Senior 3 practice book · Unit 3 of 10

Renewable and Non-Renewable Energy Sources

50 questions that complete the Senior 3 quiz for this unit: 28 core and 22 challenge. Easy and hard questions are mixed. Try each question, then tap “Show answer”.

Common misconceptions

Renewable sources have no effect on the environment at all.Every source has some effect: dams flood valleys and block fish, solar panels need mining and careful disposal, firewood can cause deforestation. Renewable means the source is replaced naturally, not that it is harmless.
Solar panels work by collecting the Sun's heat.Photovoltaic panels turn LIGHT directly into electricity; heat actually lowers their efficiency a little. It is the solar water heater that uses the Sun's heat.
A battery makes energy.A battery only stores energy (as chemical energy) that was supplied when it was charged, for example by a solar panel. It gives back less than was put in.
Saving energy is pointless because energy is always conserved.The total energy is conserved, but useful energy becomes spread out as heat that we cannot use again. 'Saving energy' means wasting less of the useful supply, so less fuel is burned.
Peat is renewable because it is made from plants.Peat forms from dead swamp plants at only about 1 mm a year, so it is used thousands of times faster than it forms. It is treated as a non-renewable fuel, and burning it releases CO₂.

What this unit covers

Topics marked new are not tested much in the quiz, so this book gives them extra questions.

Energy sources: renewable and non-renewable, and the Sun as the origin of most sources
Fossil fuels: formation, uses and why they are non-renewable
Solar energy: photovoltaic panels and solar water heaters
Hydropower and wind power: energy changes and suitable sites
Biomass and biogas
Geothermal and nuclear energy
Environmental effects: global warming, acid rain, air and water pollution
Energy calculations: power, efficiency, kWh and the cost of energy
Energy transition, sustainability, energy security and rural development
Energy conversion chains, Sankey diagrams and saving energy at home and school
Storing energy: rechargeable batteries (Ah and Wh) and pumped-storage hydro
Peat as an energy source in Rwanda, and sources Rwanda cannot use (tidal, wave)

Go to the questions

Questions (1–50)

Easier and harder questions are mixed, just like in a real exam. The 22 harder ones are marked ★ Challenge.

