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There are several advantages and disadvantages to hydro electric energy production. One big advantage is that energy is free once the dam is built.
 

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alternate bateryThe media tells us of wonderful new batteries being developed that promise long runtimes and are paper-thin, durable, cheap and environmental friendly. While these experimental packs may be able to produce a voltage, the downsides are seldom revealed. The typical shortcomings are weak load capabilities and short cycle life. Yes, even a lemon can be made into a battery. Just poke a copper coin and galvanized nail into the innards. The power is low and you need 500 lemons to light a flashlight bulb.

Using seawater as electrolyte has also been tried. The sea would produce an endless supply of electricity, but the retrieved energy is only good to light a flashlight and corrosion buildup limits the service life. Outside the much-talked-about lead, nickel- and lithium-based batteries, other systems show promise. Let’s have a closer look at them in roughly the sequence of age.

Nickel-iron

After inventing nickel-cadmium in 1899, Sweden’s Waldemar Jungner tried to substitute iron for cadmium to save money; however, poor charge efficiency and gassing (hydrogen formation) prompted him to abandon the development without securing a patent.

In 1901, Thomas Edison continued the development of the nickel-iron battery as a substitute to lead acid for electric vehicles. He claimed nickel-iron was “far superior to batteries using lead plates and acid” and counted on the emerging electric vehicle market. He lost out when gasoline-powered cars took over and was deeply disappointed when the auto industry did not adopt nickel-iron as the starter, lighting and ignition battery (SLI) for cars.

The nickel-iron battery (NiFe) uses an oxide-hydroxide cathode and an iron anode with potassium hydroxide electrolyte and produces a nominal cell voltage of 1.2V. NiFe is resilient to overcharge and over-discharge and can last for more than 20 years in standby applications. Resistance to vibrations and high temperatures made NiFe the preferred battery for mining in Europe, and during World War II the battery powered the German V-1 flying bomb and the V-2 rockets. Other applications are railroad signaling, forklifts, and power for stationary applications. NiFe has a low specific energy of about 50Wh/kg, has poor low-temperature performance and exhibits high self-discharge of 20 to 40 percent a month. This, with high manufacturing cost, prompted the industry to stay faithful to lead acid.

Nickel-zinc

Nickel-zinc batteries are similar to nickel-cadmium in that they use an alkaline electrolyte and a nickel electrode, but differ in voltage; NiZn provides 1.6V/cell rather than 1.2V, which NiCd delivers. Nickel-zinc was first developed in the 1920s but it suffered from short cycle life caused by dendrite growth. This led to electrical shorting. Improvements in the electrolyte have reduced this problem, and NiZn is being considered again for commercial uses. Low cost, high power output and good temperature operating range make this chemistry attractive. NiZn charges at a constant current to 1.9V/cell and cannot take trickle charge. The specific energy is similar to other nickel-based systems. NiZn can by cycled 200–300 times, has no heavy toxic materials and can easily be recycled. Some are available in AA cells.

Nickel-hydrogen

When research for nickel-metal-hydride began in 1967, problems with metal instabilities caused a shift towards the development of the nickel-hydrogenbattery (NiH). NiH uses a steel canister to store the hydrogen gases at a pressure of 1,200psi (8,270kPa). The cell includes solid nickel electrodes, hydrogen electrodes, gas screens and electrolyte. These components are encapsulated in the pressurized vessel.

NiH has a nominal cell voltage of 1.25V and the specific energy is 40–75Wh/kg. The advantages are long service life even with full discharge cycles, good calendar life due to low corrosion, minimal self-discharge, and a remarkable temperature performance of –28°C to 54°C (–20°F to 130°F). These attributes make NiH ideal for satellite use. Scientists are developing NiH batteries for terrestrial use and hope to supply markets for energy storage systems and the electric vehicle. The negatives are low specific energy and high cost. A single cell for a satellite application costs thousands of dollars.

