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A short class with Sarah and her students. The other ways are under More.
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Our project is to design an energy conservation plan for the school. Where should we begin?
By finding out where electricity is used. We could visit every classroom and lab.
Good. That survey is called an energy audit. What should we record in each room?
Each appliance, its power in watts from the label, how many there are and how long they stay on.
And what signs of waste might you spot?
Lights on in empty rooms, fans running during breaks, and computers left on after school.
A classroom has 8 tube lights of 40 watts, used for 6 hours a day. How much energy do they use?
8 times 40 times 6 is 1,920 watt-hours, which is 1.92 kilowatt-hours.
And with 20-watt LED tubes instead?
Half as much, 0.96 kilowatt-hours. So we save 0.96 units a day.
Over 200 school days at 8 rupees a unit?
192 units, which is 1,536 rupees a year, just for one classroom!
Why does an LED tube give the same light for less electricity?
It is more efficient. It turns more of the electrical energy into light and less into heat.
Right. Which of our ideas cost nothing at all?
Switching off lights and fans in empty rooms, using daylight and opening the windows.
And how will we know whether the plan worked?
By comparing the units on the school's electricity bills before and after.
a room-by-room survey of appliances, their power ratings, hours of use and signs of waste.
energy (kWh) = power (kW) × time (h), and 1 kWh is one unit on the electricity bill.
energy is not destroyed; wasted energy is changed into forms we cannot use, mostly heat.
useful energy output ÷ total energy input × 100%; LEDs are far more efficient than filament bulbs.
switching off, using daylight, LED lighting, star-rated appliances and solar panels.
comparing electricity bills before and after shows whether the plan works.
8 tube lights of 40 W used for 6 hours a day use 8 × 40 × 6 = 1,920 Wh = 1.92 kWh; 20 W LED tubes would use 0.96 kWh.
Saving 0.96 kWh a day for 200 school days saves 192 kWh, which is ₹1,536 a year at ₹8 per unit for one classroom.
Six 75 W fans left on during a one-hour break waste 0.45 kWh a day, or 90 kWh in 200 school days.
A rooftop solar panel changes light energy into electrical energy, so the school needs to buy less electricity, most of which in India is generated from coal.
Watts times hours, divide by a thousand, that's the units your meter counted.
Class 8B found that its fans ran through every lunch break in an empty room. Their energy monitor put up a "Last one out, switch off!" sign, and the next bill showed the savings, enough for new library books by the end of the year.
S.S.S.S.: Switch off, Sunlight in, Swap to LEDs, Star-rated appliances.
A.C.T.P. - Audit, Calculate, Transform-and-think (link to physics), Plan and present.
Term
What is an energy audit?
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Term
How do you calculate electrical energy in kWh?
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What is "1 unit" on an electricity bill?
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What happens to the energy "wasted" by a filament bulb?
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What does a BEE star label show?
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A survey that records how, where and how much energy is used, and where it is wasted.
The rate at which energy is used or transferred; measured in watts (W).
The unit of power; 1 watt means 1 joule of energy used every second.
The energy used by a 1 kW appliance in 1 hour, equal to 3.6 × 10⁶ joules; called one unit on electricity bills.
Useful energy output divided by total energy input, usually given as a percentage.
Using less energy by avoiding waste and choosing more efficient appliances and habits.
A source that is naturally replaced and will not run out, such as sunlight or wind.
The Bureau of Energy Efficiency rating on appliances in India; more stars mean less electricity for the same work.
A step-by-step group project in which you audit how your school uses electricity, calculate how much energy and money is wasted, and design a practical plan to save energy.
This project turns the ideas of the energy chapter into action. Working in teams, you carry out an energy audit of classrooms and labs, record the power rating and daily use of each appliance, and calculate energy in kilowatt-hours, the "units" on an electricity bill. You then connect your findings to physics: energy transformations, the law of conservation of energy and efficiency. Finally, you choose saving measures, from switching off lights to fitting LED tubes, star-rated appliances or solar panels, estimate the savings, present your plan and check its results on later electricity bills.
To find out where and how electrical energy is used and wasted in the school, and to design a realistic plan that reduces energy use, saves money and protects the environment.
Work in groups of four or five and share the jobs: surveyors who visit rooms, a recorder who fills in the data sheet, a calculator who works out energy and cost, and designers who prepare the final poster or report.
An energy audit is a survey of how energy is used. For each room, record:
Energy depends on power and time:
Energy (kWh) = power (kW) × time (h)
One kilowatt-hour (kWh) is the energy used by a 1 kW appliance in 1 hour. It equals 3.6 × 10⁶ joules and is the "1 unit" shown on electricity bills.
Worked example for one classroom:
Saving electricity also helps the environment, because most of India's electricity is still generated by burning coal, a non-renewable fuel whose burning releases carbon dioxide.
Present the plan as a poster or report with a table of the audit, the calculations and bar charts of energy use by room. After the plan starts, compare the units on the school's electricity bills month by month, and appoint student "energy monitors" in each class to keep the habits going.