1True or false
Solar panels cause no pollution at any stage of their life.
Show answer
Answer: False
They give no pollution while working, but making them uses energy and mined materials, and old panels must be recycled or disposed of carefully.
Common mistakeThinking 'renewable' means 'no impact at all' forgets the manufacture and disposal of the equipment.
2True or false · ★ Challenge
A wind turbine on an exposed hilltop usually produces more electricity than the same turbine in a sheltered valley.
Show answer
Answer: True
Wind is stronger and steadier on exposed hilltops, and a turbine's power rises steeply with wind speed.
Common mistakeThinking the site makes no difference ignores that the turbine can only convert the kinetic energy the wind brings.
3True or false
A nuclear power station produces electricity by burning uranium in a furnace, like coal.
Show answer
Answer: False
Uranium is not burned: its nuclei split (fission), releasing heat that boils water to drive turbines.
Common mistakeThinking nuclear fuel 'burns' confuses fission with combustion; no oxygen or flame is involved.
4Multiple choice · ★ Challenge
Which of these is NOT a fossil fuel?
1. ACharcoal
2. BCoal
3. CNatural gas
4. DKerosene
Show answer
Answer: A. Charcoal
Charcoal is made today by heating wood, so it is a biomass fuel. Coal, natural gas and kerosene (from crude oil) formed over millions of years.
Common mistakeChoosing coal confuses it with charcoal because the names are similar; charcoal is made from wood in a few days.
5True or false
A solar panel gives less electrical power on a warm, cloudy day than on a cool, clear day.
Show answer
Answer: True
PV output depends on the light reaching the panel; clouds block light, and warmth does not help.
Common mistakeThinking warm days always give more power confuses light with heat.
6True or false
Peat is partly decayed plant material from swamps, and burning it releases carbon dioxide.
Show answer
Answer: True
Peat contains carbon from plants; burning it produces CO₂, like other fuels containing carbon.
Common mistakeThinking peat is soil or rock leads learners to think it cannot burn or give CO₂.
7Multiple choice · ★ Challenge
Which problem can a large new hydroelectric dam cause, even though hydropower is renewable?
1. AFarms and homes upstream are flooded
2. BLarge amounts of sulfur dioxide are released
3. CThe river water becomes radioactive
4. DThe water is used up by the turbines
Show answer
Answer: A. Farms and homes upstream are flooded
The reservoir floods land behind the dam, may force families to move and changes the river for fish.
Common mistakeChoosing 'water is used up' repeats the wrong idea that turbines consume water; it flows on downstream.
8True or false
Firewood is a renewable source only if trees are replanted at least as fast as they are cut down.
Show answer
Answer: True
Wood regrows, but if forests are cut faster than they regrow, the supply runs down like a non-renewable one.
Common mistakeCalling firewood renewable in every case ignores deforestation: renewable depends on the rate of use.
9Multiple choice · ★ Challenge
A family's biogas digester gives much less gas in a cold month. What is the best explanation?
1. ACold weather turns the methane back into liquid inside the tank
2. BLess sunlight reaches the digester, and it runs on solar energy
3. CCold air leaks in and the oxygen burns the gas inside the tank
4. DThe bacteria that break down the dung work more slowly when cold
Show answer
Answer: D. The bacteria that break down the dung work more slowly when cold
Biogas is made by bacteria digesting dung without air; like all living things they are slower at low temperature.
Common mistakeChoosing 'it runs on solar energy' misses that the gas comes from bacterial digestion, not directly from sunlight.
10True or false
Switching off unused lamps 'saves energy' even though the law of conservation of energy says energy is never lost.
Show answer
Answer: True
Energy is conserved in total, but electricity used by a lamp ends up as low-grade heat we cannot reuse; switching off means less fuel or water is used to generate it.
Common mistakeArguing that saving energy is meaningless confuses total energy with useful energy.
11Multiple choice · ★ Challenge
A hydro plant keeps the same flow of water but a new dam doubles the height through which the water falls. How does the electrical power output change (same efficiency)?
1. AIt stays the same
2. BIt becomes four times as large
3. CIt halves
4. DIt doubles
Show answer
Answer: D. It doubles
P = efficiency × (mass per second) × g × h; doubling h doubles P.
Common mistakeChoosing 'four times' treats height like speed in ½mv²; potential energy mgh is directly proportional to h.
12Fill in the blank
The slurry left over in a biogas digester can be spread on fields as ______.
Show answer
Answer: fertiliser (manure)
