Chapter 17: Did you know . . . ?
Technological advancements usually take off shortly after a major breakthrough has occurred. Electricity was discovered circa 1600 AD (or earlier). At that time, electric power had few other applications than creating sparks and experimenting with twitching frog legs. 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 was invented to conquer the dark.
In the early 1900s, the electronic vacuum tube was invented, which enabled generating and amplifying signals. Soon thereafter broadcasting through the air by radio waves became possible. The discovery of the transistor in 1947 led to the development of the integrated circuit ten years later. Finally, the microprocessor ushered in the Information Age and revolutionized the way we live.
How much has the battery improved during the last 150 years when compared to other advancements? The progress has been moderate. A battery holds relatively little power, is bulky, heavy, and has a short life span. Battery power is also very expensive.
Yet humanity depends on the battery as a power source. In the year 2000, the total battery energy consumed globally by laptops and mobile phones alone is estimated to be 2,500MW. This equals 25,000 cars powered by a 100kW engine (134hp) driving at freeway speed.
Many travelers have experienced the exhilaration of take-off in a jumbo jet. At a full weight of over 396 tons, the Boeing 747 requires 90MW of energy to get airborne. The global battery power consumed by mobile phones and laptops could simultaneously lift off 28 jumbo jets. The energy consumption while cruising at high altitude is reduced to about half, or 45MW. The batteries that power our mobile phones and laptops could keep 56 Boeing 747s in the air.
The mighty Queen Mary, an 81,000 ton cruise ship measuring over 300 m (1000 ft) in length, was propelled by four steam turbine engines producing a total of 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 retired in Long Beach, California.
In this concluding chapter, we compare the cost of battery power against energy created by the combustion engine and the emerging fuel cell. We also examine the cost of electricity delivered through the electric utility system.
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. [17.1]
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. [17.2]
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. [17.3]
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.
The Fuel Cell
A fuel cell is an electrochemical device which combines hydrogen fuel with oxygen to produce electric power, heat and water. In many ways, the fuel cell resembles a battery. Rather than applying a periodic recharge, a continuous supply of oxygen and hydrogen is supplied from the outside. Oxygen is drawn from the air and hydrogen is carried as a fuel in a pressurized container. As alternative fuel, methanol, propane, butane and natural gas can be used.
The fuel cell does not generate energy through burning; rather, it is based on an electrochemical process. There are little or no harmful emissions. The only release is clean water. In fact, the water is so pure that visitors to Vancouver’s Ballard Power Systems, the leader in the development of the proton exchange membrane fuel cell (PEMFC), drank clear water emitted from the tailpipes of buses powered by a Ballard fuel cell.
The fuel cell is twice as efficient in converting fuel to energy through a chemical process than combustion. Hydrogen, the simplest element consisting of one proton and one electron, is plentiful and is exceptionally clean as a fuel. Hydrogen makes up 90 percent of the composition of the universe and is the third most abundant element on the earth’s surface. Such a wealth of fuel would provide an almost unlimited pool of energy at relatively low cost. But there is a price to pay. The fuel cell core (or ‘stack’), which converts oxygen and hydrogen to electricity, is expensive to build.
Hydrogen must be carried in a pressurized bottle. If propane, natural gas or diesel are used, a reformer is needed to convert the fuel to hydrogen. Reformers for PEMFCs are bulky and expensive. They start slowly and purification is required. Often the hydrogen is delivered at low pressure and additional compression is required. Some fuel efficiency is lost and a certain amount of pollution is produced. However, these pollutants are typically 90 percent less than what comes from the tailpipe of a car.
The fuel cell concept was developed in 1839 by Sir William Grove, a Welsh judge and gentleman scientist. The invention never took off, partly because of the success of the internal combustion engine. It was not until the second half of the 20th century when scientists learned how to better utilize materials such as platinum and Teflon™, that the fuel cell could be put to practical use.
A fuel cell can be thought of as electrolysis in reverse, using two electrodes separated by an electrolyte. Hydrogen is presented to the negative electrode (anode) and oxygen to the positive electrode (cathode). A catalyst at the anode separates the hydrogen into positively charged hydrogen ions and negatively charged electrons. On the PEM system, the hydrogen is catalyzed; the smaller protons migrate across the membrane to the cathode where they combine with oxygen to produce water and heat. The electrodes pick up the electrons to produce an electric current. A single fuel cell produces 0.6 to 0.8V under load. Several cells are connected in series to obtain higher voltages.
