Net Zero Energy Building
A highly efficient building that generates as much renewable energy as it uses each year.
Quick Answer
A net zero energy building is a highly energy-efficient building whose annual energy use is balanced by renewable energy generated on site or, in some definitions, off site. The U.S. Department of Energy defines a zero energy building on a source energy basis. Efficiency comes first, then renewables such as solar cover the remaining demand.
The Full Picture
A net zero energy (NZE) building is designed so that, over a year, it produces at least as much renewable energy as it consumes. It still usually connects to the grid, drawing power when generation is low and exporting when generation is high, with the annual balance at or near zero.
The U.S. Department of Energy defines a zero energy building as an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy. Other programs use different boundaries and accounting methods, such as site energy or including off-site renewables, so claims should state which definition applies.
The usual design sequence is efficiency first. Teams minimize loads through a good envelope, efficient HVAC and lighting, and smart controls, and then add on-site renewables such as rooftop solar to meet what remains. Energy modeling during design predicts performance, and measured operation confirms whether the target is met.
Net zero energy is different from net zero carbon. Energy balance counts energy use and generation, while carbon accounting also considers the carbon intensity of the energy sources and, in whole-life views, embodied carbon in materials. A building can be net zero energy and still have a meaningful carbon footprint. Occupant behavior and plug loads often cause the real-world results to differ from the model.
Real Examples
Common Misconceptions
People assume: Net zero energy means the building is disconnected from the grid.
Actually: Most are grid-connected. They import and export energy, and the annual balance is what counts.
People assume: Net zero energy and net zero carbon are the same.
Actually: Net zero energy balances energy use and generation. Net zero carbon is concerned with greenhouse gas emissions, which depend on energy sources and may include embodied carbon.
Frequently Asked Questions
How does the DOE define a zero energy building?
As an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy.
What is the difference between net zero and zero energy ready?
A zero energy ready building is very efficient and prepared for solar, but may not yet generate enough renewable energy to reach net zero.
Can a building reach net zero without solar?
Most need some on-site renewable generation, since even very efficient buildings still use energy. Some programs allow off-site renewables.
How is net zero verified?
Typically through measured annual energy data compared with generation, though some programs certify based on design modeling alone.