Energy and Its Transformations: A Comprehensive Guide
Energy and Its Transformations
Energy Sources and Transformations
We obtain energy from primary energy sources and transform it daily. We can use energy in its primary form (e.g., wind’s kinetic energy to move a boat). We distinguish between primary, intermediate, and useful energies. For example, an engine transforms the chemical energy of petrol (primary) into heat (intermediate), which can then be transformed into kinetic energy (useful). The most common intermediate energy is electricity.
Types of Energy
There are different types of energy: sound, solar, kinetic, etc. We can transform one type of energy into another, but the total amount of energy always remains the same. The SI unit for energy is the joule (J). 1 Cal = 4.184 J.
Power
Power is energy divided by time. The SI unit for power is the watt (W). P = E/T, where 1W = 1J/S.
Electricity Production
Renewable and Non-Renewable Sources
We obtain electricity from primary energy sources, which can be renewable (hydroelectric potential energy, solar light, wind’s kinetic energy) or non-renewable (energy from fossil fuels and nuclear energy).
Wind Energy
In the case of wind energy, part of the wind’s kinetic energy is transferred to an electric generator that transforms it into electricity.
Solar Energy
There are two types of solar energy: thermal-solar and photovoltaic. In thermal-solar, thermal energy is transferred to steam in a steam turbine. In photovoltaic, photons impact the electrons of a semiconductor material, causing them to move.
Hydroelectric Power Stations
Dams accumulate water, allowing us to produce electricity on demand. The water pressure at the bottom of the dam moves the blades of a turbine attached to an axis. This rotary movement is transported to an electric generator, producing alternating current (AC).
Wind Farms
A wind farm is a group of wind turbines. The wind moves the turbine blades, and the rotary movement is transported through a gearbox to an electric generator, producing AC. The gearbox increases the rotary movement because the generator needs to spin faster than the turbine. Tall turbines are more efficient than small turbines because wind speed is higher further from the ground. The best locations for wind farms have constant, non-turbulent air and access to the power grid.
Solar Cells
In solar cells, photons impact the electrons of a semiconductor material, causing them to move. The energy gap is the amount of energy needed to push the electrons away from their orbit around the nucleus. If the photons have more energy than the energy gap, the electrons can flow freely through a wire, powering appliances. Solar cells produce direct current (DC).
Energy from the Sea
Sea energy power stations utilize the energy from waves, sea currents, and tides.
Solid Urban Waste (SUW) and Biomass
SUW is what we throw in a bin. We can bury or burn it. Biomass is vegetable waste from farming, forestry, and wood industries. The combustion of SUW and biomass produces heat for a steam turbine.
Thermal Power Stations
Thermal power stations convert a primary energy source into heat to transform water into hot pressurized steam. The pressure difference between the hot steam in front of the turbine and the cold water behind it makes the steam pass through the turbine, moving it. The steam loses heat and pressure as it passes through the turbine, transforming into kinetic energy. This kinetic energy is transported to an electric generator, which transforms it into AC electricity.
Nuclear Power Stations
Nuclear power stations use the heat from controlled nuclear reactions to convert water into steam in a steam turbine.
Transportation and Distribution of Electricity
The Grid
Electricity is transported from power stations to consumers through a grid. The advantage of a grid is that there are multiple routes for electricity to travel. The cables are made of aluminum. Transported power is equal to the product of voltage and current. High current leads to energy loss due to electrons heating the cable. We can transport the same power with low current and high voltage. Transformers are used to raise and lower voltage and current.
Electricity
Electrical Magnitudes
- Voltage (V): The energy of each electron. The unit is the volt (V).
- Current (I): The total amount of electrons flowing along the circuit. The unit is the ampere (A).
- Resistance (R): The force that a material exerts against the flow of electrons. The unit is the ohm (Ω).
- Power (P): The product of voltage and current. The unit is the watt (W).
Types of Current
- Alternating Current (AC): The electrons periodically change their direction of flow. Power stations produce AC electricity. The voltage in homes and schools is typically 230V. Transformers are used to raise and lower voltage and current, which is useful for transporting electricity efficiently.
- Direct Current (DC): The electrons always flow in the same direction.
AC Generator
An AC generator, also called an alternator, generates AC electricity. It uses the kinetic energy of rotary movement and transforms it into AC. The movement of magnets and their magnetic fields pushes the electrons, causing them to move.
Transformers
Transformers work with AC, not DC. They raise and lower the voltage and current in AC circuits. Power is the product of voltage and current. Increasing the voltage decreases the current, and vice versa. This is useful for long-distance electricity transportation because it allows for the same power to be transported with lower current and higher voltage, reducing energy losses due to friction in the wires.