The Solar Decathalon – Building a Winner

Watershed Home - University of Maryland

Courtesy of DOE

We all have our pet projects.

Whether related to our careers or hobbies, they’re the essential complement to our work lives. My personal favorite comes in the variety of the former. The Department of Energy’s biennial competition, dubbed the Solar Decathlon, serves as a proving ground for solar technologies that lie between new technology research and consumer adoption.

The twist herein lies with the competitors; entrants are neither highly-experienced research engineers nor internationally renowned architecture firms, but rather students from colleges and universities from around the world.

Every two years, the DOE and its Solar Decathlon panel choose twenty schools, or teams of schools, to each build a relatively small (less than 1,000 sq. ft.) single family home. Each team creates their entry to be as environmentally-friendly and energy-efficient as possible while maintaining a beautiful design and comfortable living spaces. The competition categories include architecture, market appeal, engineering, communications, affordability, comfort zone, hot water, appliances, home entertainment, and energy balance, which are all judged and scored either by a panel of experts or by real-time performance at the competition; ten categories, ergo, the Solar Decathlon.

What makes this event so unique is its breadth; rarely are there programs of this scale available at the college level and which involve the collaboration of half a dozen or so different departments. At any given team meeting, one might find representation from the schools of engineering, architecture, business, journalism, communications, and a handful of others. They’re not working in a vacuum either; almost every task involves interdepartmental cooperation.

I’ve been lucky enough to have been on both sides of the coin, participating as a student in 2007 and again as a professional mentor in 2011 for the University of Maryland (UMD). Each competition sees students and mentors working side by side to design a home with both up and coming products from the industry and novel new applications for sustainable solutions.

Desiccant salt

Courtesy of DOE

Both Maryland entries from my time with the team included original takes on indoor climate control specifically tailored to the Mid-Atlantic’s sweltering humidity. Specially designed pumps transport liquid desiccant, a highly water-absorbing salt solution, to a chamber where all the magic happens. The air from inside the house is circulated through this chamber where it is free to interact with the desiccant effectively stealing the moisture content out of the air and reducing its humidity. After, the drier air is returned back to the spaces of the home. Hollow packing balls fill the chamber creating more surface area for the desiccant to coat, effectively increasing the interaction time between the air and the salt solution.

When the salt solution has become too saturated with water, a separate pump circulates the mixture to a heat exchanger where the excess water is evaporated out. An especially smart feature of this process is that the heat provided to the heat exchanger comes mostly from heat energy absorbed from the sun. The “regenerated” desiccant is then returned to the system for another go-round. This combined process not only creates a more comfortable feel in the home, but also relieves stress to the air conditioning system in the home, reducing the amount of energy required and thereby reducing electricity demand.

Other renewable and sustainable features of the 2011 UMD house, dubbed Watershed, include a 9.24 kW photovoltaic array, evacuated tube solar thermal system, and a living roof, providing electricity, hot water, increased insulation and environmental runoff protection, respectively. But aside from the energy efficiency measures and renewable technologies, what really sets this home apart from the traditional status quo is its design and integration with its natural surroundings.

Arguably the most striking feature of the house at a glance is its butterfly-style roof. While traditional gable roofs exemplify a protect/reject stance with respect to nature, Watershed offers a motif better described as accept/celebrate.

Courtesy of University of Maryland

Almost every inch of the house participates in its connection to the natural surroundings through its integrated wetlands, edible garden and garden wall, and, namely, the central axis of the house to which all rainwater flows and is integrated into the grey-water filtration system for repurposing. The home is even designed to sit atop a small stream where filtered, unneeded water may be returned directly to the local waterway bypassing geological erosion and sediment accumulation. Roughly 60% of the waste from the home’s inhabitants is also repurposed through composting into bedding soil for the edible garden. The concept was to focus on a structure that feeds, cleans, and runs itself, using nothing but nature.

For all the sweat and effort over two years by more than 200 students and countless more advisors, Watershed earned the coveted First-Place Overall award in the most recent competition, including podium honors in the architecture, market appeal, communications, comfort zone, hot water, appliances, home entertainment, and energy balance contests. Following the competition, the team went on to garner an arms’-full of other awards and praise from industry organizations and state programs.

While home’s like Watershed and the other Decathlon entries are a far cry from even the more environmentally-minded houses being built today, they demonstrate that these technologies and strategies really can work. In the years to come, there’s no doubt in my mind that we’ll be seeing many of these elements start to creep into even the more modestly built structures. This stuff just makes sense.

In the mean time, it’s a bit of consolation to me to know that these sorts of pet projects are out there to keep the fire for sustainable development properly fueled. The teams for the next installment of the competition were just announced by the DOE and are already hard at work on their 2013 entries. I can’t wait.


More information about UMD’s Watershed and past entries can be found at

About Evan Merkel

Evan Merkel is a Renewable Energy Engineer from Baltimore, MD. He loves the smell of PV in the morning. He can be contacted at

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