Teach and learn


Energy has a language all of its own. Here you can check the meaning of words used throughout this site.

Simply click on a word and the meaning will display at the bottom of the page.

  • Alternating Current (AC)
  • Ampere
  • Atom
  • Battery
  • Biomass
  • Carbon cycle
  • Carbon dioxide
  • Conduction band
  • Circuit
  • Climate change
  • Current (I)
  • Diode
  • Doping
  • Direct Current (DC)
  • Distribution board
  • Efficiency
  • Electrical energy
  • Electric field
  • Electron
  • Energy
  • Fossil fuels
  • Free electrons
  • Frequency
  • Global warming
  • Gold leaf
  • Greenhouse effect
  • Greenhouse gas
  • Grid-connected
  • Incident power
  • Insulation
  • Inverse square law
  • Inverter
  • Isolating transformer
  • Junction box
  • Kilowatt hour
  • Linear regression
  • Load resistance
  • Metal
  • Multimeter
  • N-type silicon
  • Nuclear reactions
  • Ohm’s law
  • Open circuit voltage
  • Photoelectric
  • Photon
  • Power dissipated in resistor
  • Photosynthesis
  • Photovoltaic (PV)
  • Photovoltaic cell
  • Photovoltaic module
  • Photovoltaic system
  • p-n junction
  • Power (electricity) meters
  • Power (P)
  • P-type silicon
  • Quantum
  • Renewable energy
  • Resistance (R)
  • Selenium
  • Semi-conducting material
  • Semiconductor
  • Short circuit current (Isc)
  • Silicon
  • Silicon wafer
  • Solar constant (S)
  • Solar cell
  • Solar panel or module
  • Solar thermal collector
  • Transistor
  • Transmitter
  • Turbine
  • Valence band
  • Volt (V)
  • Voltage (V)
  • Water cycle
  • Watt (W)
  • Work function

Alternating Current (AC)

Electricity that flows back and forth at a set frequency. AC is created by most power stations and transmitted through the electricity grid to power users.


A nit of electrical current, often shortened to 'Amps'.


An atom is the smallest particle that comprises a chemical element.


Two or more primary cells connected to provide a source of electric current.


Organic material formed by living or recently dead plants. Biomass such as wood is a source of chemical potential energy. The chemical potential energy is the result of photosynthesis transforming the sun’s energy into a stored form. Biomass can be used as a fuel in power generation with less impact on global warming than burning fossil fuels.

Carbon cycle

One of the Earth’s most important cycles along with the water cycle. The carbon cycle exchanges and recycles carbon in its various forms (carbon dioxide, methane, biomass, coal, oil etc) between the reservoirs of oceans, atmosphere, land surface, earths crust, plants and animals. By burning fossil fuels long stored underground we are upsetting the balance of carbon dioxide in the atmosphere leading to Global Warming.

Carbon dioxide

Carbon dioxide (CO2) is a naturally occurring gas in the atmosphere. It is released into the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned. For most countries carbon dioxide is the dominant greenhouse gas emission caused by human activities. In New Zealand, the greenhouse gas methane is also very significant because of the country's extensive pastoral agriculture activities.

Conduction band

The range of energy levels which an electron can exist in above the valence band, separated by a band-gap. Electrons within this energy range are free to move away from their parent atoms and are able to transport energy through the material.


A complete path through which an electric current can flow.

Climate change

Climate change refers to the variation in the Earth's global climate or in regional climates over time. It describes changes in the variability or average state of the atmosphere-or average weather-over time scales ranging from decades to millions of years. These changes may come from processes internal to the Earth, be driven by external forces (e.g. variations in sunlight intensity) or, most recently, be caused by human activities.

Current (I)

Flow of electric charge. 1 Amp = 1 Coulomb per second.


An electronic component formed by a p-type and an n-type semi-conductor placed in contact with each other to form a junction. The electric field created at the junction only allows negative or positive charges to flow in one direction. LEDs and photovoltaic cells are types of diode.


Doping is the process of adding small amounts of other elements into the crystal lattice of a pure element or compound to radically alter its electrical properties. Silicon, a Group IV element, is doped with Group III elements such as boron to form p-type silicon (see entry). When doped with Group V elements such as phosphorous, n-type silicon (see entry) is formed.

Direct Current (DC)(I)

Electricity that only flows in one direction around a circuit. A direct current or DC is created by batteries and photovoltaic cells.

Distribution board

The board which takes the incoming electrical power and distributes it to different circuits within the building such as lighting, hot water heating etc. Each circuit is protected by a fuse or circuit breaker.


Ratio of output power to input power of a device. Easy to remember as ‘what you get’ divided by ‘what you put in’.

Electrical energy

Energy is required to push electrons through the various components of a circuit. This is generally provided by a power supply that sets up an electric potential (energy) difference between its terminals.

