Fundamentals of Renewable Energy Sources

Types of Renewable Energy and Their Characteristics

Solar Energy

In order to generate electricity, solar energy is a method that utilizes the power of the sun. Photovoltaic cells, also known as PV cells or concentrated solar power (CSP) systems, are utilized in order to collect this energy.

Photovoltaic Cells: PV cells are able to directly transform sunlight into electricity by utilizing the photovoltaic effect. Typically, silicon serves as the semiconductor material in their construction. Solar photovoltaic (PV) systems can be installed on a wide range of scales, ranging from modest rooftop installations in residential areas to enormous utility-scale solar farms.

Concentrated Solar Power: Through the use of mirrors or lenses, concentrated solar power (CSP) systems are able to concentrate a considerable amount of sunlight into a very small area. The concentrated energy is then put to use by heating a fluid, resulting in the production of steam that drives a turbine connected to a generator.

Characteristics:

• Intermittency: The generation of solar electricity is characterized by its intermittent nature since it is contingent upon the availability of sunshine, which is subject to variations based on the weather conditions and the time of day.
• Scalability: Solar systems have the capacity to cater to a wide range of applications, ranging from small home setups to enormous industrial arrays.
• Environmental Impact: Solar energy generation is environmentally friendly, as it does not release any greenhouse gasses while it is in operation. However, the production of photovoltaic cells necessitates the use of potentially harmful ingredients and energy-intensive processes. Furthermore, the installation of solar arrays in vast areas may necessitate the clearing of forests, which has caused environmental concerns in a number of countries around the world.

Wind Energy

Wind turbines generate wind energy by transforming the kinetic energy of wind into mechanical power. This process is known as wind energy generation. There is the potential for this mechanical power to be transformed into electrical power.

Onshore Wind Farms: Wind farms located on land are currently the most common type of wind energy generation. Onshore wind farms are located directly on land.

Offshore Wind Farms: These wind farms are situated in bodies of water, often on the continental shelf, and are referred to as offshore wind farms. It is possible for offshore wind farms to take advantage of stronger and more regular winds; however, the installation and maintenance costs for these farms are significantly higher.

Characteristics:

• Intermittency: In addition, wind power is characterized by its intermittent nature, wherein the generation of power fluctuates based on the wind speeds, which can be highly varied.
• Efficiency: Wind turbines are known to have a high energy return on investment (EROI), which indicates that they generate a much greater amount of energy over the course of their lifespan compared to the energy that is utilized in their manufacturing and maintenance processes.
• Environmental Impact: Wind power generation does not result in any emissions being released into the environment. Nevertheless, it may have local environmental implications, such as noise, and affect animals, notably birds and bats. These problems may be caused by the noise.

Hydroelectric Energy

For the purpose of producing electricity, hydroelectric power (also known as hydropower) makes use of water to propel a turbine that is connected to a generator. Hydroelectric power, also known as hydropower, is one of the renewable energy sources that has been in existence for the longest time.

Run-of-the-River Systems: These systems redirect a portion of the flow of a river through turbines without being able to drastically modify the flow of the river or the ecosystem of the river.

Reservoir (Dam) Systems: Dams, also known as reservoir systems, are used to hold water in a reservoir. When the water is discharged, it flows through turbines, which results in the generation of energy. Additionally, grid stability can be achieved through the storage and release of energy by means of this type of technology.

Characteristics:

• Reliability: Hydropower operates with a high degree of dependability and has the potential to provide an uninterrupted power supply, provided there is a sufficient flow of water.
• Energy Storage: Reservoir systems have the ability to store potential energy, which enables them to maintain a balance between supply and demand and ensures grid stability.
• Environmental Impact: The construction of dams and reservoirs can have significant environmental and social implications, including ecosystem disturbance, community relocation, and changes to water quality and flow. Despite the fact that hydropower is generally considered to be a clean energy source, these impacts can be very severe.

