Geothermal energy

Geothermal Energy

Source: Earth's internal heat (friction, gravity, radioactive decay) Temperature range of magma: 700°C – 1300°C Mechanism:

• Heat warms underground rocks and aquifers.
• Natural steam or hot water released (geysers, hot springs).
• Human extraction by drilling wells; injecting water to produce steam.

Uses:

1. Direct heating and cooling: Geothermal Heat Pumps (GHPs)
2. Electricity generation:
   • Dry steam plants: steam used directly to drive turbines.
   • Flash steam plants: hot water flashes to steam at surface.
   • Binary cycle plants: heat transferred to a secondary fluid with lower boiling point.

Tidal Energy

Principle: Conversion of gravitational potential energy from tidal height differences. Tidal barrage power formula:

$$P = \frac{\rho A g h^2}{2 T}$$

where:

• $\rho$ = water density (kg/m³)
• $A$ = basin area (m²)
• $g$ = acceleration due to gravity (9.81 m/s²)
• $h$ = tidal height (m)
• $T$ = tidal period (s)

Tidal stream systems: harness kinetic energy of tidal currents using underwater turbines.

Ocean Wave Energy

Source: Wind energy transferred to the ocean surface, producing waves. Wave energy (per unit width):

$$E = \rho g A_b^2$$

where $A_b$ is wave amplitude, and wave height $h = 2 A_b$. Wave power formula:

$$\langle P \rangle = \frac{1}{32 \pi} \rho g^2 h^2 T$$

where $T$ is wave period (s). Wave energy conversion devices:

1. Terminators: Oscillating water columns that trap and compress air to drive turbines.
2. Attenuators: Long floating devices aligned parallel to wave direction.
3. Point absorbers: Buoy-like structures moving vertically with waves.
4. Overtopping devices: Wave water collected in reservoirs, released to drive turbines.