Why Net-Zero Is the Wrong Target

There are two common usages of the term net-zero. One is the national and corporate use of the term, about which my colleague Sami Grover recently wondered, "Is Net-Zero a Fantasy?"

Net-Zero is also applied to buildings. There are many definitions, perhaps the simplest and most coherent coming from the International Living Future Institute: "One hundred percent of the project’s energy needs being supplied by onsite renewable energy on a net annual basis." I have never really understood the concept, writing back in 2014 that it was "a useless metric."

"The phrase Net-zero energy or Zero-carbon has always troubled me. I have noted that I can make my tent net-zero energy if I have enough money for solar panels, but that's not necessarily a sustainable model. Others have been troubled by the concept as well; Passive House consultant Bronwyn Barry writes in the NYPH blog: 'I’m betting that our currently mythical ‘Net Zero Energy Homes’ – however one defines that empty integer – will be buried in a marketing graveyard somewhere.'"

I always took the position we should be going after radical building efficiency, reducing our energy demand with concepts like Passivhaus, but net-zero was so popular that even the Passivhaus Institute jumped on this unstoppable bandwagon. As solar power gets cheaper and cheaper, some like Saul Griffith, co-founder and chief scientist of Rewiring America, are proposing we shouldn't even bother with building efficiency—just zero it out by adding more solar panels. The net-zero world is looking more like my net-zero tent every day, and it seems that Bronwyn Barry and I are in that marketing graveyard somewhere.

Or maybe not: Candace Pearson and Nadav Malin of BuildingGreen have just written "Net-Zero Energy Isn’t the Real Goal: 8 Reasons Why," which makes many of the points I have tried to make over the years and has added a few more.

Most of the problems with Net-Zero Energy (NZE) projects are due to them using electricity at the wrong time, generating it in the daytime when using it in the evening. During the peak evening times, utilities have to crank up the dirty "peaker" plants. The solution proposed here is our favorite, building efficiency. "The usual passive design strategies can be used to reduce peak demand and shift loads to times when the grid is less dirty."

There is not just a daily problem, but a seasonal one, and the system has to be designed for the peak loads.

"Contrary to what one might assume, the cost of the electric grid is not driven by how many kilowatt-hours are consumed over the course of the year, but mainly by the peak demand that that grid must serve. There must be enough power generators, transmission lines, and substations to deliver whatever power is needed on the hottest or coldest (depending on the climate) day of the year. More infrastructure must be added if that peak goes up,"

Again the solution includes reducing demand rather than increasing supply. Smoothing out demand instead of having to deal with wild peaks and troughs. In an efficient building, heat pumps and water heaters can be time-shifted because it retains the hot or cold temperature. Or, as we say on Treehugger, the grid is not a bank.

NZE Buildings Are Not Resilient to Power Outages

This is one we have been over many times, most recently covering events in Texas. But BuildingGreen notes, a good envelope can give you "passive survivability" when the power goes out, which it may well do more often than before. "One impact of climate change in many parts of the world is more frequent storms, wildfires, and other conditions leading to disruptions of the electricity grid, so the need for back-up power is increasing." Or as we say on Treehugger, turn your home into a thermal battery.

NZE Buildings Don’t Account for Transportation Energy

BuildingGreen writes: "NZE is much easier to achieve in suburban locations, where there’s more room for solar panels and they aren’t likely to be shaded by adjacent structures. But with suburban development come more commuting and more cars on the road spewing emissions."

Alex Wilson and Paula Melton of BuildingGreen actually inspired Treehugger with their studies of this, which they called transportation energy intensity. We also noted earlier: "Rooftop solar disproportionately favors those who have rooftops, preferably big ones on one-story houses on big suburban lots. Those people tend to drive a lot." It's also a point Bronwyn Barry made years ago, that we cannot think of a home and its roof in isolation.

 "Our sprawling urban planning has created an infrastructure that locks us into a dependence on small vehicle transportation. This means that while many of us are obsessively focused on the house, we’re missing the much bigger picture. If we’re going to attempt to address the possibility of maintaining some form of life here on earth, we have to look at emissions from transportation."

NZE Buildings Use More Embodied Carbon

This one is interesting and very important. The realization that "there is a tipping point where certain energy-efficiency features begin contributing more carbon emissions in embodied carbon than they’ll save over the course of the building’s operation." We have been writing about what I called the Rule of Carbon:

"As we electrify everything and decarbonize the electricity supply, emissions from embodied carbon will increasingly dominate and approach 100% of emissions."

I was not sure that BuildingGreen is correct here, in that this is an issue with every building, not just NZE. The fact is that with a clean grid and an efficient building and a short time frame to reduce emissions, upfront or embodied carbon matters more than ever, and yes, the upfront carbon emissions of certain insulating materials can be greater than all the energy they save, but that is not specific to NZE. However, one of the authors, Candace Pearson, clarified for Treehugger:

"If someone is out there designing for Net-Zero, they may be adding insulation to get the loads down to get to zero, and we're pointing out that this may be counterproductive, leading to even more emissions. You can't just think about energy, but also have to have a carbon mindset."

Michelle Amt of VMDO tells BuildingGreen about her changing priorities: "The firm now thinks more about the value of renovation and 'the conversation about embodied carbon' is happening earlier." Or as we say on Treehugger, we want zero-carbon without a net.

However, NZE buildings do have a source of embodied carbon that other buildings do not: the actual solar panels. Imagine if the NZE building is built in a location with low carbon energy from renewable sources. Then if a homeowner or building owner adds solar panels, they are adding 2.5 tonnes of embodied carbon for every kilowatt of solar panels added. When designers in the U.K. calculate embodied carbon they get to ignore the panels, the thinking being that if the renewables are not on the roof then they have to be somewhere else. According to Circular Ecology, this is a mistake, because at some point soon, the embodied carbon of those panels is going to matter.

Vindication?

Many of the thankfully deleted comments on my earlier posts about Net Zero were of the "this is the most idiotic thing I have ever read and this post should be taken down" variety—it was hard at times. The BuildingGreen article makes so many of the points that we have been trying to make over the years, many of them learned from Wilson and the BuildingGreen people; they have often been voices in the wilderness too. What is important now is understanding embodied carbon, reducing demand, increasing resilience, and as they note in their last section, we are all in this together: "If you assume you can clean your load while the rest of the grid is dirty, you are under false pretenses. You should be focused on cleaning the grid for everyone.” 

It's time to throw away the net; it never actually worked as promised, and it is looking increasingly full of holes.