Technical Dimension

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1. How does energy storage work?

Energy storage devices are “charged” when they absorb energy, either directly from renewable generation devices or indirectly from the electricity grid. They “discharge” when they deliver the stored energy back into the grid. Charge and discharge normally require power conversion devices, to transform electrical energy (AC or DC) into a different form of electrical, thermal, mechanical or chemical energy.

Energy storage can be used among to store surplus energy from intermittent renewable sources, such as solar PV and wind power, until it is required.

There exist many different solutions: chemical (e. g. batteries, natural gas, hydrogen, electrolysis), mechanical (e. g. pumped storage plants, compressed air energy storage, pumped heat electrical storage, compressed storage of liquid air), and thermal (e. g. molten salt, bulk goods) storage of energy. Reflecting technical necessity various solutions are possible depending on whether a larger number of small, local storage facilities or a smaller number of large, central facilities are to be used.

The two main parameters to differentiate energy storage solutions are:

– Power: can reach from a few kW (e.g. in end user applications like residential PV) to MW (large scale generation plants) up to hundreds of MW or even GW for centralised bulk energy storage devices.

– Time: storage may perform charge or discharge functions over a few seconds or minutes (e.g. for grid services like frequency stabilisation), minutes to a few hours (smoothing or time shift of renewable generation), up to days and weeks (balancing long term fluctuations in generation and consumption). Multiplying power by time delivers the capacity or energy content of the storage.

2. What technologies do already exist to store energy?

Different energy storage systems – centralised and decentralised – consider different technological possibilities, which EASE organises in 5 energy storage classes: chemical, electrochemical, electrical, mechanical and thermal.

NB: The list below intends to be illustrative rather than exclusive. EASE is continuously scanning for new technologies and updating the list accordingly with the most prosperous ones.

Chemical energy storage includes:

  •  Hydrogen
  •  Synthetic Natural Gas

Electrical energy storage includes:

  • Super capacitors
  • SMES

Electrochemical energy storage may be subdividing in two sub-families:

  1. Classic batteries
  • Lead acid
  • Li-on
  • Li-Polymer
  • Li-S
  • Metal Air
  • Na-Ion
  • Na-NiCl2
  • Na-S
  • Ni-Cd
  • Ni-MH
  1. Flow batteries
  • Vanadium Red-Ox
  • Zn-Br

Mechanical energy storage includes:

  • Fly wheels
  • Adiabatic Compressed Air
  • Diabatic Compressed Air
  • Pumped Hydro
  • Pumped Heat Electrical Storage
  • Compressed Storage of Liquid Air

Thermal energy storage includes:

  • Heat (hot water/PCM)
  • Molten salt (Heat/CSP thermal)
  • Packed-bed heat storage
  • Smart Electrical Thermal Storage
3. How do the different technologies compare?
EASE represents all energy storage technologies. At this stage, EASE does not position one or another technology for a given application, but will work on an analysis of the different application requirements and enable benchmarking of various technology options.
4. How can energy storage support the grid?
Storage cannot provide a replacement of the transmission and distribution grid economically, but does allow for technical optimisation of generation, transportation and consumption by allowing for a time-shift between these three thus contributing to energy security. Storage is a means of postponing grid investments to a time, when this is more sensitive from the market point of view. Grid investments are necessary to integrate markets. By enabling a mismatch between generation and consumption, storage also allows for the decrease in design specifications of the transportation system: not to match possible maximum loads, either from generation or consumption, but rather an optimised solution can be realised.

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