Zinc-air

Zinc-air batteries generate electrical power by an oxidation process of zinc and oxygen from the air. The cell can produce 1.65V, however, 1.4V and lower achieves a longer lifetime. To activate the battery, the user removes a sealing tab that enables airflow and the battery reaches full operating voltage within five seconds. Once turned on, the battery cannot be reverted back to the standby mode, the chemicals dry out, and the battery has a short shelf life. Adding a tape to stop airflow slows the degeneration.

Zinc-air batteries have similarities to the proton exchange membrane fuel cell (PEMFC) in that they use oxygen in the air as fuel for the positive electrode.  Air can, to a certain extent, control the rate of the reaction. Zinc-air is considered a primary battery, however, there are recharging versions for high-power applications. Recharging occurs by replacing the spent zinc electrodes, which can be in the form of a zinc electrolyte paste. Other zinc-air batteries use zinc pellets.

At 300–400Wh/kg, zinc-air has a high specific energy but the specific power is low. Manufacturing cost is low and in a sealed state, zinc-air has a two percent self-discharge per year. Zinc-air is sensitive to extreme temperatures and high humidity. Pollution also affects performance, and high ambient carbon dioxide reduces the performance by increasing the internal resistance. Typical applications include hearing aids; high-power versions operate remote railway signaling and safety lamps at construction sites.

Silver-zinc

The silver-zinc battery has served a critical role for defense and space applications, as well as TV cameras and other professional equipment needing extra runtime. High cost and short service life locked the battery out of the commercial market but it’s on the verge of a rebirth.

The zinc electrode and separator were the primary cause of failure in the original design; the zinc electrode degraded rapidly when cycled. The battery developed zinc dendrites that pierced the separator, causing electrical shorts. Furthermore, the separator degraded whether used or not by simply sitting in the potassium hydroxide electrolyte. This limited the calendar life to about two years. Improvements in the zinc electrode and separator promise a longer service life and a 40 percent higher specific energy than Li-ion. Silver-zinc is safe, has no toxic metals and can be recycled, but the use of silver makes the battery expensive to manufacture.

Sodium-sulfur

Sodium batteries, also known as molten salt or thermal battery, come in primary and secondary versions. The battery uses molten salts as an electrolyte and operates at a temperature of 400–700°C (752–1,292°F). Newer designs run at a lower 245–350°C (473–662°F) temperature.

Conceived by the Germans during World War II and used in their V-2 rockets, the electrolyte of the molten salt batteries is inactive when cold and has a long storage of more than 50 years. Once activated with a heat source, the battery can provide a high power burst for a fraction of a second or deliver energy over several hours. The high power is made possible by the good ionic conductivity of the molten salt. Primary sodium batteries are almost exclusively used for the military as a “one-shot” engagement in guided missiles. However, interest of the reader lies in the rechargeable version.

The rechargeable sodium-sulfur (NaS) gained worldwide attention during the 1970s and 1980s, but short service life and high cost dampened the enthusiasm. The sodium-nickel-chloride battery, also known as ZEBRA,* came to the rescue and today this battery is being used successfully in many applications.

ZEBRA has a nominal cell voltage of 2.58 volts and an specific energy of 90–120Wh/kg, a level comparable with Li-manganese and Li-phosphate. The service life is about eight years and 3,000 cycles. It can be fast-charged, is non-toxic and the raw materials are abundant and low-cost. ZEBRA batteries come in large sizes of 10kWh or higher and typical applications are forklifts, railways, ships, submarines and electric cars. A growing market for sodium-based batteries is load leveling, also known as grid storage. The Think City EV has a choice of ZEBRA and Li-ion. ZEBRA has advantages when operating at extreme temperatures and when the battery is in continuous use, such as in taxis and delivery vans.

The ZEBRA battery must be heated to 270–350°C (518–662°F), a temperature that is lower than the original sodium-sulfur battery. Even though special insulation minimizes heat loss, heating consumes 14 percent of the battery’s energy per day, which results in a self-discharge of 18 percent. An active ZEBRA battery should be on charge or in use. It takes 3–4 days to cool down, and reheating takes about two days depending on the SoC at time of shutdown. Common failures include electrical shorts due to corrosion of the insulators, which then become conductive, as well as growth of dendrites, which increases self-discharge.

