Solar Decathlon Challenge Sparks Students Creativity

An extensive team of University of Cincinnati students and faculty is currently at work to design (and later build) a completely solar-powered house that, come October 2007, will be displayed on the National Mall in Washington, D.C.

UC is one of 20 international schools pursuing the construction of a solar house as part of the prestigious

Solar Decathlon

, a select competition sponsored by the U.S. Department of Energy, the American Institute of Architects, BP, DIY Network, Honeywell International, National Association of Home Builders and Sprint.

Already, the team from UC is developing high-powered design and engineering ideas it hopes will reshape green building techniques and solar-use equipment – and of course win them the Washington D.C. competition.

Innovations the students – from the university’s internationally recognized College of Design, Architecture, Art, and Planning; College of Business and College of Engineering – are developing include roofing advances, unusual utilization of evacuated tubes to create thermal energy to cool and dehumidify the house, and a unique thermo-electric heat pump that could also be used to cool and dehumidify the house. All are part of the 100-percent sustainable house where everything runs on solar power.

Supplying most of that power is a new roofing system proposed by the students. They are designing a slightly sloping roof sheathed by a grid of 36 photovoltaic (PV) solar-collecting panels. These panels alone will produce more than enough energy to power the house, energy that can be stored for a cloudy day, sold back to the grid or used to power an electric automobile.

The arrangement of the PV panels by the UC students resolves a number of challenges currently posed by use by PV panels. Anton Harfmann, DAAP associate dean, explained, “Right now, PV technology is embedded in existing roofs made of shingles. That means that the life span of the roof and the life span of the PV are interlocked. You can’t change out the PV without replacing the roof. That means the rapidly improving effectiveness of PV technology does a current homeowner using PV integrated materials no good. Second, and just as importantly, the roof commonly overheats and that actually reduces the effectiveness of the PV cells.”

The simple solution posed by UC’s Solar Decathlon team consists of a small space of separation between conventional PV panels and the insulated, waterproof roof. This allows for air flow between roof and panels and actually means that the PV panels serve to shade the roof.

“It’s light, not heat that causes the PV panels to operate at peak efficiency. So, this helps us make maximum use of light while reducing heat (by encouraging air flow between the roof and the PV panels),” explained Harfmann, adding that the system would also allow a home owner to replace PV panels at any point as panels improve in terms of technology and efficiency. And those panels are “getting better and more efficient all the time,” said Harfmann.

The second innovation consists of the use of evacuated tubes and what the students call a “magic box” to convert the sun’s heat collected in those tubes into usable thermal energy to heat and cool the space.

First, an evacuated tube consists of a “tube within a tube.” Heat is trapped within the inner tube, which also contains water. The outer tube remains cool to the touch. The students are proposing an array of such tubes be used as a patio screen. Sunlight would produce heat within the interior tube, heating the water also present within the tube. That liquid would then be moved through a heat-exchange system where it would vaporize lithium bromide gas. The gas then moves into another chamber where it would become a cooled liquid under high pressure that serves as something of an “aerosol can” that, when released from high pressure, would be used to create cold air that would cool the house as necessary.

Added Harfmann, “About 70 percent of the energy for cooling the house would come from this system, and about 15 percent would come from the roof system.”

A final solution the students will innovate, build and demonstrate uses a series of Peltier heat pumps for heating and cooling water for use in a solar home. The students will create and build a 10-piece series of thermo-electric (Peltier) heat pumps. Passing the water via a pump along either side of these heat pumps will heat the water up to about 140 degrees Fahrenheit (for household and personal use) or cool the water to about 40 degrees Fahrenheit (allowing it to be used to dehumidify and chill the air). The temperature of the water for household use would be controlled by means of the velocity by which it passes along the plate series. The thermo-electric heat pumps convert surplus electrical energy from the PV panels and one of the devices being made can heat and cool up to 60 gallons of water per day.