Energy Systems: Principles, Sources, and Technologies
Understanding Sunset and Sunrise
Why is it assumed that the sun needs to be 6° below the horizon for it to get dark? Even when the sun is below the horizon, its light can still reach us because the Earth’s atmosphere acts like a giant prism, scattering the sun’s rays. This scattering causes the sky to continue to be illuminated even after the sun has set or before it has risen. The atmosphere also refracts the sunlight, bending the light around the curvature of the Earth. So, while the curvature of the Earth plays a role, it’s mostly the scattering and refraction of sunlight in the atmosphere.
First Law of Thermodynamics for Open Systems
The First Law of Thermodynamics for an open system can be written as:
ṁ * hin = ṁ * hout + Ẇout
Interpretation for energy balance in a building: The energy that enters the building (through heating, solar radiation, electrical power, etc.) must equal the energy that leaves the building (through heat loss, work done by the building systems, etc.) plus the change in the internal energy of the building (stored heat, etc.).
Heat Sources for Buildings
Common heat sources for buildings include:
- Heating Systems: Furnaces, boilers, and heat pumps.
- Solar Radiation: The sun’s energy harnessed through solar panels or passive solar design.
- Electrical Power: Appliances, lighting, and electronics generating heat as a byproduct.
- Occupants: People generating heat through metabolic processes.
- Burning of Natural Gas.
Geographical Factors Affecting Sunrise and Sunset
Geographical parameters influencing sunrise and sunset times:
- Latitude: Distance from the equator.
- Longitude: Determines the time zone.
- Altitude: Higher locations experience earlier sunrises and later sunsets.
- Local Topography: Geographical features affecting the horizon.
- Season: Influenced by the Earth’s axial tilt.
- Axial Tilt: Affects the angle of sunlight.
- Earth’s Elliptical Orbit: The Earth’s speed varies in its orbit.
Renewable vs. Non-Renewable Energy Sources
Renewable sources compared to non-renewable sources are characterized by:
- Origin: Renewable sources originate from natural, replenishable processes.
- Availability: Renewable resources are naturally replenished; non-renewable resources are finite.
- Environmental Impact: Renewable sources generally have a lower environmental impact.
- Reliability: Many non-renewable energy sources are more reliable and less weather-dependent.
- Costs: Initial costs for renewable energy can be high.
- Greenhouse Gas Emissions: Renewable sources typically produce fewer emissions.
Primary Energy Demand
The largest share of primary energy demand currently comes from fossil fuels, accounting for 82% of global primary energy consumption in 2021. Oil had the largest share among fossil fuels.
CANDU Reactor Coolant
The CANDU (Canada Deuterium Uranium) reactor uses heavy water (deuterium oxide) as a coolant. This heavy water transfers heat from the fuel to the steam generators. The use of heavy water allows for the use of natural uranium as fuel.
Power Plant Start-Up Times
The longest start-up times among conventional power plants are typically found in thermal power plants, such as coal or nuclear power plants. These plants require time to reach the necessary temperature for power generation.
Pumped-Hydro Energy Storage
Principle of operation of a pump-hydro energy storage system: This system uses two water reservoirs at different elevations. During low demand, water is pumped to the upper reservoir. During high demand, water is released to the lower reservoir, passing through turbines to generate electricity. This method allows for the storage of energy from intermittent sources.
Coal Gasification in a Chemical Loop
Coal gasification in a chemical loop: This process converts carbonaceous feedstocks into syngas using metal oxide oxygen carriers. The feedstock is partially oxidized in a reducer reactor, while the reduced metal oxide is re-oxidized in an oxidizer reactor. The metal oxide circulates between these reactors. The syngas can be used for electricity, chemicals, hydrogen, and fuels.
Solar Thermal Power Plant Operation
Principle of operation of a solar thermal power plant:
- Solar Energy Collection: Mirrors (solar collectors) focus sunlight onto a receiver, heating a fluid.
- Energy Conversion: The heated fluid transfers heat to water, creating superheated steam. This steam drives turbines connected to generators, producing electricity.
Combined Cycle Power Plant Operation
Principle of operation of a combined cycle power plant:
- Gas Turbine Cycle (Brayton Cycle): Natural gas or oil combustion generates mechanical energy in a gas turbine, converted to electricity.
- Heat Recovery and Steam Generation: Exhaust heat from the gas turbine produces steam in a heat recovery boiler.
- Steam Turbine Cycle (Rankine Cycle): The recovered heat generates steam, driving a steam turbine connected to another generator.
Plate Solar Collector Elements
Basic elements of plate solar collectors:
- Absorbent Surface: A dark surface that absorbs solar energy.
- Glazing Cover: A transparent layer that allows solar radiation to reach the absorber but prevents heat loss.
Linde Dry Cycle
Linde dry cycle in a T-S (Temperature-Entropy) graph:
- 1-2: Compression
- 2-3: Heat Rejection
- 3-4: Throttling
- 4-1: Heat Absorption
Lowest Share of Primary Energy Demand
The lowest share of primary energy demand currently comes from renewable energy sources.
Fast Breeder Reactor Coolant
Fast breeder reactors use liquid sodium as a coolant.
Advanced Adiabatic Compressed Air Energy Storage
Principle of operation of an advanced adiabatic compressed air energy storage system:
- Advantages: High storage capacity, good efficiency, fast response, inexpensive.
- Disadvantages: Requires sealed storage caverns, economical for up to a day of storage, not yet fully developed.
Similar to pumped hydro, but air is compressed and stored in underground caverns during excess power generation.
Coal Gasification in a Flow Gasifier
Coal gasification in a flow gasifier: Coal is converted into syngas (CO, H2, CO2, CH4, etc.). The flow gasifier operates continuously, offering stability and efficiency. Syngas has applications in power generation and chemical production.
Solar Updraft Power Plant Operation
Principle of operation of a solar updraft power plant: Sunshine heats air under a large collector structure. The hot air rises in a tall chimney, driving wind turbines to generate electricity.
Pressurized Water Reactor (PWR)
Description of a Pressurized Water Reactor (PWR): A nuclear reactor using water under high pressure as coolant and moderator.
- Advantages: High reliability, proven technology, reaction shuts down at Loss of Coolant Accident (LOCA).
- Disadvantages: Low efficiency, potential for corrosion due to boric acid use.
Evacuated Tube Solar Collector Elements
Basic elements of evacuated tube solar collectors: Outer glass tube, Vacuum, Inner glass tube, Inner copper tube, Absorber, Hot water return, Hot water supply, Insulation.
Heat Pump Scheme
Scheme (elements) of a heat pump: Evaporator, Liquifier, Compressor, Expansion valve.
Heat Pump Coefficient of Performance (COP)
Definition of the heat pump’s coefficient of performance: COP = Heat output / Work output. It is the ratio of heat delivered to the electrical energy input.
Air Exchange Rate
Explanation of air exchange rate: The rate at which outdoor air replaces indoor air, expressed as air changes per hour (ACH).
Lowest Share of Primary Energy Demand in 2050
The lowest share of primary energy demand in 2050 is projected to come from coal.
High-Temperature Gas Reactor Coolant
High-temperature gas reactors use helium (He) as a coolant.
Pumped Heat Energy Storage System
Description of a pumped heat energy storage system: A heat pump stores thermal energy by moving heat from a low-temperature to a high-temperature reservoir.
Shortest Start-Up Times for Power Plants
The shortest start-up times among conventional power plants are found in: Gas turbines, Hydroelectric power stations, Wind turbines, and Photovoltaic (PV) systems.