In October 2009, the National Mall in Washington, DC will be turned into a “Solar Village”, where 20 contemporary solar homes from all over the US (and one solar home from Germany), will be on display to demonstrate all the latest and greatest in green construction, and renewable energy. This is the Solar Decathlon 2009, a bi-annual event sponsored by the US Department of Energy, many colleges and universities, as well as private businesses specializing in green building.

 

In the 2007 Solar Decathlon, Boston was represented by a Solar Home built by the MIT team and many volunteers interested in green technologies. This year it is the Boston Architectural College and Tufts University that sponsor the solar home built by Team Boston. Why Team Boston? Because many folks that participated in the 2007 Solar Decathlon are doing it again.

We and IB Roof Systems (the manufacturer of Cool PVC flat roofing membrane) had our own humble involvement by sponsoring the roof installation on top of this amazing creation of the latest architectural design and green construction technologies. Now, with a new IB 50-mil PVC membrane, this solar home will be completely water-tight and the built-in water collection system will provide it with as much H2O as needed. The roof is also very well insulated with over 5 inches of rigid ISO tapered insulation and an additional 12 inches of insulation between the rafters. The cool roofing properties of IB Roofs will minimize its cooling needs, and will waterproof the entire building. Hopefully, everyone will be eventually replacing their old black roofs with cool roofs such as IB. Also, when roof removal is required by code, calling a skip hire to remove the old material, and then installing these new highly efficient roofs is an economical and sustainable way to deal with tear-off. In some cases, the old asphalt roof can be recycled and used in synthetic roofing products.

 

About the Team Boston Solar Home:

By definition, a solar decathlon project will use different solar technologies available on the market. Team Boston has created such a design where virtually every solar system has been utilized. There will be a 4.6 KW Solar PV system consisting of 20 SunTech PV panels. There will be a large solar hot water installation using Viessmann Solar Thermal hot water panels and water storage unit. But aside from these common roof mounted solar systems, there will be a new solar thermal system that will provide up to 70% of FREE heating to this house. It is a so called “trombe wall”. I’ve discussed it in our previous article about solar thermal mass windows. But this time, the Boston Solar Home will have new and improved solar thermal windows: these are not the old 2×2′ window blocks. It will be a full size 8×2 wall/window units, covering the entire south side of this solar house to provide it with all the heat it will need in the winter. To avoid overheating in the summer, the roof will overhang the southern side by 3 feet, and an additional retractable awning will roll out to provide the shade for these thermals walls / windows.

The walls of this solar house have 2 inches of ISO insulation on the outside and 6 inches of between studs insulation. In total, there will be more than 30-r in the walls. Although this is a stick construction home, it can easily be labeled as super-insulated, and it will have minimal heat loss, while providing more than enough energy to be completely off the grid, and won’t need any outside energy sources for either heating or cooling.

Portable design of this Solar Home:

For the purpose of the competition, the house has to be transportable, therefore it is designed and built in 3 sections on portable foundation blocks, so that it can be put on flat-bed trucks and transported to DC for the competition, and then transported back.

The house is designed to be easily taken apart and put back together: all the mechanical components, bathroom, kitchen, heating and air-conditioning equipment and electrical panels are located in one part, and special quick connect ports are used when two living sections are connected. Solar PV panels, and solar thermal system are installed on removable racking systems that are mounted to the parapet walls on the roof, eliminating any roof penetrations and potential roof leaks. This also allows for easy removal and re-installation of both types of solar systems.

There will be a foldable / removable deck / patio area with a handicapped access ramp, making this home a perfect choice for comfortable living in the summer and winter, and usable by anyone.

 

Final thoughts about the solar house:

Since this solar home is still in the construction stage and many systems are not installed yet, it is difficult to get a complete picture of how it will perform. Still, this will be a true zero-energy home, and will actually produce a lot of excess electric power to be sent back into the grid. My biggest personal concern about this home is the cost: without having the exact information and costs run down, the estimates are around $800,000. This amounts to about $1000 per square foot of living space (a maximum of 800 sq. ft. of living space is one of the guidelines of the Solar Decathlon competition), which is very expensive and is not very practical. However this is just  a prototype and if it was a mass production home, the actual cost would be a lot less. This cost also includes the transportation to and from the competition site in Washington DC, and nominal expenses such as marketing, promotion, creation of the website, etc. So the actual construction costs are somewhere around $500,000-600,000.

This is just the firs report on this solar home, and there will be more, as construction goes on. Stay tuned for a complete report on the roof and solar PV system installation, as well as overview of the new solar thermal window units.