22-08-2012, 04:09 PM
Energy Storage Systems
Importance of ESS...
Thrust for Renewable Energy sources
Variable outputs
Energy Buffering
Importance in the present context
Why new technologies and devices?
Mechanical Energy StorageFly Wheels
Principle: Energy is stored in the form of Mechanical Energy.
Light weight fiber composite materials are used to increase efficiency.
Energy density
=0.05MJ/Kg, η=0.8
Advantages and disadvantages:
Very compact when compared to other energy storage systems.
Flywheels are used for starting and braking locomotives.
A flywheel is preferred due to light weight and high energy capacity.
It is not economical as it had a limited amount of charge/discharge cycle.
Operation:
Uses off-peak electricity to compress air and store it in airtight underground caverns.
When the air is released from storage, it expands through a combustion turbine to create electricity.
Energy density = 0.2~2 MJ/Kg, η=0.5
Advantages and disadvantages:
Fast start-up.
Draw back - Geological structure reliance
Electrochemical Storage
Types of Batteries:
Small Capacities
Lead-Acid Batteries
They use a chemical reaction to do work on charge and produce a voltage between their output terminals.
Energy density is 0.6 MJ/Kg.
Efficiency of the cell is only 15%
Large Scale
Application of Thermal Energy Storage
Air Conditioning:
A salt hydrate acts as a cool heat sink for the air conditioner working fluid.
The stored heat is rejected from the salt hydrate during night to heat the surrounding air.
Energy density = 0.25MJ/Kg, η=0.8
E.g.: Sodium Sulfate Decahydrate.
Which is better?
Comparing one method of energy storage with another is pointless.
The reason - None of them are optimal for all purposes.
Different storage methods differ in capacity and maximum usable storage time.
For large scale storage Underground thermal, pumped hydro and compressed air energy storage systems are preferable.
Superconductors can store energy with negligible losses.
Fuel cells are a viable alternative to petrol engines due to their high efficiency.
Flywheels have a narrow range and are not an answer for large scale operations.