Types of Energy Resources

Non-Renewable Resources: Fossil Fuels and Nuclear Power

Burning fossil fuels (coal, oil, and natural gas) transfers chemical energy to thermal energy to generate electricity, heat homes, and power transport. They contain approximately $30\,\text{MJ}$ of energy per kilogram. Natural gas has a very short start-up time (a few minutes), making it ideal for meeting sudden peaks in demand, whereas coal takes much longer to start up.

Fossil fuels cause significant environmental issues. Burning them releases carbon dioxide ($\text{CO}_2$), a greenhouse gas that contributes to global warming. Coal and oil also release sulphur dioxide ($\text{SO}_2$), which causes acid rain.

Nuclear fuel (uranium and plutonium) generates heat through a process called fission, where a large nucleus splits into smaller nuclei. Nuclear power has an immense energy density of approximately $300{,}000\,\text{MJ}$ per kilogram, but power stations have very long start-up times, so they are run continuously to provide a constant "base load" of electricity.

Crucially, nuclear power does NOT emit greenhouse gases or $\text{SO}_2$ during operation. However, it produces dangerous radioactive waste that remains hazardous for thousands of years and requires costly decommissioning (safe dismantling) at the end of the station's life.

Renewable Resources: Wind and Water

Wind power uses the kinetic energy of the air to turn turbine blades, which drive a generator. It is an unreliable resource because it does NOT generate power when the wind drops, and large wind farms can cause visual and noise pollution.

Hydroelectricity harnesses water stored high up in a reservoir. The falling water transfers its gravitational potential energy (GPE) to kinetic energy to turn turbines. A pumped storage system uses surplus grid electricity to pump water back up to the upper reservoir, acting as a giant battery to store energy for peak demand periods. Building these dams often involves flooding valleys, which destroys habitats and releases methane from rotting vegetation.

Tidal power is driven by the gravitational pull of the Sun and Moon, usually harnessed by building a tidal barrage (a dam) across an estuary. While tides are intermittent (they do not produce power 24/7), they are highly predictable. However, barrages disrupt local ecosystems, such as fish migration and bird feeding grounds.

Water waves use the up-and-down motion of the ocean to drive a turbine. They are unreliable because the waves die down when the wind drops, and they generally produce a low power output.

Renewable Resources: Solar, Geothermal, and Bio-fuel

Solar energy from the Sun is harnessed in two distinct ways. Solar cells (photovoltaic cells) convert light energy directly into electricity with an efficiency of $10-20\%$. Alternatively, solar heating panels use black pipes to absorb infrared radiation to directly heat water for domestic use. Both methods are unreliable because they depend on daylight and clear weather.

Geothermal energy captures heat released by the radioactive decay of elements (like uranium) deep inside the Earth. It is highly reliable, providing steam to turn turbines for electricity or hot water for direct heating, though it can occasionally release trapped underground methane.

Bio-fuels are derived from living or recently deceased organisms, such as plant materials or animal waste. They are considered carbon neutral because the $\text{CO}_2$ released when they are burnt equals the $\text{CO}_2$ the organism absorbed while growing. They are a reliable energy source that can be stored and burnt as needed, but growing fuel crops can take up valuable agricultural land, leading to higher food prices or deforestation.

Comparing Energy Resources

When evaluating energy resources, examiners compare their economic costs, environmental impacts, and reliability (whether the resource can generate electricity constantly or predictably).

Non-renewables generally have lower setup costs (excluding nuclear) but high ongoing fuel costs. In contrast, renewables have high initial setup costs but very low running costs because their "fuel" (like wind or sunlight) is free.

Worked Example: Replacing a Power Station

To understand the vast scale difference between reliable fossil fuels and unreliable renewables, we can calculate how many wind turbines are needed to replace a single coal station.

$$\text{Number of turbines} = \frac{\text{Total Power Required}}{\text{Average Power per Turbine}}$$

Step 1: Identify the power values.

• Total power required (coal station) = $1500\,\text{MW}$
• Average power per turbine = $0.6\,\text{MW}$

Step 2: Substitute into the equation.

• $\text{Number of turbines} = \frac{1500}{0.6}$

Step 3: Calculate the final answer.

• $\text{Number of turbines} = 2500$ turbines