Page 29 - Hybrid-Renewable Energy Systems in Microgrids

14 Hybrid-Renewable Energy Systems in Microgrids

Table 1.3 Summary of energy storage types in MG

ESS type Energy sources Purpose References

Battery Wind–PV–battery Feasibility of hybrid system [11]
to meet demand, installa-
tion, and operation costs
Pumped hydrostor- PV–wind–ESS Operation cost minimiza- [42]
age (PHS) tion and reducing burden
to the grid
Flywheel energy PV–wind–ESS To improve the system [44]
storage system stability
(FESS)
Compressed Air Wind–diesel–ESS Investigating the prospect [45]
Energy Storage of CAES in MG
(CAES)
Supercapacitor (SC) DG–ESS Providing voltage support [47]
Superconducting Wind–ESS To improve system dy- [48]
magnetic energy namic stability
storage (SMES)

6 Stability concerns in a HRES MG system

Power system stability is always a great concern because of the dynamic pattern of
load demand and generation. Stability of a RES-based grid-connected MG can be
supported by the grid generations, but in an islanded mode MG, maintaining the sta-
bility is much difficult, as there is no support from the grid. Higher capacity and other
stability arrangement may ensure the stability, but this can increase the system's costs.
Therefore a proper cost–benefit analysis is very important to ensure the stability of the
MG within economic operation.
The main stability concern related to the RES-based MG is the consistent voltage
and frequency of the system. Because the RES does not provide constant output power,
this affects the system's voltage and frequency, mainly during the peak generation
of RES and low wind speed/shading on the solar panel. Hybrid arrangements of the
RES may reduce larger fluctuations than that of a single source, thereby providing
more energy security and improved system reliability. However, in addition to pos-
sible shading during the daytime, solar is available during the day only, and therefore
the hybrid combination with PVs alone cannot fulfill the energy security requirement
during the nighttime. Therefore to reduce the intermittency impact on the MG in a
PV-connected hybrid system, an additional auxiliary source such as storage system
and diesel generator must be added to lessen the adverse impact of RES to the grid
(grid-connected mode) or to the load. This arrangement can ensure the voltage and
frequency stability of the system. This arrangement is also applicable for wind-only
operation mode. A study of frequency regulation by a conventional diesel generator is