Electric field

The electric field is due to the built-in voltage. The electric field acts on free electrons that are released by photons, forcing them to move in one direction only (towards the top layer). Force = electron charge x electric field strength.


Sub-atomic particle of negative charge that surrounds the positively charged nucleus of an atom. Electrons can be bound to their parent atom in electron shells, involved with bonding to neighbouring atoms or they can become free and mobile if they gain enough energy to escape the electrostatic attraction of the nucleus.


Necessary for things to change, or events to happen. Energy can exist purely by itself as light, or it can be a varying property of matter (kinetic and potential energy). Energy always obeys the Conservation of Energy Law. A quantity measured in Joules.

Fossil fuels

Fuels formed slowly over millions of years from buried and fossilised biomass (plants or animals). Most living things decompose when they die which releases carbon back into the atmosphere and to the carbon cycle. If the biomass is quickly buried without the chance to fully decompose the carbon can be stored geologically as coal, oil or natural gas and is removed from the active carbon cycle.

Free electrons

Electrons that are not bound to their parent atoms but are free to move around the crystal lattice and can carry energy.


The number of times a pattern or process is completely repeated in one second. The frequency of a wave is the number of times its crest or trough is repeated in one second. Units are Hertz (Hz), or per second (s-1). Frequency (f) is related to wavelength (λ) and wave velocity (v) by the wave equation v = fλ

Global warming

Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades.

Gold leaf

Pieces of gold that have been beaten into very thin sheets

Greenhouse effect

The process in which the absorption of infrared radiation by an atmosphere warms a planet. The natural greenhouse effect is due to naturally occurring greenhouse gases, while the enhanced greenhouse effect results from gases emitted because of human activities.

Greenhouse gas

Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases.


A premises is generally said to have obtained grid connection when its electricity is supplied from the national electricity grid.

Incident power

The rate at which energy strikes the surface of, for example, a photovoltaic cell or module.


Insulation is a material such as wool, polystyrene, glass wool, mineral wool, paper-based insulation and polyester that reduces unwanted heat loss or gain in a building.

Inverse square law

If something, e.g. light or sound radiates uniformly into space from a point source, then, at a distance d from the source, the power flux will be given by, P/πd2 where P is the total power emitted by the source. The flux decreases as the inverse square of the distance from the source.


lectronic device that converts the DC electrical power from the photovoltaic modules to standard AC (230V at 50 Hz) used in the home by appliances.

Isolating transformer

The term 'isolating transformer' is normally applied to mains transformers providing isolation rather than voltage transformation

Junction box

A special box that is glued in place over the positive and negative connection points on the solar module to keep the connections waterproof.

Kilowatt hour

The energy represented by 1 kilowatt of power consumed for a period of 1 hour.

Linear regression

A mathematical technique for finding the equation of a straight line that best fits a set of data, and evaluating the fit.

Load resistance

A device or appliance in the external part of an electric circuit that uses (dissipates) electrical energy.


Substances that conduct electricity and heat well due to the abundance of free electrons which act as energy carriers. Metals have no band-gap so the electrons can move easily from the valence into the conduction band.


An instrument to measure various electrical properties, usually potential difference across a component in volts, current through part of a circuit, in amps, and resistance of components in ohms.

N-type silicon

N (negative) type silicon has extra valence electrons due to doping with phosphorous (Group V element, 5 valence electrons) in the crystal lattice. Phosphorous has one more valence electron than that offered by adjacent silicon atoms. The overall charge of n-type silicon is zero/neutral due to equal amounts of protons (+) and electrons (-), but the negative charges (electrons) are mobile.

Nuclear reactions

Reactions that involve changes in the nucleus of an atom (distinct from chemical reactions). These reactions release large amounts of energy when some of the mass in the nucleus is transformed into energy according to Einstein’s great equation E=mc2. Solar energy comes from nuclear fusion reactions in the sun’s core where hydrogen nuclei are forced to combine under tremendous heat and pressure into helium.

Ohm’s law

For devices made of certain materials it is found that the ratio of the voltage across the device to the current through it is a constant i.e. does not vary as the current is varied, until electrical breakdown, or melting occurs. Such materials are said to be ohmic, and obey Ohm’s Law V = IR

Open circuit voltage

The maximum voltage produced by a device corresponding to infinite load resistance, or zero current.


The tendency for materials to release electrons from their surface when they absorb incident photons. The absorbed photon must have enough energy to overcome the electrostatic binding of the electron to its parent atoms nucleus, or it will not be released.


The smallest unit of light and other forms of radiant energy. The photon is indivisible and can be viewed as either a particle or a discrete wave. The energy of a photon increases with increasing frequency, and decreases with increasing wavelength. The energy (E) of a photon is equal to the frequency (f) multiplied by Planck’s Constant (h).

Power dissipated in resistor

The rate at which electrical energy is required to push through a resistor. P = VI. In a normal resistor, the electrical energy is generally transformed to heat.


