(True) Net Zero

Like most two word slogans, which are a simplification of a much bigger issue, net zero has some depth to it. The ‘net’ part is simply reference to an accounting approach whereby two sides of a ledger are balanced off against each other. The ‘zero’ is referencing that the balancing of the two sides results in a mathematical answer of zero; the two sides are equal.

The questions that immediately come to mind are around, what are we measuring and over what time span are we attempting to balance the two sides of the ledger?

In the Net Zero debate there does at least seem to be agreement that we are talking about carbon dioxide emissions, or other pollution that is quantified in carbon dioxide equivalent measurements. In some areas there is great debate about the measurements themselves; how much CO₂ is emitted from the flaring of gas wells? 

At a national scale, the Net Zero debate is geared around the annual balancing of the ledger; did we release more CO₂ into the atmosphere than we took from it over the past 12 months? While this is incredibly important this metric fails to engage with the science which talks about the carbon budget that we, as a planet, have. The science, simply put, suggests that a total amount of CO₂ can be released into the atmosphere before temperature increases breach various levels whether they be 1.5ºC, 2ºC or higher. There is a sombering countdown, the Carbon Clock, on the Potsdam Institute website here.

We are architects and designers of buildings, so what about our role in this…

In the building sector there is mostly consensus on the measurement of operational energy with most people using the simple, to measure and understand, metric of kilowatt hours of energy delivered on site as measured through the electricity meter. 

Interestingly, the Passivhaus standard uses a metric, Primary Energy Renewable, that also attempts to account for energy delivery to site as well as storage as it grapples with increasing renewable energy entering the grid and, very arguably, a diminishing argument for energy efficiency.

An explanation of that approach can be found here. Spoiler alert, the Passive House Institute does not think the argument for energy efficiency is diminished!

At the building scale, Net Zero can be defined as making as much energy as you produce, the balancing of the ledger, but is this consistent with a carbon budget? Maybe! 

If we assume that the building is making renewable energy from its own rooftop solar, as ~40% of Australian homes now do, then the carbon budget question hinges on where the other energy comes from. If all of the imported energy is also from renewable sources then Net Zero is achieved at the building scale on an operational basis.

If accredited GreenPower is used then there is certainty that a Net Zero claim can be justified. However, Net Zero remains an accounting exercise including accredited GreenPower providers who need to ensure that over time, the volume of energy they sell as GreenPower is equal to or less than, the amount of renewable energy they generated i.e. some of the electrons they sell may not be renewable but, on balance, they are.

The potential flaw in the Net of Net Zero is that if all of the off-site energy is needed when off-site renewables are not available then, at the larger scale, we still consume a large amount of fossil based energy. The more this occurs the more renewables need to be generated to balance this out which can lead to huge overproduction of energy at certain times. This is starting to become an issue as solar production in the middle of the day often exceeds demand producing the Duck Curve.

So what is the answer? Generally a better balancing of energy production and energy use over the day/year. Energy storage, whether at the building or grid scale, is a big part of that and although getting cheaper is still relatively expensive.

The most obvious answer is to use less energy, well designed and operated buildings do that! The well operated part can have complexity but one strategy is ‘load shifting’. It is when, in a well insulated building, the ability to heat or cool a building when renewable energy is readily available and then have the building retain that heat/coolth. Aside from all the health, comfort and resilience arguments for better quality buildings, the ability to load shift is becoming more compelling too.

So well designed, well built, healthy and comfortable buildings have a big role to play in reducing the likelihood of exceeding our global budget. Good news!

Bad news! When we build things we also emit carbon dioxide through the construction process and material production, these emissions are known as embodied or, more accurately, upfront carbon. This has two impacts… First, we need to generate even more renewable energy to balance out the energy equation to achieve Net Zero for upfront and operational energy, also called True Net Zero.

Secondly, if we emit an extra 500 tonnes of CO₂ today through construction and then gradually pay it back over the 50 year life of a building we are increasing the chances of blowing the carbon budget.

We have a case study here on our Live Lightly retrofit project in Orange should you want to jump into the rabbithole of upfront carbon.

It’s all about balance!

As a nation, and a planet, we need to address the needs of the population including housing which means both new housing in places and fixing existing buildings too. The challenge is to do so in a way that minimises upfront carbon without compromising on ongoing operational energy. There are many complex interactions between the multitude of factors but we should not let the good be the enemy of the great!

---------------------------------

As a note, this article has only talked about electricity because, at the building scale, there remains no defensible reason to use gas so we presume the world is moving on at a rapid rate.

Finally, on the politics, to not have a plan to address carbon emissions and rely on aspirations is as smart as relying on Lotto as a financial strategy. We are the Lucky Country but I’m not sure we’re that lucky!

‍