Offshore Wind Farm-Grid Integration: A Review on Infrastructure, Challenges, and Grid Solutions

Recently, the penetration of renewable energy sources (RESs) into electrical power systems is witnessing a large attention due to their inexhaustibility, environmental benefits, storage capabilities, lower maintenance and stronger economy, etc. Among these RESs, offshore wind power plants (OWPP) are ones of the most widespread power plants that have emerged with regard to being competitive with other energy technologies. However, the application of power electronic converters (PECs), offshore transmission lines and large substation transformers result in considerable power quality (PQ) issues in grid connected OWPP. Moreover, due to the installation of filters for each OWPP, some other challenges such as voltage and frequency stability arise. In this regard, various customs power devices along with integration control methodologies have been implemented to deal with stated issues. Furthermore, for a smooth and reliable operation of the system, each country established various grid codes. Although various mitigation schemes and related standards for OWPP are documented separately, a comprehensive review covering these aspects has not yet addressed in the literature. The objective of this study is to compare and relate prior as well as latest developments on PQ and stability challenges and their solutions. Low voltage ride through (LVRT) schemes and associated grid codes prevalent for the interconnection of OWPP based power grid have been deliberated. In addition, various PQ issues and mitigation options such as FACTS based filters, DFIG based adaptive and conventional control algorithms, ESS based methods and LVRT requirements have been summarized and compared. Finally, recommendations and future trends for PQ improvement are highlighted at the end

Financial viability of offshore wind on the Texas Gulf Coast

Offshore wind is already a significant component of the electricity generation mix in Europe, and improvements in technology and cost are enabling increased offshore wind penetration in new markets around the world. Thus far, the US has struggled to materially participate in this industry, with only a single 30 MW offshore project in operation. Navigating a complicated regulatory framework, the lack of a coherent national policy, and facing local opposition, the industry has experienced some spectacular failures in recent years. However, the US now has an opportunity to take advantage of the lessons learned from years of (primarily) European development and combine them with excellent offshore wind resources close to transmission-constrained load centers. By far the leader of the US onshore wind industry, and with a long history of offshore oil and gas development, Texas has some major advantages when it comes to offshore wind. Wind resources in the Gulf of Mexico are more than adequate for economic production. With shallow depths and relatively calm seas, the Texas Gulf Coast is also well suited to offshore wind construction. These factors, coupled with a pro-development state regulatory scheme and extended jurisdiction over submerged lands, suggest that Texas is an ideal candidate for offshore wind development. With no currently active projects in the pipeline, this thesis examines the economic viability of offshore wind development on the Texas Gulf Coast at the project level. Using an ideal location and cost data from National Renewable Energy Laboratory (NREL), the Energy Information Administration (EIA), and industry sources, a hypothetical “test project” was developed and evaluated against three cost estimate cases and ten regulatory scenarios. These inputs were fed into a Discounted Cash Flow model to determine potential competitiveness in the Power Purchase Agreement (PPA) market in the ERCOT region. Results indicate that without significant cost reductions or major changes to either market conditions or federal/state incentive schemes, Texas Gulf Coast offshore wind cannot compete with other forms of onshore renewable generation. With ever-decreasing costs, it is not impossible that offshore wind could become viable at some point in the future, but given current conditions, it is not likely that any projects are on the near-term horizon.Energy and Earth Resource

OFFSHORE WIND ENERGY STUDY AND ITS IMPACT ON SOUTH CAROLINA TRANSMISSION SYSTEM

As one of the renewable resources, wind energy is developing dramatically in last ten years. Offshore wind energy, with more stable speed and less environmental impact than onshore wind, will be the direction of large scale wind industry. Large scale wind farm penetration affects power system operation, planning and control. Studies concerning type III turbine based wind farm integration problems such as wind intermittency, harmonics, low voltage ride through capability have made great progress. However, there are few investigations concerning switching transient impacts of large scale type III turbine based offshore wind farm in transmission systems. This topic will gain more attention as type III wind generator based offshore wind farm capacity is increasing, and most of these large scale offshore wind farms are injected into transmission system. As expected to take one third of the whole wind energy by 2030, the large offshore wind energy need to be thoroughly studied before its integration particularly the switching transient impacts of offshore wind farms. In this dissertation, steady state impact of large scale offshore wind farms on South Carolina transmission system is studied using PSSE software for the first time. At the same time, the offshore wind farm configuration is designed; SC transmission system thermal and voltage limitation are studied with different amount of wind energy injection. The best recommendation is given for the location of wind power injection buses. Switching transient also impacts is also studied in using actual South Carolina transmission system. The equivalent wind farm model for switching transient is developed in PSCAD software and different level of wind farm penetration evaluates the transient performance of the system. A new mathematical method is developed to determine switching transient impact of offshore wind farm into system with less calculation time. This method is based on the frequency domain impedance model. Both machine part and control part are included in this model which makes this representation unique. The new method is compared with a well-established PSCAD method for steady state and transient responses. With this method, the DFIG impact on system transients can be studied without using time-domain simulations, which gives a better understanding of the transient behaviors and parameters involved in them. Additionally, for large scale offshore wind energy, a critical problem is how to transmit large offshore wind energy from the ocean efficiently and ecumenically. The evaluation of different offshore wind farm transmission system such as HVAC and HVDC is investigated in the last chapter

Offshore wind power: a reliable and renewable energy source for all?

