Clarifying carbon reduction claims and pathways to their achievement using real-world buildings

Commercial buildings are significant contributors to both national electricity consumption and the associated greenhouse gas emissions. Commercial building operators seek to reduce or eliminate the electrical energy use carbon footprint of buildings through a mix of optimisation, energy efficiency measures, and on-site renewable energy production. Remaining emissions can then be offset by purchasing carbon credits or renewable energy certificates (RECs) or entering into power purchase agreements (PPAs) with renewable energy providers.

With such a range of actions available to reduce emissions, and various claims that can be made such as “carbon neutral”, “100% renewable”, or “24/7 carbon-free”, it can be difficult to understand the differences between these claims and the pathways to achieving them for any given building or site. This study clarifies the definitions of these emissions reduction claims and explores the feasibility of achieving them.

Real-time 5-minutely carbon emissions data for the Australian National Electricity Network is combined with data from real-world office, school, and government commercial buildings equipped with on-site photovoltaic (PV) generation. This data is coupled with simulation of battery storage systems and optimisation to assess the maximum emissions reduction benefit achievable for a range of system sizes over a year of operation. Further analysis identifies the limiting factors that prevent buildings from achieving 24/7 carbon-free operations and suggested mitigation strategies are provided.

The electricity network emissions data used includes: i) regional annual average, ii) dynamic regional, and iii) substation-level dynamic emissions intensity factors. This enables comparison of the relative benefits of different emissions reduction strategies and claims. Additionally, we examine how the buildings’ locations affect their ability to transition to net zero factoring in the local weather and grid electricity generation mix.

It is found that on-site renewable generation is the limiting factor for a site to achieve 24/7 carbon-free operations without purchasing RECs or entering PPAs, regardless of the size of the battery storage available. Battery storage is found to provide diminishing returns to emissions reduction with increasing size. This is due to the battery storage being unable to satisfy demand with zero-emissions energy when there is insufficient on-site renewable generation to store. Given the spatial constraints on the installation of on-site renewables, we find that RECs and PPAs are likely essential requirements for claiming 24/7 carbon-free operations and that real time emissions factors are central to this process.