Page 17 - Hybrid-Renewable Energy Systems in Microgrids

2 Hybrid-Renewable Energy Systems in Microgrids

to the electricity has become a foremost concern in rural regions. Renewable energy
resources, mainly PV and wind, can be a good solution for rural electricity supply
[3,4]. This arrangement can provide a reliable power supply and can be actually more
profitable than the traditional electrification solutions to the rural areas, particularly in
telecommunications, hazardous chemical factories in remote location, hilly areas and
small islands, etc.
Nowadays, MG (grid-connected, standalone mode) is the paramount infrastruc-
ture of a smart grid concept. One alternative to effectively utilize the RES is to ensure
the reliability of power supply in remote areas, reducing uncertainty impact in the
grid. One way to contribute to the usage of cleaner energy is to use hybrid RES in an
off-grid mode, that is, independent operation of the main electric grid. The installed
capacity of the MG can be based on the specific application, that is, for buildings,
a community, or an entire small town, as well as the renewable energy availability
forecast in that area, storage capacity, and load demand. In many countries, off-grid
mode MG hybrid energy systems are in usage to connect and supply the electricity
in remote areas as an alternative to the diesel-generator standalone generation system
[5].
In most applications, hybrid renewable energy resources are the parallel combina-
tion of PV/wind or one of the renewable energies with a conventional energy source.
However, different system dynamics and potential large variations in RES can impact
the power quality and reliability of the MG. Energy storage and diesel generator are
the other considered primary sources of energy source in MG to maintain the system
reliability under the RES intermittency behavior over the period. Diesel generator is
primarily used to maintain the primary and secondary frequency controls, and stor-
age system can also be used as primary or secondary frequency controller based on
their capacity. Consideration and preference is given to the RES to charge the storage
system to keep the operation cost at its minimum. Storage system provides operational
flexibility, reducing the system operation costs and ensuring the overall MG reliabil-
ity. However, the degree of storage system support depends on the energy storage
capacity and the possible power imbalance resulting from the wind speed/solar irradi-
ance variation in that area.
Either in standalone or grid-connected mode, MG suffers from dynamic and tran-
sient stability issues during and after the various significant disturbances. Typically,
in a grid-connected mode, it is preferable to operate the MG in islanded mode at the
occurrence of faults in the utility grid to minimize the outage time and load shedding
in MG. Maintaining the stability of a standalone MG can be more costly in terms of
cost–benefit analysis. Grid-connected MG can be connected with the main electric
grid, whereas the standalone MG is more appropriate when the main interests are
related to the following:

• Constructing and maintaining power transmission lines are expensive or technically con-
strained.
• Remote rural areas, where connecting to the main grid is impossible.
• Preference is given to the renewable energy resources for environmental concern.
• Lower operating cost.