Plus electricity cannot be stored.
FYI:
Electricity can be stored,
1. Batteries
2. Flywheels
3. Gravitational potential energy using a pumped hydroelectric facility.
4. Compressed Air Energy Storage
5. Rail Energy Storage
6. Molten Salt Storage
7. Thermal Energy Storage
Reference: http://discovermagazine.com/2015/july-aug/26-power-stash
It should have been "electricity can not be stored in a profitable way".
None of these ways is what is considered "efficient".
It is more profitable to produce new energy instead of storing it.