It is known that energy is one of the most important foundations of modern life. If we could take advantage of the solar energy that reaches the earth, we would have basically solved the planet’s energy problem.
Generally, in order to take advantage of solar energy, we first transform it into some other forms of energy so we can store it. There are two ways to store solar energy:

• In the form of heat through solar thermal systems
• In the form of electricity through photovoltaic systems

Electricity storage is an important condition for using the maximum of Renewable Energy Sources. Storage of electricity can reduce the operating cost of an electricity plant, since it would be desirable to save excess energy in times of lower consumption to cover peak hours. In addition, on-site energy storage can cover consumers in the event of power outages.

In what ways can we make electricity storage possible?
Storing electricity is not an easy task. Some of the most common ways used around the world are:
• Power storage with dynamic energy
• Electricity storage with kinetic energy
• Electricity storage with chemical energy

• Electricity storage with dynamic energy is achieved in two ways:

-Pumped hydroelectric energy storage, which uses excess electricity (during low demand) to transfer water from a lower to a higher water reservoir during the night where we have excess power. The main limitation on the development of this method is the high cost of manufacturing artificial reservoirs, as well as geological, geographical and environmental constraints.
-Compressed air where off-peak electricity is used to compress and store air in airtight underground caverns. When needed, the stored air is released, heated and throttled through a gas turbine.

• Energy storage via kinetic energy is achieved through flywheels that store kinetic energy in a cursor and function as a mechanical battery. They both act as generators and sometimes as engines. So far, they are at an experimental stage, they are high cost and not applicable to a power plant.
• Electricity storage can also be accomplished through chemical energy in two ways:

-The most common way of storage, especially in the photovoltaic sector, is by using batteries. The advantages of those        systems are that they can achieve energy storages from excess energy, they can cover instantaneous peak demand                loads and they have long service life. On the other hand, the major cost of purchase, increased complexity and high              maintenance costs are the major disadvantages.
– An alternative way of storing electricity is by producing hydrogen by ‘’breaking water’’. Hydrogen is considered to be      the main fuel of the future since it is created by water, which is an inexhaustible energy source. Its main advantages are      that it is a renewable energy source, has no negative impact on the environment and has the capability to store and              transport over long distances through pipeline networks. Correspondingly, its disadvantages are that it has low energy        density per unit volume and that its production and liquefaction costs are still high.

Due to the small and limited network of Cyprus, energy storage is a necessary factor for the proper exploitation of Renewable Energy Sources and especially of photovoltaic systems that give the lowest production cost!