Environmental Engineering Reference
In-Depth Information
the storage efficiency of lead-acid battery systems. The second issue with two
energy conversions is the necessity to size the M/G and M/P to the maximum
power levels needed.
Hydraulic components can achieve very high power densities, in the range of
1.3 kW/kg or higher, depending on system pressure levels. The issue with operating
at pressures of 5,000 psi or higher is the level of safety afforded by containment
structures and the attendant weight added.
2.5.3 Very high voltage electric drives
This section is included to accommodate the views of some that high voltage
vehicular ac drives operating from 600 V to 3 kW or higher provide the perfor-
mance demanded by next generation hybrid vehicles [23]. The premise that higher
voltage electric machines are more efficient than lower voltage machines, all else
equal, is generally not true. The most efficient electric machines are large turbo-
generators rated up to 600 MW for utility generation operating under load at 99%
efficiency - at a single operating point, 3,600 rpm, 60 Hz and fixed voltage!
In the past 5 years there has been considerable interest in composition mod-
ified barium titanate (BaTi) sintered in a void-free matrix of very high purity. With
this ceramic material, the goal is to realize a dielectric withstand voltage of greater
than 3.5 kW for 1 mm thick sandwiches having an aluminium flash current col-
lector. The US start-up company EESTOR [24,25] had claimed to have a produc-
tion version of this ceramic ultra-capacitor available by the end of 2009, but till the
time of writing, that is the end of 2009, no samples of the EESU appeared.
The ceramic ultra-capacitor EESU [25] is claimed to store 52 kWh in a
package of 281 pounds and 2.63 ft
3
of volume. The energy stored in this ultra-
capacitor will be: each of the 31,351 slabs contain 100 CMBT capacitor chips
making a grand total of 3,135,100 chips in the EESU. The EESU consists of some
31,351 thin slabs of CMBT (composition modified BaTi) dielectric that is capable
of 610 V/
m
m at +85
C. This means the 1 mm thick slab can easily withstand the
3.5 kV that will appear across the 31,351 slabs in parallel having a combined
capacitance of 30.693 F. The energy stored in this ultra-capacitor will be
2
1
2
CU
c
¼
30
:
693
ð
3,500
Þ
W
e
¼
¼
188MJ
ð
2
:
4
Þ
2
And, a specific energy, SE, of
W
e
M
¼
52
:
2 kWh
128 kg
¼
407
:
8
Wh
SE
¼
ð
2
:
5
Þ
kg
This SE amounts to a truly phenomenal energy storage component if it materi-
alizes. Technically, this ceramic ultra-capacitor will require ultra-pure dielectric
material that is absolutely void free and protected from mechanical fracture. Elec-
trically the dielectric constant published to be in the range of 15,000 or higher must
not saturate much with voltage or the SE mark will not hold. Moreover, if this unit
