Energy-Efficient Spring Tomatoes
April 22, 2011
By the time spring rolls around, even the most committed locavore gets tired of canned tomatoes. As the soft and tender lettuces start making their way back into the market, it’s hard not to crave a nice, sweet heirloom tomato sometimes.
That’s where vendors like Bruins Farms enter the picture. Brothers Paul and Bart Bruins grow tomatoes in greenhouses covering around 2.5 acres in Winters. One and a half acres are heated, meaning the Bruins can start planting in the late fall and nurture sweet summery fruit to maturity as the rest of the farms in the area are harvesting kale and citrus.
The downside, of course, is that it takes a lot of energy to heat a greenhouse. Until a few years ago, that meant that the Bruins brothers would burn heating oil — a lot of it — to keep the temperature in the greenhouses from dipping below 60 degrees on winter nights. “In a typical season we would go through 25,000 gallons of oil,” recalls Paul. “And it would cost us around $75,000.”
A few years back, Paul began the hunt for alternative sources of fuel. Bruins farm is in walnut country; Winters is home to an industrial-sized processing plant owned by Mariani Nut Company. So the retired engineer for the UC Davis Chemistry Department started out experimenting with walnut stumps discarded from nearby orchards. But the experiment didn’t last long, because the kind heat it produced was unpredictable. “You put a big old stump in the burner and you don’t have any control over the combustion process,” says Paul. Woodchips were a little better, but not ideal. Walnut shells, on the other hand, were a different story.
“Mariani produces around 200 cubic yards of crushed shells every day for four months out of the year,” says Paul. “Fortunately the time period is exactly when we need them.”
Walnut shells are a dream material. Not only are they a waste product that alleviates the need for fossil fuel, but they cost much less. The Bruins go through 60 tons of crushed walnut shells a month, and will spend only around $3,000 for the whole season. Not that it was an easy transtion to make; after retiring Paul spent two years building a custom boiler and setting up an effective, complicated system for warming the greenhouses with the heat for the walnuts. But all that labor has paid off.
Paul says the result is a system than burns cleaner than your average household fireplace and provides around 20 times as much heat. The shells leave very little ash residue, and most of the ash is filtered out of the air and collected to use for fertilizer, thanks to Japanese kiln technology that Paul has adapted for their purposes. “We’ve gone through around 400 cubic yards of shells so far this season, and I think we’ve barely accumulated one cubic yard of ash.”
Bart Bruins works in the greenhouse full time and Paul used to be part time, before he retired. Now he has time to take on his dream projects. And he’s making his operation much more sustainable in the process. Up next? Solar-powered fans for cooling down the greenhouses in the warmer months.