Which one of the following is not a non conventional (renewable) source of energy?

Introduction / Context:
Energy resources are often classified into conventional and non conventional sources. Non conventional sources, also commonly called renewable sources, are gaining importance because they are cleaner and more sustainable. This question asks which of the given options is not a non conventional source of energy, meaning we must identify a conventional, largely non renewable source among mostly renewable options. This topic is highly relevant for environmental geography and general awareness exams.

Given Data / Assumptions:

• The options include solar energy, wind energy, tidal power, coal based thermal power, and biogas energy.
• Non conventional sources generally refer to renewable and less polluting sources like solar, wind, tidal, geothermal, and biogas.
• Conventional sources usually include coal, petroleum, natural gas, and large scale hydropower that have been used extensively for a long time.

Concept / Approach:
The key concept is the distinction between renewable and non renewable energy. Solar, wind, tidal, and biogas energy come from sources that are continuously replenished by natural processes within a human time scale. Coal based thermal power, on the other hand, depends on coal, which is a fossil fuel formed over millions of years and finite in quantity. Coal combustion also releases large amounts of greenhouse gases and pollutants. Therefore, coal based thermal power is classified as a conventional and non renewable source, not a non conventional one.

Step-by-Step Solution:
Step 1: Examine solar energy. Solar energy is derived from sunlight, is renewable, and is a classic example of a non conventional source. Step 2: Examine wind energy. Wind turbines convert kinetic energy of wind into electricity, again a renewable and non conventional source. Step 3: Examine tidal power. Tidal energy comes from the regular rise and fall of ocean tides driven by gravitational forces, and is considered a non conventional renewable source. Step 4: Examine coal based thermal power. This uses coal, a fossil fuel that is exhaustible and whose formation time scale is extremely long. It is a conventional and non renewable source. Step 5: Biogas energy is produced from the decomposition of organic waste and agricultural residues, which are continually produced, so it is treated as a renewable non conventional source.

Verification / Alternative check:
Many standard environment and geography textbooks define non conventional sources as those that were not traditionally exploited on a large scale, are renewable, and generally have lower emissions. Solar, wind, tidal, and biogas are always listed in that category. Coal and petroleum based thermal plants are always grouped under conventional fossil fuel sources. This cross check confirms that coal based thermal power is the odd one out in the list of options.

Why Other Options Are Wrong:

• Solar energy: A leading non conventional, renewable source widely promoted for clean power.
• Wind energy: Also a classic non conventional, renewable source used in wind farms.
• Tidal power: A form of marine renewable energy extracted from tidal movements.
• Biogas energy: Generated from organic waste, it is renewable and part of non conventional energy programs.

Common Pitfalls:
Some learners confuse the term non conventional with not commonly used and may think that tidal power or biogas are somehow less important or negligible, but they remain non conventional by definition. Another pitfall is to focus only on electricity generation technology and forget the underlying fuel. Even if coal based thermal plants use modern technology, the fuel source remains a conventional fossil fuel, so the energy source is not non conventional.

Final Answer:
The option that is not a non conventional source of energy is coal based thermal power.