Learning more on energy

What do we use energy for?

Various Methods of Generating Electricity


Solar cells made of semiconductor converts light energy directly into electricity. When sunlight reaches solar cells, "+" holes and "-" electrons are generated inside semiconductors. "+" holes are collected to the P-type semiconductor, and "-" electrons are collected to the N-type semiconductor. Electricity can be taken out by connecting the wires to the electrodes. However, direct current electricity taken out of the solar cells can not be used as is. Therefore, a power conditioner converts DC electricity into AC electricity and the electricity is sent to electrical appliances through a distribution board.

Wind Power

Rotation of blades by wind converts wind energy into rotational energy. A gear box accelerates the rotational energy to the speed required for power generation. The generator converts accelerated rotational energy into electrical energy.


A dam is built at the upper reaches of a river, allowing water to flow through onto a turbine blade attached to a generator to produce electricity.

During the daytime, turning the turbine through water flow from the upper reservoir generates electricity. Water used for electricity generation during the daytime is stored in the lower reservoir. During the night when less power is consumed, the water is pumped from the lower reservoir to the upper one. A pump turbine operates as a waterwheel during the day and as a pump during the night.

Geothermal power

Groundwater heated by the magmatic heat deep in the ground is pumped up. The groundwater is separated into hot water and steam in the steam-water separator. The hot water goes back into the underground while steam rotates the turbine to generate electricity in the generator. After the steam rotates the turbine, it is cooled to warm water in the condenser, and then further cooled in the cooling tower to be used as cooling water in the condenser.

What do we use energy for?

Is energy used economically?

  • 01 Where is energy from?
  • 02 What do we use energy for?
  • 03 Is energy used economically?
  • 04 The future energy technologies


  • Fossil-fuel Energy
  • Non-energy use
  • Watt (W) vs. Watt-hour (Wh)