Challenges in Integrating Renewable Sources into Traditional AC Power Systems

Intermittency and Variability: Both solar and wind power are characterized by their irregularity, which can lead to changes in the supply of electricity. These fluctuations have the potential to pose a threat to the reliability and steadiness of the electricity grid.

Grid Stability: Due to the asynchronous nature of the majority of renewable generation (for example, photovoltaic inverters and wind turbine converters), which do not inherently contribute inertia to the grid, a high penetration of renewable energy sources might have an impact on the stability of the grid.

Infrastructure Upgrades: The integration of renewable energy sources frequently necessitates the implementation of substantial changes to the grid infrastructure that is already in place in order to accommodate the new generating sources and guarantee the transmission of power in a dependable manner.

Energy Storage: In order to strike a balance between supply and demand, it is necessary to have storage solutions that are both efficient and effective. This is especially true for solar and wind power, which do not always coincide with periods of peak demand.

Solutions in Integrating Renewable Sources into Traditional AC Power Systems

Advanced Inverter Technology: Modern inverters are able to provide grid-supportive services such as voltage regulation, reactive power support, and frequency management, which contribute to the grid's stabilization.

Grid Integration and Management: Technologies such as demand response, advanced metering infrastructure (AMI), and grid modernization projects (including smart grids) improve the system's capacity to manage and integrate renewable energy sources. Smart grids are also a part of this endeavor.

Energy Storage Systems: Battery storage, pumped hydro storage, and other technologies are examples of energy storage systems. These systems have the potential to store excess energy generated during high production periods and release it during high demand periods. This aids in mitigating the fluctuations brought about by renewable sources.

Hybrid Systems: One way to reduce overall unpredictability and provide a more reliable power supply is through the utilization of hybrid systems, which involve the combination of several renewable sources, such as solar and wind, with complimentary generating profiles.

Policy and Incentives: Government policies and incentives can improve grid integration by allocating funds for research, infrastructure upgrades, and the implementation of advanced grid technology. This can encourage the development and use of renewable energy technologies.

Grid Integration Techniques

Inverter Technology for Connecting Renewable Sources to the AC Grid

Inverter technology is an essential component in the process of incorporating renewable energy sources into the alternating current (AC) power grid. Examples of such sources are solar photovoltaic (PV) systems and wind turbines. The direct current (DC) that is produced by these renewable sources requires inverters in order to be converted into alternating current (AC) that is compatible with the grid.

Types of Inverters:

String Inverters: They are a type of solar photovoltaic (PV) inverter that is commonly used in household and commercial solar PV installations. These inverters connect a string of solar panels and convert the direct current (DC) yield of the entire string into alternating current (AC). Their popularity can be attributed to the fact that they are dependable and relatively inexpensive.

Microinverters: Installed on each individual solar panel, microinverters convert direct current (DC) to alternating current (AC) at the panel level. This improves the overall efficiency and dependability of the system, particularly in installations where shading or panel mismatch problems are an issue. Systems that are equipped with microinverters do not have a single point of failure like systems that are equipped with a single central inverter. This means that the failure of a panel or microinverter does not have an effect on the remainder of the system.

Central Inverters: Converting direct current (DC) from many strings or arrays into alternating current (AC) is the function of central inverters, which are utilized in large-scale wind farms and solar farms. In big installations, they are renowned for their excellent efficiency as well as their cost-effectiveness.

Hybrid Inverters: Hybrid inverters are unique in that they are able to convert power from a variety of sources, such as solar panels, batteries, and the grid. These solutions make it possible to integrate battery storage with renewable energy systems in a seamless manner.

Advanced Features of Modern Inverters:

Maximum Power Point Tracking (MPPT): By continuously altering the electrical operating point, Maximum Power Point Tracking (MPPT) ensures that the inverter is able to collect the maximum amount of power that is possible from the solar panels or wind turbines.

Reactive Power Support: Certain inverters have the capability to supply reactive power, which contributes to the continuous maintenance of voltage levels on the grid and enhances the overall power quality.