The process by which the energy from sunlight is used to chemically combine the raw materials of carbon dioxide gas and water into glucose sugar. This energy transformation, from active radiant energy (sunlight) to stored chemical potential energy (glucose) is carried out by tiny structures inside plant cells called chloroplasts. Chloroplasts contain the green molecule chlorophyll.

Photovoltaic (PV)

The tendency for materials to become electrically charged, thus generating voltage, when exposed to incident photons of sufficient energy. The photovoltaic effect is closely related to the photoelectric effect.

Photovoltaic cell

An electronic device made of semiconductor materials that transform the radiant energy of sunlight into electrical energy. The electricity generated by each cell is about 0.6 Volts (DC) so many are added in series to produce greater voltages.

Photovoltaic module

Several photovoltaic cells connected in series and/or parallel to increase the output voltage and/or current.

Photovoltaic system

A fully functioning renewable electricity generation system. It consists of one or more photovoltaic modules (panels with PV cells in series) connected to an inverter and then the distribution board. It may or may not contain a battery bank to store unused energy for later use.

p-n junction

A positive-negative junction formed by the joining together of p-type and n-type semi-conductors (see entries). This can be thought of as a sandwich with the top and bottom layers being relatively conductive, and the filling being relatively insulating. The filling contains an electric field that only allows electrons to flow up the field-lines. This forms a one-way gate for electrons (diode).

Power (electricity) meters

A power or electricity meter is a device that measures the amount of electrical energy supplied to or produced by a home, business or machine.

Power (P)

The rate at which energy is released, transmitted or converted to another form; the rate of doing work. 1Watt = 1 Joule per second.

P-type silicon

P (positive) type silicon has fewer valence electrons due to doping with aluminium atoms (Group III element, 3 valence electrons). Al only forms bonds with 3 of the 4 offered by the adjacent Si atoms. The overall charge of p-type silicon is zero/neutral due to equal amounts of protons (+) and electrons (-), but the positive charges are mobile.


The smallest unit of energy or matter. A quantum entity cannot be divided into any smaller parts and has properties of both particle and wave.

Renewable energy

Renewable energy comes from a naturally occurring resource that is continually replenished without using fossil fuels or any other limited resource. These include water (hydroelectricity), wind farms, steam (geothermal sources) and the sun (solar energy).

Resistance (R)

An impedance to the flow of charge (current) in a circuit.


A semi-metal, chemical element that conducts electricity better in the light than in the dark.

Semi-conducting material

a solid material that has electrical conductivity in between that of a conductor and that of an insulator. Silicon is used to create most semiconductors commercially


A semiconductor material has electrical conductivity intermediate between an insulator and a conductor. A semiconductor has band-gap energy less than 4 electron Volts.

Short circuit current (Isc)

The maximum current that can be produced by a device: corresponds to the hypothetical situation of use in a circuit with zero resistance, therefore zero voltage.


A semi-metal, chemical element that can conduct electricity when small amounts of chemical impurities are added. Used to make diodes, PV, computer chips etc

Silicon wafer

A wafer is a thin slice of semiconductor material, such as a silicon crystal

Solar constant (S)

The rate of incidence of solar energy on Earth is described by the Solar constant, S, equal to the power per unit area incident on an imaginary surface perpendicular to the Sun’s rays at the top of the atmosphere. S = 1415 W/m2.

Solar cell

See PV cell

Solar panel or module

A solar panel or module is a device that collects and converts solar energy into electricity or heat.

Solar thermal collector

A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat


A device used to control or increase the flow of electricity


A device that changes sound into electricity or electricity into sound


Any of the various types of machine in which the kinetic energy of a moving fluid, as water, steam, air etc, is converted into mechanical energy by causing a bladed rotor to rotate. In electrical instances, the turbine is attached to and spins a generator to produce electricity.

Valence band

The range of energy levels which an electron can exist in below the conduction band, separated by a band-gap. Electrons within this energy range are bound to their parent atoms by electrostatic forces and can take part in bonding with neighbouring atoms.

Volt (V)

The unit used to measure voltage in a circuit.

Voltage (V)

The amount of energy carried by a unit of electrical charge. 1 Volt corresponds to energy of 1 Joule per Coulomb.

Water cycle

The cycle by which water is moved in its various forms (liquid, solid, gas/vapour) from one reservoir (oceans, atmosphere, land surface, earth’s crust, plants and animals) to another through the processes of evaporation, condensation, precipitation, runoff, freezing, melting etc. The water cycle is driven by the energy of sunlight.

Watt (W)

The Watt (symbol: W) is the SI derived unit of power, equal to one Joule of energy per second.

Work function

The minimum amount of energy required by a substance (metal or non-metal) to free an electron from its surface. The energy to free the electron may be gained through the absorption of a photon possessing sufficient energy.



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