Biomass is waste material from plants or animals that is not used for food or feed such as wood, cow dung, etc. Soil cannot be used as a biofuel rather all the biofuels convert into soil after they are consumed.

Solar panels consist of solar cells which are connected with each other by silver wiring. A solar panel does not have any moving part within it. They are widely used in artificial satellites but their domestic use is limited due to high cost and requirement of large open area.

Acid rain happens because the burning of fossil fuels releases oxides of carbon, nitrogen and sulfur in the atmosphere. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain.

In a hydroelectric power plant, more electrical power can be generated if water falls from a greater height because more the height of water, more is the potential energy stored in it. So, the larger amount of potential energy is converted into kinetic energy. More is the kinetic energy, faster it will rotate the turbine and hence more electricity is generated.

Ocean thermal energy is generated due to the difference in temperature of water at the surface of the ocean and temperature at deeper levels of the ocean. This energy comes indirectly from the sun as the heat energy from the sun is creating the difference in temperature.

Silicon is used to make solar cell and silver is used for interconnection of the cells in the panel.

Water stored in a dam at a certain height, has potential energy. This potential energy is converted to kinetic energy when allowed to flow. The kinetic energy of flowing water is used to turn the turbine, which is used to generate electric current. Hence, the overall conversion is from the potential energy of stored water to electrical energy.

The exhaustible natural resources are limited in nature and can be exhausted by different human activities. The inexhaustible natural resources are in unlimited quantity and are not likely to be exhausted by human activities. Fossil fuels are exhaustible resources, whereas hydro energy, nuclear energy, and wind energy are inexhaustible natural resources.

Given, initial potential energy = 1000 J
Final kinetic energy = 500 J
Here, potential energy is converted to kinetic energy and heat.
So, potential energy = Kinetic energy + Heat 
$\to$ 1000 = 500 + Heat
$\therefore$ Heat = 500 J

Sources which are replaced naturally and can be used again is known as a renewable source of energy. Sun, wind, biomass are some of the examples of renewable sources of energy.