Since the demand for energy not always correspond to the immediate availability, due to capcity, location or processing issues (in many cases all) energy needs to be stored to ensure awailability at the right time and location.
Energy storage involves converting energy from one form to another to create the desired flexibility in respect of demand and availability.
The energy carriers will in many cases also be the energy storage medium.
However in some cases the primeary energy source would also act as the energy storage.
Examples of energy storage
In geneeal electricity must be used as it is being generated if not it has to be converted into another form of energy, potential, kinetic or chemical.
- Elevated reservoirs, pumped or natural. Water realeased to produce electricity when needed.
- Power to gas, generation of hydrogen or methane (synthetic)
- Various types of thermal accumulators, during periods of excdess power generation electricity is used to generate heat.
Short-term thermal storage
Mainly for aircondition purposes.
- Producing ice during hours with low demaind and low electricity prices.
Long-term storage often in connection with solar thermal collectors.
- Aquifers, boreholes in geological structures.
- Sand, used to store accumulate heat from solar thermal power plants to be utilised during dark hours
Used in connection with electrical generation as well as for transportation, in boilers, turbines, internal combustion engines and fuel cells.
- Gasoline and diesel fuels
- LPG, propane, butane, ethanol
- Bio fuels
Various systems – under development, on a research or prototype stadium.
- Flywheels, store kinetic energy.
- Compressed air storage.
- Nanoscale capacitors.
- Vehicle-to-grid, using electrically powered vehicles plugged into the electrical grid as storage of electricy and as a source for electrical power during peak periods.
The calorific value of a fuel is the quantity of heat produced by its combustion – at constant pressure and under “normal” (“standard”) conditions (i.e. to 0oC and under a pressure of 1,013 mbar).
The combustion process generates water vapor and certain techniques may be used to recover the quantity of heat contained in this water vapor by condensing it.
Higher Calorific Value (or Gross Calorific Value – GCV, or Higher Heating Value – HHV) – the water of combustion is entirely condensed and that the heat contained in the water vapor is recovered
Lower Calorific Value (or Net Calorific Value – NCV, or Lower Heating Value – LHV) – the products of combustion contain the water vapor and that the heat in the water vapor is not recovered.