Grid Support Functions: Modern inverters are capable of performing grid-supportive tasks such as voltage regulation and frequency management. They can even contribute some level of inertia to the grid, which helps to improve its stability.

Grid Synchronization and Stability Issues with High Levels of Renewable Penetration

As the extent to which renewable energy sources are integrated into the power grid continues to grow, a number of difficulties concerning system synchronization and stability are brought to the forefront. It is necessary to find solutions to these problems in order to guarantee a power supply that is dependable and resilient.

Frequency Regulation: In order to function well, the electricity grid needs to have a consistent frequency, which is normally between 50 and 60 hertz. There is a possibility of frequency fluctuations due to the changeable nature of renewable sources such as solar and wind. Renewable energy systems that are based on inverters are required to incorporate frequency regulation capabilities in order to assist with grid stabilization.

Voltage Regulation: Unpredictable energy generation from renewable sources can lead to fluctuations in the power system's voltage. To maintain voltage levels within acceptable limits, advanced inverter technologies and grid support functions are required. Some examples of these functions include reactive power compensation and voltage regulation.

Grid Synchronization: Synchronization with the grid inverters is required to synchronize the phase, frequency, and voltage of the alternating current (AC) power that is generated with the grid. This synchronization ensures that the renewable sources' power is compatible with the grid and does not cause any disturbances.

Grid Inertia: Conventional power systems are dependent on the rotational inertia of huge synchronous generators in order to maintain frequency stability. Because they are based on inverters, renewable sources do not have any inherent inertia. Sophisticated inverters provide synthetic inertia, while the utilization of fast-response energy storage systems provides another solution. These systems are designed to imitate the stabilizing impact that conventional generators provide.

Fault Ride-Through Capability: The capacity to ride through grid disturbances, such as short circuits or voltage sags, without disconnecting is a requirement for renewable energy systems. This capability is referred to as fault ride-through capability. This capacity is absolutely necessary to preserve grid stability during transient events.

Curtailment and Dispatchability: In order to effectively manage the fluctuation of renewable energy sources, it may be necessary to curtail (reduce the output) during times of low demand or high generation. Implementing dispatchable renewable energy sources like solar thermal with storage or bioenergy can lead to more predictable and controllable power generation.

Grid Codes and Standards: Ensuring that renewable energy systems are in compliance with grid codes and standards gives the assurance that they will function in harmony with the grid infrastructure that is already in place. These codes specify the requirements for connecting, operating, and disconnecting renewable sources. These requirements include a wide range of topics, including power quality, protection, and control.

Energy Storage Integration: The integration of energy storage devices, such as batteries, with renewable energy sources helps address the issue of intermittency and promotes the stability of the grid. The ability of energy storage to offer backup power, frequency regulation, and load shifting also contributes to the increased reliability and grid compatibility of renewable energy sources.

Policy and Regulatory Framework

It is a combination of global and regional policies that are driving the transition to renewable energy sources. These policies are aimed at lowering emissions of greenhouse gasses, improving energy security, and supporting sustainable development. These laws create an environment that is conducive to the integration of renewable energy sources into AC power systems.

Global Policies Promoting Renewable Integration

Paris Agreement: The Paris Agreement is a historic international treaty that was adopted in 2015 and falls under the umbrella of the United Nations Framework Convention on Climate Change (UNFCCC). Its goal is to keep the increase in global temperature to far below 2 degrees Celsius above pre-industrial levels, with efforts aimed at bringing it down to 1.5 degrees Celsius. Every nation commits to what are known as Nationally Determined Contributions (NDCs), which include goals for increasing the proportion of renewable energy in their overall energy distribution.

Sustainable Development Goals (SDGs): The United Nations' 2030 Agenda for Sustainable Development comprises a total of 17 Sustainable Development Goals (SDGs), with Goal 7 concentrating on the provision of energy that is both affordable and environmentally friendly. Through the significant increase in the proportion of renewable energy in the overall energy mix, this objective seeks to ensure that everyone has access to energy that is not only affordable but also dependable, sustainable, and up-to-date.

