* Was not considered in main contest to determine overall winner.

* Was not considered in main contest to determine overall winner.

desiccant, and then use evaporative cooling. There are no commercial systems like this, however. (See "Passive Cooling," Parts 1 & 2 HP82 & HP83.)

Ground Source Heat Pumps

Using a ground source heat pump is often the most efficient method of backup heating. They have lower carbon emissions than an efficient natural gas furnace, even when operated from a low efficiency, coal-fired power plant. They require extensive digging (similar to a septic system) or well drilling to function properly.

Although no digging was allowed in the Decathlon, many teams simulated a ground source heat pump with a large water bladder or water tank under the house. A temporary water bladder will only work for so long as a ground source, and is not recommended for longer than a week or two. It

Colorado's power system—two Trace SW5548 inverters, Solar Boost 3048,Trace C40 and Outback MX-60 charge controllers, and Outback power system enclosure.

isn't a big enough thermal mass compared to the real ground. It eventually gets too cold if you are trying to suck heat out of it to heat the house, and too hot if you are trying to dump heat into it to cool the house. People with easy access to small ponds greater than one-half acre (one-fifth hectare) have successfully used them as long-term heat sink sources.

Building-Integrated PV?

Since so many of the houses tried to integrate solar technology into a standard looking house, you might wonder why none of them used Uni-Solar roofing products. This was mainly due to the high electrical loads imposed by the competition rules, and the small roof area, especially when the need to charge an electric car was added. If these designs were changed into two or three bedroom houses, then solar shingles or standing seam metal roofing with thin-film PV may have been a good option.

One school, Crowder College, was an exception to this. They used amorphous PV modules (BP Millennia) that were integrated into solar thermal collectors over part of the roof.

The amorphous PV was used because of their tolerance for high temperatures.

This was also the only house to have north-facing PV (Colorado had flat PV on its small north roof section). Simulations predicted that these were roughly 50 percent as efficient over the year as the south-facing ones. Despite having a much smaller array than most of the houses, Crowder still maintained a positive energy balance and placed fourth for distance driven in the electric car. This proved that operating a system effectively can lead to improved output without having a larger system.

A common complaint about putting PV modules on a roof instead of on a rack is that the PV modules are likely to last longer than most roofs. So how do you fix the roof underneath? Most PV mounts also put holes through the roof where they are attached, which may eventually cause leaks.

Colorado came up with an innovative solution to these problems. Their roof is a standing seam metal roof, which is warranted for at least as long as the PVs. The PV mounting system uses clamps from S-5! Solutions that hold onto the seams of the metal roof. Thus the entire PV array is mounted without a single roof penetration.

To MPPT or Not to MPPT

Over half of the entries used maximum power point tracking (MPPT) charge controllers. Most used the Solar Boost controllers (Things That Work! HP73 & HP77), and Colorado used one of the first OutBack MX-60s, a competitor to the high-powered Solar Boost 6024 that was just unveiled. The OutBack controller actually does a current-voltage (IV) sweep to determine the maximum power point, which should be more effective under varying sun and partly sunny conditions than using a fixed offset from open circuit voltage, as the Solar Boosts do.

Did MPPT help? Well, there were too many other factors for it to be a deciding one. But everyone noticed at least a slight boost in current, even on hot muggy days with a hot, roof-mounted PV array, which is when the smallest boost will be seen. A cold winter day definitely gains an advantage. The voltage conversion capability also allowed strings of five modules in series in at least one case, when modules did not fit on the roof in multiples of four for a 48 volt system. It may just be coincidence, but the top performing teams in all the engineering contests were the ones using maximum power point tracking charge controllers.

The Colorado team is now doing side-by-side comparisons of the MX-60, a Solar Boost 3048, and a Xantrex C40 on identical arrays to determine exactly how much boost they are giving, and the conversion efficiency and power point tracking efficiency of the two MPPT options. Stay tuned.

Xantrex Inverters

All fourteen teams used the Xantrex SW series inverters (Things That Work! HP48 & HP58). Most of them used stacked 4048s or 5548s. Why? Primarily because of the large 240 VAC loads. Many of the most efficient split-system air

In Maryland's modular construction, the tech pod was located on the left side of the building, next to the carport.

conditioners are available in only 240 VAC, and the 3 ton split-system air conditioning units used by at least four teams have a serious starting surge that the SW can handle. The Asko washers and dryers that were donated were only available in 240 VAC, and induction cooktops were hard to find in 120 volt units too.

Also, until relatively late in the design process, it was thought that teams would get a Th!nk City, with a 4 KW, 240 VAC charger, instead of the Neighbor, with its 1 KW, 120 VAC charger. OutBack Power System's new, modular FX series inverter was under consideration by at least two teams, but did not ship in time for the competition.

Tech Pod

The idea of having a separate room or building for all of the systems was used by Maryland and Colorado for their home designs. Instead of sticking something into every closet, they put all of the batteries, inverters, hot water system, etc. in a separate room adjacent to the house. This idea has a couple of advantages.