The first practical application of the fuel cell system was made in the 1960s during the Gemini space program, when this power source was favored over nuclear or solar power. The fuel cell, based on the alkaline system, generated electricity and produced the astronauts’ drinking water. Commercial application of this power source was prohibitive because of the high cost of materials. In the early 1990s, improvements were made in stack design, which led to increased power densities and reduced platinum loadings at the electrodes.
High cost did not hinder Dr. Karl Kordesch, the co-inventor of the alkaline battery, from converting his car to an alkaline fuel cell in the early 1970s. Dr. Kordesch drove the car for many years in Ohio, USA. The hydrogen tank was placed on the roof and the trunk was utilized to store the fuel cell and back-up batteries. According to Dr. Kordesch, there was “enough room for four people and a dog”.
Types of fuel cells — Several variations of fuel cell systems have emerged. The most common are the previously mentioned and most widely developed PEMFC systems using a polymer electrolyte. This system is aimed at vehicles and portable electronics. Several developers are also targeting stationary applications. The alkaline system, which uses a liquid electrolyte, is the preferred fuel cell for aerospace applications, including the space shuttle. Molten carbonate, phosphoric acid and solid oxide fuel cells are reserved for stationary applications, such as power generating plants for electric utilities. Among these stationary systems, the solid oxide fuel cell system is the least developed but has received renewed attention due to breakthroughs in cell material and stack designs.
The PEMFC system allows compact designs and achieves a high energy to weight ratio. Another advantage is a quick start-up when hydrogen is applied. The stack runs at a low temperature of about 80°C (176°F). The efficiency is about 50 percent (in comparison, the internal compaction motor has an efficiency of about 15 percent).
The limitations of the PEMFC system are high manufacturing costs and complex water management issues. The stack contains hydrogen, oxygen and water. If dry, the input resistance is high and water must be added to get the system going. Too much water causes flooding.
The PEMFC has a limited temperature range. Freezing water can damage the stack. Heating elements are needed to keep the fuel cell within an acceptable temperature range. The warm-up is slow and the performance is poor when cold. Heat is also a concern if the temperature rises too high.
The PEMFC requires heavy accessories. Operating compressors, pumps and other apparatus consumes 30 percent of the energy generated. The PEMFC stack has an estimated service life of 4000 hours if operated in a vehicle. The relatively short life span is caused by intermittent operation. Start and stop conditions induce drying and wetting, which contribute to membrane stress. If run continuously, the stationary stack is good for about 40,000 hours. The replacement of the stack is a major expense. [17.4] [17.5]
The SOFC is best suited for stationary applications. The system requires high operating temperatures (about 1000°C). Newer systems are being developed which can run at about 700°C.
A significant advantage of the SOFC is its leniency on fuel. Due to the high operating temperature, hydrogen is produced through a catalytic reforming process. This eliminates the need for an external reformer to generate hydrogen. Carbon monoxide, a contaminant in the PEMFC system, is a fuel for the SOFC. In addition, the SOFC system offers a fuel efficiency of 60 percent, one of the highest among fuel cells. The 60 percent efficiency is achieved with co-generation, meaning that the heat is utilized.
Higher stack temperatures add to the manufacturing cost because they require specialized and exotic materials. Heat also presents a challenge for longevity and reliability because of increased material oxidation and stress. High temperatures, however, can be utilized for co-generation by running steam generators. This improves the overall efficiency of this fuel cell system.
The AFC has received renewed interest because of low operating costs. Although larger in physical size than the PEMFC system, the alkaline fuel cell has the potential of lower manufacturing and operating costs. The water management is simpler, no compressor is usually needed, and the hardware is cheaper. Whereas the separator for the PEMFC stack costs between $800 and $1,100US per square meter; the equivalent of the alkaline system is almost negligible. (In comparison, the separator of a lead acid battery is $5 per square meter.) As a negative, the alkaline fuel cell needs pure oxygen and hydrogen to operate. The amount of carbon dioxide in the air can poison the alkaline fuel cell.
Applications — The fuel cell is being considered as an eventual replacement for the internal combustion engine for cars, trucks and buses. Major car manufacturers have teamed up with fuel cell research centers or are doing their own development. There are plans for mass-producing cars running on fuel cells. However, because of the low operating cost of the combustion engine, and some unresolved technical challenges of the fuel cell, experts predict that a large scale implementation of the fuel cell to power cars will not occur before 2015, or even 2020.
