Energy Storage News

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

Ultra capacitors utilize high surface area carbon particles surrounded by an electrolytic medium to store energy in the electric field created by chaged particles resider on the carbon surface. 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 25ēC: 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

Energy Storage News

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