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Questions and Answers
What is the approximate solar irradiance rate that arrives at the earth’s atmosphere?
What is the approximate solar irradiance rate that arrives at the earth’s atmosphere?
Wind power is considered an alternative energy source.
Wind power is considered an alternative energy source.
True
Name one example of non-concentrating solar thermal collectors.
Name one example of non-concentrating solar thermal collectors.
Flat plate
The ________ receives the highest solar irradiance all over the globe.
The ________ receives the highest solar irradiance all over the globe.
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What percentage of the sun’s energy actually reaches the surface of the earth?
What percentage of the sun’s energy actually reaches the surface of the earth?
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Solar energy is a depleting energy source.
Solar energy is a depleting energy source.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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What factor contributes to the effectiveness of solar collectors?
What factor contributes to the effectiveness of solar collectors?
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What is the primary purpose of a flat plate collector?
What is the primary purpose of a flat plate collector?
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Vacuum in evacuated tubes prevents heat from escaping through conduction only.
Vacuum in evacuated tubes prevents heat from escaping through conduction only.
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What temperature range is typical for parabolic trough collectors?
What temperature range is typical for parabolic trough collectors?
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The blank collectors have distinct advantages such as not worrying about freezing.
The blank collectors have distinct advantages such as not worrying about freezing.
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Match the following solar collector types with their characteristics:
Match the following solar collector types with their characteristics:
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Which type of collector is known for using two-axis tracking mirrors?
Which type of collector is known for using two-axis tracking mirrors?
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Tracking-type collectors are generally used for low-temperature applications.
Tracking-type collectors are generally used for low-temperature applications.
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What is one advantage of volumetric air collectors over liquid collectors?
What is one advantage of volumetric air collectors over liquid collectors?
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What is the primary coolant used in thermal storage systems as mentioned?
What is the primary coolant used in thermal storage systems as mentioned?
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Solar cells convert sunlight into electricity using the properties of conductor materials.
Solar cells convert sunlight into electricity using the properties of conductor materials.
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What is a common storage medium for solar thermal storage systems?
What is a common storage medium for solar thermal storage systems?
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A __________ type of solar storage system is sometimes used with air-type collectors.
A __________ type of solar storage system is sometimes used with air-type collectors.
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When the temperature of a PV panel increases, how does it affect the power output?
When the temperature of a PV panel increases, how does it affect the power output?
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In order to prevent water from freezing in solar thermal systems, the collector fluid must be drained back into the storage tank.
In order to prevent water from freezing in solar thermal systems, the collector fluid must be drained back into the storage tank.
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What is the function of a heat exchanger in solar thermal systems?
What is the function of a heat exchanger in solar thermal systems?
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Match the following concepts with their descriptions:
Match the following concepts with their descriptions:
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What is the relationship between wind speed and energy captured by a wind turbine?
What is the relationship between wind speed and energy captured by a wind turbine?
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Horizontal-axis turbines are often used in modern wind turbines.
Horizontal-axis turbines are often used in modern wind turbines.
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What are the two basic groups of modern wind turbines?
What are the two basic groups of modern wind turbines?
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The swept area of the turbine is represented by the formula A = ____.
The swept area of the turbine is represented by the formula A = ____.
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At a temperature of 30°C, what is the power output calculated to be?
At a temperature of 30°C, what is the power output calculated to be?
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Wind is considered a form of geothermal energy.
Wind is considered a form of geothermal energy.
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What causes winds?
What causes winds?
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Match the wind turbine type to its design or characteristic:
Match the wind turbine type to its design or characteristic:
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What is a common disadvantage of horizontal-axis wind turbines?
What is a common disadvantage of horizontal-axis wind turbines?
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Vertical-axis turbines are more efficient than horizontal-axis turbines.
Vertical-axis turbines are more efficient than horizontal-axis turbines.
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What is the primary function of the rotor in a horizontal turbine?
What is the primary function of the rotor in a horizontal turbine?
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The most common type of vertical-axis turbine is the _____ wind turbine.
The most common type of vertical-axis turbine is the _____ wind turbine.
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Match the following components of horizontal turbines with their functions:
Match the following components of horizontal turbines with their functions:
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Which of the following is NOT an advantage of vertical-axis turbines?
Which of the following is NOT an advantage of vertical-axis turbines?
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Nearly all wind turbines in use today are vertical-axis turbines.
Nearly all wind turbines in use today are vertical-axis turbines.
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Name one disadvantage of vertical-axis wind turbines.
Name one disadvantage of vertical-axis wind turbines.
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Study Notes
Alternative Use of Energy
- Alternative energy sources are non-depleting or renewable energy sources.
- Examples of alternative energy sources include solar and wind.
- Conventional energy sources like natural gas, coal, and oil were once considered alternative energy sources.
- Funding for research and development (R&D) and tax incentives for alternative energy decreased significantly in the 1980s and early 1990s.
Solar Thermal Systems
- Subtopics covered include Introduction, Solar Irradiance, Solar Thermal Collectors, and Thermal Storage Systems
Solar Energy Introduction
- Surface temperature of the sun is 5778 K (5505°C).
- Core temperature of the sun is 15.6 × 106 K.
- Power output of the sun is 3.85 × 1026 Watts.
- Energy output of the sun is 3.37 × 1027 KW·hr/yr.