Large power plants running in the 40,000kW range will likely out-pace the automotive industry. Such systems could provide electricity to remote locations within 10 years. Many of these regions have an abundance of fossil fuel that could be utilized. The stack on these large power plants would last longer than in mobile applications because of steady use, even operating temperatures and absence of shock and vibration.
Residential power supplies are also being tested. Such a unit would sit in the basement or outside the house, similar to an air-conditioning unit of a typical middle class North American home. The fuel would be natural gas or propane, a commodity that is available in many urban settings.
Fuel cells may soon compete with batteries for portable applications, such as laptop computers and mobile phones. However, today’s technologies have limitations in meeting the cost and size criteria for small portable devices. In addition, the cost per watt-hour is less favorable for small systems than large installations.
Let’s examine once more the cost to produce 1kW of power. In Figure 17-5 we learned that the investment to provide 1kW of power using rechargeable batteries is around $7,000. This calculation is based on 7.2V; 1000mAh NiCd packs costing $50 each. High energy-dense batteries that deliver fewer cycles and are more expensive than the NiCd will double the cost.
The high cost of portable power opens vast opportunities for the portable fuel cell. At an investment of $3,000 to $7,500 to produce one kilowatt of power, however, the energy generated by the fuel cell is only marginally less expensive than that produced by conventional batteries.
The DMFC, the fuel cell designed for portable applications would not necessarily replace the battery in the equipment but serve as a charger that is carried separately. The feasibility to build a mass-produced fuel cell that fits into the form factor of a battery is still a few years away.
The advantages of the portable fuel cell are: relatively high energy density (up to five times that of a Li-ion battery), liquefied fuel as energy supply, environmentally clean, fast recharge and long runtimes. In fact, continuous operation is feasible. Miniature fuel cells have been demonstrated that operate at an efficiency of 20 percent and run for 3000 hours before a stack replacement is necessary. There is, however, some degradation during the service life of the fuel cell. Portable fuels cells are still in experimental stages.
Advantages and limitations of the fuel cell — A less known limitation of the fuel cell is the marginal loading characteristic. On a high current load, mass transport limitations come into effect. Supplying air instead of pure oxygen aggregates this phenomenon.
The issue of mass transport limitation is why the fuel cell operates best at a 30 percent load factor. Higher loads reduce the efficiency considerably. In terms of loading characteristics, the fuel cell does not match the performance of a NiCd battery or a diesel engine, which perform well at a 100 percent load factor.
Ironically, the fuel cell does not eliminate the chemical battery — it promotes it. Similar to the argument that the computer would make paper redundant, the fuel cell needs batteries as a buffer. For many applications, a battery bank will provide momentary high current loads and the fuel cell will serve to keep the battery fully charged. For portable applications, a supercapacitor will improve the loading characteristics and enable high current pulses.
Most fuel cells are still handmade and are used for experimental purposes. Fuel cell promoters remind the public that the cost will come down once the cells are mass-produced. While an internal combustion engine requires an investment of $35 to $50 to produce one kilowatt of power, the equivalent cost in a fuel cells is still a whopping $3,000 to $7,500. The goal is a fuel cell that would cost the same or less than diesel engines.
The fuel cell will find applications that lie beyond the reach of the internal combustion engine. Once low cost manufacturing is feasible, this power source will transform the world and bring great wealth potential to those who invest in this technology.
It is said that the fuel cell is as revolutionary in transforming our technology as the microprocessor has been. Once fuel cell technology has matured and is in common use, our quality of life will improve and the environmental degradation caused by burning fossil fuels will be reversed. However, the maturing process of the fuel cell may not be as rapid as that of microelectronics.
The Electric Vehicle
In a bid to lower air pollution in big cities, much emphasis has been placed on the electric car. The notion of driving a clean, quiet and light vehicle appeals to many city dwellers. Being able to charge the car at home for only a dollar a day and escape heavy fuel taxes (at least for the time being) makes the electric car even more attractive.
The battery is still the main challenge in the development of the electric car. Distance traveled between recharge, charge time and the limited cycle count of the battery continue to pose major concerns. Unless the cycle life of the battery can be increased significantly, the cost per mile will be substantially higher than that of a fuel-powered vehicle. The added expense is the need to replace the battery after a given number of recharges. This could offset any advantage of lower energy costs or the absence of fuel taxes. Disposing the spent batteries also adds to the expenditure.
