Renewable Energy and Sustainable Technologies: A Comprehensive Analysis

Posted on Jan 16, 2025 in Geology

Air Exchange Rate

Air exchange rate is the rate at which outdoor air replaces indoor air within a defined space. It is a measure of ventilation effectiveness and is often expressed as the number of air changes per hour, which represents how many times the entire volume of air is replaced with fresh air in an hour. AER = Fresh air supply / volume of room.

Heat Sources for Buildings

  • Heating systems: Furnaces, boilers, heat pumps
  • Solar energy: Harnessed through solar panels or passive systems
  • Electrical power: From appliances, lighting, electronics
  • Occupants: Metabolic processes
  • Burning of natural gas

Heat Gains for Buildings

Solar panels, light management, and cogeneration units.

Geographical Parameters Affecting Sunrise and Sunset

  • Latitude: Distance from the equator
  • Longitude: Time zone
  • Altitude: Curvature of the Earth
  • Local topography
  • Season
  • Axial tilt: Angle at which sunlight hits the Earth
  • Elliptical orbit: Different speeds of the Earth’s orbit

Factors Influencing Solar Energy Reaching Earth

Latitude, season, cloud cover, time of day, and air pollution.

Heat Pump Coefficient of Performance (COP)

COP = Heat output from the condenser / Work supplied to the compressor. It is the ratio of the heat delivered to the hot reservoir to the work put into the system.

Coal Gasification in a Chemical Loop

Processes that convert gaseous and solid carbonaceous feedstocks (coal, biomass) into syngas. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. In one reactor, the carbonaceous feedstock is partially oxidized to syngas, while the metal oxide is reduced to a lower oxidation state. In another reactor, termed the oxidizer, combustor, or air reactor, the reduced metal oxide from the reducer is re-oxidized by air or steam. The solid metal oxide oxygen is then circulated between these two reactors. The reducer and the oxidizer/combustor are connected in a solids circulatory loop, while the gaseous reactants and products from the reactors are isolated by the gas seals between the reactors. This system has a smaller footprint compared to other traditional systems.

Coal Gasification in a Flow Gasifier

This process converts coal or other carbonaceous materials into a synthetic gas (syngas), which is a mixture of CO, H2, CO2, CH4, and other trace gases. This gas can be used as a fuel or feedstock for the production of various chemical fuels. The flow gasifier is used in coal gasification. It operates continuously or almost continuously, allowing for a constant coal input and a continuous output of gas. Advantages include operational stability and efficiency. The produced syngas has applications in power generation, chemical production, and as a feedstock.

Heat Pump Components

Evaporator, compressor, condenser, throttling valve. C-B: adiabatic compression, B-A: Isothermal heat release, A-D: adiabatic expansion, D-C: isothermal heating.

Underground Coal Gasification

This process takes advantage of the chemical reactions of coal to produce product gases, similar to those of conventional gasifier reactors. The main difference is that the underground coal itself becomes the reactor, so the gasification of the coal takes place underground instead of in a manufactured vessel at the surface. It has the cost-saving and simplifying advantage of not having to mine or gasify coal above ground. Injection wells are drilled into an unmined coal seam, and either air or oxygen is injected into it with water. The coal face is ignited, and high temperatures from the combustion and limited oxygen cause coal to partially oxidize into H2, CO, CO2, CH4, and H2S. These products flow to the surface through wells located ahead of the combustion zone. Advantages include no need for mining, making deep coal seams usable, fewer gas cleanup systems, and emissions kept underground. Disadvantages include potential leaching into groundwater, the need for extensive geological study, and heat losses.

Pressure Heavy Water Reactor

This is a type of nuclear reactor used for generating electricity. It operates on the principle of nuclear fission, where the nucleus of an atom splits into two or more smaller nuclei, releasing energy. It uses heavy water (D2O) as a moderator and coolant. The use of D2O as a moderator allows operation at lower pressures. The D2O slows down the fast neutrons produced during fission, making them more likely to cause further reactions. At the same time, D2O also absorbs excess heat generated during the reaction and carries it away from the reactor core.

