Maxwell Ultra Capacitors Store Relatively Small Amounts of Energy but Accept and Deliver it at High Power

BCAP3000 specs taken from K2 series datasheet:

Rated Voltage: 2.7V
Usable Specific Power: 5,900W/Kg
Stored Energy: 3.04 Wh
Energy Density: 6.0Wh/Kg (LA Batteries=30Wh/Kg)
Max Leakage Current: 5.2mA
Cycle Life at 25ºC: 1,000,000
Mass: 510gm

If the discharge current is constant at 2.7V the self discharge time in hours would be given by:

Discharge Time = 3.04/.0052×2.7 = 216 hours

The actual discharge time will be longer as the voltage and current will drop during the discharge process.

I found quoted costs for the BCAP 3000 as low as US $97 which implies that the cost/kW= $32 and the cost/kWh=$32,000. The cost per kW is low (NaS batteries cost $2500/kW. Large combined cycle gas turbines cost $500/kW), but the cost/kWh is very high (NaS batteries cost $420/kWh.). These costs are the reason that ultra-capacitors are used for short duration high power applications like regenerative braking rather than for long term energy storage. The cost of ultra-capacitor manufacturing is dominated by the cost of the high surface area porous carbon powder (usually produced from coconut shells) which hold the electrical charge.

July 3, 2011