There are 6 points on the energy flow where energy can be stored and each has benefits and drawbacks. The link below is just the article that inspired this post (but does not add much). These points are:
1) storing the energy source before being gathered
2) storing the gathered energy before transmission
3) storing energy close to the users or within the transmission system
4) storing energy by the users
5) storing energy within the appliances that use the energy
6) storing converted energy after the appliances.
#1 is exemplified by hydro power dams holding back all that water. For renewable energy, few can be stored (cannot hold sunlight or wind) and the energy density is lower so there are environmental concerns with this (as is evidenced by the decommissioning of many hydro dams)
If the energy source is far from the users, transmission costs and losses come into play. To reduce the size of the transmission lines, it is optimal for the lines to be running at maximum capacity 24/7. To do this, energy can be stored at the source (#2) to take care of the excess or deficiency of the production of energy from the source. Some wind towers contain batteries to keep the power flowing steady even if the wind is not steady. Some thermal solar systems store some of the heated fluid (or solids) to continue electricity generation during cloud cover or even after dark for as much as 24 hour continuous generation.
Battery based storage is being explored to be added to neighborhoods to handle some of the peak load and possibly with automatic disconnects, to keep the power flowing during power outages further from the community. Batteries are expensive and so is the technology to convert AC to DC. Flywheels are another alternative that does not require conversion... mechanical energy added to the flywheel's speed or extracted with generators.
"Off-grid" people store their solar/wind/hydro in batteries at their home so the technology is developed but of course it is expensive and requires maintenance so if you have the grid connected, there is little incentive to store grid energy. One industry does this though; computer continuous power supplies.
I want to use DC LED lights in my house lighting system but to move low voltage electricity, you need much thicker wires. My idea with that is to store electricity in a very small battery at the location of the light then trickle-charge the battery using 120v AC from temporarily powered source (powered when the sun is shining on solar electric system). Battery operated power tools would also fit in this category.
#6 can be seen in a refrigerator to allow it to turn off at times and still keep the food cold. With timers, some appliances including high mass heaters can use lower priced "off-peak" energy to be used later. Large buildings often make a tank full of ice for cooling the building but make that ice at night when the chillers are more efficient (cooler air on the condensers) and electricity is cheaper.http://mybigearth.com/green-planet/the-curious-disconnect-between-smart-grid-and-energy-storage/
Thermal energy shows much promise to be higher efficiency then batteries and much cheaper then any other storage if the systems to convert that energy back into a useful form or easily transported form could be more efficient, safe, and cheap. Of course if the energy is in the form of heat or cool at that point in the chain, storing it becomes much more obvious.