Global Energy Systems and Power Generation Technologies

Posted on Jan 7, 2026 in Geology

Energy Resources and Power Engineering Principles

Energy resources in the environment can be divided into renewable and non-renewable.

Classification of Energy Resources

Renewable resources include:

  • Solar energy
  • Wind energy
  • Geothermal energy
  • Biomass energy
  • Hydropower (water-course energy)
  • Waves and tides energy

Non-Renewable sources are organic fuels and nuclear fuels.

  • Organic fuels include hard coal, brown coal, peat coal, bituminous shales, petroleum, natural gas, and synthesis gas.
  • Nuclear fuels include fissionable materials (uranium, thorium) and fusion energy materials (deuterium, lithium, helium).

Another division of energy types includes mechanical, electrical, solar, chemical, nuclear, and thermal energy. All conversion processes inherently cause energy losses. The goal of power engineering is to find technologies for conversion, transmission, and use of energy that minimize these losses. If losses are lower, our natural environment suffers less because of the conversion processes.

Evaluating Fuel Resources

Fuel resources are evaluated in two categories: geological resources (possibility of future output) or fuel reserves (resources suitable for current output). The balance between these categories depends on the development of output technologies, the dynamics of depleting stocks, changes in geological conditions, and changes in fuel prices.

To evaluate fuel resource quantity, we use mass units or conventional units that show the energetic potential of the resources:

  • Solid fuels: metric ton of conventional fuel.
  • Liquid fuels: metric ton of equivalent oil.
  • Gas fuels: standard cubic meter.

Nuclear and Water Resources

Fissionable nuclear fuels are isotopes of uranium, thorium, and plutonium. Plutonium is reached in a nuclear reaction when uranium absorbs neutrons. Fusion energy fuels are hydrogen isotopes: deuterium and tritium. The source of energy is their synthesis (connection). Tritium is reached in a nuclear reaction when lithium absorbs neutrons.

Other water resources include sea wave energy, tidal energy, sea currents, and thermal energy. These resources are easy to evaluate but often hard to utilize effectively.

Renewable Energy Conversion Methods

  • Solar Energy: Converted in two ways: photothermal conversion (using solar collectors to generate heat) or photoelectric conversion (using photovoltaic cells to generate electricity).
  • Biomass Resources: Consist of specialized plants, forestry and agricultural wastes, animal droppings, and organic parts of municipal and household wastes. These are generated via photosynthesis.
  • Geothermal Energy: Comes from the Earth’s interior as hot water springs or steam.
  • Wind Energy: In wind turbines, kinetic energy is converted into mechanical energy, which can then be converted into electrical energy or used to drive working machines.

Depleting Resources Rate

The quantity of extracted raw materials and fuels depends on energy consumption and the state of production technologies. Changes over time in these processes determine the rate at which resources are depleted. The birth rate and changes in energy use per person have significant meaning. Based on this data, it is possible to evaluate the number of years until resources will be depleted.

Fuel Characteristics and Calorific Value

In power engineering, we primarily use hydrocarbon fuels, which are classified as solid, liquid, gas, and fissile substances. These are organic substances consisting of carbon and hydrogen chemical compounds. Reactions with oxygen are exothermic reactions.

Hydrocarbon Fuels and Combustion

Coal consists of combustible organic substances, mineral compounds, and moisture. Moisture can be divided into:

  • Temporary (caused by rain and washing)
  • Hygroscopic
  • Reaction (caused by oxygen and hydrogen thermal reaction)

The latter two types of moisture are often called ballast, which decreases the energetic characteristics of the coal.

Calorific Value Definitions

Heat of combustion is the energy extracted during the complete isobaric combustion of fuel, determined by specific initial and final temperatures, assuming that the extracted steam will condense. The heat of combustion is also called the Gross Calorific Value (GCV).

The Net Calorific Value (NCV) is derived from the GCV and depends on the content of carbon, hydrogen, other combustible elements, and ballast. The difference between GCV and NCV depends on the coal’s moisture and the hydrogen content in the fuel, as the latent heat of vaporization of water formed during combustion is subtracted.

In coal gasification, we obtain synthesis gas, and in further processing, we can obtain hydrogen and methanol.

Biomass Composition

Biomass consists of:

  • Agricultural production waste
  • Timber industry waste
  • Forestry waste
  • Specialized plants growing
  • Plants, products, and waste for biofuels production
  • Animal droppings
  • Organic parts of communal and industrial waste

Similar to coal, biomass can be converted into other sources of energy. Liquid fuels are mainly used in gas turbines.

Structure of Energy Systems

An energy system is a collection of objects coupled in a technical, organizational, and economic way, designed to search, extract, convert, transmit, distribute, and consume energy in all its forms. Subsystems of an energy system can include solid, liquid, and gas fuels, electric energy engineering, heat engineering, and nuclear engineering.