- Annual energy intercepted by Earth is 1.5 × 1018 KW·hr/year (0.000000045%).
- World energy demand is 1.4 × 1014 KW·hr/year (0.0093%).
- Total ratio of world energy demand to intercepted solar energy is 4.2 × 10-12%.
Solar Irradiance (Distribution)
- The Middle East and North Africa (MENA) region receives the highest solar irradiance globally.
- Distribution maps show differences in solar energy received geographically.
Solar Irradiance (Orientation)
- Maximizing solar energy collection involves orienting collectors according to the sun's position for optimal radiation.
- This ensures the collector remains perpendicular to the sunlight.
Solar Irradiance (Numerical Facts)
- Solar energy arrives at the Earth's atmosphere at a rate of approximately 1353 W/m² (428 Btu/hr ft²).
- This is known as the solar constant.
- Some of the incoming solar radiation is reflected back into space, absorbed by the atmosphere, or scattered.
- Only about two-thirds of the initial solar energy reaches the Earth's surface.
- A calculation of typical noontime solar radiation can be about 946 W/m² (300 Btu/hr • ft²) on a cloudless day at 40° North latitude.
- A solar collector that tracks the sun will theoretically maximize its collection efficiency.
- In practice, energy collection efficiencies are lower (for example, approximately 70%).
- A more realistic estimate of solar panel area needed to absorb a certain amount of energy to provide 293 kWh (1e6 Btu) of energy per day is about 53 m² (567 ft²).
Solar Thermal Collectors
- These collectors categorized into non-concentrating and concentrating types.
- Non-concentrating types include flat-plate, evacuated-tube, and volumetric air collectors.
- Concentrating types include parabolic trough, compound parabolic concentrator (CPC), solar power tower, and solar dish Stirling engine.
Flat Plate Collectors
- Commonly used for relatively lower temperature applications like heating water.
- Typically oriented South (in the Northern Hemisphere)
- Consist of glazing, absorber plates, flow tubes, insulation, and casing.
Evacuated Tubes (Vacuum Tubes)
- Similar in concept to flat-plate collectors but employ a vacuum to reduce heat loss via convection.
Volumetric Air Collector
- Advantages over liquid collectors include no freezing concerns, less damage from leaks, and reduced corrosion issues.
Parabolic Trough Collectors
- High-temperature collectors using parabolic troughs to focus sunlight.
- Temperature range generally from 250-450°C.
- Concentrating collectors are not as effective with diffuse or scattered radiation from the sky and must track direct sunlight
Compound Parabolic Concentrator (CPC)
- Uses smaller, flat mirrors to concentrate solar radiation, similar to parabolic troughs, but they are cheaper and simpler to manufacture
Solar Power Tower
- Uses many mirrors to focus solar radiation on a central receiver at the top of a tall tower.
- Molten salt (sodium nitrate) is often used as a heat transfer fluid to store thermal energy
Solar Dish Concentrator
- Uses a parabolic dish to concentrate sunlight on a receiver to directly generate AC power.
Thermal Storage Systems
- Solar energy generation is not aligned with demand, thus storage systems needed.
- Common solar thermal storage method involves water tanks.
- Air-based systems can use a rock bed for storing energy as heat.
Solar Cells (photovoltaics)
- Convert sunlight directly into electricity.
- Semiconductor materials utilized to create p-n junctions.
- Types of solar cells exist, some examples given include n-type or p-type.
- Solar cells output depends on the solar irradiance and temperature.
Wind Energy
- Wind is a form of solar energy generated by uneven heating, irregularities of the Earth's surface, and the Earth's rotation.
- Harvested wind energy used from modern wind turbines converts motion energy into usable electricity.
Wind Calculations
- Wind speed and the amount of energy in the wind vary with air density and the blade's swept area.
- Air density varies with temperature and elevation.
- Warm air is less dense than cold air, and air is less dense at higher elevations.
- Swept area increases with the blade's length.
- Wind energy is related to the cube of wind speed.
Wind Turbine Types
- Modern wind turbines are generally categorized as horizontal-axis or vertical-axis types.
- Horizontal wind turbines are similar to airplane propellers.
- Vertical wind turbines are sometimes compared to egg beaters, like the Darrieus wind turbine.
Wind Turbine Types-Horizontal Axis
-
Advantages:
- Blades positioned offset from center of gravity, leading to greater stability.
- Ability to adjust blade pitch to minimize damage during storms.
- Tall towers allow access to stronger winds due to wind shear
- Self starting ability.
-
Disadvantages:
- Difficulty operating in areas with low wind
- High transportation and installation costs due to large components.
- Require skilled maintenance.
Wind Turbine Types-Vertical Axis
-
Advantages:
- Easy to maintain
- Low construction and transportation costs
- No directional requirements
-
Disadvantages:
- Less efficient
- Low starting torque that may require energy to start turning
- Operates in low and turbulent winds
Turbine Components
- Horizontal turbines consist of blades, a drive train (including gearboxes and generators), a tower, and various supporting equipment.
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Description
This quiz explores alternative energy sources such as solar and wind, highlighting their non-depleting nature compared to conventional sources like coal and oil. It includes details on solar thermal systems and important solar energy metrics. Test your knowledge of renewable energy and its significance in today's world.
