utilize solar energy both for heating and lighting.
A solar greenhouse has thermal mass to collect and store solar heat energy, and insulation to retain this heat for use during the night and on cloudy days (EREC, 2002).
A solar greenhouse is oriented to maximize southern glazing exposure. Its northern side has little or no glazing and is well insulated. To reduce heat loss, the glazing itself is also more efficient than single-pane glass, and various products are available ranging from double pane to cellular glazing.
A solar greenhouse reduces the need for fossil fuels for heating. A gas or oil heater may serve as a backup heater, or to increase carbon dioxide levels to induce higher plant growth (NYSERDA, 2009).
Passive solar greenhouses are often good choices for small growers because they are a cost-efficient way for farmers to extend the growing season. In colder climates or in areas with long periods of cloudy weather, solar heating may need to be supplemented with a gas or electric heating system to protect plants against extreme cold.
Active solar greenhouses use supplemental energy to move solar-heated air or water from storage or collection areas to other regions of the greenhouse.