HDR Geothermal Energy Extraction Methods

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Questions and Answers

What is the primary purpose of a photovoltaic system?

To convert chemical energy into thermal energy

To convert electrical energy into mechanical energy

To convert solar radiation into direct electricity (correct)

To convert mechanical energy into electrical energy

What is the reason for the decline in the cost of solar cells?

Increase in production of solar cells

Both A and C (correct)

Decrease in the demand for renewable energy sources

Improvement in the technology of manufacturing solar cells

What is the minimum number of countries that use solar photovoltaic technology?

200

100 (correct)

What is the approximate installed capacity of solar photovoltaic power generation worldwide?

40,000 MW Signup and view all the answers

What is the process by which an electrical charge is produced when two dissimilar materials are struck by light?

Photovoltaic effect Signup and view all the answers

What is the purpose of the light in the photovoltaic effect?

To provide the energy needed to free some electrons Signup and view all the answers

What is the material used in the standard energy source for application in space?

Silicon Signup and view all the answers

What is the result of free electrons crossing the junction between two dissimilar crystals?

A negative voltage is created Signup and view all the answers

What is the purpose of a voltage or shunt regulator in systems with battery storage?

To prevent excessive overcharging of the battery Signup and view all the answers

What is the main advantage of fuel cells over conventional batteries?

No need for recharging or replacement Signup and view all the answers

What is the primary function of the anode in a fuel cell?

To oxidize the fuel gas Signup and view all the answers

What is the purpose of the electrolyte in a fuel cell?

To separate the fuel and oxidizer Signup and view all the answers

What is the main difference between a fuel cell and a conventional battery?

Continuous energy input and output Signup and view all the answers

What is the advantage of fuel cells in terms of environmental impact?

Pollution-free operation Signup and view all the answers

What is the classification of fuel cells based on the type of electrolyte?

Alkaline, Phosphoric acid, and Polymer electrolytic membrane Signup and view all the answers

What is the application of fuel cells in terms of domestic use?

Generating electricity for homes Signup and view all the answers

What is the primary function of a p-n junction in a solar cell?

To absorb photons and generate electricity Signup and view all the answers

What is the purpose of the depletion zone in a p-n junction?

To create a potential barrier for electrons Signup and view all the answers

What happens to an electron in the n-region of silicon when it absorbs a photon of light?

It is dislodged from its atom, creating a free electron and hole pair Signup and view all the answers

What is the purpose of a wire connected between the n-type silicon and the p-type silicon?

To allow electrons to flow through the external load Signup and view all the answers

What is the main difference between a stand-alone power system and a grid-connected power system?

The presence of a grid connection Signup and view all the answers

What is the purpose of a storage battery in a stand-alone power system?

To store energy from the array during periods of low irradiance Signup and view all the answers

What is the function of an inverter in a solar PV system?

To convert DC power to AC power Signup and view all the answers

What is the purpose of a charge controller in a solar PV system?

To prevent overcharging of the battery Signup and view all the answers

What is the primary method of extracting thermal energy from Hot Dry Rock (HDR)?

Pumping water or fluid through a well at the lower part of the fractured rock Signup and view all the answers

At what pressure and temperature does water boil underground in a hydrothermal resource?

7 atm and 165°C Signup and view all the answers

What is the purpose of a centrifuge separator in a vapour dominated plant?

To remove solid matter from the steam Signup and view all the answers

What is the cycle used in a vapour dominated plant to convert thermal energy into mechanical energy?

Rankine cycle Signup and view all the answers

What is the purpose of a flash evaporator in a liquid dominated high-temperature plant?

To obtain dry steam from high temperature wet steam Signup and view all the answers

What is the advantage of the Total Flow concept of geothermal energy?

It utilises both the kinetic energy and heat energy of the steam-liquid mixture Signup and view all the answers

What is the type of expander used in the Total Flow concept of geothermal energy?

Helical (or screw) expander Signup and view all the answers

What is the temperature of the rock at a depth of 5 km?