International Renewable Energy Agency (IRENA): Irena, which stands for the International Renewable Energy Agency, is an organization that assists nations in transitioning to sustainable energy. It serves as a forum for international collaboration, provides policy guidance, and facilitates the exchange of best practices to hasten the dissemination of renewable energy products.

Regional Policies Promoting Renewable Integration

European Union (EU): The European Union (EU) has established lofty goals for the use of renewable energy through the Renewable Energy Directive (RED), which was launched in 2010. The current objective is to obtain a minimum of 32 percent of the total energy consumption in the EU coming from renewable sources by the year 2030. In addition, the European Green Deal intends for the European Union to achieve carbon neutrality by the year 2050 through the implementation of substantial investments in grid infrastructure and renewable energy sources.

United States: The United States of America: In the United States, policies that encourage the incorporation of renewable energy sources are adopted at both the federal and various state levels. Both the Investment Tax Credit (ITC) for solar energy and the Production Tax Credit (PTC) for wind energy are examples of tax incentive programs that are offered by the federal government. Other examples include grant programs and loan programs. Several states, such as California and New York, have imposed strict renewable portfolio standards (RPS) mandating the generation of a specific amount of power from renewable sources.

China: China is the world leader in renewable energy capacity, spurred by legislation such as the Renewable Energy Law and the 13th Five-Year Plan for Renewable Energy Development. China is also the world leader in the production of renewable energy. These policies establish goals for the capacity of renewable energy sources, offer financial incentives, and encourage the integration of renewable energy sources into the grid.

International Standards for Grid-Connected Renewable Energy Systems

Global, regional, and national levels have developed a variety of standards and regulations to ensure the secure and dependable integration of renewable energy sources into the power grid. Specifically, these standards address the technical, safety, and performance elements of renewable energy systems that are connected to the grid.

International Electrotechnical Commission (IEC): The International Electrotechnical Commission (IEC) is responsible for developing international standards for technology areas relevant to electrical and electronic fields. The following are important IEC standards for integrating renewable energy:

• IEC 61727: is a standard that describes the characteristics of the utility interface for photovoltaic (PV) systems.
• IEC 62116: IEC 62116 refers to the test procedure for islanding prevention measures for utility-interconnected photovoltaic (PV) systems.
• IEC 61400: is a family of standards that deal with wind turbine generating systems. These standards address the design, performance, and testing of wind turbines.

Institute of Electrical and Electronics Engineers (IEEE): The standards developed by the Institute of Electrical and Electronics Engineers (IEEE) are widely utilized for the integration of renewable energy sources into infrastructure. Other important IEEE standards include:

• IEEE 1547: The standard for linking dispersed resources with electric power networks is known as IEEE 1547. This standard outlines the requirements for the interconnection's performance, operation, testing, and safety.
• IEEE 519: IEEE 519 specifically outlines the recommended procedures and requirements for harmonic control in electric power systems.

Regional and National Regulations for Grid-Connected Renewable Energy Systems

European Network of Transmission System Operators for Electricity (ENTSO-E): ENTSO-E is responsible for the development of network codes and guidelines in order to guarantee the safe and effective functioning of the European energy transmission network. It is the responsibility of the Requirements for Generators (RfG) code to provide the technical specifications for connecting generators to the grid, which includes renewable energy sources.

National Renewable Energy Laboratory (NREL) and Federal Energy Regulatory Commission (FERC) in the USA: In the United States of America, the National Renewable Energy Laboratory (NREL) and the Federal Energy Regulatory Commission (FERC) are responsible for conducting research and disseminating recommendations for the incorporation of renewable energy sources into the grid. FERC is responsible for monitoring the wholesale electricity market and the transmission network, and it ensures that regulations make it easier to incorporate renewable energy sources.

National Standards in Various Countries: Each nation has its own set of regulations and standards for renewable energy systems that are connected via the grid. For example, the Central Electricity Authority (CEA) in India is responsible for disseminating technological standards for linking distributed generation resources.