GREEN SYSTEMS ALTERNATIVE ENERGY


BY BETH SHADY CONTRIBUTING WRITER


Should your next home be a net zero energy home?


energy efficient method to heat, cool and power your home. Net zero energy is the simple concept that a home generates the same amount of energy that it consumes on an annual basis. This is accomplished when the right combination of very efficient mechanical, lighting, building materials and appliances are matched with properly sized solar systems to achieve an annual net zero energy balance. David Knight of Monterey Energy Group, a mechanical


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engineering and energy efficiency-consulting firm located in Pacific Grove, California, started Net Zero Energy Certified (NZEC) in 2009. I sat down and talked with David to learn more about the mechanics, costs and benefits of net zero energy. BS: One of the common concerns we often hear with


regard to solar power and green building is that it is too expensive and that the payback takes so long that it hardly seems worth it. Is building net zero energy affordable for the average homeowner? DK: If you had asked me that question two years ago I


would have said that concern was absolutely true. Today, however, recent significant reductions in the cost of grid tied solar electric systems (approximately 50% last year) combined with a 30% uncapped federal tax credit have made these systems very affordable compared to the grid. In addition, solar electric panels are putting out more


energy per square foot, which makes them easier to integrate into the building. Another factor is that the overall efficiency of homes keeps improving. Better insulation, energy efficient lights, windows and HVAC equipment, all standard in today’s new homes, when combined reduce the demand for energy. BS:What mechanical equipment innovations do you


see that make all electric DHW and space heating with solar power more viable? DK: The introduction of the air-to-water heat pump to


the U.S. market has been a boon to the net zero energy concept for hydronic heating contractors. These electric devices, for example, the Daikin Altherma, use variable speed inverter technology to efficiently produce hot water for domestic and space heating. These units are reversible and can also be used for cooling, which opens up a huge untapped market for hydronic contractors, who can now use chilled water for air conditioning. In colder climates, there is a 30% federal tax credit for geo-exchange heat pumps. These systems not only convert electricity into hot or cold water but their capacity and efficiency remain constant, regardless of the outside temperature, due to the constant temperature surrounding the earth. BS: How does a grid-tied solar electric system work? DK: These are simple, very low maintenance systems that convert sunlight into electricity. When the sun is out


f you are in the planning stages of building a new home or doing a significant remodel to an existing one, you are most likely considering some form of an


and your home energy consumption is typically low, the excess energy generated literally spins your electric meter backwards; you are essentially selling electricity back to the grid. Think of it like rollover minutes on your cell phone bill. When the sun goes away, you buy electricity back from the grid. The grid, not batteries, is the storage medium. Most utilities in the U.S. have net metering programs that account for your energy production and consumption on an annual basis. This is one of the keys in making net zero energy homes practical. BS:What factors do you take into consideration when


determining whether or not a net zero energy home is practical? DK: There are several factors to consider. One is the


local climate, which determines the heating and cooling loads as well as the solar production. Adequate roof space and site orientation, ideally unshaded and south facing, are also very important. Local incentives for installing solar electric systems play a key role, and the grid rate of electricity is also a strong determinant. For example, in most of California we have a mild


climate, thus low heating and cooling systems, good solar incentives and very high grid electric rates. That combination makes it very practical to do a net zero energy home. By contrast, Omaha, Nebraska, has a harsh climate and no solar incentives and an inexpensive electric rate, which means that a net zero energy home is not as practical. In other words, mild, sunny states with good solar incentives and high grid electric costs benefit the most from net zero energy. While it is nice to have all four variables, having at least two of the four can make building a net zero energy home a sensible economic decision. These statistics support Knight’s Theory, which is that


homeowners would rather produce their own electricity from solar than buy from the local utility company if the after tax price is the same or less. BS:What is the best way to determine the rate of grid-


provided electricity versus the cost of solar-provided electricity? DK: Table 1 represents the comparison between the


costs of solar provided electricity to the grid. I call this my SPER chart, which stands for solar provided electric rate. SPER is calculated by dividing the annual after incentive cost by the kilowatt-hours produced. SPER is basically your fixed electric rate for the life of the system, typically about 30 years, the same amount of time as your mortgage. To calculate the average after tax equivalent cost of


electrical power, I made the conservative assumption that the homeowner was in the 25% tax bracket and added any applicable state taxes. For example, in Illinois, the average retail electric rate is $0.113. Since mortgages are tax deductible and an electric bill is not, we added the cost of the 25% federal taxes and the 3% Illinois state


e Turn to B. SHADY on p 74


phc january 2011 www.phcnews.com


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