Test 33

Solar Power

The sun delivers about 173,000 terawatts of solar energy continuously.

Solar Energy Comparison

Solar power incident on Earth is about 10,000 times greater than human society’s total power consumption rate of around 18 TW.

Inexhaustible Solar Energy

Solar power will continue for roughly 5 billion more years, making it a perennial source.

Solar Constant Value

The solar constant is the intensity of the sun’s radiation at Earth's distance, valued at approximately 1360 W/m².

Solar Insolation Definition

Solar insolation is the solar power per unit area received at the Earth's surface.

Latitude Effect on Insolation

Solar insolation varies with latitude due to Earth's curvature; it is higher near the equator.

Global Average Insolation

The global average insolation reaching the Earth's surface is about 239 W/m², significantly lower than the solar constant.

Factors determining Solar Insolation

Solar insolation is influenced by the Sun’s output, the Earth’s geometry, and atmospheric conditions.

Ideal Lighting Conditions Insolation

Under clear skies and direct overhead sun, solar insolation can be around 1,000 W/m².

Electromagnetic Composition of Sunlight

Sunlight consists of about 50% infrared, 40% visible light, and approximately 10% ultraviolet radiation.

Active vs Passive Solar Heating

Passive solar heating relies on design elements without mechanical devices, while active uses pumps and collectors.

Elements of Passive Solar Heating Systems

Four elements: collection, insulation, distribution, and storage of thermal mass.

Collector Window Direction for Passive Solar Heating in Northern Hemisphere

Collector windows should face South for optimal sunlight capture.

Solar Thermal Power System Elements

Essential components include a concentrator, heat engine, and generator.

Concentration Ratio

The concentration ratio measures how much a solar concentrator intensifies sunlight at a focus.

Parabolic Dish vs Trough Concentrators

Dishes provide higher efficiency but are mechanically complex, while troughs are easier to scale but less efficient.

Power Towers Definition

Power towers concentrate sunlight using many mirrors to heat a central receiver for energy generation.

Semiconductor Definition

A semiconductor conducts electricity between a conductor and an insulator, with its conductivity controlled by impurities.

N-Type Semiconductors

Doped with atoms like phosphorus that have more valence electrons, creating extra electrons as charge carriers.

P-Type Semiconductors

Doped with atoms like boron that have fewer valence electrons, creating holes as charge carriers.

PN Junction Diode

Formed by joining P-type and N-type semiconductors; allows current to flow in one direction.

Band Gap Energy

The energy difference between the valence band and conduction band in semiconductors.

Factors determining Solar Panel Efficiency

Efficiency is influenced by band gap alignment, reflection losses, and recombination losses.

Energy Payback Time of Solar Panels

The time for solar panels to produce as much energy as was used in their production, roughly 2 years.

Indirect Solar Energy

Includes hydropower and wind power, contributing about 10% to US energy needs.

Countries relying on Hydropower

The Democratic Republic of Congo and Norway derive most of their electric power from hydropower.

Hydrologic Cycle Definition

The continuous circulation of Earth’s water driven by solar energy.

Hydropower Power Generation Factors

Determined by volume flow rate and pressure head of the water.

Quality of Hydropower Energy

Hydropower is a high-quality energy source, with minimal limitations by the second law of thermodynamics.

Comparative Power of Hydropower vs Fossil Fuels

Large-scale hydroelectric plants can exceed the output capacity of typical fossil fuel plants.

Environmental Impacts of Hydropower

Includes river ecosystem alterations, flooding, wildlife impacts, and land loss.

Advantages of Hydropower Plants

Quick response to electricity demand and reliability in peak load times.

Wind Power Relationship with Wind Speed

Wind power increases dramatically with wind speed, proportional to the cube of velocity.

Reliability of Wind Power

Intermittent and variable, making wind power less reliable for consistent energy generation.

Types of Wind Turbines

Horizontal-axis (HAWT) and vertical-axis (VAWT) turbines, with HAWTs generally more efficient.

Betz Power Coefficient

The theoretical maximum efficiency for wind turbines, capped at 59%.

Environmental Impacts of Windmills

Include visual pollution, noise, wildlife collisions, and land use issues.

Electricity Definition

The flow of electric charge, considered an energy carrier rather than a primary energy source.

Primary Energy Sources - US vs France

In the US, electricity is mainly from fossil fuels; in France, most electricity comes from nuclear power.

Types of Electric Power Grids

AC (Alternating Current) and DC (Direct Current) systems; AC allows for efficient long-distance transmission.

Voltage Definition

The electric potential difference measured in volts (V).

Ohm’s Law

Relationship stating that voltage equals current times resistance (V=IR).

Factors Determining Electric Power Transferred

Dependent on both voltage and current in the system.

Power Loss During Transmission

Depends on current and the resistance of the transmission line, with losses increasing with current squared.

High Voltage for Transmission

Transmitting power at high voltage minimizes losses compared to high current.

Transformer Definition

A device that converts AC voltage levels using electromagnetic induction.

Step-Up vs Step-Down Transformers

Step-up transformers increase voltage; step-down transformers decrease voltage for safety and usability.

Chemical Hydrogen as Energy Source

Hydrogen is not a primary energy source; it must be produced from other energy sources.

Hydrogen Production Methods

Include steam reforming, electrolysis, thermal splitting, and photolysis.

Applications of Hydrogen Today

Mainly used in ammonia production and petroleum refining.

Steam Reforming Definition

A process to produce hydrogen from hydrocarbons through high-temperature reaction with steam.

Electrolysis Process and Efficiency

Splitting water into hydrogen and oxygen using electricity, typically with ~75% efficiency.

Thermal Splitting vs Photolysis

Thermal splitting uses heat to break water, while photolysis uses light for the same purpose.

Fuel Cells Definition

Devices converting chemical energy directly into electricity through electrochemical reactions.

PEMFC Efficiency

Proton Exchange Membrane Fuel Cells typically convert hydrogen’s chemical energy into electricity with 50-60% efficiency.

Theoretical Maximum Efficiency for Hydrogen Fuel Cells

The maximum theoretical efficiency of hydrogen fuel cells is about 83%.