Page 334 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

Batteries and Ultracapacitors for Electric Power Systems with Renewable Energy Sources 321

stored. The energy can be released by converting back to the electrical form when needed. There are
several types of energy storage technologies, including electrochemical, mechanical, and electrical/
magnetic fields. Figure 13.1 shows the classification of electrical ESSs and examples for each cat-
egory. Electrochemical energy storages are batteries in which electrical energy is stored as electro-
chemical reactions and then released by changing back to electrical energy.
Lead-acid (LAB), lithium-ion (Li-ion), nickel–metal hydride (NiMH), sodium sulfur (NaS), and
reduction–oxidation (redox) flow batteries are the most common electrochemical ESSs. Electrical
energy is also changed to kinetic energy and saved in mechanical ESSs such as flywheel, com-
pressed air, and pumped hydro. In capacitors, electrical energy is saved in the electrical field estab-
lished between the capacitor plates.
Mechanical energy storage technologies have primarily been adapted for large-sized storage sys-
tems, while batteries and capacitors cover a wide range of applications from costumer electronics
to industrial and utility-level applications. Table 13.1 reports an estimation of total electrical energy
storage capacity that is currently installed worldwide, according to the Electric Power Research
Institute (EPRI) [1].
Currently, the majority of bulk storage capacity worldwide is in the forms of pumped hydro and
compressed air, while the rest of storage technologies account for less than 1% of the total capacity.
However, due to geographical limitations, distance from the demand, and also initial capital cost,
other storage technologies, which are accessible everywhere, are gaining market share. Batteries are
receiving significant attention for industrial and grid applications, due to their portable characteris-
tics, and they are considered to be the most promising energy storage type of future. Various charac-
teristics of the energy storage technologies, which have been extracted from [1–4], are summarized
in Figure 13.2 and Table 13.2.

Lead-acid

Lithium-ion
(Li-ion)

Electrochemical NiMH

Sodium sulfur
(NaS)
Redox flow

Flywheel

Energy Mechanical Pumped hydro
storage

Compressed air

Electric double
layer
Ultracapacitors Pseudocapacitor

Hybrid

FIGURE 13.1 Different types of energy storage systems (ESSs).