The UK Net Zero Carbon Buildings Standard Guide: Part 4: On-Site Renewable Energy Generation

MEng
Engineer
uknzcbs banner

The pilot version of the UK Net Zero Carbon Buildings Standard (the Standard) was published in September 2024. The full document can be downloaded here.

The Standard has been produced by a range of industry professional organisations including RIBA (architecture), IStructE (structural engineering), CIBSE (services engineers) and RICS (surveyors), along with a large team of other industry organisations and professionals. 

It aims to set out unambiguously, for a wide range of scenarios, the characteristics that buildings and building projects need to be aligned with the UK’s strategy to become net zero carbon by 2050. The Standard builds upon and supersedes previously published approaches such as the UKGBC Net Zero Carbon Building Framework, the RIBA Climate Challenge and the various LETI design guides.

Read more from our guide: 

Part 1: Key principles and overview 

Part 2: Embodied carbon

Part 3: Operational energy

Part 4: On-Site renewable generation

Part 5: Operational Water Use

Part 6: Fossil fuel free

Part 7: Electricity demand management 

Part 8: District heating and cooling networks

Part 9: Space heating and cooling

Part 10: Refrigerants 

Part 11: Carbon offsetting

On-Site Renewable Energy Generation

The new UK Net Zero Carbon Building Standard sets targets for the amount of renewable energy generated on site. Energy can be generated by either Photovoltaics (PV), Wind Turbines, or Hydroelectric Turbines, but PV will be the relevant technology for the vast majority of buildings. 

Targets are expressed in terms of generation per m2 of building footprint per year. This means that a 50-storey and two-storey building with the same footprint have the same generation target. 

The targets vary depending on region, and building use:

Region

Single Family Homes and Single-Storey Storage and Distribution

All other Building Types

Scotland

60 kWh/m² FP/yr

30 kWh/m² FP/yr

Middle/North England, Northern Ireland, Wales

65 kWh/m² FP/yr

40 kWh/m² FP/yr

South England

75 kWh/m² FP/yr

45 kWh/m² FP/yr

As an example, a London office building would be required to generate 45kWh/m² FP/yr. Assuming a modest solar irradiance and panel efficiency, this would require around 28% of the building footprint to be PV. This seems to be an achievable value for the majority of buildings.

London office PV illustration

The Standard does make an allowance for situations where achieving the targets would not be possible, and will accept reduced targets for the following reasons:

  • Planning or legal constraints (e.g. heritage buildings or conservation areas) 
  • Available space(s) on site (e.g. only very small or impractical installations possible)
  • Overshadowed roofs 
  • Grid connectivity constraints (e.g. limited access to the electrical grid, or grid capacity issues in the local area)

If a reduced target is to be used, a statement is to be issued providing justification with appropriate supporting calculations.

The Standard also requires that PV systems have an upfront embodied carbon of no more than 750kgCO₂e/kWp. kWp (kilo-watt peak) is the measure of peak array electrical output. There is no limit for wind turbines or hydroelectric turbines. 

Comments on the proposals

Aspects we think work well

  • Targets are straightforward and appear to be achievable for the majority of buildings, whilst still providing a meaningful amount of energy generation. 
  • Flexibility is built in, acknowledging that constraints such as grid capacity can be a major limitation on the amount of generation that is feasible for a given building. 

Aspects recommended to be considered for further development

  • Heritage Constraints - more guidance on when it is acceptable to reduce the generation target for these building types. At Max Fordham, we are well experienced in carefully integrating PVs on historic buildings, and don’t think that PVs should be automatically dismissed on the grounds of heritage concerns without due consideration. We developed the strategy for the Grade I listed Kings College Chapel, where 438 solar panels have now successfully been installed, showing that PVs can be successfully installed on high heritage value buildings.
An aerial view of a historic building and green spaces

King's College Chapel, University of Cambridge

© Barnes Construction

Two people standing on the rooftop overlooking city skyline

© Max Fordham LLP

Upfront (embodied) carbon

The upfront carbon limit of 750kgCO₂e/kWp seems like it could be reduced. It’s recommended that The Standard consider reducing this in the future. 

Attempting to assess upfront carbon compared to lifetime carbon abated for renewable energy generators isn’t trivial (and actually not possible using RICS LCA type approaches) due to the number and type of interrelated influencing factors. However, one can get a feel for the relative impacts of different technologies by looking at other published reports such as the work by Pehl et al published in Nature Energy, and excerpt from which is shown below. 

embodied energy of power stations types graph

Embodied energy use of electricity production as a percentage of lifetime electricity production. Global average values are shown by secondary energy carrier (coloured bars) for capacities built in 2050. Combined model variations over both regions and technology variants (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) are shown as grey boxplots. Adapted from Pehl et. Al. Nature Energy Article Article Published: 08 December 2017.

Related journal entries

View all journal entries