Carbon Trust persistence factor model
A persistence factor is used to calculate the lifetime carbon savings of an energy saving measure. Before using a persistence factor you must know the annual carbon savings that will result from performing the carbon saving measure. Annual carbon savings can be calculated by using activity data and conversion factors as described on the Resources – conversion factors page.
Using the annual carbon saving and the relevant persistence factor we are able to determine the lifetime carbon savings.
Carbon Trust has published persistence factors used to derive lifetime carbon savings for different classes of energy efficiency technologies, alternative energy technologies and behavioural measures.
Example
To calculate the lifetime carbon savings for replacing a boiler with a high efficiency modular boiler system, multiply the persistence factor for ‘Boilers Modular’ with your annual carbon savings:
17.6 PF x 50t CO2e = 880t CO2e
Carbon Trust use of persistence factors
There are three main areas where Carbon Trust uses persistence factor modelling, they are:
- Where customers have alternative options our account managers and consultants can give advice on which is the longer persisting option and therefore likely to lead to greater savings.
- The Carbon Trust uses the model to consistently assess the expected lifetime CO2 savings resulting from its advice activities and calculate cost-effectiveness of CO2 savings from use of Carbon Trust’s public funding.
- Carbon Trust’s interest-free energy efficiency loans scheme provides funding for energy efficient equipment. The loan size is dependent on the lifetime carbon savings that will result, and therefore the model is ultimately used to determine loan amount available for a customer project.
Adoption of new model
In 2010 Carbon Trust adopted a revised persistence factor model. Before adopting the new persistence factor model, Carbon Trust conducted an external consultation to ensure the model was sufficiently robust and widely acceptable to concerned parties.
As part of the consultation process Carbon Trust convened a Technical Advisory Group (TAG). The TAG members were called upon to review the existing persistence factor model and the feedback Carbon Trust had received from stakeholders regarding the model’s weaknesses.
As well as being asked to confirm these feedback issues were accurate, the members were then also asked to assess the validity of Carbon Trust’s proposed new persistence factor model.
The TAG group includes representatives from DECC, WRAP, EST, Salix Finance, the University of Surrey, Imperial College, Atkins, AEAT (who developed the original model) and the Carbon Trust’s limited assurance auditors.