Energy Accounting 101: No Such Thing as "Net Zero"

Don't get mad at me, it's just physics

I have some news: there’s no such thing as “net zero” buildings.

What?! Isn’t this a cornerstone of “sustainable” building, and how we should be moving toward healthier buildings for ourselves and the environment?

As usual, the marketing language and the actual truth of how things work from a physics standpoint don’t quite align. And while I don’t think everyone person on the street needs to have an in-depth understanding of thermodynamics, the laws of energy conservation, and advanced physics, I *do* think it’s worth it for folks in the building industry to have a working knowledge of this stuff.

When you understand the basic principles of how this stuff works, you can not only call BS on spurious marketing-speak, you can make better choices for your projects, the environment, *and* the bottom line [whether you’re in the role of GC, architect, engineer, consultant, or owner].

Ok, so…back to net zero.

So, as you may remember from high school physics class, E=MC2. [That’s supposed to be “squared” but I can’t figure out how to do a superscript in Substack.] That can be summarized as “energy can’t be created or destroyed, it just changes forms.”

This is why we can’t “save” or “reduce” energy use, strictly speaking. Energy is always present, it just may be in a form that you personally find less useful than another form. For example, a gallon of gas has the capacity to do work, it has “energy,” but if it’s just sitting there in a gas can it’s not all that helpful to you. You need an internal combustion engine to convert that energy to another form that makes the car go. Now it’s useful to you.

So now back to buildings.

When people talk about “net zero” buildings, they are typically referring to the idea that the building “produces” more energy than it “consumes,” usually through onsite renewable energy generation, like photovoltaics. Additionally, the “energy loads” of a building are reduced as much as possible, through good insulation, quality windows, efficient appliances and mechanical equipment, etc to keep the PV system as efficiently sized as possible.

So, if a building needs X kilowatts to operate, the PV array will produce at least X kilowatts. The building doesn’t draw on the grid, and consumes a “net zero” amount of electricity, because it produces all it needs.

This is super cool, but is not *actually* net zero.

Why?