Today, the transition to clean energy is driven by advancing and implementing renewable sources like wind, hydro, and solar power. However, with heating and cooling still comprising about 50% of global total energy consumption, dynamic solutions are needed to make a clean energy future a reality.
Energy providers are turning to thermal storage technologies to fully harness the power of renewable energy and ensure that resources are not wasted.
Thermal energy storage (TES) is a critical enabler for the large-scale deployment of renewable energy and the transition to decarbonized building stock and energy systems by 2050. This is because thermal storage allows for the preservation of energy when it is not needed so that it can be used more efficiently later.
Let’s dive into what TES systems are and how they work.
What is thermal storage, and how does it work?
Put simply, thermal energy storage is a technology that reserves thermal energy by heating or cooling a storage medium and then using the stored energy later to deliver heating, cooling, or electricity. Thermal storage helps use energy more efficiently, especially when harnessing renewable energy sources.
In the case of solar energy, thermal storage solves the issue of supply and demand imbalance. Because solar energy output is limited to the daytime and peaks at around noon each day, there is an imbalance of supply and demand in the evenings. Thermal storage systems can solve this issue by storing the excess solar output during the day and then rapidly deploying it at night to accommodate lower output levels. Excess thermal energy can be stored in the form of molten salt or other materials such as high-temperature substrate.
When it comes to cooling, a facility can use ‘off-peak’ renewable electricity rates, which are lower at night, to produce ice. Ice can be incorporated into a cooling system to lower energy demand during the day.
A thermal storage system consists of three components: a material or fluid that absorbs and retains heat, an energy source, and a way to discharge the heat.
The first element, a material or fluid that absorbs and retains heat, can take one of three forms: sensible, latent, or thermochemical.
- Sensible heat storage – A material or fluid stores thermal energy and increases in temperature.
- Latent heat storage – When a material or fluid stores thermal energy but does not increase in temperature because the material is going through a phase change (e.g., solid to liquid or liquid to gas), it is latent.
- Thermochemical storage – Thermochemical energy storage (TCES) utilizes a reversible chemical reaction and takes advantage of strong chemical bonds to store energy as chemical potential.
Secondly, the system must have an energy source to “charge” the material. This can come from concentrated solar power, nuclear heat, electricity converted to heat, heat offtake from industrial processes, and more.
Thirdly, the system must have a way to discharge the heat. This last element of TES systems typically occurs through convection, passing a heat exchange medium through the thermal battery to carry heat.
To safely transport the heat, thermal batteries often need to be co-located with the end user of the heat or converted electricity. This is one reason district energy systems are well positioned to take advantage of thermal storage technologies—district energy facilities, like Vicinity’s, are often connected to high-voltage substations and have access to transmission-level electricity rates.
Thermal batteries can also be used for cooling, but the heat coming in must first be converted to electrical energy, which is then used to cool the storage medium.
Benefits of thermal storage technology
According to the United States Department of Energy, advances in thermal energy storage would lead to increased energy savings, higher performing and more affordable heat pumps, flexibility for shedding and shifting building energy loads, and improved comfort of building occupants. When integrated with district energy systems, the benefits of thermal storage technology are amplified.
Drive energy efficiency
Thermal energy storage systems provide increased energy efficiency. For example, district heating systems promote energy efficiency by conserving and utilizing heat when required. As a result, less fossil fuel is needed, and plant emissions are decreased, resulting in lower product costs.
Reduce carbon footprint
TES systems offer a promising electrification strategy for large-scale energy operations. Because they can utilize low-cost renewable electricity to produce and store heat for later use, TES systems can provide utility-scale grid storage and help manage intermittency issues with renewable resources.
In addition, further carbon footprint reductions can be achieved depending upon the storage medium utilized. Lava rocks, for example, have a reduced environmental impact compared to other storage materials such as lithium batteries.
Improve generation capacity
Whether in a commercial office space or a busy hospital, the need for heating and cooling is rarely consistent. For most building operations, demand for heating and cooling can fluctuate depending on the season, time of day, month of the year, and region in which they operate.
To use energy more efficiently, TES systems store surplus capacity that is available during low-demand periods and preserve it for use during high-demand periods, thus reducing wasted energy.
Space savings
In facilities looking to integrate TES systems into existing systems, space constraints can present a challenge. However, different thermal storage mediums require less space per cubic feet than others. For a thermal storage system of 300 MWh capacity, for example, an electric battery storage unit would require 800,000 cubic feet of space, whereas molten salt storage would require 151,000 cubic feet of space, and thermal brick storage would require 90,000 cubic feet of space.
Less maintenance
TES systems typically require less maintenance because they use smaller chillers, cooling towers, and pumps than conventional systems. When integrated into district systems, end-users benefit from even less required maintenance because district energy systems aggregate energy production, freeing customers from asset ownership and maintenance of onsite equipment.
Integrating thermal storage with district energy systems
Around the world, innovative district energy companies are deploying thermal energy storage technology to demonstrate how the technologies can cost-efficiently replace fossil fuels, ensuring a reliable supply as a backup to intermittent renewables.
In Rønne, Denmark, Hyme Energy will deploy a 20-hour hydroxide molten salt-based thermal energy storage system. The company partnered with utility Bornholms Energi & Forsyning (BEOF) to deploy the unit at a combined heat and power plant in Bornholm, described as an ‘energy island.’
The 1MW/20MWh system will be the first in the world to deploy molten hydroxide salts. It will provide heat, power, and ancillary services for the grid in Rønne. The project demonstrates the success of deploying storage technologies to retrofit a traditional cogeneration facility.
How Vicinity Energy is utilizing thermal storage
Vicinity Energy is dedicated to transitioning to clean energy generation through innovative technologies like industrial-scale electric boilers, river-source heat pumps, and large-scale thermal storage systems. These technologies allow us to offer the nation’s first carbon-free eSteamTM product to district energy customers in Boston and Cambridge and our other systems across the country in the coming years.
Along with installing industrial-scale heat pumps and electric boilers, Vicinity Energy’s electrification strategy also embraces extensive thermal storage facilities. Unlike traditional lithium battery storage systems, thermal storage leverages the favorable thermodynamics of molten salt or high-temperature substrate to efficiently store vast amounts of thermal energy.
While Vicinity already employs the use of ice and chilled water storage systems at our Baltimore and Trenton central district energy facilities for chilled water production, we also have plans to install large-scale thermal storage technologies at our facilities. Vicinity will install thermal storage facilities that will use electricity to heat thermal material such as thermal bricks, or lava rocks, and then use the heat to produce steam during periods of peak demand.
Vicinity will procure off-peak renewable electricity to generate heat with thermal storage systems to create eSteam™ and distribute it to our customers when heating demand is high.
Vicinity’s district energy systems are connected to high-voltage substations and can access transmission-level electricity rates. This advantage reduces local utility distribution constraints and ensures a reliable and cost-effective supply of renewable thermal energy to customers.
As Vicinity progresses with our electrification strategy, marked by installing the first electric boiler at our Cambridge facility in 2024 and plans to install an industrial-scale heat pump complex in 2028, Vicinity stands as a beacon of innovation in North America’s energy transition.
Connect with a member of our team to learn how you can decarbonize your building with district energy today.