Coolants in Nuclear Reactors

  • CO2: GCR, AGR
  • He: HTR, PMBR, GT-MHR
  • H2O: RBMK, ACR, BWR, VVER, PWR
  • D2O: PHWR, CANDU
  • Liquid metal: FBR

Moderators in Nuclear Reactors

  • Graphite: GCR, AGR, HTR, PMBR, GT-MHR, RBMK
  • D2O: ACR, PHWR, CANDU
  • H2O: BWR, VVER, PWR
  • None: FBR

Energy Storage Systems

  • Thermal: Stores heat or cold to be used later. Types include tank water, ground heat, phase-changed materials, molten salts, hot oil, thermochemical heat, and pumped heat.
  • Mechanical: Stores energy in the form of mechanical potential or kinetic energy. Types include gravitational potential energy with solid masses, flywheels, pumped-storage hydroelectricity, and compressed air storage.
  • Electrochemical: Storage devices that can be charged and discharged multiple times (batteries). Types include rechargeable batteries, flow batteries, and supercapacitors.
  • Electrical
  • Chemical

Adiabatic Compressed Air Energy Storage (AA-CAES)

Principle of operation: Based on air compression and air storage in geological underground voids. During operation, available electricity is used to compress air into a cavern at depths of hundreds of meters and at pressures up to 100 bar. The heat produced during the compression cycle is stored using Thermal Energy Storage (TES), while the air is pressed into underground caverns. When the stored energy is needed, this compressed air is used to generate power in a turbine while simultaneously recovering the heat from the thermal storage. In periods with a surplus of electrical power, an electrically-driven compression train compresses ambient air from atmospheric pressure. Downstream, the compression train sends the hot air to a TES designed for the applied internal pressure and sufficiently insulated to minimize heat energy losses. In the regenerator-type TES, hot air passes through ceramic, concrete, or natural rock materials, while its heat is transferred to the storage inventory. Alternatively, TES systems can be applied as well. The cooled air is then injected under pressure into the cavern. In discharge operation, the air will leave the cavern and pass through the TES before being applied to an expansion turbine coupled to a generator, without the need for co-firing any fuel.

Pros: Capable of storing huge amounts of energy, AA-CAES capable of efficiencies of 70%, fast response times, inexpensive way to store energy.

Cons: Requires sealed storage caverns, economical only up to a day of storage, competing against other storage needs, not yet fully developed.

Pumped Heat Energy Storage

A heat pump energy storage system involves the use of a heat pump to store and later retrieve thermal energy. This process typically occurs by moving heat from a low-temperature reservoir to a high-temperature reservoir, effectively storing the energy in the form of thermal energy. Heat pump energy storage systems can be utilized for various applications, such as space heating, water heating, or industrial processes.

Flow Battery

A flow battery is a rechargeable battery in which electrolyte flows through one or more electrochemical cells from one or more tanks. With a simple flow battery, it is straightforward to increase the energy storage capacity by increasing the quantity of electrolyte stored in the tanks. The electrochemical cells can be electrically connected in series or parallel, thus determining the power of the flow battery system. This decoupling of energy rating and power rating is an important feature of flow battery systems.

Natural Light Management Methods

Natural lighting is a technique that efficiently brings natural light into your home using exterior glazing (windows, skylights, etc.), thereby reducing artificial lighting requirements and saving energy. Types include light wells, roof monitors, atriums, light ducts, light shelves, external reflectors, windows above the roof, and reflective blinds.

Why It Gets Dark When the Sun is 6 Degrees Below the Horizon

Even when the sun is below the horizon, its light can still reach us because the Earth’s atmosphere acts like a mirror, reflecting the sun’s light. This reflection 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, which contributes to the extended periods of twilight before sunrise and after sunset. For the sun’s radiation to be visible, the sun has to be at a maximum of 6 degrees below the horizon. That’s the twilight limit; then it gets dark.

Renewable vs. Non-Renewable Energy Sources

  • Availability: Replaced in a short time
  • Power output: Limited by natural reasons
  • Environmental impact: Pollutants, greenhouse gas emissions
  • Reliability: Dictated by nature
  • Costs: High investment but cheap maintenance

Basic Elements of Plate Solar Collectors

  • Absorber: Absorbs solar radiation and converts it to heat
  • Transparent cover: Mechanical boundary, reduction of convection, top insulation
  • Thermal insulation of the back and sides
  • Pipes with fluid: Transport energy
  • Housing: Mechanical boundary

Basic Elements of Evacuated Tube Solar Collectors

A solar thermal collector consists of similar elements but is housed in a different case. A thermosiphon collector heats the water. An indirect thermosiphon at the end of the pipes has a heat exchanger (possibility to use a better medium to”catc” the heat). The evacuated tube collector is made up of three main components: an evacuated glass tube with a selective coating that optimizes absorption, aluminum fins that transfer the heat inside the tube to a copper heat pipe, and a heat pipe that transfers this heat to the water. Elements include an outer glass tube, vacuum, inner glass tube, inner copper tube, absorber, hot water return, hot water supply, and insulation.

