How electricity is generated from thermal energy and when solar energy is converted to thermal energy and how is the thermal energy used?
Generating Electricity from Thermal Energy:
There are two main ways thermal energy is converted into electricity:
1. Steam turbines:
- This is the most common method, used in both fossil fuel and nuclear power plants.
- Process:Fuel (coal, oil, gas, or nuclear) is burned in a boiler, heating water to high temperatures and pressures. The hot, pressurized steam spins a turbine, which is connected to a generator. The generator converts the mechanical energy of the turbine's rotation into electrical energy. After exiting the turbine, the steam is cooled and condensed back into water, and the cycle repeats.
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Steam turbine power plant
2. Combustion turbines:
- Primarily used in natural gas power plants.
- Process:Air is compressed and mixed with natural gas in a combustion chamber. The mixture is ignited, and the hot gases expand rapidly, spinning a turbine connected to a generator. The generator converts the mechanical energy into electricity. The exhaust gases are released into the atmosphere.
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Combustion turbine power plant
Converting Solar Energy to Thermal Energy:
There are two main ways solar energy is converted into thermal energy:
1. Concentrated solar power (CSP):
- Uses mirrors or lenses to concentrate sunlight onto a receiver.
- The heat is used to:Boil water to create steam for turbines (similar to fossil fuel plants). Heat molten salts, which can store thermal energy and be used to generate electricity later.
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Concentrated solar power plant
2. Solar thermal collectors:
- Flat panels or evacuated tubes absorb sunlight and heat a fluid (water or antifreeze).
- The heated fluid is used for:Domestic hot water heating. Space heating in buildings. Driving small-scale turbines for electricity generation.
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Solar thermal collector
Using Thermal Energy:
Thermal energy has many applications beyond electricity generation, including:
- Industrial processes:Manufacturing food, chemicals, paper, and other products. Refining oil and gas. Desalination of water.
- Heating and cooling:Homes, businesses, and institutions. District heating systems that provide heat to multiple buildings.
- Cooking:Stoves, ovens, and grills.
Solar thermal power/electric generation systems collect and concentrate sunlight to produce the high temperature heat needed to generate electricity. All solar thermal power systems have solar energy collectors with two main components: reflectors (mirrors) that capture and focus sunlight onto a receiver. In most types of systems, a heat-transfer fluid is heated and circulated in the receiver and used to produce steam. The steam is converted into mechanical energy in a turbine, which powers a generator to produce electricity. Solar thermal power systems have tracking systems that keep sunlight focused onto the receiver throughout the day as the sun changes position in the sky. Solar thermal power plants usually have a large field or array of collectors that supply heat to a turbine and generator. Several solar thermal power facilities in the United States have two or more solar power plants with separate arrays and generators.
Solar thermal power systems may also have a thermal energy storage system component that allows the solar collector system to heat an energy storage system during the day, and the heat from the storage system is used to produce electricity in the evening or during cloudy weather. Solar thermal power plants may also be hybrid systems that use other fuels (usually natural gas) to supplement energy from the sun during periods of low solar radiation.
Types of concentrating solar thermal power plants
There are three main types of concentrating solar thermal power systems:
• Linear concentrating systems, which include parabolic troughs and linear Fresnel reflectors
• Solar power towers
• Solar dish/engine systems
Linear concentrating systems
Linear concentrating systems collect the sun's energy using long, rectangular, curved (U-shaped) mirrors. The mirrors focus sunlight onto receivers (tubes) that run the length of the mirrors. The concentrated sunlight heats a fluid flowing through the tubes. The fluid is sent to a heat exchanger to boil water in a conventional steam-turbine generator to produce electricity. There are two major types of linear concentrator systems: parabolic trough systems, where receiver tubes are positioned along the focal line of each parabolic mirror, and linear Fresnel reflector systems, where one receiver tube is positioned above several mirrors to allow the mirrors greater mobility in tracking the sun.
A linear concentrating collector power plant has a large number, or field, of collectors in parallel rows that are typically aligned in a north-south orientation to maximize solar energy collection. This configuration enables the mirrors to track the sun from east to west during the day and concentrate sunlight continuously onto the receiver tubes.
Parabolic troughs
A parabolic trough collector has a long parabolic-shaped reflector that focuses the sun's rays on a receiver pipe located at the focus of the parabola. The collector tilts with the sun to keep sunlight focused on the receiver as the sun moves from east to west during the day.
Because of its parabolic shape, a trough can focus the sunlight from 30 times to 100 times its normal intensity (concentration ratio) on the receiver pipe, located along the focal line of the trough, achieving operating temperatures higher than 750°F.
Solar energy is collected by a working fluid, which is converted to electricity usually via a turbine. The heat transferred to the fluid has exergy which is what is the reason for useful outputs (in this case turning the turbine). However, this requires multiple conversion of energy forms which is not ideal as many energy/exergy are lost during the process.
Additionally, thermal energy can also be converted directly to electricity via a thermoelectric generator.
Electricity is generated from thermal energy through heat-driven turbines in power plants, where steam from heated water drives the turbine connected to a generator. Solar energy is converted to thermal energy using solar collectors or thermal solar panels, which heat a fluid that transfers the thermal energy to a heat exchanger or storage system, often used to generate steam and produce electricity or to provide direct heating.
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