Page 244 - Hybrid-Renewable Energy Systems in Microgrids

Solar–wind hybrid renewable energy system 221

there is no other source of energy. Standalone systems, consists of the photovoltaic
panels as sources, are often the most cost-effective choice for applications far from the
utility grid. These kinds of systems are widely used in applications like lighthouses
and other remote stations, auxiliary power units for emergency services or military
applications, and manufacturing facilities using delicate electronics [8]. However, the
standalone systems suffer from characteristic disadvantages like low capacity factor,
excess battery costs and finite capacity to store electricity which results in the waste
of the extra energy generated [9].
Some important features of standalone systems are as follows.

• In the standalone RES, the operational capacity is designed to match the demand.
• The demand for the local region has the maximum priority in this kind of systems.
• Standalone RES is ideal for remote locations applications, where the system is required to
operate at low plant load factors.
• As the typical standalone RESs are usually based on renewable energy technologies like
solar PV, which are not available consistently throughout the year, the operation of this kind
of systems is mostly seasonal.
• As these systems are not connected to the utility grid, they need batteries for storage of the
excess electricity produced during off-peak demand periods, which leads to an extra battery
and storage costs. Otherwise the excess power generated must be thrown away.
Both grid connected and standalone have their own advantages and disadvantages.
The choice of grid connected or standalone RES depends on a number of factors. Both
types of systems mostly operate on renewable energy sources resulting in a significant
reduction in the emissions and climate change. The standalone systems are preferred
in the applications where the accessibility to the grid is the main issue. They are also
suitable to supply electricity to hilly regions and remote villages.
Other major factors affecting the decision to adopt grid connected systems or
standalone systems are the feasibility and load factors. In grid connected systems any
excess generation can be fed back to the grid. Therefore, the grid connected systems
are not affected by the low load factors which are typical characteristics of rural elec-
tricity scenario. Since the grid acts as an infinite storage unit, it facilitates continuous
operation of the system also eliminates any additional costs on storage batteries.
However, the extension of the grid excessively expensive in some rural or remote
areas. In such applications, the standalone systems are inevitable choices. Therefore,
before designing the RES for any application, it is important to study the necessary
and sufficient conditions under which the standalone and grid connected systems
become feasible.

1.3 Hybrid renewable energy systems

A drawback, which affects both the solar and wind application, is their unpredictable
nature and dependence on meteorological changes. Due to which, the variations of
generating solar and wind energy may not match with the time of distribution of load
demand [10]. This shortcoming affects the system’s energy performance and results in
batteries being discarded too early. The independent use of both energy resources may
result in considerably over-sizing, which makes the design less cost effective. It has