Energy Storage is key for Renewable Energy Sources’ penetration into power generation. Renewable Energy Sources (RES) have become of particular importance in the establishment of green, environmentally friendly applications; thus they constitute a crucial piece of the puzzle for achieving global environmental, economical and social/political sustainability.

However, we find that not all energy potential of Renewable Energy applications can yet be harnessed by existing production systems. Different applications of RES exhibit different utilization and/or efficiency levels subject to technological, economical, environmental, morphological or other factors that influence their performance and viability.

Such an example is wind-generated energy, which is greatly influenced by factors such as:

  • Unpredictability of environmental conditions;
  • Intermittency of wind;
  • Ad-hoc wind blowing leading to non-synchronised demand & supply energy generation;
  • Unreliability of wind;
  • Design and/or other technological limitations.

These factors illustrate the need for managing demand and supply fluctuations of electrical power. They also illustrate that the power output from Renewable Energy Sources is not as reliable as that obtained from traditional sources (fossil fuels) and not easily adjustable to fluctuations of energy demand. In order to be able to supply energy when energy is demanded it is necessary to utilize costly ancillary services within the production chain, such as spinning reserves or increasing production capacity. Consequently, this ‘costly’ need has lead to a whole area of technological development and industrial practices aiming to identify viable and improved solutions such as the design of ‘smart-grids’ and ‘distributed networks’, decentralized production and mainly, the incorporation of energy storage within the power generation network; thus the ability to store energy becomes of utmost importance within the power supply chain particularly for the penetration of RES into the power market.

Energy storage can provide an economical and environmentally advantageous method of responding to fluctuations in demand provided that as the stored energy is not generated from processes or fuels impacting the environment (such as carbon-generating fossil fuels).

The storage solution enables excess electricity produced at ‘off-peak’ hours, to be stored and used later to meet demand spikes, thus reducing the need for expensive spinning reserve and using existing power plants more efficiently (peak shaving and load leveling of demand). In this way we can overcome RES’ main disadvantage, thus establishing RES as reliable sources of energy production.

Different energy storage methods exist, each with different characteristics in terms of its ideal application environment, its interface with different technologies, or purpose of application. For example, given a location with morphological potential (e.g. ground height potential) and environmental potential (e.g. wind kinetic energy) a hydro-storage solution may be most appropriate; i.e. using electricity produced from wind power at off-peak-hours to pump water at a higher level reservoir (e.g. dam) which will then be available to produce electricity (by down fall) at peak-hours by hydro-power.

Several other storage methods exist, each incorporating different technologies such as hydrogen or natural gas storage (utilizing fuel cells or Internal Combustion Generators), thermal energy tanks (utilizing solar power), and others. Suitability of each method is dictated by a range of factors and by the specific circumstances.

The main technologies for storing energy are briefly mentioned below:

  1. Flywheel storage
  2. Batteries Storage
  3. Super capacitors
  4. Gas Storage (Hydrogen)
  5. Pneumatic storage (liquid piston or CAES)
  6. Stored Thermal energy

As the market for electric power is becoming increasingly regional, requiring additional interconnections between power grids to improve their efficiency, storage technologies are becoming increasingly important.The interfaces between energy generation from RES and storage technologies facilitate the utilization of next generation technologies in smart-grids and future power generation systems. Such networks, utilizing energy storage, can provide an efficient and effective solution in meeting with energy demand and uninterrupted supply of high quality electrical power.

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