B-23 Operational energy calculation – Allocation of energy production for on-site systems connected to grid”

Aspect B-23 Operational energy calculation – Allocation of energy production for on-site systems connected to grid”
Current new buildings may not only be energy-efficient, but can also produce energy on site in multiple ways.The energy produced on site may not only be consumed inside the building, but can also be exported. When energy is produced on site by grid-connected systems (photovoltaic, wind turbines, boiler connected to heating grid etc.), how is this calculated? How are the impacts allocated for both product aspects (e.g. PV cells) and operational energy production?

related study objective

stand-alone LCA comparative assertion

related study phase

goal and scope definition inventory analysis (LCI) impact assessment (LCIA) interpretation reporting

relevant for

new buildings existing buildings construction products screening LCA simplified LCA complete LCA
Provisions The principles for the calculation of exported, imported and on-site energy production should be consistent with the provisions of EN 15978 (see especially reference cases, annex B).

  • Additional provisions for grid-connected systems: the boundaries (i.e. energy uses included) for the calculation of energy demand and exported energy should be homogeneous.
  • The calculation of exported energy and energy consumed on site should consider simultaneity between the consumption and the production.

The method for allocating environmental impact for product aspects and operational aspects should be consistent with the guidance in EN 15978.

Rules from:
EN 15978: Boundary of the operational energy use (Module B6)
8.6.5 Scenarios for operational energy use (Module B6)Annex B (informative) Exported energy – Case studiesILCD:

6.8.4 Time-related representativeness

The methods for energy calculation should be consistent with the reference cases proposed in annex B of EN 15978.Supplementary recommendations are proposed for on-site energy-producing systems that are connected to the grid (case 3 of EN 15978), as follows.Boundaries for the calculation
The boundaries chosen for calculation of the energy demand should be consistent with those for calculation of the exported energy: if only building-related uses are included, the amount of energy that does not supply the uses considered should be considered as exported energy. Then two situations may be considered:

  1. Including only building-related uses in the scope of the assessment: other non-building-related uses are not accounted. The exported energy will be calculated without considering the energy demand for non-building-related uses, because these are considered to be beyond the system boundary.
  2. Including both building-related uses and non-building-related uses in the scope of the assessment: the two uses are taken into account for the calculation of exported, imported and on-site consumed energy.

Timescale for the energy calculation

For simplified and complete LCA, an hourly scale should be used in order to take into account simultaneity between energy demand and the on-site energy production.

The annual exported energy, imported energy and on-site energy consumption for the considered energy carrier i may be calculated as follows:


  • Energy production i,h is the amount of energy produced by building on-site systems at hour h for energy carrier i.
  • Energy demand i,h is the amount of  energy needed for the considered building energy use at hour h for energy carrier i.

Allocation of environmental data

Rules should be consistent with EN 15978 for both product and operational aspects.

For imported energy (Module B6) and exported energy (Module D) more representative environmental data should be used. For example. for electricity, hourly environmental data should be used in preference to monthly or annual average data. See the corresponding aspect ‘Dynamic LCA data for assessing the impact of electricity consumption’.


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