Making a building climate-neutral means avoiding CO2 emissions as far as possible and compensating for unavoidable emissions. To achieve this, all operational emissions, including those resulting from user energy use, and hidden emissions must be accounted for.
Our goal is to get it right – transparently, comprehensively, and without loopholes, so that the balance sheet not only looks good, but is also accurate. We have now developed our first version of a methodology to clarify internally important key points and to use as a guide for our projects.
It is based on existing guidance from DGNB, CaGBC and, especially, the Living Building Challenge. On some points we have different opinions. These are typically those where the certifications also differ the most.
- We apply LCA (Life Cycle Assessment) system boundaries, based on the EN15978 standard. This provides modules, or lifetime phases, for which reliable data can be found.
- The time frame for the CO2 balance is, in our view, ideally 20 years from commissioning and ends no later than 2050. By then the carbon balance should be zero. Annual measurement data are to serve as a basis.
- Renewable energy should be generated on site if possible and preferably also stored. The minimum amount to be achieved is 65% of what horizontal photovoltaics would generate on an area equal to that of the building roof. For high-rise buildings, we strongly recommend integrating PV into the facades as well as energy storage to help decarbonize the grid. Any energy surplus offsets the CO2 emissions of the building's embodied energy.
- If on-site renewable energy is not sufficient to achieve climate neutrality, renewable energy from off-site should be used. If this energy is generated in the same region/state, we can be more confident that that carbon credits will not be double counted. Other options must be considered project by project.
- CO2 emission factors for different energy sources are key inputs for calculations but make carbon accounting very academic and complex, especially since energy systems are very dynamic. There are hourly, monthly, and annual values, but also things like average and short- or long-term marginal emissions to consider, which attempt to reflect short- or long-term changes in energy demand and generation, and more. We choose emissions factors on a project-by-project basis based on data availability, assessed accuracy, project specifics, and the state of the science.
Transsolar does its best to be on the cutting edge of science for the good of the world's climate, to size systems appropriately when designing, and to balance CO2 values correctly.
More about our approach >