Research how the system works to convert energy generated at one time for storage and then can be used at a later time to generate electricity for the consumer grid. Heat or Internal Energy Storage–Molten silicon thermal energy storage, molten salt thermal energy storage

• Identify the type of energy      that is stored (for example, gravitational potential energy, thermal      or internal energy, elastic potential energy, kinetic energy, chemical      energy, etc). 
• Estimate how much energy can be      stored based on example systems in use or proposed. (Note: you might      need to learn what some of the common units are for such quantities, such      as a kilowatt-hour or kWh, British Thermal Unit, or btu, instead of      joules.) 
• Identify the pros and cons of      the system.

Problems are encountered when the shift of energy production goes from burning fossil fuels to renewable sources of energy, such as wind and solar. The time of peak energy production does not always correspond to the time of peak demand for energy. For example, solar energy can only be generated during the day, when it's not cloudy. However, a lot of electricity is used at night. Scientists and engineers are working hard to develop a variety of energy storage systems to allow the energy produced at one time to be used to generate electricity at other times. 

Before you begin, be sure to review the following resource: