The availability of significant storage capacity could help to decouple electricity supply needs from variable electricity demand. However, based on this analysis of PJM Interconnection hourly demand data from August 2012 to July 2013, a large amount of storage capacity would be required to reduce the variability in electricity supply needs over different time periods.
A previous Today in Energy article noted that because the electric industry lacks large-scale storage, supply has to adjust in real time to match demand. Hourly demand varies significantly over the day, week, and year. This suggests three potential modes for framing storage capacity requirements. Storage can charge and discharge over a day, yielding a flat supply need equal to the daily average of hourly demand (see chart above); over a week at the weekly average, or over the year at the annual average. This analysis shows that the storage capacity requirement grows significantly as storage operations move from the daily to the weekly to the annual demand cycles.
There are a variety of storage technologies used in the electric industry, such as pumped storage, compressed air, and flywheels. These technologies convert electricity into another form of energy for storage: the potential energy in water pumped uphill to a reservoir and in compressed air, and the momentum in a weight spinning at high speed. But storage in the amounts needed to flatten daily, weekly, or annual supply needs, while meeting instantaneous demand, is far above the current available level.
However, if large-scale storage of electricity were feasible and economical, electricity supply could be separated from instantaneous demand, thereby reducing the requirement for supply.
In theory, it may be possible to store electricity overnight on a large scale to supply afternoon highs (daily), on weekends to supply weekday highs (weekly), and in the spring and the fall to supply summer and winter peaks (annual). Each of these storage opportunities would likely require different storage approaches and technologies. Read the rest at:
EIA
http://www.eia.gov/todayinenergy/detail.cfm?id=13131&src=email#
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