Cost of Power

Primary Batteries

Energy from non-rechargeable batteries is most expensive in terms of cost per kilowatt-hours (kWh). Primary batteries are used for low-power applications such as wristwatches, remote controls, electric keys and children’s toys. Military in combat, light beacons and remote repeater stations also use primaries because charging is not practical. Table 1 estimates the storage capability and cost per kWh of primary batteries.

	AAA Cell	AA Cell	C Cell	D Cell	9 Volt
Capacity (alkaline)	1,100mAh	2,500mAh	7,000mAh	14,000mAh	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

Table1: Energy and cost comparison of primary alkaline cells. Energy from primary batteries is most expensive; cost increases with smaller battery sizes.

Secondary Batteries

Improved runtimes, lower unit price and the convenience of recharging have shifted many portable applications previously reserved for primary batteries to rechargeable batteries. Table 2 compares the cost of power with rechargeable batteries. The cost is based on battery price and the number of possible discharge/charge cycles. The analysis does not include electricity for charging or the cost of purchasing and maintaining charging equipment. The table compares commercial battery packs used for communications, computing or medical devices.

	Lead Acid	NiCd	NiMH	Li‑ion
Capacity	2,000mAh	600mAh	1,000mAh	1,200mAh
Battery voltage	12V	7.2V	7.2V	7.2V
Energy per cycle	24Wh	4.5Wh	7.5Wh	8.6Wh
Number of cycles	250	1,000*	500	500
Battery cost (est.)	$50	$50	$70	$100
Cost per kWh ($US)	$8.50	$11.00	$18.50	$24.00

Table 2: Energy and cost comparison using rechargeable batteries. Older technologies have lower cost/kWh than newer systems; larger cells are most cost-effective. The costs are commercial packs at estimated over-the-counter prices.

*   Cycle life is based on battery receiving maintenance.

Power from Other Sources

With dwindling fossil fuel supply, governments and the private sector are studying alternate energies. Table 3 compares the cost to generate 1kW of power by taking into account the initial investment, adding the consumption of fuel and including the eventual replacement of the system. Power from the electrical utility grid is most cost-effective; consumers in industrialized countries pay between $0.05 and $0.25US per kWh. (The typical daily energy consumption per household is 25kW.) Gasoline (and equivalent) is the most economical portable fuel.

Fuel type	Equipment to generate 1kW	Life span	Cost of fuel per kWh	Total cost per kWh
Li-ion for vehicular use	$1,000/kW (based on 10kW battery at $10,000)	2,500h (replacement cost $0.40/kW)	$0.10	$0.50 (replacement and $0,10/kWh)
Gasoline engine for vehicular use	$30/kW (based on IC engine at $3,000/100kW)	4,000h (replacement cost $0.01/kW)	$0.33	$0.34
Fuel cell - portable use - mobile use - stationary use	$3,000 – 7,500	2,000h 4,000h 40,000h	$0.35         ->         ->         ->	$1.85 – 4.10 $1.10 – 2.25 $0.45 – 0.55
Electricity electric grid	All inclusive	All inclusive	$0.10	$0.10

Table 3: Cost of generating 1kW of energy
The table includes the initial investment, fuel consumption, maintenance and eventual replacement of the equipment. The figures are estimates at the time of writing.

The fuel cell is most effective in converting fuel to electricity, but high equipment cost makes this power source expensive in terms of cost per kWh. In virtually all applications, power from the fuel cell is considerably more expensive than from conventional methods.

We now look at the energy that our bodies consume. An active man requires 3,500 calories per day to stay fit, which relates to roughly 4,000 watts in a 24-hour day (1 food calorie = 1.16 watt-hour). Traveling on foot covers about 40km (25 miles) per day and a bicycle increases the distance by a factor of four to 160km (100 miles). Eating two potatoes and a sausage for lunch can propel a bicyclist for the entire afternoon, covering 40km (25 miles), as I have experienced myself. The human body is amazingly efficient in converting food to energy.

Table 4 compares the energy per passenger/kilometer for a loaded Boeing 747, the retired Queen Mary ocean liner, a gas-guzzling SUV, a fit person on a bicycle, and a person walking on foot. The figures are estimated.

Function	Boeing 747 jumbo jet	Ocean liner Queen Marry	SUV or large car	Bicycle	On foot
Weight (loaded)	369 tons	81,000 tons	2.5 tons	100kg (220lb)	80kg  (176 lb)
Cruising speed	900km/h (560 mph)	52km/h (32mph)	100km/h (62mph)	20km/h (12.5mph)	5km/h (3.1mph)
Maximum power	77,000kW (100,000hp)	120,000kW (160,000hp)	200kW (275hp)	2,000W (2.7hp)	2,000W (2.7hp)
Power at cruising	65,000kW (87,000hp)	90,000 kW (120,000hp)	130 kW (174hp)	80 W (0.1hp)	280 W (0.38 hp)
Passenger	450	3000	4	1	1
Power per passenger	140kW	40kW	50kW	80W	280W
Energy per passenger	580 kilojoules*	2,800 kilojoules*	1,800 kilojoules*	14.4 kilojoules*	200 kilojoules*

Table 4: Power needs of different transportation modes. In terms of high-speed transportation, air travel consumes theleast amount of energy per passenger-km. The boat is efficient for slow and heavy freight. The absolute lowest energy consumption is the bicycle.

*  1 joule is the energy of 1A at 1V for 1 second, or 1 watt/s, or 0.238 calorie/s; 4.186 joules raise the temperature of 1g of water by 1°Celsius; 1,000 joules are 0.277Wh.

Bicycles are by far the most effective form of transportation. Comparing the energy consumption of a bicycle to that of a car, a cyclist would consume only 0.4 liter of fuel per 100km (630mpg). Walking is also efficient; it uses about one liter per 100km (228mpg). The problem with self-powered propulsion is the limited travel range before fatigue sets in.

In terms of energy usage, cars are one of the least efficient modes of transportation. The internal combustion engine utilizes only 25 percent of the net calorific value from the fuel for propulsion. The calculation looks even worse when taking into account the weight of the vehicle with a single passenger, the driver. The ratio of machine to man is typically ten-to-one. When accelerating a 1.5-ton vehicle, less than two percent of the energy moves the 75kg (165lb) driver, his briefcase and the lunch bag; 98 percent goes to heat and friction. Even a modern jet plane has better fuel efficiency than a car. A fully occupied Airbus 340 gets 3.4l/100km (70mpg), cruising at 950km/h (594mph).

Trains are one of the most efficient modes of transportation. The 36km Yamanote circle line connecting major urban centers in Tokyo carries 3.5 million passengers per day. During rush hour, the 11-car train runs every 150 seconds. Such a passenger volume would be unthinkable by private cars on city streets. Trains are also economical to move freight. Transporting one ton of freight consumes only 0.65 liters of fuel per 100km (362mpg).

Affluent societies want personal transportation, but with a large critical mass driving vehicles on government-funded highways with minimal contribution by the drivers and without mandated limits, this free-roaming lifestyle is taking a toll on our energy resources. Developing countries also desire personal transportation. As car become affordable to them, they will begin consuming fossil fuel too and this will increase the need for hydrocarbons further. According to the US Department of Energy, 71 percent of the oil consumed in the USA is for transportation. Out of this, 51 percent goes to passenger cars and light trucks. Smaller vehicles and the development of efficient rail systems could cut the energy for transportation in half. Read more about Hooked on Cheap Energy.