1 Petroleum
2 coal
3 solar radiations
4 Electricity from nuclear power plants

Non-conventional sources of energy refer to those sources that are alternative to traditional fossil fuels like coal, oil, and natural gas. These sources are renewable, sustainable, and have a lesser impact on the environment. Let's discuss one of the non-conventional sources of energy from the given options:

Solar Energy:
Solar energy is a non-conventional source of energy that utilizes the radiant light and heat from the sun. It is a renewable and abundant source of energy that can be harnessed and converted into electricity using solar panels or solar cells.

Key Points:
- Solar energy is a clean and environmentally friendly source of energy as it does not produce any harmful emissions or pollutants.
- The conversion of solar energy into electricity can be achieved through two main methods: photovoltaic (PV) and concentrated solar power (CSP).
- Photovoltaic systems use solar cells to directly convert sunlight into electricity. These cells are made of semiconductor materials, such as silicon, which absorb photons from the sunlight and release electrons, producing an electric current.
- Concentrated solar power systems use mirrors or lenses to focus a large area of sunlight onto a small area. This concentrated heat is then used to generate steam, which drives a turbine connected to an electrical generator.
- Solar energy can be used for various applications, including powering homes and buildings, heating water, generating electricity for remote areas, and even powering vehicles.
- The use of solar energy reduces dependence on fossil fuels, mitigates climate change, and promotes sustainable development.
- However, solar energy has some limitations such as intermittency (it is only available during daylight hours), the requirement of large areas for installation, and high initial costs of solar panel systems.

Conclusion:
Solar energy is a non-conventional source of energy that harnesses the power of sunlight to generate electricity. It is a clean, renewable, and sustainable energy source that has the potential to meet global energy demands while reducing the environmental impact.