Electricity is the only commodity in the world that is usually consumed the instant it is produced.
Most commodities can be produced in advance of consumption and stored in warehouses, grain elevators, storage depots, or bank vaults until they are used. Not electricity. The total amount of supply – i.e., power generation – must be balanced every second with demand – i.e., the sum total of appliances, machinery and lighting fixtures that consume electricity. If demand increases more generators must be activated or consumers will experience brownouts or blackouts. If demand falls and too much electricity is generated the excess power will overheat power lines and transformers or discharge itself in the ground.
Only two major forms of storage exist: Water and chemicals. A number of other technologies such as compressed air have been introduced but they represent a small part of the market. There have also been recent innovations in tidal generation that involve storage for short periods of time.
Water Storage. In water storage, dams are built to control water and release it when generation is required. The water flows over turbines which turn and generate an electromagnetic field that excites electrons. Some dams are built where they can stop the flow of rivers and streams. Others are built in so-called pump storage facilities where water is pumped behind the dam in off peak hours when rates are cheapest and released during peak hours.
Chemical Storage. In chemical storage – also known as battery storage – an electrolyte is placed between two different metals known as a cathode and an anode. When the circuit is completed, ions move through the electrolyte – which can be liquid or a dry powder or other solid form – to the cathode or positive terminal. Simultaneously, electrons – which are unable to move through the electrolyte – move in the opposite direction to the ions, following the path of least resistance outside the electrolyte from the cathode to the anode.
Batteries can be either disposable or rechargeable.
Disposable Batteries. Disposable batteries can only be used once; when their electrolyte no longer moves ions they stop working. Examples include zinc chloride batteries in which the cathode is copper and the anode zinc and the electrolyte is ammonium chloride. Alkaline batteries are similar: They have a copper cathode but the electrolyte is magnesium dioxide. When the magnesium dioxide has all broken down the battery is dead.
Rechargeable Batteries. Rechargeable batteries can be reused. When a current is introduced the flow of electrons reverses itself and moves from the positive to the negative terminal and recharges the catalyst.
Until recently the most popular form of rechargeable battery was the nickel cadmium (NiCd) battery. While reliable these batteries may require total discharge before they can be recharged.
Today NiCd batteries have been replaced by lithium ion. Lithium is a lighter metal that can store up to twice the charge of NiCd before requiring a recharge. They also pose fewer environmental risks than do NiCd; cadmium is a very toxic substance for landfills. One disadvantage of lithium ions: They may not tolerate the same number of recharges and could die earlier than NiCd.
In the lithium ion battery the cathode is typically made from lithium-cobalt oxide or, more recently, lithium-iron phosphate. The anode is usually carbon. The electrolyte varies.
Lithium ion batteries are now used in most electric cars. A Tesla car, for example, includes 6-8000 lithium-ion cells which weigh over half a ton. They have also been adapted for use alongside solar panels.