Cambridge IGCSE Physics 0625 – Energy Resources (1.7.3)
1.7.3 Energy Resources
Objective
Know that radiation from the Sun is the main source of energy for all our energy resources except geothermal, nuclear and tidal.
Why the Sun is the Primary Energy Source
The Sun delivers a continuous flow of electromagnetic radiation to the Earth. The average solar constant at the top of the atmosphere is
\$S = 1361\ \text{W m}^{-2}\$
Only a fraction of this energy reaches the surface, but it is still enough to power the majority of the energy resources we use.
Energy Resources Derived Directly or Indirectly from Solar Radiation
Solar photovoltaic (PV) cells – convert sunlight directly into electricity.
Solar thermal – use sunlight to heat water or air for domestic hot water, space heating, or to generate steam for turbines.
Wind energy – wind is caused by differential heating of the Earth’s surface by the Sun.
Hydroelectric power – the water cycle (evaporation, condensation, precipitation) is driven by solar heating.
Biomass – plants store solar energy through photosynthesis; this chemical energy can be released by burning or conversion to bio‑fuels.
Fossil fuels – originally formed from ancient biomass that captured solar energy millions of years ago.
Energy Resources Not Primarily Powered by Solar Radiation
Geothermal energy – derived from the Earth’s internal heat, produced by radioactive decay of elements such as uranium and thorium.
Nuclear energy – released from the binding energy of atomic nuclei during fission (or fusion in future reactors), not from solar radiation.
Tidal energy – generated by the gravitational interaction between the Earth, Moon and Sun; the dominant driver is the Moon’s gravity.
Summary Table
Energy Resource
Primary Energy Source
Typical Use
Notes
Solar PV
Sunlight (direct radiation)
Electricity generation
Most direct use of solar energy
Solar Thermal
Sunlight (direct radiation)
Water heating, space heating, power generation
Uses heat rather than electricity
Wind Power
Sun‑driven atmospheric temperature gradients
Electricity generation
Indirect solar origin
Hydroelectric
Sun‑driven water cycle
Electricity generation
Depends on rainfall and river flow
Biomass / Bio‑fuels
Sunlight via photosynthesis
Heat, electricity, transport fuels
Stored chemical energy
Fossil Fuels (coal, oil, gas)
Ancient solar‑derived biomass
Heat, electricity, transport
Finite, carbon‑intensive
Geothermal
Earth’s internal heat
Electricity, direct heating
Not solar‑derived
Nuclear (fission)
Binding energy of atomic nuclei
Electricity generation
Low greenhouse‑gas emissions but radioactive waste
Tidal
Gravitational pull of Moon (and Sun)
Electricity generation
Predictable but location‑specific
Key Points to Remember
Solar radiation is the ultimate source of energy for most of the world’s power generation.
Even resources that seem unrelated to the Sun (wind, hydro, biomass, fossil fuels) are driven by the Sun’s heating of the Earth’s surface.
Geothermal, nuclear and tidal energy are the main exceptions; they rely on Earth’s internal heat or gravitational forces.
Understanding the origin of each resource helps in evaluating sustainability and environmental impact.
Suggested diagram: Flow chart showing how solar radiation leads to the various energy resources (direct and indirect) and the three non‑solar exceptions.