What this lesson teaches
I can evaluate solar power and hydropower as ways to replace fossil fuels securely and sustainably.
Syllabus 9173, Topic 1.1, 3. Managing Resources. How do we manage the use of renewable energy sources?
Make a guess
A large dam stores water for power. Does that make its electricity independent of the weather?
- Yes, because the water is stored behind the dam.
- No. A drought leaves less water for power.
- No, because dams work in heavy rain alone.
- Yes, because dams make enough of their own water.
Show the answer
No. A drought leaves less water for power.
Storage smooths supply, but the reservoir is still filled by rain and rivers. Dry years cut output, and sediment slowly fills the reservoir.
Hydropower can supply low-carbon electricity when needed, but its benefits depend on river conditions and how its impacts are managed.
Hydropower uses falling or flowing water to turn turbines. A reservoir can store water and release it when power is needed. This can balance solar power, which varies, and cut fossil fuel use. Run-of-river projects have little storage and depend on the river's flow.
Supply is not guaranteed. Drought leaves less water to generate power. Mud, or sediment, slowly fills reservoirs. Power needs compete with farming, drinking water and river ecosystems. Relying on one river can mean shortages in a dry year.
Large dams cost a lot and take years to build, but can provide power for decades. Flooded land and changed flows can destroy habitats, block fish and trap sediment. Reservoirs can also release greenhouse gases, so hydropower is not always zero-emission.
People near the reservoir may lose homes, farms or sacred places, while distant cities get the power. Good compensation restores livelihoods and communities, not just buildings. When comparing solar and hydropower, judge the whole system and who pays the costs.
- Hydropower
- Water turns turbines; reservoirs store energy.
- Limits
- Drought, sediment and competing water needs.
- Trade-offs
- Habitat loss, blocked fish, displaced people.
Step by step
Find the benefit
Can storage supply power when users need it?
Follow the river
Water, sediment, habitats and downstream users.
Compare who gains
Power users versus affected communities.
Real examples to use
Three Gorges Dam, China
It has the largest installed power capacity of any power station and helps control Yangtze floods. About 1.3 million people were moved to build it.
Xayaburi Dam, Laos
This dam on the Mekong opened in 2019 and sells most of its power to Thailand. Critics warn it blocks fish migration and traps sediment.
Worked example: A reservoir in a drought
A made-up reservoir supplies power and irrigation. In a dry year, using more water for power leaves less for farms later. An agreed rule can manage this, but it cannot create water that is not there.
Watch out for this
Stored water makes hydropower independent of the weather.
Storage helps, but long droughts still cut power and other water uses.
Check your understanding
A dam gives a city cheap power, but displaced farmers cannot rebuild their livelihoods. Which judgement is strongest?
- Cheap power for the city proves the dam is sustainable overall.
- Weigh the economic gain against the lasting social costs.
- Hydropower projects give the same results wherever they are built.
Show the answer
Weigh the economic gain against the lasting social costs.
Yes. It considers both sides and who bears the costs.
Check your understanding
Which statement best describes a trade-off of the Three Gorges Dam?
- It has benefits, and its costs were fully repaid.
- It produces little electricity, as it was built for floods.
- It makes vast power and helps control floods, but about 1.3 million people moved.
Show the answer
It makes vast power and helps control floods, but about 1.3 million people moved.
Benefits in one dimension came with costs in another.