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Thursday, 13 March 2014
09:00 - 10:30 Electrical aspects and grid integration
Science & Research  


Room: Llevant
Session description

The grid integration of wind power has always been a challenge. In this session a range of speakers from academia and industry will address the impact of wind on network operation and the development of a large scale offshore HVDC grid, offshore systems, the state-of-the-art in HVDC technologies, as well as more specific topics including the design of offshore networks from a reliability perspective and the transient response of HVDC links.

Learning objectives

  • Understand the effect of wind power on grid operation and development via case studies
  • Get an overview of the state of the art in HVDC offshore grid research
  • Get acquainted with specific topics of offshore grids, including reliability and transient response aspects
Lead Session Chair:
Stavros Papathanassiou, National Technical University of Athens, Greece

Co-chair(s):
John Olav Tande, SINTEF, Norway
Reynaldo Nuqui ABB, United States
Co-authors:
Reynaldo Nuqui (1) F P Magnus Callavik (1) Anil Kondabathini (1) Jiuping Pan (1)
(1) ABB, Raleigh, United States

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Reynaldo F. Nuqui is a Principal Scientist with the ABB Corporate Research in Raleigh, NC USA. He is employed by ABB for the last thirteen years. He received his PhD in Electrical Engineering from Virginia Polytechnic Institute and State University, in Blacksburg, Virginia USA. Dr. Nuqui has been performing research and development in the general areas of high voltage transmission technologies. For the past five years, he was involved in the modeling and simulation of HVDC Grids for control, protection and economic evaluation. Dr. Nuqui is a senior member of the IEEE.

Abstract

Economic benefit calculations of an offshore wind and its HVDC grid delivery system in North America

Introduction

In North America, especially in the US there is strong government initiative to reduce the amount of greenhouse gas emissions. Bulk wind has been identified as a key energy source to meet this objective. Both land based and offshore wind is abundant in North America. The National Renewable Energy Lab reported close to 1,071 gigawatts of wind for depths between 0 – 30 meters. This paper will analyze the system economic benefits of an offshore wind demonstration case involving integration of seven gigawatts of offshore wind in the Atlantic region via a High Voltage Direct Current grid delivery system.


Approach

The approach is an economic benefit calculation procedure that is based on simulating the economic operation of an integrated generation and transmission system down to the operational level of one-hour. We have used GridView, a software tool that is able to perform transmission constrained economic dispatch of a large number of fossil fired generators and variable energy sources such as wind. The tool is able to model unit commitment and ramp rates of all generators in the model. The same tool was upgraded to support modeling the operation of the High Voltage Direct Current (HVDC) Grid delivery system. The HVDC Grid operational model determines hourly converter and cable loading with due respect to their capacity limits and thermal losses. The wind farms were modeled as hourly variable energy resources based on the hourly wind profiles representative of the offshore wind speeds in the target wind energy areas. The receiving generation-transmission system is composed of control areas within the Eastern United States which were modeled in detail in Gridview. The offshore wind and HVDC Grid delivery system model are then integrated with the receiving AC system resulting in our integrated model. We then simulated the model for one year in one-hour increments. The level of detail is necessary to cover the essential features of wind sources such as its intermittent nature and its effect on the ramp rates and unit commitment of existing fossil fired units. One year simulation was performed to capture the seasonal variations of wind energy and the corresponding seasonal variations in the electrical loads as well as the maintenance schedule of the generators in the system. Key operational indicators such as generation dispatch from fossil fired units were then saved and used to evaluate the impact of the offshore wind on the system costs and its greenhouse emissions.

Main body of abstract

Each of the nine offshore wind platforms is modeled as a real power input into the HVDC grid as a time varying series. The resulting offshore generation power is an aggregation of the energy of the wind farms situated around the platform. Based on approximated site location of the offshore platforms, wind energy profiles were determined and then scaled up based on the intended size of the wind farms. We assumed that the wind power plant capacity is equal to the capacity of the offshore converters. The expected annual wind farm capacity factor was determined to be forty percent (40%).
The HVDC grid topology is shown in Figure 2. Two cable direct interconnectors run north-south terminated by converter stations on both ends. Offshore wind platforms tee-in to several points along both interconnectors. In the same tee-in locations, cable direct connectors run to various onshore converter stations. The HVDC grid was modeled to be a 320 kV Voltage Source Converter bipole configuration, the positive and negative pole circuits are balanced at base case, that is, the flows in the positive pole circuits is equivalent to the flows in the negative pole circuits. The capacities of onshore and offshore converters of the HVDC Grid are summarized in Table 1 below. The losses of the HVDC converters have two parts: constant losses and usage losses as quadratic function of current or power. The converter losses are modeled as equivalent resistances – a shunt resistance for the constant losses and an equivalent series resistance for the variable losses.


