Page 337 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

324 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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TABLE 13.3
Characteristic Comparison between Batteries of Li-Ion Family
Chemistry, Lead-Acid, and Ultracapacitor
Energy Storage Type Power Density Energy Density Safety Cycle Life Cost
LFP 4 4 4 4 4
LTO 4 4 4 4 2
NCA 5 6 2 4 3
NMC 4 6 3 3 4
LCO 3 3 2 2 4
LMO 4 5 3 2 4
Lead-acid 3 2 3 2 6
Ultracapacitor 6 1 3 6 2

Note: The highest figure of merit, which is associated with best performance, is equal to six.

13.2.4 Other Types of Batteries and Energy Storage Systems
Some of the other common energy storage technologies include NiMH batteries, which can be
recharged and have higher energy density and shorter life cycle compared to nickel–cadmium
(NiCd) chemistries, but still suffer from strict maintenance requirements due to the memory effect.
The high rate of self-discharging is the main disadvantage of NiMH batteries [9].
Flow batteries, also known under the redox (reduction–oxidation) name, employ for storage
chemical compounds, dissolved in the liquid electrolyte and separated by a membrane. Such batter-
ies have been developed using zinc–bromide (ZnBr), sodium bromide (NaBr), vanadium bromide
(VBr), or polysulfide bromide (PSB). A unique advantage of flow batteries is that their energy
capacity is completely separated from their power, and therefore, the design can be scaled with more
flexibility [10]. Redox batteries can be matched very well for the integration of renewable energy to
the grid and for frequency regulation [11, 12]. A zinc–bromide (ZnBr) flow battery system, shown in
Figure 13.3, is used in the Power Electronics Laboratory at the University of Wisconsin–Milwaukee
(UWM) for demonstrating techniques of mitigating wind power fluctuations [12].
Energy can also be stored using electromechanical systems employing high-speed high-inertia
flywheels. The absorption and the release of electrical energy will result in an increase or decrease of
the flywheel speed, respectively. A main advantage is represented by the rapid response time, recom-
mending the technology especially for applications such as transportation, backup power, UPS, and
power quality improvement [13].
Other forms of energy storage suitable for large-scale grid applications employ pumped hydro
and compressed air. In the first case, water is pumped uphill in a natural or man-made reservoir,
for example, during off-peak hours, and released downhill to turn a turbine and produce electricity
when needed, for example, during peak hours. In the second case, air is typically stored underground
and then used as needed to generate electricity from a generator coupled to a turbine. High capi-
tal investment and installation costs, coupled with geological availability, environmental concerns,
and restrictions, represent challenges for these types of storage and may generate opportunities for
developments for electrical batteries.

13.2.5 BES Modeling and Test Setups

In order to design, analyze, and optimize the ESSs, suitable battery models, which can address the
main characteristics and the behavior for the application specifics, are a vital requirement. The bat-
tery model should be able to satisfactorily predict the dynamics of the system with a reasonable low