Feature: Solar Decathlon

By Boone Guyton on 03/22/2010

In October 2009, Claudia Cady and I traveled to the fourth Solar Decathlon in Washington, D.C., to check out what is new in the energy-efficiency, renewable-energy and smart-house market. We spent two days waiting in lines longer than those at stores on Black Friday. There were some really creative and innovative projects by 20 university teams from four countries. Most of the products were commercially available, though a few “will be out soon.”

The Solar Decathlon is billed as “a competition in which 20 teams of college and university students compete to design, build, and operate the most attractive, effective, and energy-efficient solar-powered house.” The houses were up to 800 square feet — models of another green principle: building small.

The event has several goals:

• Educate the student participants — the “Decathletes” — about the technologies behind energy efficiency, renewable energy and green building. As the next generation of engineers, architects, builders and communicators, the Decathletes will be able to use this knowledge in their studies and future careers.
• Raise awareness among the general public about renewable energy and energy efficiency, and how solar technology can reduce energy usage. 
• Help solar-energy technologies enter the marketplace faster. The Solar Decathlon competition encourages research and development. 
• Foster collaboration among students who often don’t work together until they enter the workplace, particularly those from different academic disciplines, such as engineering and architecture.
• Promote an integrated or “whole building design” approach to new construction. This differs from the traditional design/build process, because the design team considers the interactions of all building components and systems to create a more comfortable building, save energy and reduce environmental impact. 
• Demonstrate to the public the potential of zero-energy homes, which produce as much energy from renewable sources, such as the sun and wind, as they consume. Even though the home might be connected to a utility grid, it has a net-zero energy consumption from the utility provider.

What we expected and saw were lots of photovoltaic or PV panels to generate electricity, ranging from 4.2-kilowatt to more than 14-kw systems that produced all the needed electricity — and in some cases more than double what was needed — to operate the house. The Spain house had an inverted pyramid tracking roof system that automatically kept the PV-clad roof at the optimum solar alignment. Two houses used double-sided PV panels that collected reflected light from the backside, as well as the direct sunlight.

All had solar-thermal water-heating systems for domestic water use, and many had oversized systems of either vacuum tubes or flat-plate collectors that also helped with space heating, usually in radiant-floor systems.

Most had computerized system monitors that allowed the user to see the energy use and to control the systems from one display monitor. Several were also connected to the Internet for remote control while away.

Most homes had a passive-solar orientation, along with some unique means to control the light so that it did not overwhelm the small interior space. There were a lot of louvers and screens and the return of the Trombe wall (a masonry wall designed to absorb and release solar heat) within south-facing window units. One home from Arizona had clear plastic modular units that were filled with water by vacuum. Germany, which ultimately won the Decathlon, included phase-change material in both the walls and the ceilings as a means to store heat or cold.

There were also a lot of plants and carefully oriented planters, both interior and exterior, which helped with water filtration, air filtration and food production. Some planters doubled as railings and some as visual screens and herb gardens. The Penn State house had a green roof under one translucent PV array, and the plants helped cool the panels as well as the house. The array involved glass cylinders with thin-film PV inside that was curved, which provided optimum orientation throughout the day for some section of the film.

There was a lot of flex space, created through moveable walls, beds (one that lifted to the ceiling) and dividing cabinetry that allowed for multi-use space and interior/exterior space connections that gave a feeling of expansiveness.

There were some windows with aerogel, a super-insulating substance also used in wall construction. Most windows were triple-pane, low E and filled with argon or krypton gas.

The wall systems were usually around R-40, through the use of SIP panels or spray foam. The Illinois house was the only one likely to be certified by the Passive House Institute US, which means it will use 90 percent less energy than typical construction.

There were a lot of high-efficiency heat pumps, both air-to-air and geothermal. The Minnesota house had radiant-floor heating that used hot water supplied by flat-plate solar collectors to warm the house in winter and recharge an innovative desiccant dehumidification system in the summer.

There were an abundance of LED (light emitting diodes) lights as well as induction stoves, which are new and expensive, but very efficient.

There was one solar-powered popcorn popper and a smart TV (no, it wasn’t permanently off) that turned itself off when no one was in the room.

Nearly all houses had some form of rainwater catchment and reuse that went to landscaping or toilets.

All in all, the homes provided examples of a great variety of possibilities, with some being more manageable and affordable than others. The most likely, practical takeaways for Claudia and me were the use of plants and planters for multiple uses, Kirei board that was made from sorghum straw, built-in clotheslines connected to deck railings, the Trombe wall and phase-change materials resurgence, a new type of solar-water heater that needed no pumps, and the designs that provided flexibility to make small spaces more useful and meet federal standards for accessibility. The use of smart meters that displayed the energy use in real time and allowed for a centralized control of the whole house seemed useful for conserving energy use and raising awareness of the consequences of appliances and mechanical devices we take for granted.

The Solar Decathlon provided good insights into what we will all hopefully be seeing next door in our own communities in the not-too-distant future.

For more information, visit https://www.kireiusa.com/kirei_viewer/kirei.html,https://www.sunnovations.com/howitworks.html, https://www.aerogel.com/markets/building.html,https://www.ada.gov, https://www.solardecathlon.uiuc.edu/gable.html#passivehouse andhttps://www.solardecathlon.org/about.cfm.

[Boone Guyton is a partner in Cady and Guyton Construction, a HealthyBuilt Home builder. He is also a founder and current board member of the WNC Green Building Council.]