For decades, energy efficiency has been regarded as desirable in home-building and remodeling.
Now, taking that concept even further, the zero-energy home has been designed and tested.
The National Association of Home Builders defines a zero-energy home as one that “produces enough energy to offset the amount purchased from the utility, resulting in a net-zero annual energy bill.”
The NAHB’s research arm, Home Innovation Research, is partnering with builders across the country as part of its Zero Energy Home Project. A zero-energy home achieves efficiency through a combination of structure design and solar generation.
The first step is to get energy consumption down to about half of a traditional home. Then the solar energy generation system does two things:
1. Creates power for use in the home
2. Sends excess onto the grid, thereby “zeroing out” the home’s electrical use
Until recently, a major barrier has been the high cost of solar systems. System aesthetics were also a concern among builders and homeowners, according to NAHB’s Potential Impact of Zero Energy Homes report. Slimmer and smaller solar systems, like Dow Powerhouse Solar Shingles, address that concern.
The high overall cost of zero-energy homes has also been a concern, and builders have been innovative in reducing cost to construct, thereby expanding the potential market. In 2006, Ideal Homes of Norman, Okla., built a zero-energy home for a price tag of under $200,000. Based on one of their stock plans, the home is 1,650 sq. ft. and has three bedrooms, two baths and a two-car garage.
There may be a need to convince many homeowners that the extra cost (about $75,000 in this case) would pay for itself by elimination of utility costs. Rebates and incentives may help make that case.
The construction of a zero-energy home begins with optimal placement on the site. According to the U.S. Department of Energy, the most beneficial position for passive solar is with the south-facing wall within 30 degrees of due south. Right-sized overhangs on the south wall provide shade during the summer.
Other building features that meet the dual goals of efficiency and solar generation include reflective roofs, skylights and smaller windows on east, west and north walls. Low u-value and low-e windows appropriate for the climate should be used.
Insulation is a huge factor in reducing energy use, and Energy Star’s recommended thickness in walls, ceilings and foundations should be met or exceeded. In tandem, all leaks, cracks and holes need to be sealed.
Home systems and fixtures should be as efficient as can be afforded, including heating, cooling, plumbing, lighting and appliances. Every incremental gain here reduces the house’s total energy draw. Solar hot water is recommended, along with a back-up on-demand system.
The final key piece is the solar photovoltaic (PV) system. This system should be designed and installed by certified installers. The difference between standard solar installations and a zero-energy home is that the system generates excess power and is hooked to the grid for transmission of that excess.
On www.dsireusa.org in the solar section, rebates and incentives by state are available to help reduce the cost of purchase and installation for the homeowner. Buy-back programs are also listed.
There are still challenges in the refinement and adoption of zero-energy homes, but significant progress is being made. Another technology showing significant promise is the use of geothermal wells and heat exchange pumps to heat and cool buildings.