Electric Power Engineering Subsystems

Electric energy engineering subsystems are objects that produce, transmit, or distribute electric energy. They are functionally coupled to deliver this energy to consumers. We can divide them into power plants and power grids.

Power plants that produce both electric energy and heat are called thermal-electric power plants or Combined Heat and Power (CHP) generating plants. They can be steam, wind, gas, gas-steam, geothermal, etc. A portion of energy is produced in gas, gas-steam, or water power plants, and the lowest portion comes from wind and geothermal power plants.

Components of Steam Power Plants

A steam power plant consists of a power unit and a supportive system:

  • Power Unit: Consists of a steam boiler, turbine set, condenser, and unit transformer.
  • Supportive Systems: Consists of fuel preparing units, a condenser cooling system, pumps, fans, and environmental protection units.

Power Grids and Load Management

Power grids consist of transmission and distribution lines and switching stations. Power plants are connected to power grids with specific voltage ratings. Power grids transmit and distribute electricity. Control of the electric energy engineering subsystem is managed by power plants and power grids, often utilizing a load and operation dispatching system.

The daily load diagram divides consumption into three categories:

  1. Basic load
  2. Underpeak load
  3. Peak load

In the processes of electric energy and heat production, pollution is a significant problem. Pollution limits change over time and become stricter as power engineering technologies develop.

Thermodynamics and Energy Conversion Cycles

Energy is converted into required forms of useful energy. Considering current technological development, the most demanded form of energy is electrical energy. We can obtain electrical energy from various sources, including fuel energy, water and wind energy, or through the conversion of different energy forms.

Principles of Thermodynamic Cycles

The thermodynamic cycle is the main process necessary to produce heat and electric energy, which often involves the combustion of fuels. The heat of combustion is transferred to a working medium, which is converted in various machines and energy installations.

If these conversion processes are performed in a closed cycle, the technology is associated with a thermodynamic cycle, meaning that the initial state parameters are equal to the final state parameters.

A thermodynamic cycle is called a comparative cycle if all conversion processes are reversible. The Carnot cycle has the maximum theoretical efficiency and involves a reversible exchange of heat with the ambient environment in an isothermal process.

Comparison and analysis of real cycles against the reversible Carnot cycle show how imperfect they are. Since the Carnot cycle is impossible to put into practice, we use comparative cycles that have the same structure as real cycles but assume the reversibility of all processes. Because of energy dissipation, the efficiency of real cycles will always be lower than that of comparative ones. The efficiency ratio for both cycles is a measure of the thermodynamic perfection of the processes in the cycle.

Flow machines operating in open systems are installations producing electric energy that could operate in a closed or open loop. All systems involve isobaric heat rejection to the ambient. Maximum effective work is possible only if all processes are reversible. In analyzing processes in power engineering installations, we use the conservation of substance equation and the conservation of energy equation.

Power Plant Technologies and Efficiency

Steam Power Plants (Clausius-Rankine Cycle)

In many regions, most energy is produced in steam power plants where coal is the basic fuel. The comparative cycle of a power plant with medium superheat is called the Clausius-Rankine cycle. In the boiler, water is preheated, evaporated, and superheated to parameters p0 and T0. Steam then supplies the turbine, which drives a generator. Steam condenses in the condenser, carrying heat away at a constant temperature Tw.

The efficiency of the simple comparative cycle is:

ηt = (h0 − h2) / (h0 − hk) − (h2 − h1) = 1 − (h0 − h2) / (hk − h1)

Technological Structure

A steam power plant consists of:

  • A fuel-air-combustion gases unit.
  • A heat unit (boiler, turbine, condenser, regeneration unit).
  • A water system (cooling and preparing water).
  • A generator.
  • An ash removal/deslagging unit.

Modern steam parameters can reach p0 = 27–29 [MPa] and t0 = 600 [°C]. Resulting efficiencies can reach 44–45% (with cooling towers) or 46–47% (sea water cooling) for hard coal, and 41–43% for brown coal (lignite).

Improving Steam Cycle Efficiency

Efficiency can be increased by:

  • Regenerative preheating of feed water.
  • Multiple steam superheating.
  • Incoming steam with higher temperature and pressure.

Secondary steam superheating makes it possible to use cycles with high steam pressure and increases cycle efficiency.

Gas Power Plants (Open Cycle Operation)

Gas power plants operate as an open unit. Gas is delivered from a container to the combustion chamber. Air is also delivered to the combustion chamber by a compressor. Combustion gases leaving the chamber are delivered to a gas turbine. The gas turbine drives a generator, and electricity is delivered via a transformer. Combustion gases are carried out by a stack.

The efficiency of gas turbines depends mainly on the inlet temperature of the combustion gases and the proper pressure ratio. The temperature of combustion gases depends on the heat resistance of the construction elements. Nowadays, the temperature limit is about 1600 °C.

