Flywheels have been used for limited mechanical energy storage in vehicles on a short-term basis. Also, supercapacitors are being developed that may eventually be able to substitute for batteries in electrical energy storage. Phase-change materials, with their latent heat, may be useful for thermal energy storage for heating a vehicle in winter. This would take some load off electrical or mechanical energy storage systems.

The only way to store electricity is a capacitor. Still pretty expensive but becoming slightly less so.

Storing energy in other forms are generally cheaper, but all have limitations.

Mechanical (compressed air, fly wheel, springs, etc.) have issues with either safety or efficiency, suffer from wear and require maintenance.

Batteries of any type are heavy and/or expensive and also require maintenance.

As further alternatives, chemical storage in the form of Methanol or H2 are relatively easy to convert to electricity in a fuel cell and very easy to refuel.

The least weight would be required if an external connection supplies most of the energy, as is done for trams and trains. Experiments are ongoing in different parts of Sweden with new versions of both in-road and overhead electrical supply for buses, trucks and cars.

One of the distinctive characteristics of the electric power sector is that the amount of electricity that can be generated is relatively fixed over short periods of time, although demand for electricity fluctuates throughout the day. Developing technology to store electrical energy so it can be available to meet demand whenever needed would represent a major breakthrough in electricity distribution. Helping to try and meet this goal, electricity storage devices can manage the amount of power required to supply customers at times when need is greatest, which is during peak load. These devices can also help make renewable energy, whose power output cannot be controlled by grid operators, smooth and dispatchable.

They can also balance microgrids to achieve a good match between generation and load. Storage devices can provide frequency regulation to maintain the balance between the network's load and power generated, and they can achieve a more reliable power supply for high tech industrial facilities. Thus, energy storage and power electronics hold substantial promise for transforming the electric power industry.

High voltage power electronics, such as switches, inverters, and controllers, allow electric power to be precisely and rapidly controlled to support long distance transmission. This capability will allow the system to respond effectively to disturbances and to operate more efficiently, thereby reducing the need for additional infrastructure. A major challenge being addressed by DOE is to reduce the cost of energy storage technology and power electronics and to accelerate market acceptance. 

OE's Energy Storage Program

As energy storage technology may be applied to a number of areas that differ in power and energy requirements, OE's Energy Storage Program performs research and development on a wide variety of storage technologies. This broad technology base includes batteries (both conventional and advanced), electrochemical capacitors, flywheels, power electronics, control systems, and software tools for storage optimization and sizing. The Energy Storage Program works closely with industry partners, and many of its projects are highly cost-shared.

The Program also collaborates with utilities and State energy organizations such as the California Energy Commission, Massachusetts Clean Energy Center (MASS CEC), Oregon DOE, Vermont, Hawaii, Washington, and New York State Energy Research and Development Authority (NYSERDA), to name a few, to design, procure, install, and commission major pioneering storage installations that are up to several megawatts in size. It also supports analytical studies on the technical and economic performance of storage technologies as well as technical evaluations of both ES systems components and operating systems. Enhanced energy storage can provide multiple benefits to both the power industry and its customers. Among these benefits are:

-Improved power quality and the reliable delivery of electricity to customers;

-Improved stability and reliability of transmission and distribution systems;

-Increased use of existing equipment, thereby deferring or eliminating costly upgrades;

-Improved availability and increased market value of distributed generation sources;

-Improved value of renewable energy generation; and

-Cost reductions through capacity and transmission payment deferral.

The Energy Storage Program also seeks  to improve energy storage density by conducting research into advanced electrolytes for flow batteries, development of low temperature Na batteries, along with and nano-structured electrodes with improved electrochemical properties. In Power Electronics, research into new high-voltage, high power, high frequency, wide-band-gap materials such as silicon-carbide and gallium-nitride is underway. In addition, advanced power conversion systems using advanced magnetics, high voltage capacitors, packaging and advanced controls to significantly increase power density and performance is ongoing.

For more information you can see de white paper "Electrical Energy Storage". 

To find the answer try:

http://www.iec.ch/whitepaper/pdf/iecWP-energystorage-LR-en.pdf

You can store electricity using proton exchange membrane (PEM) fuel cells and compressed hydrogen gas. This is the principle behind the the fuel cell electric vehicles ( FCEVs).

I was the Principal Investigator (PI) for the U.S. Department of Energy for the research on hydrogen storage on-board light-duty vehicles in other forms than compressed hydrogen gas. Hydrogen can be stored in metal hydrides, chemical hydrides, and adsorbents such as MOF-5 and activated carbon (AC). Hydrogen can also be stored in cryogenic form.

Please feel free to read my publications on this topic and they are all uploaded in the following:

https://www.researchgate.net/profile/Yehia_Khalil3

https://yale.academia.edu/YehiaKhalil

https://www.mendeley.com/profiles/prof-yehia-khalil/

Hope this helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, United Kingdom

Dear Natarajan,

Regarding your question, we have recently published a review paper that could be helpful even if it is focused on marine energy.

Regards,

Mohamed