Another challenge associated with the electric vehicle is the high power demand that would be placed on the electric grid if too many cars were charged at a certain time. Each recharge consumes between 15 to 20kW of power, an amount that is almost as much as the daily power requirement of a smaller household. By adding one electric car per family, the amount of electric power a residence requires would almost double. Delayed charging could ease this problem by only drawing power during the night when the consumption is low.
A rapid shift to the electric car could create shortages of electric power. With the move to reduce the generation of electricity due environmental concerns, electricity would need to be imported at high costs. This would make the electric car less attractive.
If the electricity was generated with renewable energy such as hydroelectric generators and windmills, the electric vehicle would truly clear the air in big cities. The generation of electricity by means of nuclear power or fossil fuels simply shifts the pollution problem elsewhere. However, a central source of pollution is easier to contain than many polluting objects in a metropolitan area.
A hybrid car is an alternative to vehicles running solely on battery power. Here, a small combustion engine works in unison with an electric motor. During acceleration, both the electric and combustion engines are engaged. Because of superior torque, the electric motor takes precedence during acceleration. Once cruising, the combustion engine maintains the speed and keeps the batteries charged. Hybrid cars achieve fuel savings of 30 percent or better compared to the combustion engine alone.
A hybrid car is less strenuous on a battery than a conventional electric car because the battery is not being deeply discharged during regular use. A deep discharge only occurs on a long mountain climb where the small combustion engine could not sustain the load and would need assistance from the electric motor and its battery bank. Driving habits would, to a large extent, determine the service life of the battery. A light foot on the pedal will help the pocket book also with the hybrid car.
Another alternative to powering cars is the fuel cell. Although much cleaner running than the combustion engine, the fuel cell must solve a number of critical problems before the product can be offered to the consumer as an economical alternative. The major challenge is cost reduction. If fossil fuel remains as low-priced is it is today, many drivers owning high-powered cars, SUVs and trucks would be reluctant to switch to a new technology. Concerns over pollution only persuade a limited number of drivers to switch to a cleaner-running vehicle. With the slow and gradual progress in the fuel cell, it will be some time before this technology renders the combustion engine obsolete.
Europe is talking about the three-liter motor, an internal combustion engine running on gasoline or diesel fuel. Remarkably, ‘three’ does not denote the engine displacement but stands for liters of fuel consumed per 100 km traveled. There is talk about the one-liter engine also. Major car manufacturers are divided on the fuel that will power our cars in the future. Within one large auto manufacturer in Europe, opinions regarding the fuel cell and an economical three-liter engine are divided fifty-fifty.
Strengthening the Weakest Link
The speed at which mobility can advance hinges much on the battery. So important is this portable energy that engineers design handheld devices around the battery, rather than the other way around. With each incremental improvement of the battery, the doors swing open for new products and applications. It is the virtue of the battery that provides us the freedom to move around and stay in touch. The better the battery, the greater the freedom we can enjoy.
The longer runtime of newer portable devices is not only credited to higher energy-dense batteries. Much improvement has been made in reducing the power consumption of portable equipment. These advancements are, however, counteracted with the demand for more features and faster processing time. In mobile computing, for example, high speed CPUs, large screens and wireless interface are a prerequisite. These features eat up the reserve energy that the more efficient circuits save and the improved battery provides. The result is similar runtime to an older system, but with increased performance. It is predicted that the improvements in battery technology will keep par with better performance.
Wide-band mobile phones, dubbed G3 for third generation, are being offered as replacements for the digital voice phone. There is public demand for Internet access in a tiny handset that connects to the world by the push of a few buttons, twenty-four hours a day. But these devices require many times the power compared to voice only when operating on wideband. Higher capacity batteries are needed, preferably without added size and weight. In fact, the success of the G3 system could hinge on the future performance of the battery. G3 technology may be ready but the battery lags behind.
The battery has not leap-frogged at the same speed as microelectronics. Only 5 to 10 percent gains in capacity per year have been achieved during the last decades and the ultimate miracle battery is still nowhere in sight. As long as the battery is based on an electro-chemical process, limitations of power density and life expectancy must be taken into account.
The battery remains the ‘weak link’ for the foreseeable future. A radical turn will be needed to satisfy the unquenchable thirst for mobile power. What people want is an inexhaustible pool of energy in a small package. It is anyone’s guess whether the electro-chemical battery of the future, the fuel cell or some groundbreaking new energy storage device will fulfill this dream.