Comparing battery power (BU53)

Technological advancements regularly take off soon after a major breakthrough has occurred. Not so with electricity. Electrical power was discovered circa 1600 AD (or earlier). At that time, no one knew what to do with it other than create sparks and experiment with twitching frog legs. Metal plating by means of electrolysis only began in the 1800s. But soon after, a primary battery powered the first electric light using charcoal electrodes. Once the relationship with magnetism was discovered in the mid 1800s, generators were invented that produced a steady flow of electricity. Motors followed that enabled mechanical movement and the Edison light bulb appeared to conquer darkness.

The invention of the electronic vacuum tube in the early 1900s was the significant next step towards high technology, enabling frequency oscillators, signal amplifications and digital switching. This led to radio broadcasting in the 1920s and enabled the first operational digital computer (ENIAC) in 1946. The discovery of the transistor in 1947 paved the way to the integrated circuit ten years later. Finally, the microprocessor ushered in the Information Age and revolutionized the way we live.

While large primary batteries have been around for 200 years, the sealed nickel-cadmium, as we know it today, is only as old as the transistor (1947). In the meantime, batteries have become a very important energy source and demand is growing steadily.

In the year 2000, the total battery energy consumed globally by laptops and mobile phones is estimated at 2,500 mega watts. Let's make some power comparison with various transportation modes from the early beginnings to today.

3000 BC 350 BC 1800 AD 1837 AD 1900 AD 1969 AD 1974 AD

Ox pulling a load Vertical waterwheel Watt's revised steam engine Marine steam engine Rail steam engine Boeing 747 jet airplane Nuclear power plant

0.5 hp 3 hp 40 hp 750 hp 12,000 hp 100,000 hp* 1,520,000 hp

* The power of an engine is measured in (hp or kW) and a jet in thrust (lbs, kN). A cruising Boeing 747 requires 55,145 lb (245 295 N) of thrust. This relates to 87,325 hp or 65,000 kW. At take off, the plane produces full thrust at 219,000lb (973 kN) with a power requirement of 105 000 hp or 78,300kW.

Battery power and the Boeing 747 jumbo jet

Travelers experience the exhilarating take-off of a jumbo jet. Fully loaded at 400 tons, the Boeing 747 requires 90 mega-watts (MW) of energy to get airborne. This relates to 120,000 horsepower (hp). The energy consumption during cruising is reduced to half, or 45MW (60,000hp). The global battery power consumed by mobile phones and laptops could keep 56 Boeing 747s in the air.

The mighty Queen Mary, an 81,000-ton ocean liner stretching over 300 meters (1000 ft) in length, was propelled by four steam turbines producing 160,000hp. The energy consumed globally by mobile phones and laptops could power 20 Queen Mary ships, with 3000 passengers and crew aboard, traveling at a speed of 28.5 knots (52 km/hr). The Queen Mary was launched in 1934 and is now a museum in Long Beach, California.

A 275hp (200kW) motor powers an SUV or large car. The average family home is wired to draw 20kW. A large vehicle has enough power to provide electrical energy for 10 houses and satisfy peak current requirements. This is substantial when considering that most vehicles carry only the driver

An active person requires 3500 calories per day to stay fit, which relates to roughly 4000 watts in 24 hours (1 food calorie = 1.16 watt-hour). If traveling on foot, a person covers about 40 km per day (25 miles). In Figure 1 we compare energy per passenger-kilometer for a loaded Boeing 747, the retired Queen Mary ocean liner, a gas-guzzling SUV and a fit person on a bicycle and on foot. The figures are estimated.



Figure 1: Power needs of different transportation modes. Air travel requires the lowest energy per passenger-km in terms of mechanized transportation. The boat becomes efficient for heavy freight. The absolute lowest energy need is a person on a bicycle
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* 4.186 joules are required to raise the temperature of 1g of water by 1 degree Celsius.
More on mechanical power: http://en.wikipedia.org/wiki/Power_%28physics%29


How are newer battery chemistries faring?

Lithium-ion is the winner for portable applications. Among the most popular lithium-ion are the 18650 cylindrical cells and a variety of prismatic cells in metal package.

Lithium-ion-polymer serves well when the cell geometry must be less than 4mm or when specialty packs are required. High power lithium-ion-polymer pouch cells allow convenient stacking to create a powerful and compact battery pack with optimum space allocation. There is a price premium, however. Lithium-ion-polymer cost about 10% more than lithium-ion without gaining extra capacity. Some room allocation for swelling must to be considered when stacking pouch cells.

Lithium-ion is being tested in medical instruments and hybrid cars with mixed results. Short service life and high price are major hurdles. These markets will continue to be served by the more rugged and lower-cost lead and nickel-based batteries.

There are no new battery chemistries on the horizon that will replace the classic lead-acid for automotive and wheeled-mobility markets. Lead-acid is mature and the manufacturing costs are low. The spiral wound lead-acid, a technology similar to the valve regulated lead acid and the absorbent glass mat (AGM) are gradually replacing the flooded car battery on high-end applications. Again, there is a price premium on these more advanced batteries but the longer service life will pay back the investment.

References: Barry Huret, president of battery consulting company Huret Associates Inc. in Yardley, Pa, USA (www.huret.com)
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Created: April 2003, Last edited: September 2006