Part 1: What is Zero Energy?
Note: This series was originally posted in January 2016. Due to continued interest in this topic this series has been updated with new information to maintain relevancy as of March 2020.
In 2015 the U.S. Department of Energy (DOE) Building Technologies Office created a formal designation for buildings, campuses, and communities that want to demonstrate that they are providing for their own energy needs on an annual basis. The DOE developed a report outlining these designations in conjunction with a team of subject matter experts and the National Institute of Building Sciences. The report focuses on the term “zero energy,” which differs from the more common industry “net zero” designation in several key aspects.
Because “zero energy” is ultimately a more complicated concept to grasp or explain, we believe the likelihood that it will supplant the traditional net zero goal is minimal, though we laud the intent of the program.
The most critical difference between the traditional “net zero” and this new “zero energy” designation is as follows:
- The net zero definition almost always addresses only the site energy usage; the annual quantity of energy consumed by the project must be less than or equal to the amount of renewable energy created onsite. This definition is fuel-neutral, meaning production and consumption of a unit of energy is considered the same regardless if it is electricity, natural gas, etc.
- The zero energy definition focuses on balancing onsite production with source energy usage, which accounts for the amount of energy it takes to provide the site with the energy it demands, accounting for transmission losses and energy generation efficiency. This definition is fuel-dependent, meaning the offset calculation must account for the differences in source energy needs for different fuel sources. One unit of natural gas consumed DOES NOT require on unit of electricity to be produced.
It is worth noting that some definitions of net zero or zero energy are more lenient and may allow the purchase of renewable energy credits (renewable energy generated off-site) to offset energy use. Others are more stringent, such as the Zero Energy Certification offered by the International Living Future Institute (ILFI, the same organization that administers the Living Building Challenge). ILFI requires not only balanced energy consumption and production over the course of the year, but they also rule out the use of any on-site combustion use.
The DOE likely decided to break from the common “net zero” nomenclature in no small part because there are already so many competing definitions and certifications based on that term. Our next Mindshare post will provide a case-study example comparing and contrasting what it might take to claim zero energy versus net zero status for a building project.