15-03-2011, 12:13 PM
Presented By:
Nisha Sinha
[attachment=10194]
Technical seminar on ultracapacitor
Energy Storage
• In the past 2 classes we have discussed battery technologies and how their characteristics may or may not be suitable for microgrids.
• Batteries are suitable for applications where we need an energy delivery profile. For example, to feed a load during the night when the only source is PV modules.
• However, batteries are not suitable for applications with power delivery profiles. For example, to assist a slow load-following fuel cell in delivering power to a constantly and fast changing load.
• For this last application, two technologies seem to be more appropriate:
• Ultracapacitors (electric energy)
• Flywheels (mechanical energy)
• Other energy storage technologies not discussed in here are superconducting magnetic energy storage (SMES – magnetic energy) and compressed air (or some other gas - mechanical energy)
Ultracapacitors
• Capacitors store energy in its electric field.
• In ideal capacitors, the magnitude that relates the charge generating the electric field and the voltage difference between two opposing metallic plates with an area A and at a distance d, is the capacitance:
• In ideal capacitors:
• Equivalent model of real standard capacitors:
Flywheels
• Kinetic energy:
where I is the moment of inertia and ω is the angular velocity of a rotating disc.
• For a cylinder the moment of inertia is
• So the energy is increased if ω increases or if I increases.
• I can be increased by locating as much mass on the outside of the disc as possible.
• But as the speed increases and more mass is located outside of the disc, mechanical limitations are more important.
• However, high speed is not the only mechanical constraint
• If instead of holding output voltage constant, output power is held constant, then the torque needs to increase (because P = Tω) as the speed decreases. Hence, there is also a minimum speed at which no more power can be extracted
• If and if an useful energy (Eu) proportional to the difference between the disk energy at its maximum and minimum allowed speed is compared with the maximum allowed energy (Emax) then
Nisha Sinha
[attachment=10194]
Technical seminar on ultracapacitor
Energy Storage
• In the past 2 classes we have discussed battery technologies and how their characteristics may or may not be suitable for microgrids.
• Batteries are suitable for applications where we need an energy delivery profile. For example, to feed a load during the night when the only source is PV modules.
• However, batteries are not suitable for applications with power delivery profiles. For example, to assist a slow load-following fuel cell in delivering power to a constantly and fast changing load.
• For this last application, two technologies seem to be more appropriate:
• Ultracapacitors (electric energy)
• Flywheels (mechanical energy)
• Other energy storage technologies not discussed in here are superconducting magnetic energy storage (SMES – magnetic energy) and compressed air (or some other gas - mechanical energy)
Ultracapacitors
• Capacitors store energy in its electric field.
• In ideal capacitors, the magnitude that relates the charge generating the electric field and the voltage difference between two opposing metallic plates with an area A and at a distance d, is the capacitance:
• In ideal capacitors:
• Equivalent model of real standard capacitors:
Flywheels
• Kinetic energy:
where I is the moment of inertia and ω is the angular velocity of a rotating disc.
• For a cylinder the moment of inertia is
• So the energy is increased if ω increases or if I increases.
• I can be increased by locating as much mass on the outside of the disc as possible.
• But as the speed increases and more mass is located outside of the disc, mechanical limitations are more important.
• However, high speed is not the only mechanical constraint
• If instead of holding output voltage constant, output power is held constant, then the torque needs to increase (because P = Tω) as the speed decreases. Hence, there is also a minimum speed at which no more power can be extracted
• If and if an useful energy (Eu) proportional to the difference between the disk energy at its maximum and minimum allowed speed is compared with the maximum allowed energy (Emax) then
