Basic 9 · Science · Energy
Conserving Energy and Calculating Energy Use
In this topic you will list ways of conserving energy, explain the importance of energy conservation in daily life and calculate the electrical energy consumed over a period of time.
By the end of these notes you should be able to:
- List ways of conserving energy
- Explain the importance of energy conservation
- Calculate electrical energy consumption
What you already know
- Energy conversion
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Forces & Energy
- Sub-strand
- Energy
- Indicator
- B9.4.1.1.1 – List the ways to conserve energy. Examples: ironing in bulk using energy efficient appliances and switching off appliances when not in use
Introduction
Some energy use is necessary, and some is simple waste. Small changes in how we use electricity can save a family a great deal of money.
1. Saving Electricity
| Action | Why it works |
|---|---|
| ironing in bulk | the iron does not reheat many times |
| using energy-efficient appliances | they use less power |
| switching off when not in use | no waste on empty rooms |
| using LED bulbs | less energy lost as heat |
| unplugging chargers | removes standby use |
| using natural light | no electricity needed |
| defrosting fridges | they work more efficiently |
2. Energy Labels
Ghana's Energy Commission uses star labels on appliances, such as fridges and air conditioners. More stars mean greater efficiency. The law discourages importing used fridges, as these often use a great deal of electricity. Before buying an appliance, compare both the price and the power rating. A cheap device with a high power rating may cost more in the long run.
3. Saving in Transport and Cooking
Energy conservation also applies to fuel. Walking and sharing transport use less fuel. Keeping tyres at the correct pressure and servicing vehicles reduces fuel use. In cooking, keep lids on pots, cut food into small pieces and use improved stoves. Using dry firewood produces more heat and less smoke. These actions help to conserve fuel and forests.
4. Building Design
Buildings can be designed to save energy. Light-coloured roofs reflect the sun. Good ventilation reduces the need for fans. Large windows, placed to catch daylight, reduce the need for lighting. Trees shade a building and cool the air around it. Local materials such as earth bricks keep houses cool, and many traditional homes in northern Ghana used these principles.
5. Making a Plan
- List the appliances you use.
- Identify the waste.
- Choose changes you can make.
- Tell your family.
- Check your bill or meter after a month.
Prepaid meters make it easy to see how quickly units are used. Even a family with few appliances can benefit from these habits. Energy conservation is a habit, and it starts with paying attention.
New words
- conserve
- To use carefully.
- standby
- A low-power waiting mode.
- efficient
- Using little energy for the same job.
- power rating
- The power used by an appliance.
Summary
- Simple habits can save electricity.
- Efficient appliances save money in the long term.
- Conservation also applies to fuel and buildings.
Class activity: Energy Survey
- List the appliances at school.
- Note how they are used.
- Suggest ways to save.
You need: Sample ECG electricity bill, LED bulb, Calculator
Exercises
Answer in your exercise book first, then check your answers.
1. Which saves electricity?
- A. ironing in bulk
- B. leaving lights on
- C. opening the fridge often
- D. using old bulbs
Show answer
Answer: ironing in bulkHabit.2. Star labels show…
- A. energy efficiency
- B. the price
- C. the colour
- D. the age
Show answer
Answer: energy efficiencyLabel.3. Standby mode uses some electricity.
- A. True
- B. False
Show answer
Answer: TrueWaste.4. LED bulbs waste less energy as ______.
Show answer
Answer: heatEfficiency.5. Give three ways of saving energy at home.
Show answer
Answer: Switch off lights, unplug chargers and iron in bulk.Any three.6. Why might a cheap appliance cost more in the long run?
Show answer
Answer: It can use more electricity, which raises bills.Value.
Lesson 2
- Strand
- Forces & Energy
- Sub-strand
- Energy
- Indicator
- B9.4.1.1.2 – Explain the importance of energy conservation in daily life
Introduction
Each unit of electricity saved is money kept, fuel not burned and pollution avoided.
1. Why It Matters
| Area | Benefit |
|---|---|
| household | lower bills |
| business | lower costs, more profit |
| national | less fuel imported |
| environment | less carbon dioxide |
| supply | fewer outages |
| future | resources last longer |
2. Energy and Money
Electricity and fuel are major costs for families, schools and businesses. A school that saves on electricity can spend more on books. A business that cuts energy costs can employ more people. At a national level, less electricity demand means less fuel burned in thermal plants, and this can save foreign exchange.
3. Energy and the Environment
Burning fossil fuels gives off carbon dioxide, which adds to global warming. Hydroelectric dams flood land, and solar panels need materials. Every form of energy has a cost, so the cleanest energy is the energy that we do not use. Saving charcoal also protects trees. For every bag of charcoal saved, there is less pressure on the forests of the transition zone.
4. Energy Security
Energy security means having a reliable, affordable supply. Ghana's dumsor years showed how shortages harm businesses, hospitals and schools. Conservation reduces demand, and so it reduces strain on the system, particularly at peak times. A country that wastes less can serve more people. This matters since Ghana is still working towards full electricity access in remote communities.
