Call me crazy, but I want to get this straight once and for all. Here is how I understand zero energy for a residential building. Please feel free to way in with comments.
Step 1) Zero Site Energy
energy produced on site = energy used on site
Step 2) Zero Energy (edit: Zero Source Energy)
energy produced on site = primary energy used at provider to produce site energy
(assuming all systems are grid-tied and all incoming energy comes from the grid, all outgoing energy goes to the grid)
Step 3) Carbon Neutrality or Zero CO2
energy produced on site offsets CO2 in the amount of CO2 used in primary energy production at provider to produce site energy
(assuming systems are grid-tied and all incoming energy comes from the grid, all outgoing energy goes to the grid)
In reality, I think the Zero Energy and Zero CO2 standards can be achieved without offsetting all theoretical primary energy and primary energy production CO2, since that amount of energy is never fully utilized from the provider—some part of it is directly produced and consumed on site.
Step 4) Carbon Offset & Net Positive Energy
enough energy is produced on site to offset additional carbon and add additional energy to the grid
It appears to me that the only way to make a dent in energy consumption and CO2 production by buildings is to build a bunch of “Step 4” buildings. Feel free to disagree with me in the comment section.