Every year, Energy Saving Trust's savings data is updated. We publish information on how much money and carbon can be saved in the home across a range of measures, such as insulating your home or buying the most efficient TVs.
We spoke to our Insight & Analytics team to get the low-down on this year’s numbers – and why calculations change.
Are changes every year really necessary?
I&A team: Definitely. Firstly, fuel prices do change from year to year, and sometimes quite substantially. Naturally, this affects how much you can expect to save from installing energy efficiency measures. This year thanks to changes in the global energy market, heating oil prices went up by 29% this has had a major impact on the cost effectiveness of certain measures. Gas and LPG prices have not changed substantially over the last 12 months but standard electricity has increased by around 10%.
Secondly, although the pace of change might have slowed recently, housing is becoming more efficient year-on-year. We have to factor this into our savings, as the more measures you install, the less is saved per measure.
Aside from oil, where do you see the largest shifts in the figures?
I&A team: The biggest changes often come in renewables, where incentives can change and the up-front cost changes annually. In the case of solar PV in particular, the system costs have fallen quite dramatically and in April 2019, the Feed-in-tariff will come to an end.
What’s the process involved in making changes to the figures?
I&A team: First we look at the state of the housing stock – with data sources such as the English Housing Survey and statistics available from the Department of Business, Energy and Industrial Strategy. We can then work out how much insulation is installed and assess the average efficiency of boilers across the UK. We’ve seen a big shift over the last decade, as non-condensing boilers have been phased out so that in general homes have much more efficient heating systems. Then we review domestic energy prices. From there, it’s about cross-checking and validating our existing models, and making changes where necessary.
Are there any challenges you face in updating the figures?
I&A team: One of the main challenges is to get that clear picture of what’s realistically achievable for the average household. There are many ways to save energy, and some households can save more than others through different measures. We have to be careful to ensure that our savings do not exaggerate or underestimate what is achievable.
Furthermore the UK has a fairly heterogeneous housing stock: there is a great deal of diversity in terms of the ways homes are built, heated and insulated. We try as best as possible to provide savings that are relevant to as many people as possible.
Should householders looking to install energy efficiency measures see the figures as definitive?
I&A team: They’re certainly a good start, and will give you a solid idea of what to expect. If you’re looking to install something expensive, though, you should look at getting a more in-depth report that’s specific to your home. For instance a Green Deal advice report would show you what to install for maximum cost-effectiveness. It might suggest you focus on your insulation before replacing your heating system.
Is the quality of data improving over time?
I&A team: Yes. As time goes on, more criteria can be measured, and factored in. For example, our heating savings are modelled alongside improvements to the Standard Assessment Procedure, or SAP, which is the methodology used to assess the energy efficiency of homes. Recent changes have included incorporating regional differences in climate, say between Scotland and the South West, when it comes to heating requirements. We also look to model new technologies when they come along, such as new, more efficient, electric storage heaters.
How can you be sure it is as accurate as possible?
I&A team: Field trials and other in-situ monitoring are really valuable, giving us more data to check our assumptions against. We’re always looking for the best available data out there to best represent the current situation for householders.