The digested dung still contains plant nutrients, so it is a useful fertiliser.
Common mistakeThinking the slurry is useless waste ignores one of the main advantages of biogas over burning dung.
13Multiple choice · ★ Challenge
Why can Rwanda not use tidal or wave energy?
1. AIts rivers flow too fast for tidal turbines to work
2. BIt has no sea coast, and lakes have tiny tides and waves
3. CIts lakes are too deep for any waves to form
4. DIt is too close to the equator for tides to happen
Show answer
Answer: B. It has no sea coast, and lakes have tiny tides and waves
Tidal and wave power need an ocean coast; Rwanda is landlocked, and its lakes are far too small for useful tides.
Common mistakeChoosing 'too close to the equator' is wrong: tides happen at all latitudes; the problem is having no ocean.
14Fill in the blank
Wind, rain-fed rivers, wood and even fossil fuels all got their energy, directly or indirectly, from the ______.
Show answer
Answer: Sun
The Sun heats the air (wind), evaporates water (rain and rivers) and drives photosynthesis (wood, and the ancient plants that became fossil fuels).
Common mistakeAnswering 'Earth' or 'wind' misses the original source; only geothermal, nuclear and tidal energy do not come from the Sun.
15Short answer · ★ Challenge
Methane gas in Lake Kivu is slowly produced by bacteria and volcanic activity. Discuss whether it should be called a renewable source when it is used to generate electricity.
Show answer
Model answer: It forms naturally, but very slowly, while power stations extract it far faster than it is replaced. So in practice it is treated as a non-renewable source (like natural gas), even though some new gas keeps forming.
Common mistakeSaying it is renewable just because new gas forms ignores the RATE: a source is renewable only if it is replaced as fast as it is used.
16Fill in the blank
When a rechargeable battery is charged from a solar panel, the electrical energy is stored in the battery as ______ energy.
Show answer
Answer: chemical
Charging drives chemical reactions; discharging reverses them and gives back electrical energy.
Common mistakeAnswering 'electrical' suggests charge is simply kept in a box; the battery stores energy in its chemicals.
17Multiple choice · ★ Challenge
In a hydroelectric station the turbine is 85% efficient and the generator is 95% efficient. What is the overall efficiency?
1. A90%
2. B180%
3. C10%
4. D81%
Show answer
Answer: D. 81%
Overall = 0.85 × 0.95 = 0.81 = 81%.
Common mistakeChoosing 90% averages the two efficiencies; for stages in a chain the efficiencies multiply.
18Multiple choice
Which list contains ONLY renewable energy sources?
1. ASolar, peat and geothermal energy
2. BCoal, wind and biomass from forests
3. CHydropower, uranium and solar energy
4. DWind, biogas and hydropower
Show answer
Answer: D. Wind, biogas and hydropower
Wind, biogas and hydropower are all replaced naturally. Peat, coal and uranium are finite.
Common mistakeChoosing the list with peat is tempting because peat comes from plants, but it forms far too slowly to be renewable.
19Multiple choice
Which action most improves Rwanda's energy security?
1. AImporting more diesel to run the existing generators
2. BRelying on one large power station for the whole country
3. CUsing several local sources: hydro, solar and Kivu methane
4. DBurning more firewood in towns and in the countryside
Show answer
Answer: C. Using several local sources: hydro, solar and Kivu methane
Energy security means a reliable supply; many local sources reduce dependence on imports and on any single plant.
Common mistakeChoosing one large power station puts every user at risk if that one plant fails.
20True or false · ★ Challenge
A fully charged 12 V, 100 Ah battery could keep a 120 W vaccine fridge running for about 10 hours if all its energy were used.
Show answer
Answer: True
Energy = 12 × 100 = 1200 Wh; time = 1200 ÷ 120 = 10 h.
Common mistakeDividing 100 Ah by 120 W (0.8 h) mixes units; first change Ah to Wh by multiplying by the voltage.
21Multiple choice
How does a pumped-storage hydro scheme store energy?
1. AWater is pumped uphill when demand is low, then released at peaks
2. BWater is heated by spare electricity and stored in insulated tanks
3. CTurbines are kept spinning all night so that they keep their energy
4. DElectricity is stored inside the water itself until it is needed
Show answer
Answer: A. Water is pumped uphill when demand is low, then released at peaks
Spare electricity pumps water to a high reservoir, storing gravitational potential energy; at peak times it flows down through turbines.
Common mistakeChoosing 'electricity is stored in the water' misunderstands the change: the energy is stored as potential energy of the raised water.
22Multiple choice
In a geothermal power station, what turns the turbines?
1. AHot lava pumped up from inside the volcano
2. BSteam from water heated by hot rocks
