Grass clippings have potential as alternative energy

For something small and seemingly insignificant, grass clippings get a lot of attention. Everyone seems to have an opinion: some are proponents of leaving grass clippings on lawns to help improve turf health; others have customers who don’t like that aesthetic; some worry (mistakenly) that leaving grass clippings in place can lead to thatch buildup; some cities and states have banned disposal of yard waste in landfills and even prohibited composting; and some argue that grass clippings and other lawn debris should be composted and turned into valuable soil amendments.

For Steve Wahls, a lawn care operator, manufacturing expert and self-proclaimed capitalist, grass clippings may be most valuable as an energy source. With oil prices volatile and a national debate on climate change taking place, Wahls thinks grass clippings might be able to play an important role in both conversations. “Grass clippings are green gold, and we’ve been feuding about where to throw them away,” he marvels.

“There’s a whole army of guys out here collecting this resource already,” says Steve Wahls of the amount of grass clippings and other lawn debris being handled by lawn care pros every day. “It takes so much energy, and then it often gets thrown away.”
Photos courtesy of Steve Wahls.
Steve Wahls, a lawn care operator and manufacturing specialist, developed a debris collection bin to help those in the green industry collect and handle grass clippings more efficiently.

Wahls has been researching the feasibility of using grass clippings as a source of cellulose, which could then be utilized for energy. Cellulose is a material that’s present in nearly every living plant. It’s being used already to produce biofuels; corn-based ethanol, for example, is made using the cellulose in that plant. Wood and switchgrass are other increasingly popular sources of cellulose for biofuels. Wahls thinks grass clippings (and yard debris like leaves) might be the next big thing.

Wahls, a former agricultural products engineer, worked on equipment that tested tractors running on alternate fuels, such as biodiesel made using sunflowers and the use of corn-based alcohol injection to boost horsepower on turbocharged tractor engines. He saw first-hand the potential of these fuels.

He also owns a lawn care company, purchased from a friend who had to leave the business due to illness. That has given him a first-hand look at the quantity of grass clippings generated, and often discarded. “I have a nice Walker mower with a bagging unit, and I would back that up onto the trailer and unload the grass clippings, but I couldn’t haul very much unless I got a pitch fork out and really piled it up, and if I didn’t get out to the dump site before they closed at the end of the day, I’d have a mess to unload in the morning. I really didn’t like the grass-handling aspect of the business. It wasn’t very efficient.”

In fact, Wahls used his engineering and manufacturing experience to build a truck-mounted lawn debris shuttle bin ( designed to help lawn care companies better collect, handle and dump grass clippings. The bin is made out of an open cloth that allows air to pass through it. In that way, the grass along the outer edge dries out quickly, and stays dry. “Dumping the grass clippings is much easier. I’ve had grass clippings in the bin for up to three weeks, and even then I could hit the button and it would dump and completely unload without sticking,” says he says. “Most grass clipping bins are plastic and the grass can stick to them within an hour, and you’ll need to get a rake to scrape it out.”

In many cases, yard waste is brought to a disposal site like this, where it is simply piled up, resulting in methane gas being released. In the future, this yard waste may be put to use producing energy.

While the debris bins improved the grass-handling experience, Wahls wondered what happened to all the grass clippings once he dumped them. “We have a community site, and we just dump it. They pile it up with a loader and it just sits there, they don’t even turn it. Toward the end of the season, they collect it and spread it on cattle fields with big manure spreaders. I would be dumping the grass, thinking it was too bad that we couldn’t better utilize it,” says Wahl. “Plus, we’re supposed to be trying to reduce greenhouse gas emissions these days, and here was this huge pile of rotting grass sitting there allowing methane to escape into the air.”

Not only is dumping the grass time-consuming, it’s expensive. “You’ve got the drive time and the fuel to go out to the dump and back. There are some businesses that go around and pick up the clippings and lawn debris, but there’s a cost to that, and then that service gets charged out at the dump, so there’s money changing hands, all to throw away this valuable resource,” he says.

Wahls began researching just how much grass there is in this country. He discovered NASA satellite research showing there are some 50,000 square miles of lawns in the U.S. He also found statistics revealing that, on average, about 10,000 pounds of cellulose (in this case, grass clippings) per acre, per year could be produced. “You can expect about 7,000 BTUs per pound of dried cellulosic material, depending on water content,” he explains. “That’s 70 million BTUs per acre, and there are 640 acres per square mile. With 50,000 square miles of lawns in the country, that’s the BTU equivalent of hundreds of millions of barrels of oil. All by harvesting the clippings from the lawns in this country, which often are being thrown away right now, and causing greenhouse gas emissions.”

There are others following a similar train of thought. Wahls has found a farmer/businessman in Nebraska already preparing for the possibility of using corn stover to fire traditionally coal-fired power plants. “He’s baling thousands of acres of corn stalks, running them through a processor, compressing them and turning them into pellets,” says Wahls. There’s no reason the same process couldn’t be applied to grass clippings, he says, pointing out that corn stalks can only be harvested once per year during a limited window of time. Grass clippings, on the other hand, are harvested many times each year on a continual basis, and the clippings tend to be cleaner than corn stalks would be after being harvested from fields. “Plus, there’s already a whole army of people out there harvesting the stuff, and looking for a place to send it,” he says. “To me, it’s a total no-brainer.”

Wahls feels that a system using grass clippings as cellulosic fuel would work best with lawn care companies continuing to bring clippings to a dump site, and then having them moved regularly to large processing centers. There, it could be used to produce natural gas, or alcohol-based fuels, or simply burned as cellulosic material. “It doesn’t matter where it’s going,” says Wahls. In any case, it would be offsetting fossil fuels, and that could be done using what essentially is a waste product, rather than requiring corn or some other valuable crop.

“Plus, you’d almost totally eliminate the methane being released by grass clippings,” says Wahls, adding that there would be further emissions savings by replacing the fossil fuels being used to fire power plants now. Environmental advocates often harp about the amount of acreage in lawns, and the resources required to maintain them. If energy was being harvested in the process, though, the entire debate could change.

It’s big thinking about a seemingly small resource, but given the amount of lawns, and grass clippings, throughout the country, Wahls feels the idea has real potential.

Instead of letting grass clippings and leaves pile up at dumpsites, emitting methane gasses, Wahls envisions a day when these valuable resources will be used as energy.

Indeed, Argonne National Laboratories in Batavia, Ill., is about to begin an experiment in which grass clippings would be collected and processed through a cutting-edge gasifier which will power hydrogen fuel cells and produce ethanol that will power municipal vehicles in Naperville, Ill. According to the city, “This pilot project will use only 3 percent of the annual landscape waste collected by the city. If all 48,000 cubic yards of Naperville’s landscape waste were used in a full-scale Green Fuels Depot, it would be enough to fuel all 300 vehicles in the city’s fleet.”

“There is a unique, refreshing twist to this proposal,” said Glenn Keller, vehicle testing activities manager in Argonne’s Center for Transportation Research. “It’s a utopian vision to have this closed-loop circuit, where a city can turn its own yard waste into fuels that will benefit their community.”

So, perhaps Wahls is on to something. “Maybe it’s too early to get us laymen, the lawn care guys, involved in the process, but sooner or later, it’s all going to come through us,” he says. “There’s a whole army of us out here already harvesting this resources that’s often going unused. The key is just to develop the infrastructure to be able to get the job done.”

Patrick White is a freelance writer and editor who has covered every aspect of the green industry in the past 13 years. He is based in Middlesex, Vt., and is always on the lookout for unusual stories.