Climate change is a major challenge of the 21st century with potential severe consequences of global warming on all biological systems. The main reason is the CO2 emissions caused by human activities. In this context, renewable energies are one of the most promising solutions to strive against this issue. This master’s thesis aims to a better understanding of the offshore wind power, by studying the advantages, drawbacks and potential of this technology. Wind offers a large and clean resource of power, available all over the world. Wind power plants have first been developed onshore in 1980 as it is an easy and cheap technology. However, onshore wind is limited in terms of capacity suffering from volatile wind conditions and limited acceptance from the population. Conversely, offshore wind power allows very large-scale development, featuring larger turbines in areas where a stronger and more consistent wind blows. This allows to generate more power and to have better capacity factors, explaining why offshore wind power has recently emerged as an excellent asset to develop renewable energies at large-scale. Yet, offshore wind power currently suffers from one major drawback: the shallow-water requirement. Wind turbines are currently placed on fixed foundation that can reach a maximum water depth of 60 meters. This drastically limits the possible development areas and has led to large development inequalities across the world. Floating wind turbines are being developed to remove this restriction. Several approaches are under testing to tackle stability issues, all successful so far. This would be a game changing technology because it would unlock countless areas to implement offshore wind farms particularly for countries that do not have offshore shallow waters

A review on DC collection grids for offshore wind farms with HVDC transmission system

Abstract: Traditionally, the internal network composition of offshore wind farms consists of alternating current (AC) collection grid; all outputs of wind energy conversion units (WECUs) on a wind farm are aggregated to an AC bus. Each WECU includes: a wind-turbine plus mechanical parts, a generator including electronic controller, and a huge 50-or 60-Hz power transformer. For a DC collection grid, all outputs of WECUs are aggregated to a DC bus; consequently, the transformer in each WECU is replaced by a power converter or rectifier. The converter is more compact and smaller in size compared to the transformer. Thus reducing the size and weight of the WECUs, and also simplifying the wind farm structure. Actually, the use of offshore AC collection grids instead of offshore DC collection grids is mainly motivated by the availability of control and protection devices. However, efficient solutions to control and protect DC grids including HVDC transmission systems have already been addressed. Presently, there are no operational wind farms with DC collection grids, only theoretical and small-scale prototypes are being investigated worldwide. Therefore, a suitable configuration of the DC collection grid, which has been practically verified, is not available yet. This paper discussed some of the main components required for a DC collection grid including: the wind-turbine-generator models, the control and protection methods, the offshore platform structure, and the DC-grid feeder configurations. The key component of a DC collection grid is the power converter; therefore, the paper also reviews some topologies of power converter suitable for DC grid applications

Concrete Support Structures for Offshore Wind Turbines: Current Status, Challenges, and Future Trends

Today’s offshore wind turbine support structures market is largely dominated by steel structures, since steel monopiles account for the vast majority of installations in the last decade and new types of multi-leg steel structures have been developed in recent years. However, as wind turbines become bigger, and potential sites for offshore wind farms are located in ever deeper waters and ever further from the shore, the conditions for the design, transport, and installation of support structures are changing. In light of these facts, this paper identifies and categorizes the challenges and future trends related to the use of concrete for support structures of future offshore wind projects. To do so, recent advances and technologies still under development for both bottom-fixed and floating concrete support structures have been reviewed. It was found that these new developments meet the challenges associated with the use of concrete support structures, as they will allow the production costs to be lowered and transport and installation to be facilitated. New technologies for concrete support structures used at medium and great water depths are also being developed and are expected to become more common in future offshore wind installations. Therefore, the new developments identified in this paper show the likelihood of an increase in the use of concrete support structures in future offshore wind farms. These developments also indicate that the complexity of future support structures will increase due to the development of hybrid structures combining steel and concrete. These evolutions call for new knowledge and technical know-how in order to allow reliable structures to be built and risk-free offshore installation to be executed

Wind Power Development: Opportunities and Challenges

In this study, the prospects of wind power at the global level are reviewed. Existing studies indicate that the earth’s wind energy supply potential significantly exceeds global energy demand. Yet, only 1% of the global electricity demand is currently derived from wind power despite 40% annual growth in wind generating capacity over the last 25 years. More than 98% of total current wind power capacity is installed in the developed countries plus China and India. Existing studies estimate that wind power could supply 7% to 34% of global electricity needs by 2050. Wind power faces a large number of technical, financial, institutional, market and other barriers. To overcome these, many countries have employed various policy instruments, including capital subsidies, tax incentives, tradable energy certificates, feed-in tariffs, grid access guarantees and mandatory standards. Besides these policies, climate change mitigation initiatives resulting from the Kyoto Protocol (e.g., CO2-emission reduction targets in developed, the Clean Development Mechanism in developing countries) have played a pivotal role in promoting wind power.wind energy, renewable energy, electricity grids