Passive Solar Greenhouse Grows Sustainable Farming

The SunCatcher, a passive solar greenhouse, could change local agriculture while reducing fuel use and CO2 emissions.

| May 27, 2010

In today’s high-tech society, what would it look like to rediscover the simple but ancient wisdom of using only the sun for our heating needs? Knowledge and use of passive solar design to heat buildings has been around since ancient times. Greek, Roman, and Native American structures, as well as many others, were designed to maximize the use of the sun for heating. With the advent of technology and modern eras of cheap energy, the importance of passive solar design became obsolete and the knowledge was all but lost in U.S. building design. However, with present energy crises and uncertainty of future energy sources, passive solar design is being revived as a way to reduce carbon dioxide emissions and dependence on foreign oil.

Specifically, local food production is one area that stands much to gain from passive solar design. Especially in areas with more extreme winters, greenhouses serve to lengthen both ends (spring and fall) of the growing season, as well as offering a greater measure of control over growing conditions. This can dramatically increase yields and provide more food and profit for growers. The community also benefits from the availability of more fresh, locally grown, and possibly organic food. However, the only way conventional greenhouses can offer these benefits is with the input of expensive fossil fuel energy. Conventional greenhouses use the sun’s light while ignoring its heat contributions and often require additional heating on cold nights and on cloudy winter days or a mechanism of cooling on sunny winter days. This extra energy is typically supplied by using fossil fuels such as natural gas or propane and electricity. While this may have been cost effective in times of cheap energy, rising fuel prices are rendering most conventional greenhouses uneconomical to operate, and virtually eliminating the possibility of year-round use in some regions. Enter: a resurrection of this ancient knowledge of passive solar design to help combat the modern world’s problems of fuel, carbon dioxide emissions, and food production through the work of SunCatcher Design Group.

The Problems: Food, Fuel, CO2

Supporting local growers is a simple answer to all three of these problems. Food production and distribution represent large ecological impacts, including high energy use. For every dollar spent on food, only 19 cents goes to the farmer. As much as 58 cents is spent on expenses associated with packaging and transport. One 2003 Iowa State University study reveals that much of the food we consume travels an average of almost 1500 miles from farm to table. This further exacerbates fuel and CO2 problems, and makes most people dangerously dependent on far away, less wholesome food. The sustainability movement is encouraging more locally grown food to reduce energy use and improve food quality. This is often difficult in regions where the climate provides an abbreviated growing season, making greenhouses essential for many crops that might be grown locally. For many locations, growers must start seedlings indoors in early spring. Conventional greenhouses meet this need, but are costly due to high energy use for heating, cooling, and venting the structure. With the use of passive solar heated greenhouses, greater growth can be achieved at less than 10 percent of the ongoing energy costs. The term passive solar greenhouse generally refers to greenhouses whose light and heat requirements are largely provided by the sun. All greenhouses receive most of their light from the sun, but conventional greenhouses have no method of retaining the heat they collect during the day and that heat is usually vented as waste energy. The conventional greenhouse must then be reheated at night and on cloudy winter days.

SunCatcher Design Group has specially designed energy efficient passive solar greenhouses, or as we like to call them, SunCatchers, to help farmers and growers in the same ways conventional greenhouses do, but without extra heating. SunCatchers have the ability to directly harness the sun’s thermal energy and make it available for heating the greenhouse at night and on overcast winter days. This is accomplished through the use of thermal mass, insulation, glazing, and an east-west orientation of the long axis of the SunCatcher to collect, convert, and store the low-angle winter sun’s energy for heating the SunCatcher 24 hours a day.

The passive solar process minimizes the SunCatcher’s interior temperature fluctuations without venting the excess solar heat during the day, but instead storing that heat to be used at night. These characteristics separate SunCatchers from conventional greenhouses, providing as much as 90 percent savings or more in fuel use for growers.

Because many local growers use organic principles, increasing their productivity will enable them to be more competitive with non-sustainable growers, without the large costs associated with transportation and packaging. As a very important part of sustainable agriculture, the energy-efficient SunCatcher allows local organic growers to grow year round and still remain competitive in a market that traditionally favors large-scale, fossil fuel intensive agriculture. Local farmers can start growing seedlings indoors long before winter weather typically allows, and crop production can be extended well into the fall without the major expense of heating a conventional greenhouse. If increased local food markets are the answer to our modern problems of food, fuel, and CO2 emissions, the SunCatcher is a key player in fostering their growth and prosperity.

6/6/2010 9:38:59 PM

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