Scientists at Lawrence Berkeley National Laboratory (LBNL) have published a new analysis which highlights the benefits provided by thermal energy storage.

To overcome some of the limitations of traditional water-based thermal energy storage, Berkeley Lab scientists are looking at developing next-generation materials and systems to be used as a heating or cooling medium. They are also creating a framework to analyse costs as well as a tool to compare cost savings. In a series of papers published this year, Berkeley Lab researchers have reported important advances in each of these areas.

“It is very challenging to decarbonise buildings, particularly for heating,” said Ravi Prasher, Berkeley Lab’s associate lab director for energy technologies. “But if you store energy in the form of the end use, which is heat, rather than in a form of the energy supply, which is electricity, the cost savings could be very compelling. And now, with the framework we have developed, we will be able to weigh the costs of thermal energy storage versus electrical storage, such as with lithium batteries, which has been impossible until now.”

According to the International Energy Agency (IEA), buildings account for over one-third of total global energy consumption, much of which goes toward thermal loads including space heating and cooling, as well as water heating and refrigeration. By 2050, this demand is expected to increase dramatically as natural gas is phased out and heating is increasingly powered by electricity.

“If we use thermal energy storage, in which the raw materials are more abundant to meet the demand for thermal loads, this will relax some of the demand for electrochemical storage and free up batteries to be used where thermal energy storage cannot be used,” said Sumanjeet Kaur, lead of Berkeley Lab’s Thermal Energy Group.

As our society continues to electrify, the need for batteries to store energy is projected to be huge, reaching to an estimated two to ten terawatt-hours (TWh) of annual battery production by 2030 from less than 0.5 TWh today. With the lithium-ion battery as the dominant storage technology for the foreseeable future, a key constraint is the limited availability of raw materials, including lithium, cobalt, and nickel, essential ingredients of today’s lithium battery.

Thermal energy storage can be deployed at a range of scales, including in individual buildings – such as in homes, offices, or factories – or at the district or regional level. While the most common form of thermal energy uses large tanks of hot or cold water, there are other types of so-called sensible heat storage, such as using sand or rocks to store thermal energy. However, these approaches require large amounts of space, which limit their suitability for residences.

To get around this constraint, scientists have developed high-tech materials to store thermal energy. For example, phase-change materials absorb and release energy when transitioning between phases, such as from liquid to solid and back.

“This new technology is truly unique because it combines thermal and electric energy into one device,” said applied energy materials group leader Gao Liu. “It functions like a thermal and electric battery. This capability also increases the thermal storage potential because of the ability to tune the melting point of the material depending on different ambient temperatures. This will significantly increase the utilisation of phase-change materials.”

Another Berkeley Lab study earlier this year addressed the problem of supercooling, which makes the material unpredictable in that it may not change phase at the same temperature every time. Led by Berkeley Lab graduate student assistant and UC Berkeley PhD student Drew Lilley, the study, published in the journal Applied Energy, was the first to demonstrate a methodology to quantitatively predict the supercooling performance of a material.

A third Berkeley Lab study, published in Applied Physics Letters this year, describes a way to develop atomic- and molecular-scale understanding of phase-change, which is critical for the design of new phase-change materials.

A fourth study, just published in Energy & Environmental Science, develops a framework that will allow direct cost comparisons between batteries and thermal energy storage, which had not been possible until now.

And finally, a study with researchers from UC Davis and UC Berkeley demonstrated the techno-economic feasibility of deploying HVAC systems with thermal energy storage based on phase-change materials. First the team developed simulation models and tools needed to assess the energy cost savings, peak load reduction, and cost of such a system. The tool, which will be available to the public, will allow researchers and builders to compare system economics of HVAC systems with thermal energy storage to all-electric HVAC systems with and without electrochemical storage.

“If you think about how energy is consumed around the world, people think it is consumed in the form of electricity, but in fact it is mostly consumed in the form of heat,” said Noel Bakhtian, executive director of Berkeley Lab’s Energy Storage Center. “If you want to decarbonise the world, you need to decarbonise buildings and industry. That means you need to decarbonise heat. Thermal energy storage can play a significant role there.”

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