Renewable energy sources are naturally replenished on human timescales and generally produce little or no greenhouse gas emissions during operation. VCE Environmental Science covers seven main types: biomass, biofuels, solar, hydroelectric, wind, tidal and geothermal.
Definition: Organic material used as fuel — wood, agricultural residues, dedicated energy crops, organic waste.
How it works: Combustion of biomass produces heat → steam → turbine → electricity (same as coal). Can also be used directly for heat.
GHG status: Technically carbon-neutral if biomass growth re-absorbs CO$_2$ emitted from combustion. However:
- Net GHG benefit depends on what land the biomass displaces (clearing native forest for bioenergy plantation is not carbon-neutral)
- Transportation and processing add emissions
- Air pollution from combustion remains a concern
Victorian example: Timber processing residues used in Morwell for electricity (wood waste from sawmills).
Definition: Liquid fuels derived from plant material — ethanol (from sugarcane, corn, wheat) and biodiesel (from vegetable oils, algae).
Types:
- First-generation: Crops grown specifically for fuel — competes with food production
- Second-generation: Agricultural residues (straw, bagasse) — fewer food security concerns
- Third-generation: Algae-based — high productivity, no land competition; still in development
Environmental considerations:
- Net GHG benefit varies widely depending on feedstock and land use
- Biofuels from cleared tropical forest have higher lifecycle emissions than petrol
- Sugarcane ethanol from Brazil has ~70% lower lifecycle emissions than petrol
Mechanism: Potential energy of stored water released through turbines as water flows downhill.
Types: Impoundment dams; run-of-river; pumped storage (stores excess electricity by pumping water uphill).
Advantages: Very low operational emissions; highly dispatchable; long facility life; provides grid storage via pumped hydro.
Environmental impacts:
- Dams alter river hydrology, sediment transport and fish migration
- Flooding of valleys — loss of terrestrial ecosystems and sometimes communities
- Methane emissions from decomposing vegetation under reservoirs (especially in tropics)
Australian example: Snowy Hydro scheme (Kosciuszko NP); pumped hydro expansion (Snowy 2.0).
Mechanism: Kinetic energy of wind turns turbines; generator produces electricity.
GHG emissions: ~7–15 g CO$_2$e/kWh (one of the lowest lifecycle emissions of any energy source)
Advantages: Rapidly declining costs (competitive with new coal); no water use during operation; land around wind turbines can still be farmed.
Disadvantages:
- Variable (depends on wind speed)
- Bird and bat mortality from blade strikes
- Noise and visual impacts; community opposition in some areas
- Offshore wind: higher cost but stronger, more consistent wind; potential seabird and marine mammal impacts
Mechanism: The kinetic energy of tidal currents or the potential energy of tidal height changes is harnessed via turbines (tidal stream) or barrages (tidal range).
Advantages: Predictable (tides are astronomically determined); no fuel costs; very low emissions.
Disadvantages:
- Very site-specific — requires strong tidal flows or large tidal range
- Barrages alter estuarine ecosystems significantly
- Tidal stream generators risk impacts on marine life
- Currently limited in scale; mostly in early development or demonstration phase
Example: Tidal stream generators in Pentland Firth (Scotland); tidal barrage at La Rance (France) since 1966.
Mechanism: Heat from Earth’s interior used to generate steam and drive turbines. High-temperature hydrothermal resources (near volcanic activity) are most suitable.
Types:
- Hydrothermal: Steam or hot water extracted from naturally permeable rock
- Enhanced Geothermal Systems (EGS): Water injected into hot dry rock; heat extracted; potentially available anywhere
Advantages: Low emissions; very high capacity factor (reliable 24/7 generation); small surface footprint.
Disadvantages:
- Limited to geologically suitable areas for conventional hydrothermal
- EGS is expensive and technically challenging
- Risk of induced seismicity (minor earthquakes from water injection)
Australian context: Australia has large hot dry rock resources (Cooper Basin, SA) but lack of hydrothermal systems limits development. EGS projects are in development stages.
| Source | Dispatchable? | Water Use | Land Use per kWh | GHG (g CO$_2$e/kWh) |
|---|---|---|---|---|
| Biomass | Yes | Moderate | High (if crops) | Variable |
| Biofuels | Yes | High (irrigation) | Very high | Variable |
| Solar PV | No (variable) | Very low | Moderate | 20–50 |
| Hydro | Yes (if storage) | High (evaporation) | Low | 4–30 |
| Wind | No (variable) | Very low | Low (shared) | 7–15 |
| Tidal | Predictable | Minimal | Low | Low |
| Geothermal | Yes | Low–moderate | Very low | 15–55 |
VCAA FOCUS: For each renewable source, be able to describe the mechanism of electricity generation, identify two advantages and two disadvantages, and explain how it relates to sustainability principles. Note that ‘renewable’ does not mean ‘zero environmental impact’ — evaluate each source critically.
