17.1 The Cost of Mobile Power
Among the common power sources, energy from non-rechargeable
batteries is the most expensive. Figure 17-1 reflects the cost
per kWh using non-rechargeable batteries, also referred to as
primary batteries. In addition, non-rechargeable batteries have a
high internal cell resistance, which limits their use to light
loads with low discharge currents.
In the last few decades, there has been a shift from
non-rechargeable to rechargeable batteries, also known as secondary
batteries. The convenience of recharging, low cost and reliable
operation have contributed to this. Another reason for the
increased popularity of the secondary battery is the larger energy
densities available. Some of the newer rechargeable lithium systems
now approach or exceed the energy density of a primary battery.
|
|
| |
AAA Cell |
AA Cell |
C Cell |
D Cell |
9 Volt |
|
|
| Capacity (alkaline) |
1100mAh |
2500mAh |
7100mAh |
14,300mAh |
600mAh |
| Energy (single cell) |
1.4Wh |
3Wh |
9Wh |
18Wh |
4.2Wh |
| Cost per
Cell (US$) |
$1.25 |
$1.00 |
$1.60 |
$1.60 |
$3.10 |
| Cost per KWh (US$) |
$890 |
$330 |
$180 |
$90 |
$730 |
|
|
Figure 17-1: Energy and cost
comparison of primary alkaline cells.
Energy from primary batteries is most
expensive. The cost increases with smaller battery
sizes.
Figure 17-2 compares the cost of power when using
rechargeable batteries. The analysis is based on the purchase cost
of the battery and the number of discharge-charge cycles it can
endure before replacement is necessary. The cost does not include
the electricity needed for charging, nor does it account for the
cost of purchasing and maintaining the charging equipment.
|
|
| |
NiCd
AA Cell |
NiMH
AA Cell |
Lead Acid
(typical pack) |
Li-ion
18650 Cell |
Reusable Alkaline AA Cell |
|
|
| Capacity |
600mAh |
1000mAh |
2000mAh |
1200mAh |
1400mAh 1 |
| Battery Voltage |
7.5V |
7.5V |
12V |
7.2V |
7.5V |
| Energy per
cycle |
4.5Wh |
7.5Wh |
24Wh |
8.6Wh |
6.3Wh |
| Cycle life |
1500 |
500 |
250 |
500 |
10 |
| Cost per
battery (ref. only) |
$50 |
$70 |
$50 |
$100 |
$6.00 |
| Cost per kWh ($US) |
$7.50 |
$18.50 |
$8.50 |
$24.00 |
$95.00 |
|
|
Figure 17-2: Energy and cost
comparison using rechargeable cells.
Older battery technologies offer lower
energy costs compared to new systems. In addition, larger cells are
more cost-effective than small cells. The battery packs taken for
comparison are for commercial applications at over-the-counter
prices.
For this calculation, 840mA is used since subsequent capacities are
rated at 840mA (60% of initial capacity). If the battery is
discharged partially, a higher cycle life can be
obtained.
Figure 17-3 evaluates the cost to generate 1kW of energy.
We take into account the initial investment, add the fuel
consumption and include the eventual replacement of each
system.
Power obtained through the electrical utility grid is most cost
effective. Consumers in industrialized countries pay between $0.05
and 0.15US per kWh. The typical daily energy consumption of a
household is 25kWh.
|
|
| |
Investment
of equipment to
generate 1kW |
Lifespan
of equipment before major overhaul or replacement |
Cost of fuel
per kWh |
Total Cost
per kWh, incl. fuel,
maintenance and equipment replacement |
|
|
NiCd
for portable use |
$7,000, based on 7.2V, 1000mAh at
$50/pack |
1500 h, based on 1C discharge |
$0.15 for electricity |
$7.50 |
| Gasoline Engine for mobile use |
$30, based on
$3,000/100kW (134hp) |
4000 h |
$0.10 |
$0.14 |
Diesel
Engine
for stationary use |
$40, based on $4,000/100kW
(134hp) |
5000 h |
$0.07 |
$0.10 |
| Fuel Cell |
$3,000 – 7,500 |
|
$0.35 |
|
| - for portable
use |
|
2000 h |
--> |
$1.85 – 4.10 |
| - for mobile
use |
|
4000 h |
--> |
$1.10 – 2.25 |
| - for stationary
use |
|
40,000 h |
--> |
$0.45 – 0.55 |
Electricity
from electric grid |
All inclusive |
All inclusive |
$0.10 |
$0.10 |
|
|
Figure 17-3: Cost of generating 1kW
of energy.
This takes into account the initial
investment, fuel consumption, maintenance and eventual replacement
of the equipment. The most economical power source is by far the
utility; the most expensive is portable batteries.
The fuel cell offers the most effective means of generating
electricity, but is expensive in terms of cost per kWh. This high
cost is made economical when comparing with portable rechargeable
batteries. For mobile and stationary applications, the fuel cell is
considerably more expensive than conventional methods.
Note: The costing information obtained
on the fuel cell is based on current estimates and assumptions. It
is anticipated that improvements and wider use of this technology
will eventually lower the cost to be competitive with conventional
methods.
