Lessons from California Community to Inform Large-Scale Deployment of Super-Efficient Homes
While strolling among the handsome stucco houses and landscaped playgrounds of the Sierra Crest development in Fontana, California, most pedestrians will not notice that an innovative experiment is happening here.
Twenty zero net energy homes have revealed important insights on the cost-effectiveness and grid impacts of such residences, paving the way for similar communities elsewhere. EPRI led the initiative to integrate energy efficiency and solar generation into the new homes, resulting in the first zero net energy neighborhood by a production builder. The team, which included Southern California Edison and developer Meritage Homes, designed and constructed the houses to California’s Title 24 Zero Net Energy standards and then monitored the houses for a year.
Funded by the California Public Utilities Commission through the California Solar Initiative, the project is intended to explore the grid impact and economics of zero net energy communities and provide guidance for scaling them. As part of California’s goal to reduce carbon emissions by 80% between 1990 and 2050, the state aims to achieve zero net energy in all new residential buildings by 2020.
The Challenge of Zero Net Energy
Zero net energy homes have rooftop solar arrays and include more energy efficiency and electric end uses than traditional homes. Such communities pose a challenge: During the afternoon, solar panels may generate excess electricity that can flow back to the grid. During evening hours, the houses may dramatically ramp up demand for electricity. The resulting two-way power flows can strain the distribution grid, and utilities want to understand how this will affect grid operations and planning.
“Before this study, data on zero net energy homes was limited,” said EPRI Technical Executive Ram Narayanamurthy. “We combined solar with energy efficiency on a neighborhood scale, and looked at how real people interact with real homes and how that impacts the grid.”
Efficiency features included LED lighting, smart thermostats, energy management systems, efficient air conditioners and appliances, electric heat pumps, and heat pump water heaters. Spray foam insulation, which is far more effective at limiting air gaps than traditional insulation, was applied to the underside of roofs.
Because the homes were so well-insulated, builders could use smaller heating and cooling systems. “That allows you to electrify heating,” said Narayanamurthy.
Meritage targeted buyers who weren’t home-shopping based on energy efficiency. “The objective was to sell these homes just as a builder would sell any other home,” said Narayanamurthy.
Lower Utility Bills, Lower-Than-Expected Peak Load
While average residential utility bills in the region are about $115 per month, the Fontana residents’ monthly bills average about $20 for electricity and $20 for natural gas. A major component of both is customer connection charges. Additional mortgage costs for the solar and energy efficiency measures were more than offset by utility bill savings.
As a result of the energy efficiency measures, evening peak load in the homes was lower than what is predicted by existing models for high-solar-penetration neighborhoods. The models indicated that electrification of water and space heating systems could test transformer capacity limits, but these limits were not exceeded over the year in actual operation. The timing of high energy use varied from home to home depending on when people woke up, returned from work, used hot water, did laundry, and ran the dishwasher. This reduced the magnitude of aggregate peaks and valleys in energy use.
Energy storage batteries, added to 9 of the 20 homes, demonstrated limited future potential. The still-maturing technology marginally reduced peak load at the transformer but was not cost-effective for grid balancing. To enhance cost-effectiveness and controllability by grid operators, EPRI recommends further research on deploying storage on the utility side of the meter in community solar systems or on transformers, feeders, and substations. Also, further development of various aspects of residential storage—such as controls, communication approaches, rate structures, and ownership models—can improve storage economics and support grid flexibility.
The project revealed that the most reliable path today for integrating zero net energy communities in distribution planning is to increase transformer and utility wire sizing, rather than to rely on customer-sited battery storage. Researchers also observed that better insulation and air sealing drives greater efficiency, reducing the size of the solar array needed for zero net energy. This benefits the grid by reducing surplus solar generation during midday hours and reducing steep increases in energy demand after the sun goes down.
“We’re working with EPRI to augment batteries with advanced construction techniques to manage excess generation and demand peaks,” said C.R. Herro, vice president, energy efficiency and sustainability at Meritage Homes. Meritage is also looking at using appliances during off-peak demand times and shifting heating and cooling loads.
The Fontana project demonstrated the technical and economic feasibility of zero net energy homes, and the state of California is now considering incorporating EPRI’s findings into its building codes and distribution planning proceedings. EPRI is initiating similar zero net energy projects with Duke Energy and Southern Company in the Southeast, as well as larger, community-scale projects with utilities and builders in California.
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