Introduction to A Review of Interconnection Rules for Large-Scale Renewable Power Generation

Abstract Around the world penetration levels of renewable-based power into power systems have been increasing rapidly over the last few years. In the year 2011, almost half of the estimated 208 GW of newly added electric capacity was reported from renewable-based generation. Wind and solar photovoltaic (PV) generators accounted for almost 40 % and 30 % of new renewable capacity, respectively, followed by hydropower. Besides rooftop and small-scale systems, the trend toward very large-scale wind farms and ground-mounted PV systems continued to play an important role. It is evident that renewable-based generation will be comparable to conventional power generation in the coming decades. Therefore, many transmission system operators (TSOs) and regulators around the world have come up with interconnection rules/codes to request these volatile renewable resource-based power plants to have more or less the same operating competence as conventional power plants. Depending on system characteristics and renewable penetration levels, the level of requirements imposed by these grid codes are getting more stringent over time to ensure the common aim of secured and reliable power system operation. This chapter presents a comprehensive study of the grid interconnection rules set by various TSOs and regulators for large renewable-based power plants. A brief discussion explaining the necessity of grid codes has been presented in the beginning, followed by a list of principal static and dynamic operation issues usually addressed in existing grid codes. A comparative study has then been carried out to compare various rules among grid codes around the globe. The study focuses on the primary concerns such as active and reactive power regulations under static operation, active and reactive power response during and after faults, and fault ride-through requirements imposed by the codes. A useful discussion on future trends for synchronizing diverse grid codes has also been presented. The contents of this chapter will be helpful for regulators as well as for renewable-based generator manufacturers to form better frameworks, which will ultimately result in secure system operation with increased penetration of large-scale renewable generation.

Keywords Renewable power plants Large-scale integration Grid code Transmission system operators Continuous operation Low voltage ride through High voltage ride through

Introduction

Standard interconnection rules for renewable-based generators are a comparatively recent policy innovation to accelerate the growth of clean energy supply [1]. Grid code regulations were primarily developed by transmission system operators (TSOs)/regulators to summarize both privileges and responsibilities of all generation units/customers connected to the transmission system. Developing such codes also promoted competition in power generation and supply, hence ensuring reliability and efficiency of power generation, transmission, and distribution [2].

As the level of penetration of renewable energy-based generation was insig- nificant compared to fossil fuel-based generation systems, earlier grid standards did not include rules for wind and solar power plants. However, the situation has altered over the last few years as number of countries around the world have observed a remarkable rise in the quantity and capacity of renewable power plants (RPPs) included into their electricity networks [3].

As a global trend for exploration of clean and renewable power, wind power generation has drastically increased in the generation scenarios of many countries and is set for additional growth over the coming years. Global wind power plant (WPP) installations reached approximately 283 GW by the end of 2012, resulting in the greatest capacity additions of any renewable-based technology. As in 2011, more new capacities were added in developing countries and emerging markets than in the countries listed in the Organization for Economic Co-operation and Development (OECD). With improvements in wind power interconnection poli- cies and economics, the United States and China together accounted for nearly 60 % of the global market in 2012, followed distantly by Germany, India, and the United Kingdom. Renewable resources accounted for almost 70 % of addition to existing electricity generation capacity in European Union in the year 2012. Majority of these additions were from wind power and solar photovoltaic (PV). Germany remained the largest wind power market in Europe in 2012. Besides the

domination of large wind turbines and farms, the small-scale (\100 kW) wind industry also continued to mature in 2012 [4].

Solar PV grew the fastest of all renewable technologies during the period from 2006 to 2012. The operating capacity of PV plants increased by an average of 58 % annually, followed by concentrating solar-thermal plant (CSP), which increased almost 37 % annually over this period from a small base of 367 MW. Almost 30 GW of PV operating capacity was added in 2012, mounting the total global capacity to approximately 100 GW. This was led by Europe, with signifi- cant additions in Asia late in the year. The trend toward large-scale ground- mounted systems continued, while small-scale rooftop systems continued to play a significant role. From the end of 2007 through 2012, total global capacity of CSP grew at an average annual rate of 43 %. In 2012, with an addition of 970 MW CSP in Spain, the total global capacity was doubled relative to the 2011 capacity and reached 2,550 MW [4].

Increased share of RPP is starting to affect the structure and management of Europe’s electricity system and is increasingly facing barriers that include direct competition with conventional electricity producers and saturation of local grids. It is just a matter of time that the same phenomenon might be observed by other systems where capacities of RPPs are becoming comparable to existing large-scale power plants. Therefore, several TSOs/regulators around the world have come up with newly developed grid standards requesting the RPPs to have essentially similar operating capabilities as conventional plants. Other TSOs are also engaged in revising their grid codes. This chapter explains the basic needs of developing new grid codes for RPPs under changing generation scenario. Different features in principal grid codes developed by various TSOs for integrating large RPPs are also explained. The authors believe that the discussion presented in this chapter would facilitate TSOs to assess their present requirements versus requirements set by other TSOs and would also assist generator manufacturers to develop grid code compatible RPP units.

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