Grid friendly

Abstract: A Recent rapid Photovoltaic (PV) price reduction has significantly increased the competitiveness of PV-generated electricity, which has now reached grid parity in many markets, i.e., electricity is produced at the same or a lower price than conventional electricity sources. Along with other factors stimulating the global growth of renewable energy, this cost decline has greatly increased both the number and size of utility-scale solar plants, especially PVs, that are deployed on the power grid. The impact on power systems of integrating PV generation, especially as it relates to grid reliability and stability, needs to be addressed.

Abstract: A typical photovoltaic (PV) power plant consists of multiple power electronic inverters and can contribute to grid stability and reliability through sophisticated 'grid-friendly' controls. The availability and dissemination of actual test data showing the viability of advanced utility-scale PV controls among all industry stakeholders can leverage PV's value from being simply an energy resource to providing additional ancillary services that range from variability smoothing and frequency regulation to power quality. Strategically partnering with a selected utility and/or PV power plant operator is a key condition for a successful demonstration project. The U.S. Department of Energy's (DOE's) Solar Energy Technologies Office selected the National Renewable Energy Laboratory (NREL) to be a principal investigator in a two-year project with goals to (1) identify a potential partner(s), (2) develop a detailed scope of work and test plan for a field project to demonstrate the gird-friendly capabilities of utility-scale PV power plants, (3) facilitate conducting actual demonstration tests, and (4) disseminate test results among industry stakeholders via a joint NREL/DOE publication and participation in relevant technical conferences. The project implementation took place in FY 2014 and FY 2015. In FY14, NREL established collaborations with AES and First Solar Electric, LLC, to conduct demonstration testingmore » on their utility-scale PV power plants in Puerto Rico and Texas, respectively, and developed test plans for each partner. Both Puerto Rico Electric Power Authority and the Electric Reliability Council of Texas expressed interest in this project because of the importance of such advanced controls for the reliable operation of their power systems under high penetration levels of variable renewable generation. During FY15, testing was completed on both plants, and a large amount of test data was produced and analyzed that demonstrates the ability of PV power plants to provide various types of new grid-friendly controls.« less

Abstract: With the rapid growth of voltage source converter based high-voltage direct current (VSC-HVdc)-integrated offshore wind farms, wind turbines (WTs), and VSC stations are required to provide frequency regulation to maintain the onshore system frequency stability. However, after a temporary power increase during the initial period of a disturbance, WTs and VSC stations must reduce their output power to restore their own initial operating states. If there is no other power injection to offset the corresponding power shortage, a significant second frequency drop (SFD) may occur. To address this issue, this paper proposes an adaptive frequency regulation method with grid-friendly restoration. Different frequency regulation strategies are designed to adaptively use the releasable kinetic energy in WTs or the electrostatic energy in VSC stations according to their own real-time operating status. In addition, a system-level grid-friendly coordination is proposed to use the persistent energy reserves of WTs with a deloading strategy to increase the instantaneous power injection and avoid a significant SFD while other WTs or VSC stations restore their operating states. The quantitative calculation and switching mechanism of the additional power injections of deloading WTs are highlighted, and the effectiveness of the proposed method is verified in a case study.