Credit: Mark McGinnis
First there was Energy Star. Then came Passive House. Now net-zero-energy homes are the latest rage in the world of energy-efficient construction. Many builders don’t yet think of zero-energy homes as a realistic option, but if they’re building in California and not paying attention they may be in for a rude awakening.
“In California, net-zero-energy is the goal for the residential building code in 2020,” says John Morton, residential new construction program manager at Southern California Edison. Net-zero-energy homes generate as much energy as they use over the course of a year. The California Public Utilities Commission and the California Energy Commission are driving towards that goal with aggressive code changes arriving in 2014 and planned for 2017.
But can it be done without making the homes too expensive for most buyers?
“Net-zero-energy homes can be built—at a price. And that’s the rub: the price,” says Robin Sinha, director at Natural Resources Canada. Sinha’s research team is developing an optimization tool to help designers find the most cost-effective route to zero energy based on location and a host of other variables. “The standard guidelines work for a classic south-facing house with thick insulated walls on a big lot,” Sinha explains. “Our optimization takes into account less-optimal orientation, using thin walls that fit on tight lots that can be cost competitive with solutions for large south-facing lots.”
There are two parts to the cost of zero-energy homes. The first part is the price of upgrading the home’s energy efficiency to the point where a reasonably sized photovoltaic (PV) system can generate as much energy as the home uses. That gets the house to zero-energy-ready status. The second part is the cost of the PV system—including panels, an inverter to convert the DC power from the panels into AC power for the house, and installation.
“It is entirely feasible to build a net-zero-energy house for comparable upfront costs as a non-net-zero-energy house,” says Dave Gauthier, SmartHomze division president for Vantem Panels. SmartHomze kits achieve net–zero–energy–ready status for about $150 per square foot, according to Gauthier.
By investing in a high-efficiency building envelope and replacing expensive central heating and cooling with point-source systems such as ductless mini-split heat pumps, Gauthier and other ambitious builders are achieving the necessary levels of efficiency without any price premium, even at the affordable end of the price range.
PV prices have dropped by about 50 percent over the past two decades; installed costs are now in the range of $3 to $6 per watt. But even at $5 per watt, the cost of a typical 6-kW array is $30,000—too much for most homebuyers to swallow without some extra help. In California, Massachusetts, and New Jersey, incentives are available to buy down much of that cost. In some cases the system can even be installed at no additional cost to the homeowner. The catch? The utility company technically “owns” the energy that the system generates, leaving the homeowner with free but not necessarily green power from the grid.
For most buyers that’s not a deterrent. However, it’s about encouraging innovative builders. And the hope shared by industry analysts is that homes will one day generate enough power for their inhabitants and for the electric vehicle in their garage as well.