I have previously wondered, what the heck is a carbon positive house? Now I'm even more confused by what's called a net zero energy house. When the house illustrated above was in the news a year ago, websites called it "America's most energy-efficient home." It's not by a long shot, but the headline writers were confused. It is, in fact, what is known as a net zero energy house, meaning that it generates more energy in the course of a year from its solar panels than it draws from the electrical grid. That website has changed its headline, but confusion still reigns in this field. Strictly speaking, this house is really a net zero site energy building type B, option 1 ... I think. 

Because it's so hard to know! At National Renewable Energy Laboratory (NREL), there are four classifications with four energy supply options. I try to follow the flow chart and I can’t figure out whether the house (grid tied with solar panels on roof) is NZEB:A or B. 

NZEB flow chart

When I take my drafty 100-year-old house that is powered by gas and electricity, I find that since I pay a lot of money for green electricity and biogas, it actually qualifies to be a NZEB:D, where I purchase renewables off-site. But I can show you my fuel bills and they ain’t net-zero. 

packard foundation

Packard Foundation Headquarters are net zero. (Photo: Living Building Challenge)

Then, out of the blue we have the Living Building Challenge, which developed its own Net Zero Energy Building Certification that ensures that the building is "harnessing energy from the sun, wind or earth to exceed net annual demand." It’s totally unrelated to the NREL.

There is also the question of net zero carbon vs. net zero Energy. Matt recently covered what was called a carbon positive house; TreeHugger recently covered a carbon negative data center. They both mean the same thing — the Australians just put a happy positive face on it. Net zero energy buildings are not supposed to produce any carbon, so I suppose it means the same thing, but who knows? Since carbon is really just an inaccurate way of saying CO2, perhaps energy is better.

Could it get any worse? Yes. The Australians have conveniently collated many of the terms from around the world, and it just gets more confusing, with climate positive and zero emissions added to the jumble. (I attached a long list of terms at the bottom of this post.) They list terms from Europe, Britain, Canada and the U.S., all meaning different things or the same thing; again, who knows? This is just insanely complicated and unwieldy. 

my tent

Is net zero energy a good target in the first place?

Finally, there's the most important question of all: is the whole idea any good at all? I have joked that I can make my tent net-zero energy if I have enough money for solar panels, but it doesn’t mean it’s green, or even something that we should be striving for. Rooftop solar favors those who happen to own rooftops, preferably in suburbs with lots of room around them and not a lot of pesky trees providing shade.

British architect Elrond Burrell notes that anyone who is dependent on the grid for part of the year is still part of the problem.

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!
Under that scenario (and also on hot, still summer evenings), the grid system still has to have the capacity to meet the demand. Burrell suggests that we should not aim for net zero energy, but for radical building efficiency, so that our houses don’t create those peaks of demand and can actually fend for themselves when the going gets tough. 

Even as it gets cheaper and cheaper, a rooftop full of solar that makes a house net zero energy is no substitute for good urban design that gets us out of our cars, and a resilient building envelope that uses less energy in the first place. 

Passive House consultant Bronwyn Barry wrote: “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.” 

She’s right. We shouldn't just be covering our suburban roofs with solar panels to meet our demand for energy; the better option is to reduce our demand in the first place, aiming for radical building efficiency. Then we can put a little solar cherry on top to run our LEDS. 

And for everybody's sake, let's come up with some international definitions, preferably comprehensible and sensible ones. 

Related on MNN and TreeHugger:

Here are some of the various variations on net zero energy, collated by the Australian Sustainable Built Environment Council:

Net zero definitions

NZEB definitions continued

NZEB definitions final

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.