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Renewable Energy Warming Vermont Greenhouses

woman standing next to corn stove in greenhouse
At New Leaf Farm in Dummerston, Elizabeth Wood uses a corn stove to heat her greenhouse.

There is a growing consensus that we need to develop farming and food systems that reduce our reliance on fossil energy. Given the upward trend in both price and worldwide demand for a finite supply of fossil fuel, coupled with concern about global climate change, many farmers would like to use renewable energy in their operations. Heating of greenhouses in Vermont is an area where renewable energy is ripe for application.

Greenhouse use extends the growing season and thus helps meet the rapidly growing demand for local produce, and greenhouse production is on the increase. However, most greenhouses in Vermont rely on fossil fuels for heating. “Greenhouses offer a significant opportunity for greater use of renewable energy on Vermont’s farms,” says Vern Grubinger, Extension vegetable and berry specialist, “because our greenhouse production is on the increase, as demand for local products increases.”

Greenhouse production in Vermont covers 2 million square feet (ft2) and produces $19 million in crops, of which about $4 million are vegetables. Based on recent survey of greenhouse growers, it has been calculated that the state uses approximately 296,000 gallons of propane and 59,000 gallons of fuel oil each year to heat greenhouses. At $2 per gallon for propane and $3 per gallon for fuel oil (as of July 2010), this equates to a cost of $768,000 per year and 2,458 tons CO2 emissions per year, roughly equivalent to 6.2 million automobile miles.

The UVM Extension Greenhouse Biomass Furnace project was developed to help growers reduce their energy expenses while at the same time avoiding greenhouse gas emissions. The goal of the project is to help Vermont’s greenhouse vegetable growers adopt clean burning bio-mass furnaces, as an alternative to fossil fuels or outdoor wood-fired burners that can cause pollution. The project provides financial cost-share on the purchase of biomass systems, and technical assistance from UVM’s vegetable and berry specialist, Vern Grubinger, as well as Chris Callahan of Callahan Engineering. Funding for this project comes from the High Meadows Fund of the Vermont Community Foundation, UVM Extension, Renewable Energy for Agriculture program grants to farmers, and direct farmer investment.

From 2008-2010, 14 growers received cost-share funds for installation of greenhouse biomass heating systems. These heating systems have now been operated for two to three growing seasons by each grower to heat a total of 39,281 ft2 (average of 2,806 ft2 per farm). The average fuel cost savings per farm is $2,589 per year and about $36,242 total for the farmers included in this demonstration group. This results in a simple payback period for the biomass heating systems of 3.4 years (2.4 years when crediting the cost-shared portion).

Records of fuel use by the growers from 2008-2010 indicate a total of 5.2 trillion BTU of energy being provided to these greenhouses from biomass sources as a result of these installations (equivalent to 56,592 gallons of propane), with a typical annual biomass energy use of 2.5 trillion BTU (approximately 27,087 gallons of propane equivalent). The growers in this project pay an average of $13.34 per million BTU for their fuels (compared to $21.70 per million BTU for $3.00/gal fuel oil or $2.00/gal propane).

The net carbon dioxide emissions avoided by this substitution of fuel is estimated to be 110 cumulative tons at an average, normalized annual avoidance rate of 5.8 lbs CO2/ft2/yr (taking into account the greenhouse area heated). This latter figure allows for an estimate of the total carbon dioxide avoidance possible in Vermont. If the portion of the Vermont’s two 2 million square feet of greenhouse growing area heated by fuel oil or propane (35%) were to be heated by renewable biomass sources, approximately 2,016 tons of CO2 emissions would be avoided each year. This is approximately equal to 5.1 million automobile passenger miles (about 515 vehicles at 10,000 miles per vehicle per year).

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