The Dilution of the ZNE Brand

There is a growing trend of governments mandating zero net energy (ZNE) for new buildings, which started in California. However, this trend has led to a big problem—the meaning of ZNE is being diluted and has the potential to become less impactful.

Back to the Basics of the ZNE Definition

The foundational definition of ZNE is that a building generates as much electrical power as it uses (as measured over 1 year). This concept is simple, powerful, and inspiring.

Becoming ZNE is supposed to involve a building design that minimizes the need for energy, uses the latest energy-saving technology for lighting and appliances, and has onsite renewable generation. The first two qualifications are relatively non-controversial. The third, onsite renewable generation, is where definitions of ZNE run into trouble.

In many circumstances, rooftop-mounted solar panels would not generate enough power over 1 year to achieve ZNE. Homes or buildings may be situated among trees, located adjacent to hills, or in valleys that reduce the amount of sunlight reaching the structure. Multistory buildings are problematic because multiple stories share a single rooftop that can only create a fixed amount of power.

California Is Dreaming Up Ways to be ZNE

California leads in mandating ZNE. Back in 2006, the state decreed that all new homes as of 2020 must be ZNE, with commercial buildings following by 2030. At the time, this seemed like a tall order. As it turns out, California pragmatically implemented the ZNE policies by allowing local zoning boards flexibility. Buildings that cannot be ZNE are designated “ZNE Capable” or “ZNE Ready,” meaning that the buildings are as energy efficient as possible though they do not have the ability for onsite renewable power generation.

Variations on a Theme

Just as California is free to modify the term ZNE to meet its needs, so is everyone else. National Renewable Energy Laboratory offers five variations in Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply. The US Department of Energy adds another four in A Common Definition for Zero Energy Buildings.

NGOs also are involved. The Continental Automated Buildings Association document Toward Zero Net Energy (ZNE) Super High-Rise Commercial Buildings refers to eight more variations. More recently, the International Organization for Standardization (ISO) authorized a team to create a standard called Energy management and energy savings - Guidance for zero net energy in operations. Called AWI 50010, the standard’s first challenge is to define ZNE so that it can be measured. That there have been numerous attempts to define ZNE shows the importance of the idea. However, none of the variations have caught on in a permanent way.

How Far Can the Definition Go?

Relying on rooftop solar panels alone to achieve ZNE is too limiting. For example, it is unrealistic to expect a 40-story building to generate enough power for the entire building solely from the rooftop. The issue lies in how far you let ZNE drift from this model. A case in point is Boston, where city officials are making plans to require new large structures to be ZNE. To buttress this effort, officials like to point to ZNE projects such as the one at Boston University, which claims offsets from a wind farm in South Dakota. Constructing an efficient building in Boston can be a good thing. Investing in a wind farm also has value. However, attributing power generated more than 1,500 miles away that needs to cross five transmission balancing authorities to get to the building stretches the definition of ZNE.

If offsets are to count universally for ZNE, there is the risk that every building can be declared to be ZNE if the building owner is willing to pay a price. The best hope is that the ISO effort can create a standard for ZNE that is universally accepted.