Global Energy Resources: Trends, Intermittency, and Innovation

Global Electricity Supply and Solar Trends

• Solar power supply grew from near $0.5\%$ in $2012$ to approximately $3.7\%$ by $2021$.

• Growth is driven by declining technology costs and government subsidies aimed at reducing greenhouse gas emissions.

Challenges in Energy Planning

• Economic Instability: Volatile energy prices influence the appeal of renewables compared to fossil fuels.

• Rapid Innovation: Technological breakthroughs in battery storage or solar efficiency can render $10\text{-year}$ plans obsolete quickly.

• Political Shifts: Election cycles impact subsidies, international treaties, and policy backing for energy projects.

Reliability and Intermittency Issues

• Renewables are weather-dependent: Cloud cover can reduce solar output by $90\%$ in minutes, while wind turbines require specific speed ranges.

• Demand Management: Massive storage is essential to handle sudden surges in demand due to the unpredictability of wind and solar.

Biofuels and Wood Combustion

• Biofuels: Ethanol from sugar cane provides high energy density and reliability, utilizing existing infrastructure.

• Carbon Neutrality Debate: While the fuel absorbs $CO_2$ during growth, the use of fossil fuels in tractors and fertilizers adds carbon to the cycle.

• Wood Burning: Burning wet wood (>20\% moisture) is illegal in some areas due to incomplete combustion and high particulate matter emissions ($\text{PM2.5}$ and $\text{PM10}$).

Wind and Solar Technology

• HAWT (Horizontal Axis): High efficiency and better wind speeds at height; blades use variable pitch to manage storm damage.

• VAWT (Vertical Axis): Omni-directional and quieter; generator is at ground level for easier maintenance; ideal for urban rooftops.

• Photovoltaic (PV): Uses silicon semiconductors to convert photons to DC electricity.

• Photothermal: Uses mirrors to focus heat and drive steam turbines.

• Passive Solar: Uses orientation and thermal mass (e.g., concrete floors) to trap heat without mechanical systems.

Radiation and Nuclear Waste

• Ionising Radiation Types:   - Alpha ($\alpha$): High ionising; low penetration.   - Beta ($\beta$): Moderate ionising and penetration.   - Gamma ($\gamma$): Low ionising; high penetration.

• Half-Life: The time for half of the radioactive nuclei in a sample to decay; defines the duration of the hazard.

• Waste Management: Methods include Cooling Ponds, Vitrifaction (solidifying waste in glass), and Deep Storage in stable rock formations.