Handbook of Energy Storage for Transmission or ... - W2agz.com
Handbook of Energy Storage for Transmission or ... - W2agz.com
Handbook of Energy Storage for Transmission or ... - W2agz.com
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EPRI Proprietary Licensed Material<br />
T&D SYSTEM ENERGY STORAGE SYSTEM APPLICATIONS<br />
• Analysis <strong>of</strong> hourly wind data to identify opp<strong>or</strong>tunities <strong>f<strong>or</strong></strong> energy st<strong>or</strong>age to enhance<br />
the value <strong>of</strong> daily and seasonal variations <strong>of</strong> the wind resource, e.g., characterizing<br />
daily “time-shift” available wind energy from <strong>of</strong>f-peak to on-peak usage intervals<br />
and seasonally switch the energy st<strong>or</strong>age system from wind stabilization to grid<br />
supp<strong>or</strong>t functions such as AGC.<br />
• Development <strong>of</strong> a business model based on the prevailing electricity rate structure,<br />
e.g., establishing arrangements in which <strong>com</strong>mitments to supply on-peak firm<br />
power are hedged via power purchased from the grid, and in which <strong>of</strong>f-peak energy<br />
to recharge the energy st<strong>or</strong>age media is purchased from the grid during periods <strong>of</strong><br />
insufficient wind.<br />
• Assessment <strong>of</strong> the incremental value <strong>of</strong> energy st<strong>or</strong>age, i.e., conducting parametric<br />
assessments to identify the optimal amount <strong>of</strong> energy st<strong>or</strong>age to maximize revenue.<br />
The primary energy st<strong>or</strong>age function is analogous to load leveling in that the energy<br />
st<strong>or</strong>age medium is charged to capacity by <strong>of</strong>f-peak wind generation <strong>or</strong>, as required,<br />
supplemental generation, and discharged to supplement direct wind generation during<br />
periods <strong>of</strong> peak load. This application also requires an interactive PCS to dynamically<br />
supplement on-peak direct wind generation and to st<strong>or</strong>e <strong>of</strong>f-peak wind generation in<br />
response to temp<strong>or</strong>al variations in the wind resource. 3<br />
Acc<strong>or</strong>dingly, this system can<br />
provide reactive power and voltage/frequency supp<strong>or</strong>t during those periods when it is not<br />
engaged in charging <strong>or</strong> discharging the energy st<strong>or</strong>age media. The value <strong>of</strong> energy<br />
st<strong>or</strong>age is derived from both shifting <strong>of</strong>f-peak generation to serve peak load and from<br />
ensuring that transmission assets are efficiently utilized during energy delivery.<br />
3.2 <strong>Energy</strong> <strong>St<strong>or</strong>age</strong> System Requirements<br />
Top-level technical requirements <strong>f<strong>or</strong></strong> energy st<strong>or</strong>age systems to serve the applications described<br />
above are listed in Table 3-1. System power, discharge duration, and energy capacity have been<br />
selected as representative <strong>of</strong> <strong>com</strong>mercial “building blocks” based on market assessments, with<br />
specific values chosen to facilitate assessment. Likewise, system response time and duty cycle<br />
are representative values <strong>f<strong>or</strong></strong> each application.<br />
Requirements <strong>f<strong>or</strong></strong> system efficiency are also representative <strong>of</strong> <strong>com</strong>mercial options <strong>f<strong>or</strong></strong> these<br />
applications, but the basis noted <strong>f<strong>or</strong></strong> their calculation deserves further explanation. Three <strong>of</strong> the<br />
four applications identified use grid interactive PCSs and must respond within milliseconds to<br />
application demands. This functionality requires that the power electronics be maintained in<br />
“hot” standby <strong>f<strong>or</strong></strong> a high fraction <strong>of</strong> their duty cycles, which typically entails a loss <strong>of</strong> about 2%<br />
during standby. This loss must be <strong>com</strong>bined with power conversion losses (e.g., rectifier,<br />
inverter and DC battery efficiencies), as well as other system inefficiencies such as standby heat<br />
3<br />
<strong>Energy</strong> st<strong>or</strong>age implemented via a PCS integrated with wind turbine output can also be used to stabilize sh<strong>or</strong>t<br />
duration (seconds to minutes) wind variations which can cause excessive voltage and/<strong>or</strong> frequency excursions on the<br />
grid. The economic value <strong>of</strong> these functions is difficult to quantify because <strong>of</strong> the need to integrate wind generation<br />
and energy st<strong>or</strong>age PCSs. A NAS battery demonstration <strong>of</strong> this application is briefly described in Ref. 3-1.<br />
3-3
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