You can always store solar electricity indefinitely as hydrogen (which is an energy carrier rather than an energy storage medium) using a hydrogen system (water electrolyzer, hydrogen storage, and fuel cell). However, the cost is very high and the efficiency (defined here as the output electric power from the hydrogen system to the input electric power into the hydrogen system) is still low for most hydrogen systems (about 90% for electrolyzer, 95% for storage, and 50% for fuel cell)..

Modern batteries (especially Li-ion) are proving to be more efficient and durable everyday. So unless you plan on storing very large quantities of solar electricity for your research, I would recommend batteries. If things are not very clear, then the only choice becomes conducting a thermoeconomic comparison between your different storage alternatives..

I hope this helps!

You can always store solar electricity indefinitely as hydrogen (which is an energy carrier rather than an energy storage medium) using a hydrogen system (water electrolyzer, hydrogen storage, and fuel cell). However, the cost is very high and the efficiency (defined here as the output electric power from the hydrogen system to the input electric power into the hydrogen system) is still low for most hydrogen systems (about 90% for electrolyzer, 95% for storage, and 50% for fuel cell)..

Modern batteries (especially Li-ion) are proving to be more efficient and durable everyday. So unless you plan on storing very large quantities of solar electricity for your research, I would recommend batteries. If things are not very clear, then the only choice becomes conducting a thermoeconomic comparison between your different storage alternatives..

I hope this helps!

Hot water system are also treated as storage devices in the realm of Smart Grid, even though they do not typically supply electricity back.

Yes you are right Manaz, We can use solar pond to store (for a little time) the solar heat in salted water in solar pond. Thereafter, by using some appropriate cycle (like carnot cycle), the heat can be converted into electricity. But the efficiency is very important parameter in this regard.

Yes, of course, in such cases efficiency would be low. The hot water systems that I referred are those used in domestic applications. Such as hot water storage tanks. These systems could be used to store excess energy produced by solar PV and then the hot water could be used at a later time (during night).

http://en.wikipedia.org/wiki/Hot_water_storage_tank

The above article claims that a heavily insulated hot water storage tank can retain heat for days.

Have a look at http://www.docunator.com/bigdata/1/1367142535_c566e7d75e/reviewexample2.pdf. There are more of these papers on the internet.

You can store thermal energy in phase change materials (it is more for buffering). For long term storage you could think of thermochemical storage materials. In these materials heat can be stored by forcing crystals to hydrate.

Water electrolyzer can be opted .. to split hydrogen from water and then can be fed to fuel cell

Also just have a look at REDOX flow batteries ...

Thank you partha, i will get to know about these systems

You can look at liquid metal storage

http://www.ambri.com/technology/

Thanks Prof. Prinsloo for your informative answer.

There are many more.  Pumped water storage.  Compressed air.  Flywheels are quite efficient and capable of delivering large power output.  Super capacitors.  Using PV to drive desalinization plants can be thought of a method of storage.

World's first solar battery claimed to "run on light and air"

http://www.gizmag.com/solar-cell-battery-hybrid/34119/