Energy Storage Technologies: PHS, CAES, Flywheels, and Batteries
Pumped-Hydroelectric Storage (PHS)
Advantages:
- Massive quantities of energy for relatively long durations.
- Reliable technology.
- Long life.
- Low self-discharge.
- Low operation and maintenance costs.
- Potential use of abandoned mine shafts for coal or groundwater systems to store water and machinery.
Disadvantages:
- High capital costs (land acquisition, civil works, structures, and mechanical/electrical machinery).
- Compliance with local regulations.
- Costs associated with transmission lines.
- Long development time.
- Environmental impact.
- Noise.
- Site availability.
Main Characteristics:
- Two types: Conventional (over-ground) and underground, used for power regulation and frequency stabilization.
- P = density [kg/m^3] * flow rate [m^3/s] * g * h * efficiency
- Annual electric energy production depends on the available water supply.
Compressed Air Energy Storage (CAES)
Advantages:
- Suitable for many scales: for long and short duration applications.
- Reliability.
- Flexibility.
- Long life.
- Low operation and maintenance costs.
- Low self-discharge.
- High volumetric and mass energy and power outputs in comparison to PHS.
Disadvantages:
- Location constraints for storage.
- Cost of installation.
- Difficult operation in certain locations.
- Rapid air compression leads to thermal energy increase and subsequent loss of efficiency. Isothermal processes are needed to reduce losses.
Main Characteristics:
- Compression, storage, and expansion.
- Highly variable depending on the price of gas/electricity.
- Use of tanks/caverns (natural containers).
- Most typical configurations: adiabatic, isothermal.
Flywheels
Advantages:
- High efficiencies for short duration storage.
- Temperature-independent deep discharge.
- Low environmental impacts.
- High specific power and power densities.
- Good specific energy and energy densities.
- Fast response times.
- Very low capacity degradation.
- Long life.
- High scalability.
- Very little maintenance.
Disadvantages:
- High self-discharge rates.
- Safety concerns due to high speeds.
- Requirement for lower density and higher strength materials.
Main Characteristics:
- Store energy in a rotating mass.
- Five subsystems: flywheel, bearing, electrical machine, power converter, and containment chamber.
- High speeds achieved with electromagnetic and superconducting bearings. Losses can be reduced by 5%.
- E = 0.5 * I * w^2
Li-Ion Batteries
Key Parameters:
- SOC (State of Charge): Instantaneous charge relative to maximum cell capacity.
- Nominal Voltage: Voltage of a single cell based on the chemical potential difference.
- End of Charging Voltage: Maximum cell voltage during charging.
- End of Discharging Voltage: Minimum voltage during discharging.
- OCV (Open Circuit Voltage): Voltage of a single cell when no current is flowing.
- Nominal Cell Capacity: Capacity on a previously defined charging-discharging cycle.
- Nominal Cell Energy: Nominal cell capacity multiplied by the nominal voltage.
- Energy Density: Energy per volume or energy per mass.
- Internal Resistance: Sum of the ionic and electric resistance.
- C Rate: If it is 3C, it is the nominal capacity x3.
Advantages:
- High energy density.
- High power density.
- Light weight.
- Lithium availability.
- High potential electrode.
Disadvantages:
- Cost.
- Cycle life limitations.
- Calendar life limitations.
- Safety concerns.
Lead-Acid Batteries
Advantages:
- Low cost.
- Wide operating temperatures.
- Relatively high power outputs.
- Low maintenance.
Disadvantages:
- Low performance in terms of volume and weight.
The normal use of the battery is to keep it fully charged and use the accumulated energy when required. If not, balancing problems can occur when serializing.
Electrostatic and Magnetic Energy Storage
SMES (Superconducting Magnetic Energy Storage)
SMES systems store energy in the magnetic field created by the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature.
Advantages:
- Long lifespan.
- High cycle life.
- High efficiency.
- Fast response.
- Very high discharge rates.
Disadvantages:
- Low specific energy.
- High capital cost.
- Need for large cooling systems.
Supercapacitor Magnetic Energy Storage
Advantages:
- High capacitance.
- Huge cycle life.
- Wide operating temperature range.
- Very high discharge rates.
Disadvantages:
- Low voltage.
- High cost.
- Poor energy performance.
- Parasitic losses.