Environmental Engineering Reference
In-Depth Information
then a similar opportunity likely exists for energy storage in hydroelectric facilities in
the United States and Canada. Installed hydroelectric capacities are listed [137] as
27.53 GWin Norway, usage 0.49, compared toU.S. capacity 79.5 GW, usage 0.42, and
Canadian capacity 89.0GW, usage 0.59 [137]. Present pumped hydro capacity in the
United States is 27 GW.
This suggests that the typically unused U.S. hydro capacity, about 46.1 GW, with
installation of uphill pumping capacity, could provide about 10% storage capacity for
all U.S. electric power.
10.6.1
Batteries: from Lead
-
Acid to Lithium to Sodium Sulfur
Beyond hydroelectric and hydrogen storage (presently nearly hypothetical), a prac-
tical approach to storage is in large-scale batteries [138].
A large-scale battery project undertaken by a U.S. utility entails 6MW of capacity
at a total cost of $27 million, thus a capital cost of $4.5/Wp or $0.64/Wh. The basic
units, rated at 1MW, are about the size of a double decker bus and use sodium
-
sulfur chemistry and operate at about 800
F. The battery is said to deliver 1MW for
about 7 h, so a more conventional rating for the capacity would be 7MWh per battery.
The batteries are said to be 80%ef
cient, andwill be used to smooth power fromwind
turbines and make that power easier to connect to their basic coal-
red generating
electrical grid. The batteries [138] will charge at night, when the wind is strong but
prices are low, and give the electricity back the next afternoon, when there is hardly any
wind but power prices are many times higher. A sodium
-
sulfur, NaS, battery of
4MWp, total 32MWh capacity and cost $25M, is reported (http://inhabitat.com/bob-
americas-biggest-sodium-sulfur-battery-powers-a-texas-town/) in Presidio, Texas.
This cost is then $0.78/Wh of storage. It appears that these stated costs are higher
than necessary, compared to $400/kWh
$0.4/Wh given by U.S. Department of
Energy for NaS batteries [139]. The same article estimates the cost of pumped
hydroelectric power as 0.1$/Wh.
Rechargeable batteries reversibly interchange chemical and electric energy. These
are categorized by open-circuit voltage (
V
), and electrical energy (Wh/kg) or (Wh/l).
The equivalent circuit is an electromotive force voltage, EMF, arising in the
underlying chemical reaction, with a series resistance (Figure 10.8).
A battery consists of an array of individual cells that are connected in series to
obtain a desired total voltage and in parallel to reach a necessary current capacity.
Often, the peak rate of discharge and maximum power output are important.
The traditional lead
-
acid automobile battery consists of dense and heavymaterials,
lead and sulfuric acid, and is used primarily in high current applications such as
starting conventional automobile engines.
Energy density is at a premium in modern applications, for example, in cellular
telephones, and also in larger scale applications such as hybrid automobiles. Li-ion
batteries are used in consumer electronics, notably cellular telephones and laptop
computers, because of their high energy density, in the range 160Wh/kg and
350Wh/l. The Li-ion battery has the largest portion of the portable battery market,
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