200°C Signup and view all the answers

What is the primary function of a fuel cell?

To convert the chemical energy of a fuel directly into electrical energy Signup and view all the answers

What is the main component of a fuel cell that is responsible for the conversion of chemical energy into electrical energy?

Electrolyte Signup and view all the answers

What is the temperature at the centre of the earth?

10,000 K Signup and view all the answers

What is the primary source of heat in the earth's interior?

Decaying process of radioactive isotopes Signup and view all the answers

What is the process of extracting heat from Hot Dry Rock (HDR) geothermal systems?

Drilling deep into hot rocks and then cracking it to form a cavity or fractures Signup and view all the answers

What is the purpose of the catalyst in a fuel cell?

To change the fuel type used in the fuel cell Signup and view all the answers

What is the name of the type of fuel cell that uses a proton conducting polymer membrane as the electrolyte?

Polymer electrolyte fuel cell Signup and view all the answers

What is the temperature of the magma near the earth's surface?

3000°C Signup and view all the answers

Study Notes

Direct Energy Conversion

Photovoltaic (PV) system: generates electrical power by converting solar radiation into direct electricity using semiconductors that exhibit the photovoltaic effect.

Photovoltaic Effect

Process where two dissimilar materials in close contact produce an electrical charge when struck by light or radiant energy.
In a p-n junction, electrons are not free to move from n-region to p-region due to the potential barrier.
Light provides the energy needed to free some electrons, creating a negative voltage with respect to the other side.
The photovoltaic effect can continue to provide voltage and current as long as light falls on the junction.

Solar Power

Production of electricity directly from sunlight.
PV power is produced using the photovoltaic effect, releasing electrons from the p-n junction and pushing them across a potential barrier or electric field.
Sunlight is composed of energy packets called photons, which may be reflected, absorbed, or pass through the p-n junction.
Absorbed photons generate electricity, and the light travels in packets of energy called photons.

Stand-alone Solar PV System

Designed to meet any electrical load.
Principal components:
- Photovoltaic array (PV) consisting of interconnected modules.
- Storage battery (supplies energy during periods of low solar irradiance and stores energy during periods of high irradiance).
- Power conditioner (regulates voltage output of the PV array to prevent overcharging or discharge).

Fuel Cells

Electrochemical device that converts the chemical energy of a fuel directly into low-voltage, direct current electrical energy.
Advantages:
- High conversion efficiencies.
- Low maintenance.
- Can be installed near the use point.
- Odorless and noiseless.
- Fast response time.
- Space requirement is minimal.
- Simple and safe.
- Pollution-free.
- No cooling water required.
- Capacity can be increased as demand grows.
- Long life.
Disadvantages:
- High initial cost.
- Low service life.
- Refueling problems in vehicles.
Applications:
- Domestic use.
- Automotive vehicles.
- Central power stations.
- Defense applications.
- Space projects.

Components and Working Theory of a Fuel Cell

Components:
- Anode (fuel electrode).
- Cathode (oxidant electrode).
- Electrolyte.
- Container.
- Separators.
- Fuel supply.
Working theory:
- Fuel gas diffuses through the anode and is oxidized, releasing electrons to the external circuit.
- Oxidizer diffuses through the cathode and is reduced by the electrons.
- Fuel cell keeps the fuel molecules from mixing with the oxidizer molecules, allowing the transfer of electrons by a metallic path.

Classification of Fuel Cells

Based on the type of electrolyte:
- Alkaline fuel cell (AFC).
- Phosphoric acid fuel cell (PAFC).
- Polymer electrolyte membrane fuel cell (PEMFC).
- Molten carbonate fuel cell (MCFC).
- Solid oxide fuel cell (SOFC).
Based on operating temperature:
- Low temperature fuel cell (25-100°C).
- Medium temperature fuel cell (below 100-500°C).
- High temperature fuel cell (500-1000°C).
- Very high temperature fuel cell (Above 1100°C).
Based on the types of fuel and oxidant:
- Hydrogen-oxygen fuel cell.
- Hydrogen-air fuel cell.
- Hydrazine-oxygen fuel cell.
- Ammonia-air fuel cell.
- Synthesis gas-air fuel cell.
- Hydrocarbon (gas) - air fuel cell.
- Hydrocarbon (liquid) - air fuel cell.

