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Thermal Energy Storage: Putting Green Solutions on Site
Thermal Energy Storage: Putting
on SiteBy John E. Flory, Loren W. McCannon, Stan Tory,
Donald L. Geistert, and James PattersonA recent study coordinated by the California Energy Commission shows how stored-cooling applications provide both environmental and competitive benefits in a summer-peaking market.As California prepares for a more competitive electric future, the California Energy Commission (CEC) is taking another look at some key customer technologies. One CEC program, known as Opportunity Technology Commercialization (OTCOM), carries a mission to boost market penetration of energy technologies that offer "compelling energy, environmental, diversity, and economic
development benefits." OTCOM selected thermal energy storage (TES) as just such a promising technology. As defined here, TES denotes a chiller system operated during the night to store energy for air-conditioning use during the day. Traditionally, building owners have employed TES to trim power costs by reducing peak-demand charges. But TES offers other benefits for both energy users and suppliers.
To address market barriers that might stand in the way of TES applications, OTCOM organized a collaborative of TES users, utilities, governmental agencies, consultants, and TES manufacturers. As a first step, the collaborative enlisted a study to measure the potential impacts of TES in California. The highlights of that study, Source Energy and Environmental Impacts of Thermal Energy Storage, are presented here.
The study split the analysis of the energy use by TES into two components:
s Source energy use: Units of fuel (in Btus) required at the power plant source to supply one kilowatt-hour of energy. (The study presumed that shifting generation away from the peak would reduce the energy needed to supply each kilowatt-hour.)
s Site energy use: Electric energy (in kilowatt-hours) required to provide a ton-hour of cooling at the customer site.
To analyze the source energy use of TES, the study focused on the two largest electric utilities in California (em Pacific Gas and Electric Co. (PG&E) and Southern California Edison Co. (SCE) (em which together supply almost three-fourths the electricity used in the state. It employed two cost analysis methods: the "incremental energy method" (the standard planning method used in California1) and a variation termed the "marginal plant method."2 (The primary difference is that the incremental energy method captures the fuel savings from reduced need for "unit commitment" (em i.e., committing a power plant unit to run much of the day to be available to meet daily peak demand.)
The results showed that the source energy savings for a particular TES system at a particular building depend on a number of factors, including:
s Building usage: the building's normal air conditioning usage pattern without TES (em e.g., What percent of the cooling is summer vs. winter, or day vs. night?
s Thermal system: the design and operating strategy for the
TES system (em e.g., Is the TES storage tank sized so that the air-conditioning compressor runs only at night (full storage) or all day (partial storage)?
s Utility's fuel mix: the characteristics of the utility supplying the electricity (em e.g., How much hydroelectric power is available?
s Cost tracking method: the method