Context
The standard assumption eTool makes when conducting an LCA is applying the current emission factor of the electricity grid for the specific region over the life of the building. While renewable energy source do not currently make up a large percentage of the energy grid, the cost of renewable technologies has fallen dramatically over recent years. The Australian government also has a legally binding obligation to reduce its emissions by 5% on 1990 levels, under the Kyoto protocol. The Australian government has also committed to an 80% reduction by 2050.
If the decreasing cost of renewable energy trend continues and becomes competitive with coal and gas, the market will naturally shift away from fossil fuels, particularly if fossil fuel subsidies recede. There is also a small but growing consumer demand for more ethical electricity tariffs. This shift of energy sources into the electricity grid opens a potential for a change in the way grid emissions are calculated with life cycle assessment.
Modelling Decarbonisation
Presently in eTool we assume that the grid fuel mix remains at today’s levels for the life of the building. Whilst this is a good conservative position, and drives the right behaviour in terms of energy efficiency, it may divert some focus from other areas of the building, which may be more important if a more realistic future scenario of grid electricity impacts are used.
In response, we have created two other grid emission factors: a 2050 grid and a 2030 grid.
The 2050 grid assumes an 80% reduction in the current grid intensity. The 2030 grid takes the average grid intensity over the next 40 years, assuming a linear move towards 80% renewable generation by 2050. The modelled reduction in CO2e intensity is achieved by:
- Eliminating the most carbon intensive fuels from the current Australian electricity mix and replacing these with a combination of renewable sources, and
- Increasing the thermal efficiency gas powered generators from 34% up to 50% (implementation of combined cycle turbines)
The fuel mixes and assumed thermal efficiencies for the different grids modeled is shown in Table 1.
Table 1: Modeled Grid fuel mixes
There are a few flaws in this method that we need to declare: Firstly, the scenarios assume reductions in CO2e intensity of tailpipe emissions only. It does not account life cycle emissions for electricity, which includes impacts associated with fuel extraction and transport upstream from the power plant as well as downstream impacts associated with transmission and distribution.
Secondly, if we accepted that this would be enough to meet the 80% reduction in emissions required, the demand for electricity (or energy in general) could not increase. If there is an increase in demand, we would need to further reduce the intensity of Australian emissions and the target is on absolute GHG pollution, not pollution per dollar of GDP, per capita or per kWh. Nevertheless, we think the approach is suitable for the purposes of illustration and discussion, which is the goal of this technical article.
Life Cycle Impacts of Residential Buildings
The graph below illustrates how the lower grid scenarios impact on a single residential dwellings life cycle emissions. Proportionally, embodied emissions have a much larger impact than operational as the grid de-carbonises.
Reconsidering Design Decisions
Generally speaking, there will be a move toward electric based solutions as the grid de-carbonises and the impacts of electricity become competitive with gas. A few recommendations that we typically apply to residential dwellings are shown for the different grid scenarios below.
In this instance, the annual CO2e savings associated with PV have more than halved in the 2050 scenario. Savings from embodied impacts in materials become much more important as the grid decarbonises and materials make up a larger proportion of a buildings CO2e. Moving to fly-ash concrete or replacing carpets gives greater savings than installing a gas hot water unit, which under todays grid scenario would ordinarily provide significantly more.
It’s important to note is that while the transition to a low carbon grid will likely occur incrementally over the coming years, the embodied impacts of the materials are locked in from the day of manufacture. Providing that the grid does decarbonise, material choice can be considered to be equally as important as operational energy, especially when dealing with buildings with a long design life.
What about the gas grid?
We have yet to add a CO2e intensity for future gas grids but watch this space. There is potential for a reduction in the gas grid emission factor with more input into the gas grid from landfill collection and anaerobic digestion. Then again, potential impacts of shale gas fracking will also need to be considered.
The technologies that make up a dwellings services (cookers, boilers, heat pumps etc.) typically have a lifespan of no more than 20 years. Our approach at eTool remains to recommend the lowest carbon solution based on today’s grids with the assumption/hope that they will be replaced with whatever the lowest carbon solution happens to be in 20 years time.
The future may also bring an appropriate price on carbon and studies show that $150+/tonne reflects the true cost of climate change (social and economic cost), which will drive behavior. For example, a gas hot water system is significantly lower in carbon emissions today but in 20 years time when it is replaced, the electricity grid may have decarbonised such that a heat pump is now the low carbon option. Perhaps the occupant will be further incentivised by the price of a renewable electricity grid versus finite gas with a high carbon price.
What about Materials Future Impacts?
The manufacturing of some materials will decarbonise over the coming years, such as the use of biomass in the heating processes in cement production. However, for a building constructed today, the key structural elements of a building such as the impacts associated with the concrete or steel are locked in on the day of construction. The recurring impacts of replacing high carbon materials like plasterboard and carpet may also decrease as the economy de-carbonises. For some elements, this may be due simply to using renewable electricity in the manufacturing plant. For others it may require something more innovative such as developing sheep food that does not make them burp and fart.
There is a high level of uncertainty associated with future impact intensities for the system processes and materials making up a buildings use phase. For example, as Australia’s economy de-carbonises, the impacts associated with energy inputs, maintenance, replacement, repair, water use, and transport will likely decrease (particularly with regard to global warming potential). This has not been accounted for in the analysis. One could potentially model the effects of this parameter on GWP alone as we do know Australia’s current commitments to reduced greenhouse gas emissions, however, even this is very speculative as we do not know how the economy will decarbonise (through efficiency, reduced growth, alternative fuels, renewable energy sources or other mechanisms). The building energy inputs, and the fuel mix for manufacturing products used through the building life span has therefore been assumed constant, and set at today’s values throughout the modelled life cycle of the building.
What else might change?
Australia has been seeing first-hand the effects of climate change for a number of years. The meteorology department has confirmed that 2013 was the hottest year on record experiencing a greater number and intensity of heat waves than ever before. Even if global CO2e emissions are kept within the threshold for a 2 degree global rise in temperature, we will still need to adapt to the climatic changes that have resulted from our current emissions. The Garnet Institute makes the following predictions regarding changes to climate in Perth assuming no mitigation:
– 4 degree rise in average temperature in Perth,
– 56% increase in number of days over 35 degrees by 2070
– 15% – 45% reduction in rainfall in Perth by 2070
– 15 – 65% increase in number of days with “Extreme fire risk”
In the best case scenario with emissions stabilising at 450 ppm, there is still a 2 degree rise in average temperature across most of Australia. The reality is that we have already passed 400ppm and 550ppm (3 degree rise) is realistic. To adapt to these changes we will see a greatly increased use of air conditioning across all building types to maintain thermal comfort.
-Researched and written by Pat Hermon
Research Sources
- http://www.therenewableenergycentre.co.uk/solar-heating/
- http://www.home-energy-metering.com/solar-thermal-energy.html
- http://www.garnautreview.org.au/chp5.html
