Page 21 - Hybrid-Renewable Energy Systems in Microgrids

6 Hybrid-Renewable Energy Systems in Microgrids

auxiliary support sources. Spinning reserve is needed to ensure steady-state operation
of the system as well as to avoid system collapse during the worst weather conditions.
With the reliability concern of the PV–wind-based hybrid MG, diesel and storage
system can be a viable option to ensure the quality and reliability of the MG. Because
the storage system is predictable and dependable in terms of dispatchability, quick
response storage system provides the feasibility of reliable standalone hybrid power
system. The combination of RES and storage system is appropriate in the sense of cost
and benefit, as well as for providing customer comfort. Storage system can ensure no
load is shed especially during the peak period of the day by storing the surplus energy
in the daytime, thereby reducing the total energy cost. The storage system can be in
several forms such as battery [10,11] or any other storage system as explained in Sec-
tion 5, and mainly depends on the costs of the storage system and other preliminary
constraints. Along with the storage system, conventional diesel [12] or prospective
biodiesel is used in some places [13–15] to make sure that load demand can be ful-
filled if the storage capacity is not enough to satisfy the load. However, increasing the
capacity of the energy sources may guarantee a higher reliability of the system but will
cause additional costs to the system. Therefore cost–benefit ratio is always crucial in
designing a hybrid system.

4 Optimization of hybrid system

A MG, regardless of the grid-connected or standalone operation mode, must ensure
reliable, efficient, and cost-effective operation. The purpose of the optimization is
to reduce the cost of the system at the best operating point while satisfying all the
required constraints; mainly technical and economic. Optimization not only depends
on the operation and maintenance of the system, but also on the proper dispatch strat-
egy with sufficient storage system to provide the operational flexibility and make the
proper use of maximum generation from the renewable energy to minimize the opera-
tional costs.
An optimization is a formulation of a mathematical problem based on the pre-
ferred outcome within the design constraints. Designing an optimum arrangement of a
PV–wind hybrid RES requires extensive research on wind speed and solar irradiance
throughout the year for that particular area. Without an appropriate estimation of the
preferred site, optimization will not be the optimal solution, as incorrect sizing will not
be able to satisfy the load demand, or storage size may not be sufficient to store the
available surplus energy. Optimal sizing problem is formulated to find the kind and
capacities of the RES, storage, and generator (in standalone) to achieve the expected
results while ensuring the necessary constraints are in their best limit. To achieve
optimal design, several design methodologies, tools and techniques, and algorithms
have been widely used by the researchers. A large number of research work has been
done and published on design methodologies of an optimal, cost-effective hybrid sys-
tem to ensure the fulfillment of load demand [8,16]. Several optimization algorithms
have been used to solve the optimization problem [17–19]. Several computer-aided