A new subdivision 50 miles east of Los Angeles includes 20 net-zero energy 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) 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 framing techniques with 2×4 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-value 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.
- LED 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-e, double-glazed windows with a solar heat gain coefficient of 0.22 and a whole-window U-factor 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 design and controls and thermal mass 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.