In the past, we haven’t had to worry too much about when we heat our homes. If we felt cold, we could just head over to the thermostat, turn it up to a comfortable temperature, and our boiler would provide the burst of heat needed to warm up the house. However, as we move away from gas and oil guzzling boilers towards clean, electrically-powered heating, we need to start taking into account when we use our heating appliances. The price and carbon-intensity of electricity varies significantly throughout the day, so it’s important to use heating at the cheapest and cleanest times. You can read more about this in our Insight ‘Why heat pumps need smarter control – smart electricity tariffs’.
This comes with an obvious problem. The times we need to be warm haven’t changed. Heating up the house at three in the afternoon isn’t helpful if you want to be warm in the late evening! This is where thermal storage can come in. Thermal storage is a broad term referring to any mechanism for storing heat and then using it at a later point in time. In a world of electric heating, this is important for driving down costs and ensuring the stability of the UK’s electricity system. Before we dig into the benefits thermal storage can provide, let’s look at what types of thermal storage are already available.
Heat batteries
Heat batteries are a direct way of storing heat for long periods of time. As the name suggests, heat batteries work similarly to standard batteries, but they store thermal energy instead of electrical energy. There are a few different ways that heat batteries store energy. Some use a solid mass, equivalent to a stack of bricks, to trap the heat within the objects themselves. This is the most common form of heat battery in the UK, as it’s the system used by traditional night storage heaters, which utilise cheap overnight electricity prices to charge up and then release heat gradually through the day. Other batteries use Phase Change Materials (PCMs), special substances which trap and emit thermal energy in the process of solidifying and melting. The liquid contained in gel hand warmers is an example of a PCM!
A Sunamp Thermino PCM Heat Battery
Hot water tanks
Hot water tanks are an incredibly effective way of storing heat, and one that many people already have in their homes. Hot water tanks are designed specially to preserve heat as long as possible. While they cannot be used to store heat specifically for heating the home, they still present a valuable way of shifting heat demand. An added benefit of using hot water to shift demand instead of space heating is the all-year-long availability. Most homes will only turn their heating on during the winter, but hot water is required throughout the year.
Building fabric
While the previous two technologies have been dedicated thermal storage solutions, simply using the fabric of a building provides a cheap, effective way of shifting heating demand. When you heat a home, the heat doesn’t immediately disappear out the front door. The house stays warm, the heat kept within the building by the different insulation measures installed. This allows the home to be ‘pre-warmed’, providing a little bit of extra heat to keep the house warm enough while the heating appliance is turned off. Although working out exactly how much extra heat to provide to maintain comfortable temperatures can be tricky, utilising the thermal fabric of a building provides an effective thermal storage method without any extra cost.
Why is thermal storage important?
Thermal storage allows us to separate the times at which we run our heating appliances from when we actually use the heat. As the proportion of renewable generation in our electricity mix grows, we need to make the most of that clean generation and reduce the need to fall back on fossil fuels. Heating and hot water make up over 80% of an average household’s energy demand and using electrical heating appliances when the sun is shining and wind is blowing can help match the home’s demand to when generation is at its highest. Thermal storage grants the freedom to actually generate the heat whenever is cleanest and utilise the heat when it’s needed, reducing both electricity costs and carbon emissions.
Passiv has been utilising thermal storage to shift heating demand as part of its flexibility service, Greener Grid Payments. Over winter 2023/2024, Passiv customers across the country supported the grid by reducing their heat pump demand at peak times. This was all done automatically without impacting their home comfort. Using Passiv’s market-leading heat pump optimisation and thermal modelling algorithms, each property was given just enough additional heat ahead of time such that the building remained comfortably warm with the heat pump turned off. Participants reported that they didn’t notice any impact to their comfort levels, and each was rewarded for supporting the stability of the National Grid.
Thermal storage in all its forms provides a valuable tool in our continuing journey to decarbonising home heating. Successfully balancing electricity demand and generation whilst ensuring that households across the country stay warm will not only cut down the UK’s carbon emissions, but reduce electricity costs for everyone. Smart control solutions, such as the Passiv Smart Thermostat, help achieve the necessary demand shifting with maximum efficiency and at minimal cost.
