Topic 9: Energy Resources
A dilute source of energy is an energy source that provides low energy per unit area or volume, meaning it is spread out and not concentrated. To harness useful amounts of energy from a dilute source, large collecting areas or long collection times are needed.
Examples of Dilute Energy Sources:
Solar energy: Sunlight delivers only about 1 kW per square metre at Earth’s surface, so large panels are needed to gather significant energy.
Wind energy: Wind has low power density, so turbines must be large and spaced out.
Tidal and wave energy: Though consistent, their energy is spread over large ocean areas.
Contrast:
Concentrated sources (e.g. fossil fuels, nuclear fuels) release large amounts of energy from small volumes or masses.
Concentrated Energy Sources
| Energy Source | Why It’s Concentrated |
|---|---|
| Fossil Fuels | High energy density; small quantities give lots of energy |
| – Coal | Contains stored chemical energy from ancient biomass |
| – Oil | Easily transported and combusted for heat and power |
| – Natural Gas | Burns efficiently, high calorific value |
| Nuclear Fuels | Extremely high energy from a small mass via fission |
| – Uranium-235 | 1 kg can release energy equal to millions of kg of coal |
| – Plutonium-239 | Used in reactors and nuclear weapons |
| Hydrogen (compressed or liquefied) | High energy content per kg when used in fuel cells or combustion |
| Hydroelectric Energy (at dam sites) | Gravitational potential energy stored in large volumes of water |
These sources are typically easier to store, transport, and use in compact systems compared to dilute sources like wind or sunlight.
Energy Sources on Earth – Categorized
We can divide energy sources into two groups:
A. 
Sun-Derived Sources (Most sources)
B. 
Non-Solar Sources: Geothermal, Nuclear, Tidal
A. SUN AS THE ORIGINAL SOURCE — HOW?
1. 
Wind Energy
Wind is caused by differences in air pressure.
These pressure differences result from uneven heating of the Earth’s surface by the Sun (equator heats more than poles, land heats faster than water, etc.).
Moving air (wind) is a direct consequence of solar heating.
So wind energy originates from the Sun.
2. 
Hydroelectric Energy (Waterfalls, Dams)
The Sun heats water in oceans, lakes → causes evaporation.
Water vapor forms clouds → precipitation (rain) falls on high land.
Stored in rivers/dams, water flows down due to gravity → turbines turn → electricity.
Hydropower is driven by the water cycle, which is powered by the Sun.
3. 
Biomass & Fossil Fuels (Coal, Oil, Natural Gas)
Plants use sunlight in photosynthesis to make food.
Dead plants/animals buried over millions of years form coal, oil, gas.
Fossil fuels are ancient sunlight stored in chemical form.
4. 
Biofuels
Grown crops (e.g. maize, sugarcane) are used to make ethanol/biodiesel.
Crops need sunlight to grow via photosynthesis.
So biofuels are directly solar-powered.
5. 
Solar Energy (obviously!)
Solar panels (photovoltaics) or solar heaters use sunlight directly.
No transformation — it’s pure solar input.
B. NON-SOLAR SOURCES
These few energy sources do not originate from the Sun:
1. Geothermal Energy
Comes from heat inside Earth’s core, left over from planet formation and radioactive decay.
Not related to the Sun.
2. 
Nuclear Energy
Comes from nuclear fission of uranium/plutonium atoms — radioactive materials formed in ancient stars, not the current Sun.
Not solar in origin.
3. 
Tidal Energy
Caused by gravitational interaction between Earth and the Moon, and to a lesser extent, the Sun.
Mainly lunar, not solar.
Summary Statement
Except for geothermal, nuclear, and tidal energy, all other energy sources on Earth — including wind, water, biomass, fossil fuels, and solar — originate from the Sun’s energy. The Sun powers the weather, water cycle, and photosynthesis, making it the ultimate driver of nearly all life and activity on Earth.