Waste Not

After two years of planning and testing, the farm managers at Stone Barns have launched a new heating system that harnesses the energy produced from compost to fuel the growth of seedlings. The new system holds promise not only as an alternative energy source, but also as an inexpensive model for farmers to replicate.

The part of the compost energy generator that one can see is two side-by-side bins built onto the outside of the greenhouse. At the center of each bin is a coil of copper piping connected to black pipe laid underneath the seed propagation beds indoors. After each bin is filled with some three cubic yards of compost, the heat generated from the decaying compost—up to 150⁰F—heats the copper pipes and thus the water in them circulating beneath the plant containers. This concentrated subterranean hot-water heat helps the seeds germinate and precludes our having to heat the room.

“This system let’s biology do its thing,” says Gregg Twehues, Compost Farm Manager at Stone Barns. “The bacteria present in the compost of animal manures and leaves produce heat as they reproduce. All they need is food, water and oxygen.”

The food and moisture are readily available in the compost matter, but oxygen needs a boost. So Gregg has fitted a small air blower onto the front of the bins. The blower kicks on every six hours for a couple of minutes, blowing air into the compost. “This acts as a lung,” says Gregg. “The fan blows just enough air to give the bacteria the oxygen it needs.”

The compost will eventually settle and reduce in size and so must be replaced every three to four weeks. The system is backed up by a traditional hot-water heater for times when the compost temperature drops below 130⁰F. Eventually, the plan is to have the compost energy generator running from October through April.

The whole system cost only a few hundred dollars to assemble, and with materials from the local hardware store. “This is a great, low-barrier tool for beginning farmers,” says Gregg, who is already demonstrating the system to apprentices and farmers visiting Stone Barns.

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