Cells and batteries of several cells convert stored chemical energy into electrical energy.
A Cell A Battery with three Cells
Rechargable batteries reverse the chemical reaction during the charging process.
Batteries contain two or more cells.
If you buy a single AA battery, electronics engineers would call that a cell.
Battery capacity is measured in either AMPERE HOURS or Joules per kilogram.
Sales and adversising materials often used milliamp hours to make the cell look 1000 times more impressive.
More about Stored and Renewable Energy
Here is a Spanish Power Station - The video title is misleading.
Solar heat is used to warm vast tanks of liquid salt solution.
This heat is used 24 hours per day to generate electricity.
The Cost of Electricity
If 230 Volt mains power is available, this is generally the lowest cost way to get power. Mobile devices and remote locations do not have access to mains power so the alternatives below can be considered. Mains power is not 100% reliable so mission / life critical systems need backup power sources.
Measuring Stored Energy - Joules per Kilogram
This is measured in Joules per Kilogram or more often kilojoules per kilogram.
This figure is useful when weight is an issue.
Battery Capacity - Ampere Hours
A 40 ampere-hour battery can supply, for example,
40 amps for one hour
1 amp for 40 hours or
5 amps for 8 hours.
Battery_Life = Ampere_Hours / Current_Flowing
Fixed Installations
Use mains power but if the mains power fails, a backup may be needed for example
Telephone exchanges
Operating theatres
Underground railway stations.
Backup Power
Battery
Diesel or Petrol Generator
Fuel Cell
Capacitors ( low voltages only, hold less charge than batteries, fast re-charging )
Small Mobile Devices
Have to use stored energy.
Robots
Phones
Tablets and PDAs
Power Sources
Battery Power
Fuel Cells (methanol)
Large Mobile Devices
Have to use stored energy.
Electric Cars
Power Sources
Diesel or Petrol Generator
Large Batteries
Fuel Cells (hydrogen or methanol)
Battery Types
Most rechargeable batteries take two or more hours to charge.
Non rechargeable
Alkaline batteries
The most expensive option for heavily used devices
After a period of use, cells may leak potassium hydroxide which corrodes connectors and surrounding circuits
Rechargeable
Lead Acid
Poor energy-to-weight ratio 150kJ/kg
Able to supply very large currents for short times (Good for starting up trucks or cars).
Able to supply very large currents. This makes misuse hazardous!
Nickel Metal Hydride
Better energy-to-weight ratio 300 kJ/kg
Slower loss of charge when not in use
Lithium Ion
Popular
Best affordable energy-to-weight ratio 500 kJ/kg
No memory effect - other cells can behave as though they are flat even when quite fully charged.
Slow loss of charge when not in use
High energy density but this may cause them to explode if mistreated.
Lithium Polymer
Best capacity at 1000 kJ/kg
Less likely to explode
Costly
New types are being developed!
Metal Air batteries use oxygen from the atmosphere as one of the reactive chemicals. This allows higher energy densities to be achieved.
Inverters
Convert low voltage DC into high Voltage AC ( Often 230 V ).
Contain an oscillator circuit.
Contain a push pull amplifier.
Contain a transformer to step up the AC output Voltage.
Are not very energy efficient.
Are used to provide a short lived 230 Volt supply allowing time to start up a petrol or diesel generator.
Are used to keep computer servers, phones and computer networks working for a short time.
This allows time to start a backup generator or a controlled computer shut down can take place.
Fuel Cells
Can be recharged extremely fast by simply re-filling with hydrogen or alcohol.
Fuel cell technology is becoming cheaper and may soon be preferred to batteries.
Small battery-sized fuel cells may soon be common.
Alcohol (methanol) - Easy to store and transport.
Hydrogen - Difficult to store and transport.
Supercapacitors
These are low voltage capacitors with capacitances measured in Farads.
They are useful for temporary power backup to cover short mains power failures.
They provide low current memory backup while the main power source is turned off.
There is rapid progress with this technology and there is a possibility that these capacitors might one day replace batteries.
They charge and discharge faster than conventional batteries but slower than ordinary capacitors.
Hybrid vehicles can take advantage of supercapacitor properties as well as conventional battery properties.
Supercapacitors can ge charged and emptied more often than rechargable batteries before they fail.
Renewable Energy Sources
Better for the environment but there are still problems to be considered.
Wind Turbines - Well established by 2009 and still growing fast.
Photovoltaics - Commonly used and increasingly with larger installations. Still expensive.
Wave Power - Still Experimental.
Tidal Power - Still Experimental.
Solar Furnace - Still Experimental.
Geothermal Power - In Iceland, heat from volcanoes is used for electric power generation and for heating homes and agriculture.
Photovoltaic Farm
Here is a hillside in Spain covered in photovoltaic panels. The panels could be made slightly more efficient by having them track the sun.
Solar Furnace
This is used for experimental science but a similar device could be used for power generation.
Subject NameLevelTopic NameQuestion HeadingFirst NameLast NameClass IDUser ID
You can attempt a question as many times as you like.
If you are logged in, your first attempt, each day, is logged.
To improve your scores, come back on future days, log in and re-do the questions that caused you problems.
If you are logged in, your most recent wrong answers get remembered. This might help you and your teacher to correct your understanding.
In the grade book, you can delete your answers for a topic before re-doing the questions. Avoid deleting unless you intend re-doing the questions very soon.