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Ice-based Thermal Energy Storage for a Lower Carbon Future

According to the EPA, global greenhouse gas (GHG) emissions from human activities increased by 35 percent between 1990 and 2010. Moreover, carbon-dioxide emissions, which account for approximately 75 percent of these total emissions, went up by 42 percent during this same period. We must reduce our carbon and GHG emissions drastically if we intend to keep global temperature increase below two degrees Celsius, a limit outlined by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

One unexpected way to help achieve these carbon reduction goals is with ice. Ice is a medium that can be stored as a form of energy for later use, such as in ice-based thermal energy storage systems. These thermal energy storage systems help reduce strain on the grid by addressing the main culprit of peak grid demand – air-conditioning – and can boost the utilization of renewable resources as much as 50%. In addition, there are a number of different forms of energy storage to compare, and some are better for a lower carbon future than others. After all, fossil fuels are by definition a form of stored energy and inherently related to energy storage.

Energy storage may be new to some industry professionals and commercial building owners. To fully realize the benefits of thermal energy storage, we must first understand what energy storage is, what impact it can have, and the challenges we should anticipate.

What exactly is energy storage?

By definition, energy storage is the capture and storing of energy produced for use at a later time. Fossil fuels, major carbon emitters, have long been the standard forms of stored energy. So as we try to replace fossil fuels with renewable sources of energy, such as wind and solar, we must consider not just how to replace the pure forms of energy, but also its storage for later use. As we move toward a lower carbon future, we’ll need the collection and storage of these clean sources to replace the full value of what fossils fuels once were for the energy industry.

Consider different types of energy storage, with their varying benefits. For example, batteries are most widely recognized, with others such as thermal heat and pump hydro storage gaining mind-share in this space. Batteries operate best for smoothing short-term power fluctuations of solar and wind power. However, using batteries to run a compressor which in turn is creating instantaneous cooling is a waste of the stored electrons.  Instead, store cooling in the form of ice and save the stored electrons for running a computer screen or lights.

Making the case for ice-based thermal energy storage

Storing ice has a number of benefits making it a more sustainable and cost effective energy storage option for building managers to consider as part of their energy management plans. Conventional air-conditioning systems for schools and other large buildings typically run a chiller during the day to instantaneously cool space. By adding ice, these cooling systems can run that same chiller at night to create ice which is stored in thermal energy storage tanks. The ice can then be used to cool the building the following day along with instantaneous cooling from the chiller.

The benefit of this ice and chiller duo is unsurpassed operational flexibility to take advantage of varying electric rates and renewable inputs. Not only does the option of stored cooling reduce peak energy usage – and thus their emissions – but it can also boost the value of renewable resources as well as help reduce overall energy costs. For example, ice can be stored at night when wind is plentiful, transmission and distribution losses are lower and energy is less expensive. During the day, ice can be discharged as energy costs rise or as solar power input slows.

Overcoming the challenges of thermal energy storage

The greatest challenge related to ice-based thermal energy storage today is raising awareness around its benefits from both an environmental and cost-savings perspective.  Most energy codes and standards average a building’s energy use rather than considering its peak load demand. These codes, standards and other energy saving initiatives are focused on site energy, but thermal energy storage requires a more holistic view of energy use, which accounts for savings of source energy and energy efficiency as it relates to transmission and distribution losses. Building energy use is also only one part of the picture as it relates to utility bills. The demand charge component is mostly misunderstood yet can make up to 70% of the bill, according to a CALMAC whitepaper. This energy cost is based on peak load demand that can be mitigated with thermal energy storage.

With a better understanding of the benefits of energy storage – particularly in the form of ice – consider also that ice-based thermal energy storage systems can reduce peak energy usage by approximately 35 percent by reducing the need for carbon-emitting peak plants, or power plants used in times of high demand for electricity. Not only does this reduce operating costs for building owners and allow for better use of renewable forms of energy, but it also reduces strain on public utilities when there is high demand. Bearing all of these benefits in mind, it’s evident that thermal energy storage will be the holy grail of renewables as we move forward toward a lower carbon future.

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