California Project Tinkers With a Net-Zero Future
In advance of the state’s 2020 requirement for net-zero energy building, a collaboration of public and private interests studies 20 test houses
A new subdivision 50 miles east of Los Angeles includes 20 net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. homes that will help California builders and electric utilities get ready for new residential efficiency requirements that take effect in 2020.
The Electric Power Research Institute (EPRI), which is leading the effort, says that the Sierra Crest development in Fontana, California, is the first net-zero energy community in the state. The 20 net-zero houses are part of a much larger subdivision being built by Arizona-based Meritage Homes. The houses will help the California Public Utilities Commission and others evaluate how clusters of net-zero buildings equipped with photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) systems can be integrated onto the grid most effectively.
In 2020, all new houses in California will be required to produce as much energy as they use on an annual basis. Sierra Crest is designed in part to proving the concept is workable, says Clay C. Perry, a EPRI spokesman.
"Over the next several years, the project team will study how these houses and their advanced technologies can be effectively integrated into the utility's electric grid," EPRI said. "Simultaneously, researchers will investigate avenues that improve the scalability and economic feasibility of these communities across the state."
The houses are ready for sale
C.R. Herro, vice president for environmental affairs at Meritage, says there are 187 lots at Sierra Crest, divided into three communities. The net-zero houses are split into two groups, one group in the "Grand Canyon" neighborhood and another 11 homes clustered in the "Yosemite" neighborhood.
Meritage, Herro said, is the eighth largest homebuilder in the U.S. and constructs some 8,000 homes per year, principally in warm weather parts of the country (Fontana, for example, is in Climate Zone 3). The company has focused on energy-efficient construction over the last six years and now makes solar and net-zero performance available on every home it builds, anywhere in the country, he added.
"What we hope to do is demonstrate that what most customers think is a future potential is available right now," he said in a telephone interview. "You don't have to wait. It's something that consumers should learn to demand from their new homes."
Some of the features in houses at Sierra Crest include:
- Advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. techniques with 2x4 walls that are insulated with a continuous layer of R-5 polystyrene on the outside of the walls, and stud cavities insulated with open-cell polyurethane foam for a total R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of roughly R-19.
- Conditioned attics insulated with 6 inches of open-cell foam. (The roughly R-24 of the insulation falls below the level required by the International Energy Conservation Code, but Herro says Meritage follows a performance path allowed under California's Title 24.)
- Heat-pump hot water heaters.
- Variable speed air-source heat pumps for heating and cooling.
- LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. lighting.
- Air leakage rates of between 1 and 1.2 air changes per hour at a pressure difference of 50 pascals.
- Uninsulated, post-tensioned concrete slabs.
- Low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor., double-glazed windows with a solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.22 and a whole-window U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of 0.34.
- Grid-tied PV systems with an average rating of 4 kW.
The net-zero energy houses range in size from about 1,900 square feet to 2,900 square feet, with costs from about $379,000 to $432,000. HERS scores on the houses average -3.
Developers will study PV impact
Both of the clusters of net-zero energy houses will be connected to batteries, but in different ways. In the smaller of the two groups, each house will have its own 3 kWh lithium-ion battery provided by Sun Power; in the Yosemite neighborhood, net-zero houses will be connected to a single, larger battery.
In each case, batteries are designed to even out the load on the grid over the course of the day, not provide long-term backup power.
What worries utilities serving solar customers is something called the duck curve, which represents production and demand for electricity in houses with grid-tied PV systems and their impact on the grid as a whole. During the day, there's typically an overproduction of electricity, but when the sun fades in late afternoon and PV production falls off there's a spike in demand as those houses begin drawing on utility power. In chart form, the demand curve looks a lot like a duck.
Dividing the houses into two groups — one with residential-sized batteries and another with a communal battery — will help utility researchers understand PV grid integration a little better. But the idea is the same: the excess power produced during the middle of the day can be applied to the grid when PV production declines in the evening.
"The Holy Grail now is how do you make this a win-win," as Herro puts it. "And the big win is we need to make flat load shapes."
"It’s not a case of whether renewable energy is good or bad, it’s how to you integrate it," he continued. "We shouldn’t be optimizing for southern exposure, we should be optimizing for western exposure. We should think about smart ventilation practices and smart HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. design and controls and thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. should come back in. Nobody’s talked about thermal mass for 20 years, but thermal mass is the best opportunity to start leveling these really energy-efficient homes out.”
Net-zero energy still not in high demand
California's upcoming requirement for net-zero performance represents a big shift in residential building, but at the moment even consumers who are given the chance to buy a net-zero house often don't.
Meritage can offer a net-zero option to any homebuyer in the country for a relatively modest increase in cost, Herro said, but only about 1 percent of buyers take advantage of it.
"I don't think it's whether they want to or not," he said, "it's whether they're even aware they can have it... If you’re a new home buyer, you’re kind of overwhelmed by location, design, and price, and you’re not yet challenging the homes you’re looking at for these advanced features. You should, but I think it’s really a matter of of home buyer sophistication and the quicker buyers start expecting more from the homes the faster the market will change.
"They don't even know they can have what they can have, so they're settling for conventional," he added.
A 2,800-square-foot home built by Meritage would typically need about $12,000 in solar panels in order to hit the net-zero mark. When that's rolled into a mortgage, Herro said, the incremental increase in payments is more than offset by lower energy bills.
- Meritage Homes