Wind energy storage technologies - Wind Power Generation and Wind Turbine Design - page 686

Figure 14: Supercapacitor energy storage device [ 24 ].

10 − 12 F/m). Therefore, to increase the energy stored within a capacitor,
the voltage or capacitance must be increased. The voltage is limited by the maximum
energy fi eld strength (after this the dielectric breaks down and starts conducting), and
the capacitance depends on the dielectric constant of the material used.
Supercapacitors are created by using thin fi lm polymers for the dielectric layer
and carbon nanotube electrodes. They use polarised liquid layers between con-
ducting ionic electrolyte and a conducting electrode to increase the capacitance.
They can be connected in series or in parallel. SCES systems usually have energy
densities of 20-70 MJ/m 3 , with an effi ciency of 95% [2].

space (8.854 ×

4.7.1 Applications of SCES
The main attraction of SCES is its fast charge and discharge, combined with its
extremely long life of approximately 1

10 6 cycles. This makes it a very attractive
replacement for a number of small-scale (<250 kW) power quality applications. In
comparison to batteries, supercapacitors have a longer life, do not suffer from memory
effect, show minimal degradation due to deep discharge, do not heat up, and produce
no hazardous substances [1]. As a result, although the energy density is smaller,
SCES is a very attractive option for some applications such as hybrid cars, cellu-
lar phones, and load levelling tasks. SCES is primarily used where pulsed power is
needed in the millisecond to second time range, with discharge times up to 1 min [2].

×

4.7.2 Cost of SCES
SCES costs approximately $12,960/kWh [2] to $28,000/kWh [1]. Therefore,
large-scale applications are not economical using SCES.

4.7.3 Disadvantages of SCES
SCES has a very low energy storage density leading to very high capital costs
for large-scale applications. Also, they are heavier and bulkier than conventional
batteries.