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Unlike some zero energy home certification systems, natural gas has never been forbidden in Earth Advantage (EA) Zero Energy certified homes. In fact, we’ve certified a few homes that have natural gas cooking ranges, fireplaces, or both. That said, the amount of solar photovoltaic (PV) panels needed to make up for the gas use in a house with gas space heating, gas water heating, or both, has been too large and costly to be practical when we measured energy on a site basis. In most cases, there isn’t even enough roof space to accommodate the number of solar panels needed. Therefore, the vast majority of the 50+ homes Earth Advantage has certified since 2011 as Zero Energy or Zero Energy Ready have been all electric, or at least had electric space and water heating systems.

With a simple switch from a site definition of energy use to a source definition of energy use, all of that changes. But, before we get into the details, let’s first define the terms. Earth Advantage currently requires Zero Energy certified homes to be EA Platinum certified and to be able to produce at least 90% of the energy consumed on-site from an annual energy basis through on-site renewable power. An EA Zero Energy Ready home certification can be achieved by following the same criteria—except that solar ready infrastructure, and a bid from a solar contractor showing the potential of a future solar PV system on-site stands in the place of an actual installed solar PV array. “On-site” energy use is defined by the energy consumed by the home on an annual basis within the lot lines of that particular home. “Source” energy is defined as a home’s site energy plus all the delivery and production losses, such as the amount of energy used to produce electricity at the power plant and the losses during transmission, or, in the case of natural gas, the amount of natural gas lost while being delivered.

Changing the definition of energy use from site to source allows us to account for ALL the energy used (site energy plus production and delivery losses)and helps us more fully address the associated carbon impact of burning fossil fuels to create electricity. The inconvenient truth of electric energy consumption lies in the production of the energy. By including the energy used to produce electricity and the line losses associated with transmission to the end user (our homes, businesses, and more) electric energy used on-site has a source energy factor nearly three times that of natural gas piped from the utility to the end user. That means that roughly two-thirds more energy is used to produce electricity and get  it to its final destination than is used to get natural gas from source to site.

Applying this new source multiplier to site energy use and production changes nothing for the all-electric EA zero energy candidate for certification. The real change is that homes that have gas space heating and water heating systems have a real apples-to-apples chance at EA zero energy certification for the first time.

When natural gas is used in an Earth Advantage certified zero energy home, the amount of solar electricity generated on site must also include the energy value of the natural gas consumed. That means that a zero energy house that burns natural gas must produce more solar electricity on site than it buys from the electric utility. Most net metering rules say that the utility is allowed to credit solar homeowners for their solar production only up to the amount that they use. This means that the occupants of the home will not be credited for a portion of the electricity that they send back to the grid. This could well be an advantage, as having additional free electricity may encourage these homeowners to use an electric lawn mower or charge an electric vehicle.

Does this change from a site to source energy use definition make certification to Earth Advantage’s Zero Energy standard easier for gas homes? Definitely not. The 5 cost effective steps of designing and building a Zero Energy home still apply. This change simply levels the playing field for both fuel types to advance our residential construction industry towards a keen focus on smart design and the highest levels of energy efficiency.

Ryan Shanahan is a Senior Green Building Consultant with Earth Advantage.