What it shows
Reading the electricity meter daily and logging how long each appliance runs shows which ones use most of the units. In most homes a few items, such as the geyser, air conditioner, old refrigerator and ceiling fans running all day, account for most of the bill, and small changes cut it without any discomfort.
The science
Energy in kilowatt-hours, the units on the bill, equals power in kilowatts times time in hours. An appliance's rated watts come from its label; multiplied by its daily hours and divided by 1000 it gives units per day. Adding all appliances should come close to the meter's daily change, and the gap shows hidden loads such as chargers and standby. Heating appliances draw the most power, so a geyser used for an hour can equal a fan running for a whole day.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Access to the house electricity meter reading (looking only, never opening it)
- The last three electricity bills
- A list of appliances with their rated watts from their labels
- A log sheet with hours of use per day
- A calculator or spreadsheet
- Chart paper
Safety
For this project: Read labels and the meter display only. Never open a meter box, switchboard or appliance, and never touch wiring; an adult must be present when reading the meter.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
9 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
With an adult, note the meter reading at the same time each day for seven days.
List every appliance and copy its rated watts from its label or manual.
For each day, write how many hours each appliance ran, asking family members to help.
Calculate units per day for each appliance: watts times hours divided by 1000.
Add them and compare with the meter difference for that day; note the unmeasured gap.
Average the week and rank the appliances by units.
Draw a pie chart of the household's electricity by appliance.
For the top three, propose a change: a timer on the geyser, a higher AC set point, switching to LED, or defrosting the fridge.
Estimate the monthly saving in units and rupees using the per-unit rate on the bill.
What you should see
A pie chart where two or three appliances take more than half the units, a logged total within about 15 per cent of the meter, and a saving plan worth a few hundred rupees a month.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is one unit of electricity?
One kilowatt-hour: 1000 watts running for one hour.
2How many units does a 2000 watt geyser use in half an hour?
One unit.
3Why did your sum differ from the meter?
Chargers, standby lights and appliances whose hours were not logged.
4Which appliance type uses most power?
Heating appliances such as geysers, irons and heaters.
Take it further
Repeat the week after the changes and compare the two pie charts and bills.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Investigatory Projects for Class 11 and 12
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