3. CWind blowing across the warm ground
4. DMethane gas burned to heat a boiler
Show answer
Answer: B. Steam from water heated by hot rocks
Water is heated by hot rocks deep underground; the steam (or hot water flashing to steam) drives the turbines.
Common mistakeChoosing 'hot lava' imagines lava is used; only the heat of the rocks is used, carried up by water.
23Short answer · ★ Challenge
Explain how the greenhouse effect keeps the Earth warm, and why burning more fossil fuels makes the Earth warmer.
Show answer
Model answer: Sunlight passes through the air and warms the ground. The warm ground gives out infrared radiation, which greenhouse gases (CO₂, methane, water vapour) absorb and send partly back down, trapping heat. Burning fossil fuels adds CO₂, so more heat is trapped and the average temperature rises.
Common mistakeSaying CO₂ 'makes a hole' that lets in more sunlight confuses the greenhouse effect with the ozone layer.
24Short answer · ★ Challenge
Give one advantage and one disadvantage of nuclear power, and explain why a country planning nuclear power needs a long-term plan for its waste.
Show answer
Model answer: Advantage: a small mass of fuel gives a huge amount of energy with almost no CO₂ while running. Disadvantage: uranium is finite, and accidents are serious. The used fuel stays radioactive for thousands of years, so it must be stored safely and guarded far into the future.
Common mistakeSaying nuclear power is 'clean, so no problems' ignores the radioactive waste.
25Multiple choice
In a Sankey diagram, what does the width of each arrow show?
1. AThe speed at which the energy moves
2. BThe amount of energy flowing that way
3. CThe temperature of that form of energy
4. DThe time taken for the energy to flow
Show answer
Answer: B. The amount of energy flowing that way
Widths are drawn to scale: a wide arrow means a large amount of energy.
Common mistakeChoosing speed or time adds an idea the diagram does not show; it only shows amounts of energy.
26Multiple choice
Which gas makes up most of the biogas produced in a farm digester?
1. ACarbon dioxide
2. BMethane
3. COxygen
4. DHydrogen
Show answer
Answer: B. Methane
Biogas is about 50–70% methane, the gas that burns; the rest is mainly carbon dioxide.
Common mistakeChoosing carbon dioxide is tempting because it is present, but CO₂ does not burn and is the smaller part.
27Short answer · ★ Challenge
Rwanda generates some electricity by burning peat. Give one advantage and one disadvantage of peat power, and suggest why some people object to draining peat wetlands.
Show answer
Model answer: Advantage: a local fuel that reduces imports and gives power day and night. Disadvantage: burning peat releases a lot of CO₂ and the supply is finite. Draining wetlands destroys habitats and releases carbon stored in the peat; wetlands also store water and reduce flooding.
Common mistakeCalling peat power 'green' because the fuel is local ignores the CO₂ it releases.
28Multiple choice
Which energy changes happen when diesel burns in the engine of a minibus?
1. AKinetic → chemical → heat energy
2. BHeat → chemical → electrical energy
3. CChemical → heat → kinetic energy
4. DElectrical → kinetic → chemical energy
Show answer
Answer: C. Chemical → heat → kinetic energy
The fuel stores chemical energy; burning releases heat, and the engine turns part of it into kinetic energy (the rest is wasted as heat).
Common mistakeChoosing 'heat → chemical' reverses the order: the chemical energy of the fuel comes first.
29Short answer · ★ Challenge
A learner says: 'Solar panels work by collecting the Sun's heat, so they are best in hot deserts.' Correct the learner and explain what a panel's output really depends on.
Show answer
Model answer: PV panels turn light, not heat, into electricity. The output depends on the light intensity reaching them (Sun height, clouds, dust, the angle of the panel) and on the area and efficiency. Very hot panels are slightly less efficient, so a cool, bright place is best.
Common mistakeAgreeing that heat drives a PV panel confuses it with a solar water heater.
30Multiple choice
Which change would save the most electrical energy for lighting a school classroom?
1. APainting the classroom walls a dark colour
2. BFitting a thicker cable to the lamps
3. CReplacing filament lamps with LED lamps
4. DUsing lamps of higher power rating
Show answer
Answer: C. Replacing filament lamps with LED lamps
LEDs give the same light for a fraction of the input energy, so far less is wasted as heat.
Common mistakeChoosing a thicker cable has a tiny effect; the lamps themselves waste most of the energy.
31Short answer · ★ Challenge
Kigali is introducing electric moto taxis charged from the national grid. Explain two ways this can reduce pollution in the city, and one condition for it to really cut CO₂ emissions.
Show answer
