A Case Study - of a 3000 Sq Ft Year-Round Solar Greenhouse in Boulder, Colorado
Step into the solar greenhouse at The Golden Hoof Farm outside Boulder, Colorado, and you’re greeted not by a monoculture of greens, but by a forest of fruit trees — guava, avocado, mango, banana, lemon, dragon fruit and cinnamon, to name a few. Taller trees create a canopy above, while shorter shade-tolerant varieties form the understory, mimicking the layers of a tropical forest. The floor of the greenhouse is covered with more conventional crops, like kale, chard, mustard greens and tomatoes. In between the vegetables, a green blanket of nitrogen-fixing clover borders pathways and fills in any excess spaces. On a spring day, you step from the dry Colorado landscape, surrounded by corn fields, into this lush humid forest, and it’s clear that this is anything but your ordinary commercial greenhouse.
The greenhouse is a small component of Alice and Karel Starek’s dynamic “slow-food” farm: they produce sustainably raised pork, lamb, beef, chicken, duck, eggs and vegetables. The birds are fed pre-consumer kitchen scraps from local restaurants and roam freely around the acres of property. Pigs are also fed pre-consumer waste, while the ruminants rotationally graze the pastures. All in all, The Golden Hoof operates more like a farm in the 1900s than a farm of today, except that instead of just root vegetables, they are eating homegrown bananas, lemons and figs.
Much of this is possible due to the greenhouse’s energy-efficient design and systems. The structure, designed by Alice, an architect, has R-38 insulated walls, and an R-52 roof. Tri-wall polycarbonate forms the south-facing glazing. A Ground-To- Air Heat Transfer (GAHT) system provides much of the climate control, storing heat in the ground. Exhaust fans supplement the many passive vents that line the lower south wall beneath the glazing, and a misting system helps keep things cool in the summer.
The greenhouse also houses one of the farm’s power stations. In the center of the south-facing roof, there is a 10 kW solar PV system that powers all of the loads for the greenhouse in addition to some of the outbuildings and the home. Housed in a corner of the greenhouse, the battery bank is comprised of nickel-iron Batteries (a less-common choice, which is why we left them out of the discussion above). Though the panels and batteries produce/store enough power to supply the greenhouse’s energy, the farm as a whole, is still largely grid-tied. Alice says that if they were to do it again, they would try to go entirely off-grid. Making a greenhouse completely net-zero energy and still a tropical forest required a significant investment in structure and systems. The Stareks wanted their slow-food farm to have an extra level of resilience. “We wanted to have fruits and veggies year round, and this is a very brittle environment,” says Alice. The Stareks reduced costs where possible by integrating recycled materials and doing much of their own labor. The exterior siding is reused corrugated metal. Old barn doors form the entrances, imbuing the greenhouse with a spunky character that makes it truly one of a kind. More information can be found at thegoldenhoof.com.