Types of Fuel Cells

Hydrogen-Oxygen Fuel Cell:
- A cell that generates an electric current by converting the chemical energy of a fuel directly into electrical energy.
- Fuel in a suitable form is supplied to the negative electrode and oxygen to the positive electrode.
Phosphoric Acid or Hydrogen-Oxygen Fuel Cell:
- Fuel: hydrogen.
- Oxidant: oxygen.
- Electrolyte: phosphoric acid.
- Electrodes: porous nickel.
- Output: 1.23 V at 25%.
- Efficiency: 85%.
Alkaline Fuel Cell:
- Fuel: hydrogen or hydrogen-rich gas.
- Oxidant: oxygen or air.
- Electrodes: porous nickel.
- Electrolyte: KOH (40%).
- Output: 1.23 V at 90°C.
Polymer Electrolyte or Proton Exchange Membrane Fuel Cell:
- Fuel: hydrogen.
- Oxidant: oxygen.
- Electrodes: deposited platinum layers.
- Electrolyte: proton-conducting polymer membrane.
- Output: 1.23 V at 25°C.

Geothermal Energy

Thermal energy present in the interior of the earth.
Can be extracted from the earth's interior in the form of heat.
Volcanoes, geysers, and hot springs are visible signs of the large amounts of heat lying in the earth's interior.
The geothermal energy from the earth's interior is almost inexhaustible.
Useful geothermal energy can be extracted at only certain suitable sites.

Hot Dry Rock Geothermal System

Composed of hot dry rock (HDR) but no underground water.
Represent the largest geothermal resources available.
Recovery of heat from HDR involves drilling deep into hot rocks, then cracking it to form a cavity or fractures.

Vapor-Dominated Plant

Water boils underground in a hydrothermal resource when it has a pressure of about 7 atm and a temperature of about 165°C.
The plant consists of:
- Production well to extract steam from the hydrothermal resource.
- Centrifuge separator to remove solid matter from the steam.
- Turbine to convert thermal energy into mechanical energy.
- Generator coupled to the turbine to generate electric power.
- Condenser to condense wet steam exited from the turbine into water.
- Cooling tower to cool warm water exited from the condenser.

Wet Steam or Liquid-Dominated Plant

Can be divided into high-temperature (above 175°C) and low-temperature (range of 95-175°C) systems.
High-temperature plant:
- Flash evaporator to obtain dry steam from high-temperature wet steam.
- Turbine with directly coupled generator to extract energy from dry steam.
- Condenser to condense used steam into water.
- Cooling tower to cool warm water.
Low-temperature plant:
- Uses a low-boiling-point refrigerant as the working medium.
- The plant runs on a binary cycle.
- The refrigerant is evaporated in a heat exchanger using the heat of water obtained from the hydrothermal reservoir.
- The refrigerant vapor runs the turbine with a generator coupled to it.

Total Flow Concept of Geothermal Energy

Utilizes both the kinetic energy and heat energy of the steam-liquid mixture produced by flashing the geothermal brine.
The overall efficiency for conversion into electrical energy should be greater than other methods.
This system utilizes the principle of the Lysholm machine, known as the helical (or screw) expander or mixed-phase expander.
Requirements of mixed-phase expanders:
- They should be able to overcome the losses associated with the impingement of liquid droplets on blades.
- They must be able to withstand the corrosive and erosive effects.

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Description

This quiz covers the methods of extracting thermal energy from Hot Dry Rock (HDR) reservoirs, including the use of high explosives, nuclear explosions, and hydraulic fracturing. It also discusses the process of pumping water or fluid through a well to extract the thermal energy.