First, it allows the rest of the house to be more conventional in design. Whether it is grid connected, stand alone, or even if it is just superinsulated with no renewable energy systems, the electrical and water system of each house is exactly the same. Second, it allows building code issues to be dealt with more easily, and will make solar technology more accepted by the masses when it is something that sits out in a service room, just like a well pump, instead of a stack of batteries hiding in a closet.

Window Technology

Most of the houses used high performance windows with R-values between 5 and 10. These are not quite the best technology (experimental, around R-14, which is better than many walls), but are the high end of what is readily available.

Most of the windows were double pane with suspended low-E films and krypton or argon gas fill. These cut down on the weight and cost of triple or quad pane windows,

Colorado's tech pod being hoisted in place. You can see the water storage tanks and hot water tank in the upper section.

while actually having higher R-values and better light transmittance. Some houses used different windows for different orientations. This idea is gaining popularity on office buildings, especially in Europe, but has not typically been applied to residential design.


All of the houses used compact fluorescent bulbs for almost all lighting. A few halogen accent lights and some linear T-5 fluorescents were also used. The continued use of incandescent lightbulbs for most residential lighting in America is an embarrassment.

Why are supermarkets here just starting to stock compact fluorescent bulbs? In a "backwards" country like Mauritania, it is impossible to buy an incandescent bulb. The country has only a few power plants, so it's more obvious that the cost of installing a lightbulb is not just the lightbulb cost, but also the cost of the power plant and its operation. The government couldn't afford to install power plants if everyone installed incandescent bulbs.

PV may be sexy, but if you want to make a difference in your energy impact the cheapest way possible, get together with four of your friends, buy a 20 pack of 15 or 20 watt spiral CF bulbs (about US$3 per bulb) and each replace four of your most used lights. (See Guerrilla Efficiency in HP91, HP92, & HP93.)

For new construction, indirect lighting with linear T-5 fluorescents is the most effective means of giving overall lighting to a space. They produce 80 to 90 lumens per watt, compared to 60 to 70 lumens per watt for CFLs, and 15 to 20 lumens per watt for incandescents. CFLs are more common because they are smaller and can be used in standard fixtures, whereas T-5s come in 4 foot (1.2 m) long tubes. (Metal halide and sodium lights are more efficient, but not suited to residential lighting.) Although indirect lighting is not as efficient as direct lighting, it provides a much more pleasant lighting environment, so lower light levels can be used.

A number of houses, including most that placed high in the lighting contest, used daylight controls that automatically dimmed the lights in response to the amount of daylight available. Studies have shown that people do not turn on lights if a space has sufficient daylighting. But if they turn on lights in the morning, they will usually forget to turn them off all day, even though daylighting becomes sufficient.

Green Materials

Although environmentally friendly materials and construction were not stated requirements of the competition, most of the teams included them in their designs, along with energy independence. Several houses used bamboo flooring, which performs as well as hardwood, but only takes a few years to grow. Currently it is imported from China, but the right variety of bamboo will also grow in the Pacific Northwest, and efforts are being made to establish an American supply.

Composite fiber cement siding, which is fireproof and can have a 50 year warranty, made its way onto several houses. Reclaimed lumber was used in various applications, from cabinets to flooring to shading louvers. Colorado and Auburn used Parallam laminated beams made from aspens and other fast growing trees as exposed beams, instead of hiding them as is usually done in conventional building.

A variety of recycled products, including Faswall blocks, sunflower seed board and wheat board, recycled poly carpeting, and newsprint countertops were used. Several houses used low VOC (volatile organic compounds) paint, which was noticeably odorless after repainting only one day before opening for tours.

State of the Art vs. State of the Shelf

Some entries went for state of the art technology, such as the translucent aerogel insulation used by Virginia Tech. Others were proud of the fact that everything in their house is commercially available to the average person. Far from being un-innovative, they felt that this was in fact more innovative. After all, one-of-a-kind solar houses have been built for 30 years. A design that can be mass-produced and appeal to the average consumer is something new.

The Cost of a "Green" House

The estimated costs (if all the materials and labor had to be bought at retail values) for most of the houses seemed to fall a little to the high side of US$200,000. Many of the visitors to the Decathlon were surprised by these costs, not that they were so high for a one bedroom house, but that they were so much lower than their impression of what solar technology costs.

Many people seemed to think that a roof covered with PVs would be half a million dollars itself, whereas in reality the most expensive PV system was "only" around US$50,000. And the PV systems are the least cost effective measure found on these houses. Other design features, such as superinsulation and high efficiency air conditioners would pay for themselves in a few years, even on a grid-connected house.

The building industry obviously knows and plays off of people's impression that solar energy and super efficiency is "too expensive." Not a single major home developer was interested in sponsoring the event (although manufactured home companies worked with a few teams).

One developer that touts itself as being especially green and has corporate grants ostensibly dedicated to furthering green building research and public education repeatedly turned down applications for sponsorship. Their thoughts were that just low-E windows, a programmable thermostat, and basic Energy Star compliance on insulation constituted a high efficiency house. For comparison, most of the Decathlon houses, if they had all the PV and solar thermal collectors removed, would use only one-third of the energy of a basic code compliant house the same size, and about half the energy of an Energy Star compliant house.