Model answer: 1) No exhaust gases (CO, NOₓ, smoke) are released in the streets. 2) Electric motors are quieter, cutting noise pollution. Condition: the grid electricity must come mostly from low-carbon sources (hydro, solar, methane rather than diesel or peat), or the CO₂ is only moved to the power station.
Common mistakeSaying electric motos give 'zero emissions' forgets the emissions of the power stations that charge them.
32Multiple choice
A family burns charcoal on a stove inside a closed room. What is the most immediate danger?
1. AAcid rain falling on the roof
2. BGlobal warming of the room
3. CCarbon monoxide poisoning
4. DRadiation burns from the stove
Show answer
Answer: C. Carbon monoxide poisoning
Burning with too little air makes carbon monoxide, a poisonous gas with no smell that can kill in a closed room.
Common mistakeChoosing global warming mixes up a slow, worldwide effect of CO₂ with the immediate danger of CO.
33Multiple choice
A school has a solar water heater and a photovoltaic (PV) panel on its roof. What is the main difference between them?
1. AThe heater gives electricity; the PV panel gives hot water
2. BThe heater gives hot water; the PV panel gives electricity
3. CBoth give electricity, but the heater works at night as well
4. DBoth give hot water, but the PV panel is the more efficient
Show answer
Answer: B. The heater gives hot water; the PV panel gives electricity
A solar water heater absorbs the Sun's radiation as heat in water; a PV panel turns light directly into electrical energy.
Common mistakeChoosing 'both give electricity' mixes up the two devices because both are on roofs and both use sunlight.
34Multiple choice · ★ Challenge
A learner records the output of a solar panel on a clear day: 9:00 → 120 W, 12:00 → 300 W, 15:00 → 150 W. What best explains the highest output at noon?
1. AThe Sun is highest, so more light falls on each square metre
2. BThe air is warmest at noon, and panels work using heat
3. CThe panel has had all morning to store up the sunlight
4. DThe panel is cleanest at noon, after the morning dew dries
Show answer
Answer: A. The Sun is highest, so more light falls on each square metre
When the Sun is high its rays strike the panel more directly and pass through less air, so more light power reaches each m².
Common mistakeChoosing 'the air is warmest' thinks PV panels use heat; they use light, and heat actually lowers their efficiency.
35Fill in the blank
One kilowatt-hour of energy is equal to ______ MJ.
Show answer
Answer: 3.6
1 kWh = 1000 W × 3600 s = 3 600 000 J = 3.6 MJ.
Common mistakeAnswering 1000 forgets the hours: a kWh is 1000 W for 3600 s, not for 1 s.
36Multiple choice · ★ Challenge
A filament lamp gives 10 J of light for every 100 J of electrical energy. An LED gives the same 10 J of light from only 20 J. What is the efficiency of the LED?
1. A50%
2. B10%
3. C20%
4. D200%
Show answer
Answer: A. 50%
Efficiency = useful output ÷ input = 10 ÷ 20 = 0.50 = 50%.
Common mistakeChoosing 20% divides 20 by 100, comparing the two lamps' inputs instead of the LED's output with its input.
37Multiple choice
Peat burned at the Gishoma power plant in Rusizi is best described as:
1. AA renewable fuel, as it comes from plants
2. BA nuclear fuel, as it is dug from the ground
3. CA non-renewable fuel, as it forms very slowly
4. DA clean fuel that gives out no carbon dioxide
Show answer
Answer: C. A non-renewable fuel, as it forms very slowly
Peat builds up from dead swamp plants at about 1 mm a year, far slower than it is dug and burned.
Common mistakeChoosing 'renewable, as it comes from plants' ignores how slowly peat forms.
38Multiple choice · ★ Challenge
A school lights 10 LED lamps of 10 W each for 5.0 hours a day for 30 days. Electricity costs 200 RWF per kWh. What is the cost?
1. A3 000 000 RWF
2. B3000 RWF
3. C300 RWF
4. D100 RWF
Show answer
Answer: B. 3000 RWF
E = 10 × 10 W × 5.0 h × 30 = 15 000 Wh = 15 kWh; cost = 15 × 200 = 3000 RWF.
Common mistakeChoosing 3 000 000 RWF multiplies watt-hours by the price per kWh; divide by 1000 first.
39Short answer
Give two advantages and two disadvantages of using fossil fuels to generate electricity.
Show answer
Model answer: Advantages: high energy per kilogram; power stations can run day and night and be turned up quickly. Disadvantages: they release CO₂ (global warming) and SO₂ (acid rain); they will run out; Rwanda must import oil, which is costly.
Common mistakeListing only disadvantages, or giving 'cheap' without reason, misses that fossil fuels are reliable and concentrated.
40Fill in the blank
An electric motor takes in 500 J of energy and gives out 350 J of useful kinetic energy. The energy wasted (mostly as heat and sound) is ______ J.
Show answer
Answer: 150
Energy is conserved: wasted = 500 − 350 = 150 J.
Common mistakeAnswering 70 gives the efficiency as a percentage, not the wasted energy.
41Multiple choice · ★ Challenge
A solar home system has a 12 V battery rated 100 Ah. About how much energy can it store?