A key driver for offshore wind is energy independence and security for North America. A one year simulation was performed in Gridview without the offshore wind farm and its HVDC grid. Table 2 shows the calculated average locational marginal prices at the receiving onshore converter stations. Note the huge disparity in the prices ranging from 29 USD/MWH (megawatt-hour) to a peak of 58 USD/MWH. Similarly, a one year simulation was conducted with the offshore wind case and its HVDC Grid delivery system in place. The same figure shows the corresponding locational marginal prices at the same onshore substations. It can be seen that the offshore wind has drove the locational marginal prices of electricity down to lower levels. Furthermore, it can also be observed that the HVDC grid has close to leveled these locational marginal prices.

At the current capacity factor forecasted at the wind farms, it is estimated that a total of 657.6 TWH (terawatt-hour) of electricity can be generated for a period of 25 years. The price of this wind energy could range from 22 BUSD to 36 BUSD for the lifetime of the wind farms at current electricity prices [6]. The lower bound was calculated based on the latest 2012 marginal prices in the study area. If the cost of CO2 is factored into the equation, the clean wind energy will have displaced 695 million tons of CO2 emissions. At the current assumed price of 20 USD per ton of CO2 in the EU, the CO2 emissions could easily add 14 BUSD to the total value of the wind energy.


Conclusion

This paper has investigated the economic benefits of offshore wind in North America using a demonstration case located in the Atlantic region. The offshore wind power totaled 7.7 GW that is collected by a total of nine offshore converter stations. The offshore converter stations are connected to an HVDC grid that runs in the North-South direction and terminating at select onshore substations. An economic benefit calculation software was used to simulate system operations to the hourly level to capture the day-to-day operations of the receiving power system in terms of unit commitment and economic dispatch as well as transmission constraints. This software simulation tool was enhanced with a HVDC Grid function capability. For the assumed lifetime of twenty five (25) years the wind farms were forecasted to generate an estimated 658 TWH (terawatt-hours). During this period, the HVDC grid is also expected to provide transmission access to an additional 280 TWH more energy transfer from low cost to high cost regions for land based generators in the host AC grid. Using current locational marginal prices in the study area, the wind energy was valued at 22 BUSD (billion US Dollars). By factoring in the cost of carbon into the equation, the value of this wind energy goes up by additional fourteen (14) BUSD to thirty-six (36) BUSD. The HVDC Grid is expected to provide transmission access to an additional 280 TWH economic energy transfer, worth 4.2 BUSD from the low cost to high cost regions bringing the calculated benefit of the offshore wind and HVDC grid project to a total of 40.2 BUSD.


Learning objectives
To evaluate the technical and operational feasibility, economic and environmental impacts of integrating bulk offshore wind energy systems in North America using High Voltage Direct Current Grid delivery system


References
[1] NREL, Large-Scale Offshore Wind Power in the United States: ASSESSMENT OF OPPORTUNITIES AND BARRIERS, September 2010. Available at: http://www.nrel.gov/docs/fy10osti/40745.pdf

[2]ABB, HVDC Light. It’s time to connect, with off-shore wind supplement, available at http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/2742b98db321b5bfc1257b26003e7835/$file/Pow0038%20R7%20LR.pdf

[3] 3E (coordinator), dena, EWEA, ForWind, IEO, NTUA, Senergy, SINTEF, “Offshore Electricity Grid Infrastructure in Europe – A Techno Economic Assessment,” Final Report, October 2011.

[4] PJM, Market and Operations Historical Data, available at http://www.pjm.com/markets-and-operations/energy/real-time/historical-bid-data.aspx