Storing
the Energy is an essential requirement for all facets of our life and
it has been recognized as a basic human need. It is the key to
accelerating economic growth, generation of employment, elimination of
poverty and growth of human development especially in rural areas. In
contrast to fossil fuel and nuclear-fuel based energy, the initial input
power of a renewable energy source is outside our control. The use of
renewable energy supplies constitutes a diversion of a continuing
natural flow of energy; there are problems in matching supply and demand
In a given time domain, i.e., matching the rate at which energy is
used. The mismatch varies with time on scales of months {e.g.. house
heating in temperate climates}, days (e.g., artificial lighting) and
even seconds (e.g., starting motors).
The
means of storing energy in a readily recoverable form when the supply
exceeds the demand for use at other times is known as energy storage.
Storage of primary fuels (e.g., coal, oil and gas) is also a form of
energy storage, but the term ‘energy storage’ generally applies to
secondary energy rather than to primary energy.
The performance of various energy-storage mechanisms can be measured and compared in (i) MJS (ii) MJm3 (iii) MJKg -1.
The first is a very important and deciding factor but is difficult to
estimate. The second is important where space is a prime consideration
(e.g., indoor applications). The third is considered when weight is
vital (e.g., in aircrafts).
NECESSITY OF RENEWABLE ENERGY STORAGE
1.
The effective utilization of intermittent and variable energy sources
such as sunlight, wind, etc. often requires energy storage
2.
In some circumstances, electrical energy may be generated ether on land
or at sea, at a location that is too distant from a consumption centre
for conventional transmission lines to be used for example Ocean Thermal
Energy Conversion. Means must then be found for both storing the energy
and transporting it economically to a load centre.
3.
Electrically propelled vehicles, which are expected to come into
increasing use, also require some form of energy storage. Since the
vehicle must carry its energy supply, the storage system must be readily
transportable.
4. Energy storage is also required
for ‘Load levelling’ in an electric utility to reduce the overall cost
of generating electrical power. More efficient plants may be operated
continuously at a rated power level, and the excess power during
off-peak period is stored for use when the demand exceeds the base load.
Thus, the use of less efficient units to meet the additional demand for
power during peak load periods is eliminated.
ENERGY STORAGE METHODS IN RENEWABLE ENERGY:
Energy
can be stored in various forms and the storage methods are classified
on the basis of the form in which it is stored. Some of the important
energy storage methods are the following:
1. Mechanical energy storage
(a) Pumped storage
(b) Compressed air storage
(c) Flywheel storage
2. Chemical energy storage
(a) Batteries storage
(b) Hydrogen storage
(c) Reversible chemical reactions storage
3. Electromagnetic energy storage
4. Electrostatic energy storage
5. Thermal (heat) energy storage
(a) Sensible heat storage
(b) Latent heat storage
6. Biological storage
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