Standby v switch off: does it really make a difference

Discuss some aspects of energy-efficiency and energy wastage with students, and demonstrate how simple behavioural changes can have an impact on an individual’s energy consumption. The focus is particularly on the usage of devices such as TVs, and the impact of leaving them on standby.

 

LESSON OBJECTIVES

  • Understand how to measure the electricity used by an electrical item such as a TV
  • Work out how to calculate the cost of the electricity used
  • Compare the difference in the amount of energy used to power a TV when it is switched on to how much it uses on standby
  • Report these findings in simple graph form
  • Think about the implications of this and how individual behaviour affects energy consumption

Time required: 30 minutes

Resources & preparation required

TV and, if possible, other electrical devices with a standby function (e.g. photocopier, printer) and/or a mobile phone charger, hand held monitoring device.

Introduction

standby-buttonAsk students to name some electrical devices that have a standby function. Why do people use standby and how often? How much energy do they think a TV, for example, uses on standby – what percentage of the power that it uses when it is turned on? How much of the time do they think their TVs at home are left on standby?

This exercise will show how much energy is used by a TV while on standby, and how much money can be wasted by not switching off completely.

Plug the TV in to a normal electrical socket via a monitoring device. Explain to students that it contains a smart meter, which will measure the amount of electricity that is passing through it – i.e. the amount used by the TV.

Show them the graph of energy usage for the TV. It should show that no power is currently being consumed. Switch on the TV and watch the graph change. Record the figure, in Watts, of how much power is used. Now turn the TV on to standby and record how much electricity is being used.

Explain to students that these figures are not an amount of energy used but the rate of energy usage. Electrical power is measured in Watt-hours (Wh) or Kilowatt-hours (kWh).

To measure electrical energy, you need to use the formula: Energy = Power (in W or kW) x Time (in hours) e.g. if the TV uses 100W and is switched on for an hour, its energy usage is 100 x 1 = 100Wh or 0.1 kWh.

energy-graphWork out how much it would cost to have the TV switched on for 4 hours, compared to how much it would cost to leave it on standby for 4 hours. Base the calculation either on your school’s actual electricity tariff, or using the average cost of 10p per kWh e.g. if the TV uses 100W, then 100 x 4 = 400Wh, or 0.4kWh. This costs 0.4 x 10p = 4p.
Ask students to draw a simple bar chart to show how much electricity is used, and its cost, when switched on compared with in standby mode. If you have other devices available with standby modes, you can repeat the exercise to compare their power usage and running costs when active and on standby. You could also use a

Discussion / summing up

How significant is the amount of energy/money wasted by leaving devices on standby? Ask students to think of all the different devices in their homes and at school that could be contributing to this waste. Do they think people are aware of the energy and money they may be wasting by not switching off electrical equipment?

Extension / homework suggestion

  1. Ask students to count the number of TVs they have in their home and estimate how many hours they are in use each week. How many more hours are the TVs left on standby? Using these estimates, ask students to calculate how much money it costs to power the TVs for four weeks, and how much money is wasted by leaving them on standby during this same time period.
  2. Design a poster to encourage people not to waste energy by leaving electrical equipment on standby.

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