One of the nation’s most important (and sadly too little discussed) intercollegiate competitions is nearing its conclusion in Washington, DC: the biennial Solar Decathlon. 19 University teams from around the globe are competing in 10 (hint, ‘decathlon) arenas to determine the overall winner. Lost amid, perhaps, the fanfare is that every single one of the teams put together a home that people could live in (now) and every single team brought to the table concepts and capabilities and pathways forward worth exploring. Thus, having visiting all 19 homes (with overview of the Decathlon and the 19 entries here), it seems worthwhile to bring some focus to each of the teams.
Imagine a path to convert some of the most unused space in the world into productive and sustainable space with the flick of a pen. New York City’s Mayor Mike Bloomberg has just such an opportunity. The City College of New York’s entry into the Solar Decathlon, the Solar Roofpod, is based on a simple truth: urban rooftops are potentially highly valuable real estate that, for the most part, is going to waste.
“Our most abundant energy resource is the sun and our most underutilized urban space is our rooftops.” -Team New York member
And, combined with that, a real understanding that the most sustainable lifestyles in the modern world are actually found in dense urban environments rather than at the end of a long drive from the nearest grocery store.
As Team New York describes it:
We’ve called our Solar Decathlon entry “The Solar Roofpod.” It is designed for the most underutilized real estate in the city: the flat rooftops of existing mid-rise (4 to 10-story) residential or commercial buildings. These roofscapes offer tremendous potential as living space because of their direct access to solar energy, ventilating breezes, and nourishing rain. Team New York’s Solar Roofpod is designed to enable eco-conscious urban dwellers to live lightly, as stewards of a more resilient urban environment, cost-effectively producing solar power and heat, cultivating roof gardens, and retaining and recycling stormwater.
Team New York’s concept “responds to the fact that urban
rooftops are largely under-used.” The idea: increase density by putting additional dwellings on existing mid-rise buildings. Dwellings that produce excess (clean) power (to help power other units and help stabilize the grid) and which reduce rainwater runoff (reducing pollution, loads on sewage systems and, therefore, societal costs and risks). And, they also increase real estate values (read: increased local tax revenue) while fostering increased sustainability (relatively small dwellings (translating into reduced purchases as there is nowhere to hide the unwanted items) with high walkability scores (translating to reduced transportation energy demands)).
To be fair to all, it is time to take a moment for honesty. 
Solar Roofpad truly intrigues me. Not because I want to live in the Solar Roofpad (hard to see my family of five in it) nor because I don’t see tremendous things in other houses (again, every single Decathlon house has some significant appeal) nor due to any questioning about other team’s achievements (and, well, I am sincerely enthusiastic about the diversity of approaches and impressed by the quality of all 19 homes) but because I see this as having one of the most straightforward paths to market while helping assist sustainable living for its inhabitants while addressing larger sustainable issues.
- This has an immediate market if a major city (read New York) would not include structures like this in density calculations. (Have an existing apartment building, here is a path to add additional units without having zoning hearings …) Almost literally with a swipe of a pen, Mayor Bloomberg could take a tangible action aligned with his sustainability goals while also creating business activity, additional housing units, and future tax revenue for New York City. If the Mayor would ‘waive’ zoning density hearings for sustainable additions (much like, with their inception, affordable housing allows increased density) to existing structures this would turn deploying Solar Roofpads into a very straightforward path that would almost certainly attract serious attention and activity. Zonign density is a messy business that would be put aside and thus allow questions focused on technical issues (can the roof handle the weight, is there safe and appropriate access to the roof, etc …) (Informal discussions with the appropriate staff suggests to the team that would mean about 25-50% of New York City’s multi-family residences (with a flat roof) could handle these.) And, if this occurs, perhaps Mayor Bloomberg could spark a Selling New York competition for realtors seeking to sell these prime new penthouse units.
- Simple fact: urban living is more sustainable, globally, than suburban living. This puts small footprint housing in the middle of small-footprint living rather than fostering a ‘sustainable’ vision that relies on a couple gallons of gas car ride to get there from work.
This vision, however, is not necessarily shared by the judges since, at this time, Solar Roofpad is in 18th place out of 19 teams (about 140 points below the leading University of Maryland (634.637) after eight competitions. (Note that ‘Market Appeal’ isn’t yet scored (where it might do well) but neither is energy balance where, I estimate, they will not be one of the top entrants due to how they heated up their water storage). Note that the 18th place is in part because this Decathlon entry, targeted at a New York market where >$1 million apartments are not unusual, failed poorly in the affordability contest. (Consider, do housing and energy costs differ between rural Appalachia; Purdue, Indiana; … and downtown New York City (or Paris or Tokyo or …).)
Solar Roofpad provides
something between an efficiency and one bedroom apartment (its Murphy bed is shielded from the living area by the heating, kitchen, bathing, etc area). While very attractively put together, there are several ‘technical’ and design elements that seem truly interesting:
- The building envelope is comprised of 64 equal-sized units. This creates flexibility in placing windows and solid walling to meet each purchasers’ desires with a standardization of components that enables ‘assembly-line’ manufacturing of both parts and overall units.
- The glass has “bird-safe” glazing. A UV- reflective patterned coating visible to humans (at least this human) only with focused attention but very visible at birds. This matters, considering the 100,000s of birds killed by striking glass windows in New York City each year.
- The heating and cooling system is solar thermal based.
“The new system cools with no moving parts, aside from a few small pumps and little added energy. The liquid carrying heat from the building rises as a vapor. Instead of going to a compressor, the vapor moves into a saturated salt solution of lithium bromide. The solution is warmed with solar heat, evaporating the vapor, which moves into the condenser and cools, restarting the process.”
- As with several other teams, Team New York deployed phase change material (PCM). In this case, to replace water for storing heat collected by the solar thermal tubes thereby increasing efficiency while reducing cubic space required for the same heat storage.
Now, while the public focus on the Solar Decathlon is, quite understandably, “solar”, efficiency is even more critical: efficiency first. The Solar Roofpad’s heating and cooling systems seem to set a real standard in this regard:
energy efficiency ratio, or EER, for a top-notch system in current use would be about 12-15, notes Professor of Mechanical Engineering Jorge Gonzalez. “The EER of this system will be about 30 – that’s huge.”