Handbook of Energy Storage for Transmission or ... - W2agz.com

EPRI Proprietary Licensed Material
Regenesys Electricity Storage Technology
• Maximum and minimum charge to discharge terminal voltage ratios: Innogy declines to
disclose information at this level of detail. However, from overall round trip efficiency of
60-65% projected by Innogy, the PCS efficiency of 95% estimated above, and given 5-10%
shunt current and pumping power losses, it can be inferred that the voltaic efficiency during
10-hour discharges followed by 10-hour charge will be 70-75%. Then, given a 10%
variation of OCV for a 100% change in state-of-charge, the maximum charge to discharge
terminal (DC) voltage ratio can be estimated as very approximately 1.5, while the minimum
value of this ratio will be very approximately 1.3.
• Typical electrical power limits: The current reference design of a Regenesys plant is for a
power output of 12MW. Larger power capabilities are of course possible According to an
Innogy spokesman 2 the cell stacks can be discharged at 50% higher power than the nominal
amount more-or-less continuously, although the efficiency will be lower than at the rated
power output, see above. There will be no theoretical lower limit to power output, although
the efficiency will be lower for very long (very low power) discharges because of the
requirements to power auxiliaries.
• Typical storage capacities: Innogy states on their Web page that 5 hours of discharge
capacity is the minimum being considered, while our estimation (see Costs and Benefits
section, below) indicates ten hours as more economically attractive than 5. Innogy have
indicated a minimum storage capacity of 100MWh, with higher capacities being more
attractive from an economic perspective.
• Typical energy to power ratios: Although it is theoretically possible to design a Regenesys
energy storage plant with a very short discharge time, it appears that longer discharge times,
with say energy to power ratios of ten or thereabouts, are more economically attractive. This
is because Innogy believes that multiple economic benefits can realized with the higher
energy to power ratios. (See Applications section.)
• Typical response time for standby to full-power output: On their web site, Innogy quote a
response time of 100ms for standby to full-power output. There are several factors that can
influence this value, the most important of which is the period for which the full-power
output is required. For shorter discharge times (as for transmission stabilization) there should
be adequate capacity in the electrolytes contained within the cells for a much shorter
response time, assuming of course that the converter is configured and programmed to
provide the response. The response time quoted by Innogy is thought to reflect what is
required for the Little Barford demonstration plant (see Demonstration Programs, below)
rather than that needed to satisfy other applications.
2 Mark Kunzt, Innogy USA, Chicago. Except where otherwise noted, Mr. Kunzt supplied other information credited
to “Innogy” in this chapter.
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