A Space View on Household Energy Efficiency
Satellite imagery is commonly used in many applications from forest monitoring to disaster relief, but Astrosat’s data scientists found an innovative application in estimating the energy efficiency of homes across Great Britain. Partnering with the energy company E.On for the ThermCERT project and supported by the European Space Agency (ESA) Astrosat developed novel applications of thermal data obtained from satellites. Similar data was recently featured on ITV.
Assessing the Efficiency of Household Heating
Modern houses are built to a high standard of energy efficiency, to meet current regulations, but older houses are often less energy efficient, because regulations in the past were much weaker building materials were not as technologically advanced and energy efficient as they now are. There are many improvements that owners of such houses can make to reduce their heating bills and their environmental impact. The UK Government runs schemes to encourage energy companies to support such improvements, but the challenge lies in trying to find those households that would benefit from these improvements.
Previously, the only accurate way to estimate the energy efficiency of a house is for an engineer to go and physically inspect it; looking at things like the type and quality of the windows and doors, the thickness of walls and level of insulation in the roof or attic. This is however a very time consuming and impractical task to accomplish at large scale.
Instead, when energy efficiency is graded such as when a house is put on the market and an Energy Performance Certificate (EPC) is required, energy efficiency is estimated based on factors such as the age and type of house as well as the type of materials used to build the house. But these estimates are not always very reliable. Many are simply out of date, having not taken recent improvements into account, and many older houses that have not been sold in recent years have no EPCs at all.
A new method to measure household heating efficiency that’s both practical and reliable is needed.
A New Perspective – from Space
At Astrosat, we believe that satellite data might provide the answer. Earth Observation (EO) satellites pass over every part of the world every day, and as well as collecting images in visible light, some satellites are equipped with thermal infrared sensors. Instead of detecting reflected sunlight in the visible and near-infrared spectrum (lower wavelengths), these are sensitive to thermal radiation (at higher wavelengths) emitted directly from the surface of the Earth as well as any buildings and objects on the surface. The intensity of thermal radiation is directly related to the temperature of the surface or emitting object. In the case of buildings internally heated in the winter (when the outdoor temperature is lower than that indoors), thermal radiation from the rooftop is a direct result of poor insulation as heat escapes through the roof.
Heat loss through the roof is only one form of thermal inefficiency. Satellite data is not able to detect heat loss through the windows, doors, walls and floor of a building, or convective heat loss. Most of the time, however, the greatest proportion of heat loss from a house is through thermal radiation from the roof. Additionally, it would be a fair assumption that houses with poor insulation in the roof are likely to have poor insulation elsewhere.
We use data obtained from the USGS/NASA satellite Landsat-8, which collects thermal infrared images over the UK once every 16 days. We designed an algorithm to aggregate data acquired during cold winter days when households are likely to be heated, avoiding cloud cover and other nuisance data, and averaging over several winters to derive the relative energy loss from all houses within predefined areas (each area may represent from around 100 to several thousand houses). We collected this data over the whole of Great Britain.
Energy loss is only part of the story. Energy efficiency is related to how much of the energy put in to heating a home is lost through the roof, walls etc. To complete the picture, we combined our measurements of heat loss with UK Government data on household energy consumption, thus obtaining estimates of the average efficiency of insulation in all houses in each small area of Great Britain.
Where Can We Go From Here?
Universal estimates of the average energy efficiency of houses are useful for many purposes. Particular strengths of our measurements are that they are objective, consistent, complete and unbiased across all areas of Great Britain. One of the ways we have used this data is as an input to our fuel poverty model. By combining measurements of energy efficiency with satellite-derived measurements of building age, along with census data and other ground-based datasets, we were able to use machine learning to accurately estimate the fraction of households in an area suffering from fuel poverty.
These algorithms provide the data which is then visualised using Astrosat’s data visualisation, analysis and reporting platform (ORBIS) to allow businesses, governments, and non-governmental organisations to digest, analyse, and act on reliable and comprehensive information that would otherwise take an impossible length of time to interpret and almost as long to report on and communicate.