Alternative Energy and Solar Thermal Systems

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Questions and Answers

What distinguishes alternative energy sources from conventional energy sources?

Alternative energy sources are renewable and non-depleting, while conventional sources like coal and oil are finite.

Explain the significance of the solar constant in solar energy collection.

The solar constant, approximately 1353 W/m2, represents the amount of solar energy arriving at the Earth's atmosphere.

What is the primary function of a flat plate collector?

To harvest solar radiation to raise the temperature of a fluid above ambient conditions.

How does the angle of solar radiation affect energy collection?

The energy collection is maximized when the solar radiation angle is perpendicular to the collector's surface. Signup and view all the answers

What are the two main types of solar thermal collectors mentioned?

The two main types of solar thermal collectors are flat plate collectors and non-concentrating collectors. Signup and view all the answers

What distinguishes evacuated tubes from flat plate collectors?

Evacuated tubes utilize a vacuum to trap heat and minimize convection losses. Signup and view all the answers

Why was there a sharp decline in government funding for alternative energy R&D during the 1980s and early 1990s?

Government funding and tax incentives for alternative energy sources dropped sharply due to changing economic priorities. Signup and view all the answers

What are the advantages of volumetric air collectors compared to liquid collectors?

Volumetric air collectors do not freeze, have lesser corrosion concerns, and leaks are less detrimental. Signup and view all the answers

In what temperature range do parabolic trough collectors typically operate?

Parabolic trough collectors operate in the temperature range of 250-450°C. Signup and view all the answers

How does a solar power tower harness solar energy?

It uses a set of two-axis tracking mirrors to reflect sunlight to a tower top. Signup and view all the answers

What is the primary function of molten salt in solar thermal systems?

Molten salt serves as a coolant due to its huge thermal capacity. Signup and view all the answers

How does a solar dish concentrator generate electricity?

It uses a generator at the receiver to directly generate AC power. Signup and view all the answers

Why is thermal storage important in solar energy systems?

Thermal storage is crucial because energy demand does not always align with solar energy availability. Signup and view all the answers

What types of storage systems are commonly used in solar thermal applications?

Common storage systems include water tanks and rock-bed systems. Signup and view all the answers

How do solar cells convert sunlight into electricity?

Solar cells use semiconductor properties to convert sunlight directly into electricity. Signup and view all the answers

What is a p-n junction in the context of solar cells?

A p-n junction consists of p-type and n-type materials that create an electric field for electron flow. Signup and view all the answers

What happens when a solar cell's p-type material is illuminated?

Excess electron-hole pairs are generated, leading to a flow of electrons and holes. Signup and view all the answers

How does the temperature affect the power output of a PV panel?

Higher temperatures generally decrease the power output of PV panels. Signup and view all the answers

What is the formula for calculating the power output of a PV panel?

The power output is calculated using the formula: $P_{mp} = P_{STC}(1 - eta(T - 25) × n)/1000$. Signup and view all the answers

What is the significance of the solar radiation value of 1000 W/m²?

1000 W/m² is the standard test condition (STC) used to rate the output of solar panels. Signup and view all the answers

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
In the past, natural gas, coal, and oil were classified as alternative energy sources
Government funding for research and development (R&D) and tax incentives related to alternative energy decreased in the 1980s and early 1990s

Solar Thermal Systems

Includes introduction, solar irradiance, solar thermal collectors, and thermal storage systems
Solar energy arrives at Earth's atmosphere at approximately 1353 W/m²
This is referred to as the solar constant
About 2/3 of solar energy reaches Earth's surface
Noontime radiation rate (40° North latitude, clear day) is about 946 W/m²
Solar thermal collectors come in different types: flat-plate, evacuated tubes, volumetric air

Solar Thermal Collectors - Subtypes

Flat plate collectors: Relatively low temperature applications, commonly used for heating water.
Evacuated tubes (vacuum tubes): Design resembles flat plates but use vacuum to reduce heat loss, thus achieving higher temperatures than flat plates.
Volumetric air collectors: Use air as a heat transfer medium, resistant to freezing.

Solar Irradiance (Numerical Facts)

Solar energy arrives at the Earth's atmosphere at a rate of about 1353 W/m² (428 Btu/hr ft²)
Part of this radiation is reflected back to space, part is absorbed by the atmosphere and re-emitted, and part is scattered by atmospheric particles.
Consequently, only about two-thirds of the sun's energy reaches Earth's surface.
The 'solar constant' is the average insolation reaching the Earth's upper atmosphere

Solar Irradiance (Orientation and Distribution)

The MENA region typically receives the highest global solar irradiance
The amount of energy collected from sunlight largely depends on where the collector is oriented, thus an accurate estimate of solar radiation angle across different timelines is vital

Solar Cells (Photovoltaics)

Converts sunlight directly into electricity using semiconductor material and p-n junction diodes
Includes information on how solar cells and PV systems function, including the different types of solar cells

Wind Energy

A renewable energy source derived from the uneven heating of the atmosphere by the sun,
This results in the motion or flow of wind, which can be harnessed for electricity generation

Wind Calculations

Wind power is calculated using the formula Pr = ½ρAυ³
Factors influencing wind power: air density (influencing atmospheric pressure, affects the amount of mass present per volume unit), swept area (size of an area swept by the rotor), and wind speed (affecting the volume of air).
Greater wind speeds, larger swept areas, and high air density correspond to greater power output.

Wind Turbine Types

Two types are commonly used: horizontal and vertical axis.
Horizontal axis is the most prevalent design, typically resembles airplane propellers, and usually has three blades. Taller turbines use longer blades to generate more electricity.
Vertical axis wind turbines, such as the Darrieus turbine, are simpler to manufacture and operate, typically resembling egg beaters.

Wind Turbine Components

Key elements including blade/rotor, drive train (gearbox, generator), tower, and other components (controls, support equipment etc) are discussed

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Description

This quiz covers alternative energy sources, focusing on solar thermal systems and their subtypes. Participants will explore concepts such as solar irradiance and the efficiency of various solar thermal collectors. The historical context of alternative energy funding is also discussed.