10.03.2020 | Do you speak volts, watts and hertz?

The ABC’s of energy terminology

If you want to take part in the discussion on climate change, a reliable electricity supply and the Energy Strategy 2050 you need to understand some basic terms. Remember your school physics class? A long time ago? Here's a tutorial.

Electricity comes from the socket - continuously and at all times. That's our experience in daily life. We've heard of volts and watts in connection with our electrical appliances, but what about voltage, output, current and frequency?

Simple! Here's an explanation. Let's take water supply as an example. Water flowing through a pipe is under a certain pressure. That is also the case for electricity that flows through a line - and this pressure is called voltage. Voltage is measured in the unit volt.

Electricity with 380 kilovolts (kV) or 220 kV is transmitted through the Swiss high-voltage grid. When the power reaches the local distribution grid (electrical socket) the voltage is 230 volts. Car batteries usually generate a voltage of 12 V, lightening has a voltage of 100 mega-volts or a 100 million volts.

We @Axpo have Herz (heart) und Hertz...

Resistance can also be explained with the water pipe analogy. A thin cable represents higher and a thicker cable smaller resistance. Electric resistance is measured in the unit ohm. The strength of the current flowing through the cable is denoted in amperes. If one multiplies current (volt) times strength (ampere) the result is the output. Output is measure in watts. A watt is the amount of energy consumed per second. A 100-watt light bulb uses five times more energy per second than a 20-watt bulb.

Vacuuming and bike riding

The authors of the book "Energiewende in 60 Minuten" (see note below) calculate that as a rule a vacuum cleaner has an output of 1000 watts (1 kilowatt/kW). At a voltage of 230 volts, about 4.5 amperes would "flow". A common fuse for electrical sockets in residential buildings in Switzerland has 13 amperes. If one were to operate three vacuum cleaners simultaneously, the fuse would blow...

If a vacuum cleaner with an output of 1 kW is operated for an hour, it uses precisely one kilowatt-hour of electricity. To sum it up: Watt=output,  watt-hours=work (energy volume). Here's another example. If you ride a bike up a mountain pass for an hour, the effort equals 400 watts. If you take two hours the output decreases to 200 watts. However, the work that the two bikers have performed when they reach the pass is 400 watt-hours for both of them.

And this is what you can do with one kWh of electricity:

  • run 1 washing machine with clothes
  • Illuminate a room with an energy-saving lamp for 50 hours
  • watch television for 7 hours
  • Cook food for 4 people

Last but not least: Hertz. Hertz deisgnates the utility frequency of the current oscillations. In Europe, a frequency of 50 hertz is used for electrical energy supply by means of alternate current. In order for this frequency to remain stable, the balance between production and consumption of electrica Output must always be maintained. Deviations result in a Change of the grid frequency. If grid frecquency decreases or increases, electrical devices as well as generators can be damaged - or worst: it could cause a blackout.

The power of the sun

In the field of photovoltaics, one also encounters another abbreviation - it is the term Watt Peak or Kilowatt Peak, abbreviated kWp. The term indicates the maximum output in watts or kilowatts of a photovoltaic system and is used to compare different PV modules under standard test conditions (STC). However, the real operating conditions usually deviate greatly from these test conditions, which is why solar module manufacturers often work with other, more realistic specifications (Normal Operating Cell Temperature/NOCT). In Switzerland, a PV system with an output of 1 kWp can be expected to produce an average of almost 1000 kWh of electricity per year.

Terms at a glance

Volt – voltage

Ampere – current (strength)

Ohm – resistance

Watt – output

Watt-hour – work/energy volume

Hertz - frequency

More information on this topic is available in the book "Energiewende in 60 Minuten". Ein Reiseführer durch die Stromwirtschaft; Kästner Th.; Kiessling A. 2016 ISBN 978-3-658-11560-9

Understood? Did a light dawn on you? Hopefully!
Full of energy

Energy isn't simply energy. The energy in its natural state is called primary energy. Crude oil, natural gas, coal and uranium belong to the non-renewable category. Hydropower, wind, solar, geothermal and biomass are renewables.

If one transforms primary energy into another energy form in a power plant or other technical facility the result is called secondary energy. Gasoline from the filling station or electricity from the socket are end energies. In appliances such as refrigerators, lamps, or car motors end energy is transformed into so-called useful energy (heat, light, etc.).

The term grey energy refers to the energy volume needed for production, storage, sales and disposal of a product. All the precursors including the extraction of the raw materials and energy consumption of the entire production process are included in the calculation.


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