Is a Net-Zero Energy Building Really the Right Target?

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."

Bronwyn continues:

If we study the vast majority of our country’s urban planning design, it reveals that we favor detached homes in remote, idyllic locales. 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. (My apologies for the tone here. It’s hard to not sound mildly hysterical when talking about climate change.)

Rooftop solar disproportionately favors those who have rootops, preferably big ones on one-story houses on big suburban lots. Those people tend to drive a lot.

© Bronwyn Barry

Electric vehicles are not a panacea either. While they may serve as a transitional technology, they still require massive infrastructure. Roads, freeways, tunnels, bridges and parking garages all require the use of asphalt and concrete. These materials generate carbon emissions during their manufacturing process – tons of it – and are never included in vehicle Co2 emission calculations. When all these added costs and emissions are finally included in the home energy equation, our current obsessive focus on right-sizing a home’s solar PV to zero out the utility bill will soon look quaintly myopic.

If we are going to work our way out of this crisis we are going to have to live closer together in walkable communities in buildings that don't use much energy per capita, and that doesn't leave a lot of roof per capita for solar collectors.

© Margaret Badore

(Although TreeHugger's Margaret Badore visited a building yesterday that could prove me wrong)

Flickr/CC BY 2.0

I was thinking about this issue yesterday after Michael Graham Richard wrote his post Game-changer: Rooftop solar will be at grid parity in all 50 U.S. states by 2016- How in fact does this change the game? Are people who can't put solar on their roof now going to pay more for power than those who can? Does the game-changer disproportionately favor suburban sprawl?

© Elrond Burell

Coincidentally, a lot of my questions about the quest for net-zero were answered by British architect Elrond Burrell in a long and thoughtful post. He is using the term Zero-Carbon but I think the terms are, for this discussion, pretty much interchangeable. He gives 9 good reasons why it's the wrong target, some of which I repeat here:

‘Zero-Carbon Buildings’ are not an efficient use of resources.

At the scale of a single building, especially a house, renewable energy generation is expensive and inefficient use of materials and technology.... And when these technologies are installed on a building there is an opportunity cost incurred. The same money would in many cases be better spent on increasing the building energy efficiency and thereby reliably reducing CO2 emissions by design. Building energy efficiency is more resource efficient, can radically reduce CO2 emissions and almost always has the best return on investment.

‘Zero-Carbon Buildings'; only in the right location?

Again, the issue of constraints imposed by surroundings, like trees, other buildings, limited rooftop area.

But one of the most significant points that he makes relate to what happens when the sun doesn't shine and the wind doesn't blow.

‘Zero-Carbon Buildings’ don’t reduce peak demand on the national grid

In the dark freezing depths of winter, with a gale howling outside, everyone has their heating turned up high and all the lights switched on ... and since the sun isn’t shining the photovoltaic systems on the ‘Zero-Carbon Buildings’ aren’t generating electricity. And since the wind is gale force and highly changeable the wind turbines have switched to safety-mode and aren’t generating electricity! So all the ‘Zero-Carbon Buildings’ are back to drawing electricity from the national grid, like every other building. And if the ‘Zero-Carbon Buildings’ are only mildly above-average energy efficient, they present quite a demand for electricity!
We could hope that this type of scenario would never happen in a country where peak demand is in the height of summer. However, on a very hot, still evening, just after the sun has gone down, everyone wants the lights and entertainment on, along with some comfort cooling... the renewable generation isn’t there to match demand.

The answer to this is to not aim for Net Zero Energy, but to aim for Radical Building Efficiency, to build levels of insulation into our homes and buildings so that they don't create the peaks of demand at times when the renewables aren't there to meet it.

The dropping cost of solar power is, as Mike notes, a game-changer that will lead to significant reductions in CO2 emissions. But it is no substitute for good urban design that gets us out of our cars, denser housing types that can support walkable communities, and better buildings that use less energy in the first place. As Elrond notes:

Stringent space heating and cooling energy targets along with comfort targets ensure that the building fabric has to do the majority of the work. The building fabric, which will last the lifetime of the building, will be highly energy efficient and ensure a comfortable building by design, regardless of how and where the required energy is generated.
Radical building energy efficiency can ensure a comfortable building and reliably low CO2 emissions for the lifetime of the building.