It is not possible to construct a gas turbine unit for the optimal pressure ratio that yields both the highest efficiency and the highest generated power. Highest efficiencies of gas turbines are around 45%. The gas turbine unit operates as an open unit: gas and air are taken from the ambient, and combustion gases are returned to the ambient.

Gas-Steam Combined Cycle Power Plants

Gas-steam units connect steam power plants with gas power plants to increase total efficiency. The idea of operation is the use of combustion gases from the gas turbine unit to heat water into steam in the waste heat boiler of the steam turbine unit. Efficiencies of gas-steam units can reach 60%.

The increase in efficiency in combined units can be further enhanced by:

  • Use of a regenerative heat exchanger.
  • Use of interstage cooling in the compressor.

Both methods increase the investment costs of the already expensive unit. Typically, the gas unit generates about two-thirds of the total power, and the steam unit generates about one-third.

Nuclear Power Plants and Fission Energy

Energy is produced from conversions in the atomic nucleus, controlled in nuclear reactors. The operational principle is similar to a steam power plant; the only difference is that instead of a boiler, we have a nuclear reactor.

Nuclear fuel is put into the reactor not as a single load but as separate units, often in special rods. Due to this design, moderator substances (heavy water, graphite, or beryllium oxide) are used to slow down neutrons. This makes heat transfer and control of the fuel amount easier. The chain reaction is controlled by rods (their number, dipping depth, and the use of safety rods).

Heat from the reactor is delivered by substances that do not absorb neutrons (e.g., liquid sodium). The reactor is cooled by liquid and gases with proper thermal properties. Coolants go to a heat exchanger where water becomes steam. Efficiencies of nuclear power plants are slightly lower than those of steam power plants, reaching 30–40%. A single nuclear unit can produce more energy than a single steam unit (e.g., 1400 MW vs. 900 MW).

The biggest problem of nuclear power plants is radioactive waste, which is exchanged on average every three years. Radioactive waste can also appear at the site of uranium ore output. Crucially, a nuclear power plant does not emit carbon dioxide during operation.

Renewable Energy Generation Technologies

Wind Power Plants (HAWT and VAWT)

A wind turbine is a device that converts the kinetic energy of wind into mechanical energy (rotational movement of the impeller with blades). Mechanical energy, via a system of gears and a generator, is changed into electrical energy. We generally divide wind turbines into those with a horizontal axis of rotation (HAWT) and those with a vertical axis of rotation (VAWT). HAWT turbines generate about 95% of the power among all wind turbines. Wind turbines can operate on the ground and offshore. A wind farm is a group of wind power plants.

According to Betz’s Law, an ideal wind turbine can transform only 16/27 of the kinetic wind energy into mechanical energy. This means that the theoretical maximum efficiency of wind turbines must be lower than 59.3%.

Solar Power Plants (Photothermal and Photovoltaic)

Natural thermal energy coming from the Sun can be used in three ways:

  • Direct production of heat (solar panels). Efficiency is about 80%.
  • Direct production of electricity (photovoltaic panels). Efficiency is about 20%.
  • Indirect production of electricity from thermal energy (Concentrated Solar Power, CSP, or solar towers).
  • Combined installations supported by traditional solutions.

If advanced solutions are used, photovoltaic efficiency can rise to 30%.

Geothermal Power Plants

Energy from the Earth’s interior is a natural source of energy. For every kilometer deeper, the temperature of the water rises about 30 °C. Water is heated by magma (silicates and aluminosilicates).

  • If water temperature is lower than 120 °C, it is used for heating.
  • If the temperature is 120–300 °C, an extra cycle with a special working medium must be used.
  • If the temperature is higher than 300 °C, the operational idea is the same as classical power plants.

After operation, the water must return to the Earth’s interior. To build a geothermal power plant, a minimum of two wells is required: the first to extract hot water, and the second to return the cooled water. Efficiencies of classical geothermal power plants are around 30%. Efficiencies of geothermal power plants using a special working medium (where water heats the medium, which drives the turbine) are around 10–15%. Carbon dioxide emission from geothermal power plants is 10 times lower than from classical power plants.

Biomass Power Plants

Biomass can be used as an additional fuel (co-firing) in classical steam power plants. In this case, a biomass co-generator is added where biomass is combusted in its basic or transformed form. Typically, the amount of biomass used is 10–15%, rarely reaching 25%. Biomass can also be used as the main fuel in smaller, dedicated boilers. Another method of biomass use is oxideless fermentation of organic matter.

The use of biomass in power plants generally decreases their efficiencies. In older types, efficiency could be around 20%; in modern types, efficiencies are around 30%. The main challenge lies in achieving proper granulation (fixed to the particular type of boiler) and maintaining the required steam temperature. Efficiencies of fermentation processes differ depending on the biomass components and implementation methods.

Hydropower Plants (River PP)

These plants convert the energetic potential of rivers into power. They can be classified as:

  • Run-of-river
  • Regulatory with a big or small reservoir
  • Cascading
  • Pumped storage