The housing market at large will only change when people start demanding better. We hope that the Solar Decathlon is a start in showing people that better alternatives exist, and they are a lot further along than what they are being told they can have.

What's Next?

The competition attracted thousands of people—more than even the contest organizers hoped for. It showed the American public the many advances of solar energy since the "solar heyday" of the late 1970s. People saw some of the existing technology that they can use right now, and some new technology that sounds great, but still has some bugs to be worked out.

Several of the houses are on display at their respective university campuses, at least for the next year, and most teams are maintaining their Web sites to further educate the public about solar energy and energy efficient buildings. And a new generation of engineers and architects, now entering the workplace, learned how to implement solar design as a reality, not just as textbook theory.

The next Solar Decathlon competition will be held in 2005. The Department of Energy is in the process of selecting eighteen schools to participate for next time.


Zeke Yewdall is a graduate student in solar engineering at the University of Colorado, Boulder, 838 19th St., Boulder, CO 80302 • 303-443-0090 • [email protected]

Catherine Buxton is an undergraduate mechanical engineering student at the University of Maryland, College Park, 4230 Knox Rd. #1313, College Park, MD 20740 • 301-233-8213 • [email protected]

To download the Decathlon scoring spreadsheet, go to > Magazine > Files & Downloads > Promised Files

Solar Decathlon, Richard King, U.S. Department of Energy, 1000 Independence Ave., SW, Washington, DC 20585 •

202-586-1693 • Fax: 202-586-8148 • [email protected]

National Renewable Energy Laboratory (NREL), 1617 Cole Blvd., Golden, CO 80401 • 303-384-6516 • Fax: 303-384-6490 • [email protected]

Structural Insulated Panel Association, PO Box 1699, Gig Harbor, WA 98335 • 253-858-7472 • Fax: 253-858-0272 • [email protected] • Links to all U.S. SIP manufacturers

Thermomax Technologies, 5560 Sterrett Pl., Suite 115, Columbia, MD 21044 • 410-997-0778 • Fax: 410-997-0779 • [email protected] • SHW collectors

Sun Utility Network, 373 West Palmer Ave., Suite A, Glendale, CA 91204 • 800-822-S0LA(R) or 818-244-4919 • Fax: 818-244-4920 • [email protected] • Suntube evacuated tubes

S-5! Solutions, a division of Metal Roof Innovations, Ltd., 8655 Table Butte Rd., Colorado Springs, CO 80908 • 719-495-0518 • Fax: 719-495-0045 • [email protected] • PV mounts

Alpen Glass, Alpen Inc., 5400 Spine Rd., Boulder, Colorado 80301^ 303-530-1753 or 800-321-1753 • Fax: 303-530-1150 or 800-882-4466 • • Window technologies

K-X Faswall Corporation, PO Box 88, Windsor, SC 29856 • 800-491-7891 or 803-642-8142 • Fax: 803-642-6361 • [email protected] • Faswall blocks

EcoProducts, 3655 Frontier Ave., Boulder, CO 80301 • 303-449-1876 • Fax: 303-449-1877 • [email protected] • Recycled carpet, sunflower seed board, cotton insulation, etc.

Phenix Biocomposites, PO Box 609, Mankato, MN 56002 • 800-324-8187 or 507-388-3434 • Fax: 507-388-3434 • [email protected] • Environmentally friendly panel products

Trus Joist, 2910 E Amity Rd., Boise, ID 83716 • 800-338-0515 or 208-395-2400 • Fax: 208-364-3633 • • Parallam laminated beams

Skywall Translucent Systems, a division of Butler Manuf., PO Box 629, Terrell, TX 75160 • 800-259-7941 or 972-551-6470 • Fax: 972-551-6421 • [email protected] • Aerogel building materials

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P.O. Box 1101, Areata, CA 95518-1101 Phone: 707-822-9095 • Fax: 707-822-6213 • www.sunfrost.eom

RV Power Products, 2598 Fortune Way, Suite K, Vista, CA 92083 • 800-493-7877 or 760-597-1642 • Fax: 760-597-1731 • [email protected] • MPPT charge controllers

OutBack Power Systems, 19009 62nd Ave. NE, Arlington, WA 98223 • 360-435-6030 • Fax: 360-435-6019 • [email protected] • MPPT charge controller

Xantrex Technology Inc., Distributed Power Markets, 5916 195th St. NE, Arlington, WA 98223 • 360-435-8826 • Fax: 360-435-2229 • [email protected] • Inverters

Efficient Windows Collaborative, Alliance to Save Energy, 1200 18th St. NW, Suite 900, Washington, DC 20036 • 202-530-2231 • Fax: 202-331-9588 • [email protected] • • Information on energy efficient windows

Southwall Technologies, 3975 E. Bayshore Rd., Palo Alto, CA 94303 • 800-365-8794 or 650-962-9111 • Fax: 650-967-8713 • [email protected] • Window technologies

Smartwindow • 888-854-9520 • Fax: 888-854-9552 • [email protected] • Window technologies

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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