Thermal Energy Storage

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As states like California, New York, and Massachusetts mandate energy storage targets, utilities and their customers are looking for storage solutions that help manage peak demand, gain control over energy bills, and improve grid resiliency. The first thought in storage is often traditional battery technology, but the thermal energy storage (TES) market is expected to generate revenue of around $7.45 billion by the end of 2024. Utilities across the US are now realizing that for commercial and industrial applications such as the energy-intensive cold storage industry, TES technology leveraging phase change material (PCM) has a much lower Levelized Cost of Energy ($0.015 per kWh) than other forms of storage, does not require additional storage space, and has a discharge time of up to 13 hours.

The cold storage industry, including frozen food warehouses and grocery stores, maintains the highest energy demand of all other industrial categories per cubic foot, accounting for more than $40 billion of electricity annually. The US alone has more than 2,200 industrial cold storage warehouses consuming an average of 24.9 kilowatt hours (kWh) of electricity and 9,200 British thermal units (BTU) of natural gas per square foot per year. As the $175 billion global cold storage industry and its electric load continue to grow, there is opportunity for distributed energy resources like TES to store nearly 6,000 megawatts (MW) inside existing cold storage facilities within the US alone.

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A recent measurement and verification (M&V) study of a TES project in a California cold storage warehouse demonstrates just how beneficial TES can be for utilities and their customers. Results include over 40% lower energy consumption and almost 30% lower demand over 13 hours every weekday. The profound results of this study are increasingly relevant as more utilities look for ways to reform their business models, deferring costly capital investments in transmission and distribution infrastructure and increasing capacity supply, while reducing capacity waste to meet the needs of their most energy intensive commercial and industrial customers.

Dreisbach Enterprises, a family-owned business offering cold chain supply solutions throughout the West Coast, was in search of a solution for its cold storage facility to manage the high energy consumption and peak demand costs of a 93,000-square-foot, low-temperature warehouse. This Richmond, CA, facility—running on a central ammonia refrigeration system with multiple staged screw compressors and water-cooled condensers—was accruing nearly 50% of its annual energy costs during their 13-hour peak demand period (8:30 a.m. to 9:30 p.m., Monday through Friday).

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While reducing the refrigeration equipment’s mechanical run time during high-cost periods is seemingly a simple response, it can only be applied for short periods of time before temperatures inside the freezers reach their safety limits. Without very careful control of this technique, food quality could be at risk. Dreisbach needed a solution that could extend the length of time that the temperatures could remain stable without active refrigeration and mitigate the associated risk to temperatures and food quality.

After weighing options to minimize peak period energy costs, the facility owners chose to test a modular TES technology comprised of environmentally friendly PCM and intelligent controls. As the PCM transitions from solid to liquid, it absorbs up to 85% of the heat infiltration, maintaining constant temperatures and protecting the food with minimal refrigeration. To collect baseline data, sub-meters and temperature sensors were installed throughout the facility. Three variables (temperature as a function of time, power consumption [kWh], and power load [kW]) were then recorded for three weeks in five-minute intervals.

During the same month one year later, the PCM was installed directly in the airflow path of the refrigeration evaporator on the top cross-members of the existing racking structure and intelligent TES controls were integrated with the existing refrigeration control system. The TES control system’s algorithms enabled the refrigeration system to optimize temperature requirements, mechanical run time, and the utility rate structure. New data for the same three variables was then collected.

The results included an overall decrease in refrigeration energy consumption of 35%. Over the 13-hour peak period energy consumption was decreased by 43% (4,086 kWh) and the peak refrigeration load was decreased by 29% (251 kW). This reduction in energy usage was achieved while simultaneously delivering a 50% improvement in temperature stability. Even after the study, utility-sourced load analyses continue to validate both consumption and peak demand reductions with many months showing even greater results than the original study.

While there are a variety of energy- and cost-saving options available for large commercial and industrial customers in the cold storage industry, such as variable speed drives or upgrading to energy-efficient lighting systems, many fall short of addressing the large amounts of energy that refrigeration uses. These TES systems are the only technology that adds efficiency and the energy flexibility for extended load shedding for the cold storage industry. Facilities in the global cold chain that have implemented TES systems have seen an average kWh reduction of 26%, improved temperature stability, and energy cost reductions up to 50%. As utilities look for new ways to manage capacity and accommodate more intermittent renewables on the grid, TES technologies, especially in the energy-intensive cold chain, may help unlock new large-scale opportunities for improved demand management. De Bug Web

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