1. A112 Wh
2. B8.3 Wh
3. C1200 kWh
4. D1.2 kWh
Show answer
Answer: D. 1.2 kWh
E = V × capacity = 12 V × 100 Ah = 1200 Wh = 1.2 kWh.
Common mistakeChoosing 112 Wh adds volts and amp-hours; energy is the product V × Ah.
42Multiple choice
Why are hydroelectric stations in Rwanda, such as those on the Rusizi river, built where the river drops steeply?
1. ASteep rivers carry water that is denser than in flat rivers
2. BFast water is colder and turns the turbines more easily
3. CEach kilogram of water falls further, giving more energy
4. DSteep valleys keep the sunlight from heating the turbines
Show answer
Answer: C. Each kilogram of water falls further, giving more energy
Potential energy lost = mgh, so a larger height drop gives more energy per kilogram of water.
Common mistakeChoosing 'denser water' is wrong; river water has the same density everywhere; it is the height h that matters.
43Short answer · ★ Challenge
Compare charcoal and biogas as cooking fuels for a rural family, in terms of renewability, effect on forests and health.
Show answer
Model answer: Charcoal is made from trees, so heavy use causes deforestation; it is renewable only with replanting, and its smoke and carbon monoxide harm health indoors. Biogas comes from dung (renewable daily), saves trees, burns with a clean flame and little smoke, and leaves fertiliser.
Common mistakeCalling both 'renewable, so the same' ignores their very different effects on forests and on the family's lungs.
44Short answer
Rwanda has many small, fast streams in its hills. Explain why micro-hydro plants suit rural villages, and give one limitation.
Show answer
Model answer: They use a free, local, renewable source, need no fuel, can run day and night, and can supply villages far from the grid. Limitation: in the dry season the flow falls, so the output drops (also: high building cost, flooding or silt damage).
Common mistakeSaying hydropower works 'all the time' forgets that the output depends on the river flow, which changes with the seasons.
45Short answer · ★ Challenge
A village wants a micro-hydro plant giving 35 kW of electrical power. The water can fall 25 m and the plant is 70% efficient. What volume of water must flow through it each second? (Density of water 1000 kg/m³, g = 10 N/kg)
Show answer
Model answer: Input power = 35 000 ÷ 0.70 = 50 000 W. Mass per second = P/(gh) = 50 000 ÷ (10 × 25) = 200 kg/s, so the volume is 200 ÷ 1000 = 0.20 m³ per second.
Common mistakeForgetting the efficiency (giving 0.14 m³/s) assumes all the water's energy becomes electricity.
46True or false
Solar mini-grids at rural health centres can improve vaccine storage and care at night.
Show answer
Answer: True
Reliable electricity powers vaccine fridges and lights, which is one way renewable energy supports rural development.
Common mistakeThinking electricity only matters in towns misses its role in rural health and education.
47Multiple choice
A 1500 W electric cooker is used for 2.0 hours a day. How much electrical energy does it use per day?
1. A3.0 kWh
2. B3000 kWh
3. C0.75 kWh
4. D750 kWh
Show answer
Answer: A. 3.0 kWh
E = Pt = 1.5 kW × 2.0 h = 3.0 kWh.
Common mistakeChoosing 3000 kWh uses 1500 instead of 1.5 kW; change W to kW before multiplying by hours.
48Multiple choice · ★ Challenge
A 12 V, 50 Ah battery may only be run down to half its capacity. It supplies a 20 W TV and three 5 W LED lamps. For how long can they all run?
1. A17 h
2. B30 h
3. C4.3 h
4. D8.6 h
Show answer
Answer: D. 8.6 h
Usable energy = 0.5 × 12 × 50 = 300 Wh. Load = 20 + 3 × 5 = 35 W. t = 300 ÷ 35 ≈ 8.6 h.
Common mistakeChoosing 17 h uses the full 600 Wh; the question limits use to half the capacity.
49Short answer · ★ Challenge
A charcoal stove (imbabura) receives 1000 J of chemical energy; 200 J heats the food in the pot and the rest heats the air and the stove. Describe the Sankey diagram, find the efficiency and suggest two ways to improve it.
Show answer
Model answer: One arrow of 1000 J splits into a 200 J useful arrow (pot) and an 800 J waste arrow (air, stove body), with widths in the ratio 1 : 4. Efficiency = 200 ÷ 1000 = 20%. Improvements: insulate the stove walls (clay lining), fit the pot closely and use a lid, shield from wind.
Common mistakeDrawing the useful arrow wider than the wasted one ignores the scale; 800 J must be four times wider than 200 J.
50Short answer
Give two advantages and one disadvantage of pumped-storage hydro compared with large batteries for storing energy for a national grid.
Show answer
Model answer: Advantages: it can store a very large amount of energy for a long time; it lasts many decades and uses only water and rock. Disadvantage: it needs two reservoirs at very different heights and costs a lot to build (also some energy is lost in pumping).
Common mistakeSaying pumped storage creates energy forgets that it gives back less than was used to pump the water.