Solar Updraft Power Plant

The solar updraft tower (SUT) is a design concept for a renewable-energy power plant for generating electricity from low-temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines, placed in the chimney updraft or around the chimney base, to produce electricity.

Tidal Stream Generator Power Plant

Tidal stream generators use the kinetic energy of moving water to power turbines, similar to the way wind turbines use wind. Tidal barrages use the potential energy created because of the difference in hydrostatic height between high and low tides. Sluice gates on the barrage control water levels and flow rates to allow the tidal basin to fill on the incoming high tides and to empty through an electricity turbine system on the outgoing ebb tide. A two-way tidal power system generates electricity from both the incoming and outgoing tides.

Ocean Thermal Energy Conversion

This is a renewable energy technology that uses the natural temperature difference in oceans to produce clean, reliable electricity, day and night, year-round. The heat from the warm ocean surface and cold from the deep ocean drives a Rankine Cycle, which produces electricity. Warm surface water is pumped through an evaporator containing a working fluid. The vaporized fluid drives a turbine/generator.

Gravitational Water Vortex Power Plant

The water passes through a straight inlet and then passes tangentially into a round basin. The water forms a vortex over the center bottom drain of the basin. A turbine withdraws rotational energy from the vortex, which is converted into electric energy by a generator.

Solar Thermal Power Plant

A solar thermal power plant harnesses solar energy by concentrating sunlight onto a receiver using mirrors or reflectors. The concentrated sunlight heats a working fluid, creating steam to drive a turbine connected to a generator, producing electricity. This renewable energy source offers a sustainable alternative to fossil fuel-based power generation, with minimal greenhouse gas emissions. Thermal energy storage means heating or cooling a medium to use the energy when needed later.

Types of Thermal Energy Storage

  • Tank water heat storage
  • Ground heat storage: There are three typical underground locations in which thermal energy is stored: boreholes, aquifers, and caverns or pits. The storage medium typically used for this method of thermal energy storage is water.
  • Phase-changed materials: As it transitions from the solid to the liquid phase, it will continue to absorb heat, but its temperature will remain essentially constant.
  • Molten salts heat storage: An economical, highly flexible solution that provides long-duration storage for a wide range of power generation applications.
  • Hot oil storage
  • Thermochemical heat storage
  • Pump heat energy storage: Works by turning electricity into heat using a large-scale heat pump. This heat is then stored in a hot material.

Wind Power

The energy of wind originates from solar radiation energy. It is estimated that approximately 1-2% of the solar radiation reaching the surface of the Earth is converted into the kinetic energy of wind. Average wind resources across the globe are more than 1700 times greater than the energy produced by all existing thermal power plants.

Horizontal Axis Turbines

Advantages: Have higher efficiency than turbines with a vertical axis rotation.

Disadvantages: Due to the high RPM rate during strong winds, they require an RPM reduction mechanism. They also require a wind direction following mechanism. If the generator is placed in a nacelle, sliding connections are required.

Vertical Axis Turbines

Advantages: Efficiency independent of wind direction – does not need a wind direction following mechanism, simple mechanical design and control, can be easily mounted on objects – it is not necessary to build high towers, mounting possibility on the roofs of buildings, poles, spires of existing structures, strong wind resistance, lack of intensive vibrations, it is possible to design it as portable, thanks to simple assembly and dismantling, relatively low cost in comparison with classical horizontal axis rotors.

Disadvantages: Low efficiency: to produce the same amount of energy as traditional turbines requires a much larger size. Due to the small rotational speed, it needs a reentrant generator or a gearbox, which further reduces the efficiency and increases the noise level.

Geothermal Energy

Classification based on the type of energy carrier:

  • Deposits of geothermal waters: Depending on the pressure, shape, and surface morphology:
    • Artesian deposits: The water can effortlessly flow through the borehole to the surface by itself.
    • Subartesian deposits: Water in the borehole reaches significant heights by itself but does not reach the surface.
    • Gravitational deposits: Water can be pumped from a depth similar to the depth of the deposit location.
  • Deposits of superheated steam
  • Deposits of hot dry rocks

Multiple Well Open Loop Geothermal System

In this case, geothermal water is taken from the deposit using a submersible pump placed in the production well and is directed to the main heat exchanger. In the heat exchanger, geothermal water heats the network water. In the case of low geothermal water temperature, a heating pump or a peak load boiler can be additionally used to obtain the required network water temperature. The cooled geothermal water returns to the aquifer through an absorption well. The interaction of production and injection wells plays an important role in exploitation.

Usage of Geothermal Energy

  • District heating
  • Water geothermal power plants
  • Binary geothermal power plants