To broaden the use of various renew

To broaden the use of various renewable energy sources is one of
the core national energy policies in many countries, especially for
those areas without considerable traditional natural resources.
Popularization of renewable energies can be expected in the near
future due to the fact that energy prices increase dramatically and
the progress of various renewable energy technologies has
advanced in recent years. Different renewable energy technologies
such as wind, photovoltaic, biomass, ocean, and geothermal, to
name a few, are implemented in different areas, depending on
properties of their available natural resources. Among them, the
wind, photovoltaic, and biomass, are the most popular choices. One
drawback that cannot be neglected for these renewable energies for
electricity generation is their intermittent operation characteristics.
Thus some kinds of energy storage capacity are usually needed for
temporary storage of surplus electricity. The electricity supplied
from grid (for electricity) is especially important to give support to
time-dependent demands from various appliances. An electricity
supply/demand system with some renewable electricity sources
supported by the public grid can be defined as a HPS (hybrid power
system). The analysis and targeting of the HPS thus becomes one
important task for the generalization of renewable energies.