Should the U.S. Be Harvesting More Energy From Nuts?

Turkey has plans to heat an entire town with pistachio shells. Why can't that happen in California? 

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AP Photo/Justin Kase Conder

Turkey made headlines last month with a plan to heat a new "eco-city" by burning pistachio shells. The proposed project would be located in the southeastern Gaziantep region, which exported 8.8 million pounds of pistachios last year. Burning the shell waste is expected to produce enough energy to heat 60 percent of the buildings in the new 8,000-acre development.

Converting biomass—which can include anything from plant material to animal waste to yes, nut shells—into heat and electricity is nothing new for European countries like Denmark and Sweden, where similar processes have been in place for decades. Turkey is just the latest to try to capitalize on resources they naturally have in abundance.

When it comes to nuts in particular, though, the U.S. in theory has a lot more material with which to work. According to the California Department of Food and Agriculture, the Golden State alone produces 80 percent of the world's almonds and 40 percent of the world's pistachios (which, in 2012, meant a whopping 275 million pounds). Much of the orchard waste removed from tree nut farms in California are in fact already sold to biomass processors that generate steam for electricity. However, those plants typically dump large amounts of heat byproduct into the atmosphere, unlike the combined heat and power plants more common in Europe.  

A much more efficient biomass energy recycling operation can be found on Dixon Ridge Farms in Northern California, which is one of the very few U.S. nut farms that converts shells to both electricity and heat on-site. Using a technology called BioMax100, Dixon Ridge converts 1.6 million pounds of walnut shells into enough fuel to power the farm for a year—that's 840,000 KwH annually, with 100 percent of heat produced going into drying nuts in the fall and heating buildings in the winter. Owner Russ Lester says while typical steam power plants get about 17 to 18 percent efficiency, his operation reaches about 85 percent. 

Despite the potential for significant economic and environmental benefits, there are tangible reasons operations like Dixon Ridge Farms are still rare in the United States.

Top: walnut shell waste produced at Dixon Ridge Farms. Bottom: A view of the BioMax100 system (screenshots via Youtube)

Up until 2012, California law only allowed solar, wind, and fuel cell generators to connect to the grid through the state’s Net Energy Metering program. The state also only allowed one type of renewable energy per meter. Lester, who had wanted to incorporate biomass on top of several thousand square feet of solar panels, wrestled hard with those regulations.

California Governor Jerry Brown finally signed into law the Renewable Energy Equity Act in late 2011. The new regulation approved connecting all renewable energy types, including biomass and biogas, to the grid, as well as mix-and-matching multiple types on one meter. Though he’s happy about these changes, Lester says big energy companies in the U.S. continue to fight independent energy production initiatives like his.

Elias Marvinney, a graduate student studying orchard cropping systems and biomass energy at U.C. Davis, has found that California’s current cap-and-trade program—a market-based approach to reducing carbon pollution—doesn’t necessarily encourage farmers to go all out with burning nut shells. Currently, carbon credits for recycling nut shells go to the power plants that burn the shells, not the farmers who actually produce them. Marvinney says most farmers still need incentives before they'll aggressively prune and gather biomass waste.

That’s why Marvinney is modeling California nut farms over their entire lifespans, evaluating the comprehensive impact of biomass and whether burning it can offset total greenhouse gas and energy footprints. He hopes his research can help restructure state laws so producers of biomass are rewarded for recycling as much of it as possible. Based on his preliminary analyses, if the amount of biomass produced and burned is maximized, almond, walnut, and pistachio production could all be carbon-negative, meaning they take more greenhouse gases out of the atmosphere than they put into it.

Marvinney also says that judging from the energy output levels seen on Lester’s farm, it’s possible that maximizing biomass production and recycling could produce an energy surplus, which could then go toward nearby homes.

That, however, would involve something perhaps even harder to change than laws. If biomass like nut shells were to power and heat housing efficiently, as in Scandinavian countries, Americans would have to tolerate the idea of biomass processors being closer to the center of town. 

Though often categorized as "clean energy," many U.S. biomass projects have been attracting criticism for causing significant pollution. A recent report analyzing 88 emissions permits found that, compared to coal plants, biomass plants emit more nitrogen oxides, volatile organic compounds, particulate mater, and carbon monoxide, as well as nearly 50 percent more carbon dioxide for every megawatt-hour of electricity produced. The concern is that burning wood is inherently polluting, plus biomass plants extract relatively little "useful" energy for the pollution they emit.

Lester thinks that, when it comes to burning nut shells as opposed to wood and using the more efficient combined heat and power plants instead of retrofitted coal plants, local opposition would be far less. "If you came out here and saw the biomass plant operating, you can’t see anything coming out," he says in a phone interview.

"It’s not like there's smoke swirling around or anything like that ... it's actually cleaner than almost all vehicles on the road today." 

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