Question

Give scientific reasons:

Hydroelectric energy, solar energy and wind energy are called renewable energies.

Answer 1

1. Renewable energy is any energy that comes from natural resources such as wind, water, sunlight, and geothermal heat, which is heat that is retained in the earth.
2. Renewable energy is called renewable because it can be replenished easily without human intervention.
3. There are several types of renewable energy that are used in different ways to make them usable to humans. 
4. Wind energy is converted into wind power. When the wind is harnessed with turbines, it can generate electricity. Because of advances in turbine technology and the ability of utility companies to lock in a set price for wind energy, since the fuel is free, the overall cost of wind power to consumers is lower than in past years.
5. It is important to understand that with this type of electricity, one should live in a region where natural wind resources are plentiful.
6. Sunlight, also known as solar energy, is a common renewable energy source.
7. Sunlight is harnessed by humans for electricity generation through the emission of electromagnetic radiation.
8. Once electromagnetic radiation is captured, usually with photovoltaic cells in a conductive material, it generates electricity and heat.
9. The conductor material ordinarily is silicon because of the abundance of the material.
10. The initial start-up costs for installing solar energy panels in a consumer’s home are usually very high. It may even take up to ten years to see a return on the investment. Geothermal energy is found inside the Earth’s core.
11. Utility companies can drill into geothermal energy reservoirs to harness the heat. Once the heat or hot water has been trapped, it can spin turbines to make electricity.

Answer 2

1. Hydroelectric energy, solar energy, and wind energy are obtained from flowing water, solar radiation, and wind, respectively. 
2. These sources are naturally replenished and are available in abundant quantities. They are sustainable and do not get exhausted with use.
3. In contrast, conventional energy sources such as coal, petroleum, and natural gas are finite and cannot be replenished within a short period. Continuous use of these resources may lead to their depletion.

Therefore, hydroelectric, solar, and wind energy are considered renewable energy sources because they are naturally replenishable and sustainable.