5. Careers in Energy
| Career | Work |
|---|---|
| electrical engineer | designs and maintains systems |
| solar technician | installs solar panels |
| energy auditor | finds waste in buildings |
| environmental scientist | studies the effects of energy use |
As renewable energy grows, new jobs are appearing. Young people with science skills are needed. Learning how to use energy wisely now is good preparation for these careers, and for adult life.
New words
- energy security
- Reliable access to energy.
- peak time
- The period of highest demand.
- foreign exchange
- Money from other countries.
- energy audit
- A check of energy use.
Summary
- Conservation saves money and protects the environment.
- It supports reliable energy for the nation.
- Energy creates new career opportunities.
Class activity: Energy Campaign
- Prepare a short message on saving energy.
- Present it at assembly.
- Ask for one action.
You need: Sample ECG electricity bill, LED bulb, Calculator
Exercises
Answer in your exercise book first, then check your answers.
1. Saving electricity lowers…
- A. bills
- B. marks
- C. rain
- D. ages
Show answer
Answer: billsBenefit.2. Which is a benefit of conservation?
- A. fewer outages
- B. more pollution
- C. higher costs
- D. less food
Show answer
Answer: fewer outagesBenefit.3. Burning fossil fuels adds carbon dioxide to the air.
- A. True
- B. False
Show answer
Answer: TrueEnvironment.4. The period of highest demand is ______ time.
Show answer
Answer: peakTerm.5. State three benefits of energy conservation.
Show answer
Answer: Lower bills, less pollution and more reliable supply.Any three.6. Why is the cleanest energy the energy not used?
Show answer
Answer: All sources have some environmental cost.Reasoning.
Lesson 3
- Strand
- Forces & Energy
- Sub-strand
- Energy
- Indicator
- B9.4.1.2.1 – Explain how to calculate energy consumed over a period of time
Introduction
Your electricity bill is not a mystery. It is simple arithmetic.
1. Power and Energy
Power is the rate of using energy. It is measured in watts (W). 1,000 W = 1 kilowatt (kW). Energy used depends on both power and time. The formula is: E = P × t. If power is in kilowatts and time is in hours, then energy is given in kilowatt-hours (kWh). One kWh is one unit on an electricity meter. In joules, 1 kWh = 3,600,000 J.
| Appliance | Power (W) |
|---|---|
| LED bulb | 10 |
| fan | 60 |
| television | 100 |
| fridge | 150 |
| electric iron | 1,000 |
| water heater | 2,000 |
2. Worked Examples
Single appliance
A 1,000 W iron is used for 2 hours. Find the energy used in kWh.
- P = 1 kW.
- E = 1 × 2.
Answer: 2 kWh
Several appliances
A home uses five 10 W bulbs for 6 hours, and a 100 W TV for 4 hours a day. Find the daily energy.
- Bulbs: 5 × 10 W = 50 W = 0.05 kW; 0.05 × 6 = 0.3 kWh.
- TV: 0.1 × 4 = 0.4 kWh.
- Total: 0.3 + 0.4.
Answer: 0.7 kWh per day
Cost
At GH₵2 per kWh, find the cost of 0.7 kWh a day for 30 days.
- Energy: 0.7 × 30 = 21 kWh.
- Cost: 21 × 2.
Answer: GH₵42
Tariffs change with time, and the rates here are for practice only.
3. Comparing Bulbs
Saving with LEDs
Compare a 60 W filament bulb and a 10 W LED, each used for 5 hours a day for 30 days.
- Filament: 0.06 × 5 × 30 = 9 kWh.
- LED: 0.01 × 5 × 30 = 1.5 kWh.
- Saving: 9 − 1.5.
Answer: 7.5 kWh saved each month
4. Reading a Meter
Meters show the kWh used. For an old meter, subtract the last reading from the new one to find the units used. On a prepaid meter, the display shows the remaining units. Watching this helps you to see what uses the most energy. Appliances that heat, such as irons and water heaters, use the most power.
New words
- watt
- The unit of power.
- kilowatt-hour
- A unit of electrical energy.
- tariff
- The price of electricity.
- meter
- A device that measures use.
Summary
- E = P × t.
- Use kW and hours to get kWh.
- Cost = energy × tariff.
Class activity: Energy Bill
- List appliances and hours of use.
- Calculate the daily and monthly energy.
- Estimate the cost.
You need: Sample ECG electricity bill, LED bulb, Calculator
Exercises
Answer in your exercise book first, then check your answers.
1. The unit of power is the…
- A. watt
- B. litre
- C. kilogram
- D. metre
Show answer
Answer: wattUnit.2. A 2,000 W heater used for 3 hours uses…
- A. 6 kWh
- B. 5 kWh
- C. 2 kWh
- D. 600 kWh
Show answer
Answer: 6 kWh2 × 3.3. 1,000 W = 1 kW.
- A. True
- B. False
Show answer
Answer: TrueConversion.4. Energy = power × ______.
Show answer
Answer: timeFormula.5. Find the energy used by a 100 W TV in 5 hours.
Show answer
Answer: 0.5 kWh0.1 × 5.6. Find the monthly cost of a 150 W fridge running for 24 hours a day, 30 days, at GH₵2 per kWh.
Show answer
Answer: 108 kWh, costing GH₵216.0.15 × 24 × 30.
Homework
- Calculate your household's daily electricity use for three appliances.