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SBR Methodology

The SBR is a measure of demand flexibility. Its methodology is driven by technologies in the home that contribute to its capacity to shift electricity demand in time. This will evolve over time to reflect changes in technology, consumer behaviour, and evidence of building performance. While we envisage the methodology to be overseen by a public or professional body in future, here we present a proof-of-concept version to help demonstrate its potential value.

Definition

The proof-of-concept methodology defines flexibility as the amount of a home’s electricity demand that smart appliances can reduce or shift out of the peak demand period, without affecting its occupants or increasing carbon emissions. The need to avoid impact on occupants means technologies that shift energy must employ some form of storage. For heating systems this means either heat stored in the fabric of the building or dedicated heat storage, typically a hot water tank, storage heaters or a heat battery. For other electrical devices this involves some form of battery storage, either a home battery or an electric vehicle via a charger.

It measures the capacity of the building to shift demand, not the behaviour of its inhabitants. For example, a home with a smart EV charger is capable of shifting large electricity loads, but this relies on the occupants operating this in a “smart” way, such as a time-of-use tariff. This also depends on the occupants having a car; while the metric captures this potential source of demand, it is not intended to reward car ownership. Equally, the “potential rating” captures assets that could be installed, but this will depend on the building - not all homes have space for a heat pump or solar. It only includes technologies attached to the premises, not assets that may move with its occupants (e.g. a fridge) - while this requires some generalisations, it captures assets with the highest impact.

The savings that can be delivered by flexible smart technologies are highly dependent on the assumptions made on the time-of-use tariff and how it varies over the course of a year. This is a rapidly changing picture, but the SBR is based on the ability to shift kWh of electricity. The result is that some technologies which have a positive impact on carbon emissions and cost savings, such as solar photovoltaics, have little impact on the SBR. However, taking the EPC and SBR together, the benefits of solar to the home’s energy bills show up clearly in the EPC.

Key assumptions

  • Peak demand is assumed to be 16:00 to 18:00 on a weekday winter evening; this provides a proxy to assess the relative flexibility provided by different technology combinations.

  • Assets in the home are operated in a “smart” way by its inhabitants, based on some form of automation

  • Electricity prices vary over the course of the day, which are passed on to the consumer in some form, such as a time-of-use tariff.

  • The home has the ability to measure and report energy used every half hour - therefore, a smart meter is an essential pre-requisite to receiving a rating.

  • As our definition means no increase in carbon emissions, solutions that substitute gas for electrical demand (e.g. a hybrid heat pump and gas boiler), while delivering flexibility, are considered ineligible.

  • The amount of flexibility a home can provide per unit area is independent of the size of the building - as an approximation, larger houses will have both a higher demand and greater storage cancelling each other out.

  • Counterfactuals have also been defined to quantify the flexibility that specific technologies could provide rather than being the likely operating scenario in practice. For example, in practice storage heaters and heat batteries would not be operating during times of peak demand but to create a meaningful counterfactual, the model considers what would happen if they were operated continuously.

Calculation

  1. For each technology, a flexibility rating is calculated based on how much electricity (in kWh) it enables to be shifted out of the defined peak demand period. We also apply a simple adjustment for the efficiency of the heating system, based on average coefficients of performance, to account for the low-carbon aspect of our definition of “smart”.

  2. The impact of technology combinations is then calculated. For example, a non-smart electric vehicle charger has no flexibility on its own but when combined with a home battery any demand that it might have placed on the grid during the demand peak can be shifted to a later time. Hence a battery and charger combination delivers more flexibility than the sum of the two technologies on their own.

  3. Based on what technologies are fitted in the home, the total flexibility is then calculated by summing the flexibility of individual technologies and technology combinations.

  4. A score is then calculated by normalising this flexibility figure on a scale of 100 compared to the maximum possible flexibility with all technologies fitted. This is then mapped to a scale from A to G designed to provide a clear distinction as the amount of smart technology in the home increases.

See further detail underpinning the methodology here.