Growing Year-Round

A Boulder inventor’s revolutionary off-the-grid thermal system is perfect for heating greenhouses, homes, garages and studios year-round.

By Lisa Truesdale Greenhouse Photos courtesy Central Solar Inc.

In October, Joanne Lederhos still harvests plenty of tomatoes, while her neighbors at Bailey’s 9,000-foot elevation are unable to grow them at all. In a properly constructed greenhouse, SunnyTherm (the six gray panels at the bottom of the greenhouse) should keep temperatures warm enough for winter crops, with supplemental heat recommended on nights that go below -20 degrees.

Although Joanne Lederhos loves living high up in the mountains near Bailey, one thing always bothered her: She wasn’t able to grow tomatoes at 9,000 feet, even in the middle of summer in her freestanding custom-built greenhouse. Then she discovered SunnyTherm, a solar-heating system made by Loveland’s Central Solar Inc. Owner Gary DuChateau, who lives in Boulder, invented the system, which absorbs heat from the sun and returns heated air into the designated space. Now, Lederhos is happily harvesting a steady supply of her precious tomatoes as late as mid-October. She could continue growing crops through wintertime, but because she must haul water to the greenhouse she chooses not to grow over the harshest months.

Simple System

After years of enduring brutal winters in rural South Dakota and being forced to pay exorbitant prices for propane just to stay warm, DuChateau began experimenting with a variety of off-grid ways to heat a home. “Unfortunately, the reliability of utilities is waning,” he says, “and we’re not spending money to improve the infrastructure. So people who live in remote areas, who are stuck with expensive propane that often isn’t delivered on time just when it’s needed most—I was thinking of them. There’s no reason at all that anyone, anywhere, should ever be freezing.”

Heat collected in SunnyTherm’s solar panels is ducted into a “rock-box” heat bank in Joanne Lederhos’s high-altitude greenhouse. The stones store heat from the sun and release it after dark.

The heat bank completely filled with stones and with the ductwork in place.

Warmth radiates through the heat bank’s sheet-metal top.

Because of his background in construction management, DuChateau had worked with solar hot-water heating systems before, and he wasn’t satisfied at all with the fact that they require concrete tanks, toxic antifreeze, all manner of pipes and pumps, rigorous maintenance, and a high price tag. He had also seen firsthand the extensive, costly and dangerous damage that a leak can cause, and such leaks are not uncommon. He spent years researching and experimenting until he hit upon what he believes is the ideal heating system.

Looking much like a window, this six-panel SunnyTherm warms a chilly kitchen in downtown Boulder. It doesn’t heat water or generate electricity; it’s simpler than that. Heat from the sun, collected in the panels, blows directly into the room, sometimes for hours after sunset.

“I really wanted something people could install themselves, with no special tools,” he says. “I wanted it to be an inexpensive, air-based system, without a lot of moving parts.” It’s those moving parts, he explains, that lead to frustrating maintenance issues. So SunnyTherm’s only moving part is the blower fan, which has a projected life span of 50,000 hours. (Since it would take more than 17 years of 8-hours-a-day usage to reach that many hours, DuChateau is pretty confident in his blower’s design. And even if it failed, a replacement costs less than $150.) As an added bonus, the minimal power needed for the blower fan is about the same as needed for a 7-watt light bulb. DuChateau also offers a solar-powered blower fan for those who want a completely off-grid SunnyTherm system. SunnyTherm’s weatherproof, UV-resistant panels are 2 feet square and about 3 inches thick, and their polycarbonate double-glazing makes them much stronger than glass. The panels, which weigh only about 15 pounds each, can be mounted on any exterior wall with good exposure to direct sunlight. The number of panels and their configuration are customized to the unique needs of each site. Each panel heats about 100 square feet, and the blower moves the heat from the panels to the space being heated.

bAILEY-6-15-13-001 — Tomato plants coming along nicely in mid-June 2013.

Tomato plants growing strong three weeks later.

Plants grown in bins right on top of the heat bank stay especially cozy.

Because the panels absorb radiant heat from the sun—not the sun’s light, as with photovoltaic panels—they’re able to function even on overcast days. A six-panel system starts at around $1,400, with the average system price being $2,200. DuChateau says the system pays for itself in two ways: “It consumes much less energy than a conventional heating system, and it reduces wear and tear on that existing system as well.” SunnyTherm can be used in one of two ways, he adds. Most systems he’s installed so far utilize the heat generated by the panels during the day, and then rely on the home’s regular furnace at night. Or, they heat a space only during the day, such as a workshop that doesn’t need to be heated at night. But there’s also a heat-storage option with a special heat bank that captures and stores the heat during the day so that it can be used at night. The latter option is perfect for greenhouses like Lederhos’s, which would get way too cold overnight, especially at such a high altitude. “I’m grateful SunnyTherm was able to extend my growing season,” she says. “I give it a big thumbs-up.” SunnyTherm has also had rather unusual applications, such as heating a small chinchilla barn near Steamboat Springs, which was so cold that the creatures wouldn’t mate.

A six-panel SunnyTherm being installed on a workshop in the mountains near Boulder (the blue rectangle above the panels is a solar panel that runs the blower fan, making this system completely off-grid). The owner, a weaver, was tired of having to wait for hours for her studio to warm up enough to work in. With the system in place, the space is warm in the morning when she wants to use it, she reports, and her electric-heating costs have dropped 80 percent.

Lucky Locavores

What started as an off-grid heating system for rural homes evolved into the perfect solution for heating smaller structures like cabins, and outbuildings such as workshops, detached garages and—happily for gardeners—greenhouses. In fact, DuChateau says he is especially pleased with the greenhouse application for his invention. “A lot of greenhouses simply become storage sheds in the winter, and that’s too bad. And most commercial greenhouses shut down completely during the colder months, because heating those would cost so much more than the value of the plants they’re able to grow.” But after bringing SunnyTherm to the marketplace, DuChateau has high hopes his invention could someday completely change the way we grow our food. “Because of SunnyTherm, I know now that it’s possible to heat a greenhouse year-round without it costing a fortune. That means we could have fresh local produce all year, without having to get any of it shipped in. Wouldn’t that be great?” For more information, visit www.centralsolarinc.com.

Growing Year-Round

A Boulder inventor’s revolutionary off-the-grid thermal system is perfect for heating greenhouses, homes, garages and studios year-round.

Simple System

Lucky Locavores

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