Reusable Alkaline

Introduced in 1992, the reusable alkaline serves as an alternative to disposable batteries; however, the anticipated breakthrough never occurred and today the reusable alkaline satisfies only a small market niche. The lack of consumer appeal is regrettable when considering the environmental benefit of having to discard fewer batteries. It is said that the manufacturing cost of the reusable battery is similar to that of a regular alkaline and the ability to recharge, although only for a limited time, offers definite advantages.

Recharging alkaline batteries is not new. Ordinary alkaline batteries have been recharged in households for many years, but manufacturers do not endorse this practice for safety reasons. Recharging is only effective if the alkaline is discharged to less than 50 percent before recharging. The number of recharges depends on the depth of discharge and is limited to just a few cycles at best. Each recharge stores less capacity until the battery is finally worn out. There is a cautionary advisory: charging ordinary alkaline batteries may generate hydrogen gas that can lead to explosion.

The reusable alkaline overcomes some of these deficiencies, but not all. With each recharge, the battery loses charge acceptance, and the longevity is in direct relationship to the depth of discharge. The deeper the discharge, the fewer cycles the battery can endure. At 50 percent depth of discharge, we can expect 50 cycles. The manufacturer may have overestimated the eagerness of the user wanting to recharge early; most users run a battery empty and recharge when necessary.

Tests performed by Cadex on “AA” reusable alkaline cells show a capacity reading on the first discharge that is similar to that of a regular alkaline. After the first recharge using the manufacturer’s charger, however, the reusable alkaline settles at only 60 percent, a capacity slightly below that of NiCd. Repeat cycling in the same manner resulted in further capacity losses. The discharge current was 200mA (0.2 C-rate, or one-fifth of the rated capacity) and the end-of-discharge threshold was set to 1V/cell.

An additional limitation of the reusable alkaline system is its low permissible load current of 400mA (lower than 400mA provides better results). Although adequate for flashlights and personal entertainment devices, 400mA is insufficient to power most digital cameras and communication devices.

Table 1 compares the specific energy, voltage, self-discharge and runtime of over-the-counter batteries. Available in AA, AAA and other sizes, these cells can be used in portable devices designed for these norms. Even though the cell voltages may vary, the end-of-discharge voltages are common, which is typically 1V/cell. Portable devices have some flexibility in terms of voltage range. It is important not to mix and match cells and to always use the same type of batteries in the holder. Safety concerns and voltage incompatibility prevent the sales of lithium-ion batteries in AA and AAA formats.

Battery type

Specific energy

AA cell

Voltage

Self-discharge

Capacity after
1 year storage

Runtime

Estimated photos
on digital camera

Regular alkaline

4,300mWh;
non-rechargeable

1.5V

95%

100 shots

Reusable alkaline

2,000mWh; lower on subsequent recharge

1.4V

95%

100 shots

Eneloop*

2,400mWh, rechargeable

1.2V

85%

500 shots

NiMH

2,700mWh, rechargeable

1.2V

50%

600 shots

Table 1: Comparison of alkaline, reusable alkaline, Eneloop and NiMH

*   Eneloop is a Sanyo trademark, based on NiMH.

Karl Kordesch, professor and co-inventor of the reusable alkaline, expressed disappointment in the market failure of this battery by saying, and I paraphrase, “If only people could be taught to recharge the battery sooner, before the energy is fully depleted.” The reusable alkaline could indeed provide extended service life if the user discharged the battery by only a small amount before recharging, but this does not suit consumer behavior. A user expects to get the full use of a battery before having to recharge.

NiMH has since replaced the reusable alkaline. Price is important and to lower cost for the consumer market, some battery manufacturers have reduced the capacity of the AA cell from 2,700mAh to 2,000mAh. The 2,700mAh AA cell is still available. Manufacturers are well tuned to customer needs and make the necessary adjustments to best serve the market. 

*              ZEBRA battery, so-called for the Zeolite Battery Research Africa Project.

Text taken from  batteryuniversity.com