Editor’s note: This article is the executive summary of an article by DNV-GL regarding Kermit, a software method for evaluating grid performance.
Rapid worldwide integration of variable renewable resources on a large scale, combined with retirement of many conventional fossil resources in parts of the world, poses a new set of challenges to power system planners and operators. The high variability of wind and solar generation creates levels of net load ramping and system regulation requirements never observed in the past. The retirement of conventional power plants, along with displacement of other fossil plants as a result of renewable generation, is dramatically eroding the levels of system inertia, governor response, and regulation present in a system to control system frequency.
On the other hand, the arrival of utility-scale energy storage on the scene is adding a whole new category of fast regulating resource options and innovative market products have potential for addressing some of these issues. These new challenges in grid operation highlight a need for advanced modeling tools to study grid performance and effectiveness of new operational strategies.
Analyzing complex systems
DNV GL’s simulation tool Kermit is proving to be valuable in analyzing these complex factors for power systems of all sizes. In a recent gathering at the Electric Reliability Council of Texas (ERCOT), the electricity grid and market operator in Texas, grid and market operators and researchers from academic institutions from the U.S. and Europe discussed recent studies and future needs for analyzing and improving grid control in a changing power system.
This whitepaper highlights several important applications of the Kermit tool as discussed by users and DNV GL’s client support team at the 2014 Kermit User Summit. The presentations made by each Summit participant are summarized in Section 0. Evaluating operational challenges and frequency control Increasing renewables, and the inherent uncertainty in supply they bring, require changes to current operations and planning processes.
ERCOT, for example, is evaluating future scenarios with high-wind penetration and presented a new approach for evaluating future resource adequacy that incorporates Kermit into their long-term transmission planning process. High wind ramps and constrained transmission pose challenges to grid balancing in Texas and the goal is to understand how renewables behave in different seasons and locations and affect levels of operating reserves assumed for long term scenarios.
There are other examples as well. The British grid operator, National Grid U.K., is evaluating whether changes need to be made to current frequency control and balancing techniques in order to deal with increased levels of wind. The Nordic region, on the other hand, is currently experiencing unexplained, low-frequency oscillations on the interconnections. The oscillations are a challenge for operators, cause wear and tear on regulating units, and force additional capacity to be set aside for regulation. The Norwegian technical university in Trondheim (NTNU), is planning to use Kermit to analyze the origin and potential remedy for these oscillations.
Presentations from ERCOT, National Grid U.K., and NTNU pointed to the need for a tool to address frequency performance and oscillations and an end-to-end modeling approach for integrated analysis of planning, operations and renewables production.
Assessing new market products to address operational needs
The industry is seeing a need for new market products to deal with the impact of large scale renewables and to enable and leverage new technologies, such as energy storage technologies, entering the energy markets.
Kermit is used by PJM Interconnection (PJM) and California ISO (CAISO) as part of their toolkit for assessing new market concepts. PJM presented the results of its work using Kermit to determine the effectiveness of the AGC in controlling fast and conventional resources in the PJM frequency regulation market and the resulting system performance for each scenario based on CPS1 and BAAL scores.
The CAISO presented an overview of the new ancillary service market product for flexible ramping it is getting ready to launch. The product is intended to address ramping capability between market clearing intervals. In a related presentation, an approach for considering uncertainty in wind energy production, as well as sub-hourly ramp rates of generating units, in the day-ahead unit commitment was presented by IIT-KTH. Presentations from PJM, CAISO, and IIT-KTH (Spain) pointed to the need for a dynamic, sub-hourly modeling platform to fine-tune design and test effectiveness of these innovative market product concepts in system operations.
Monitoring grid system performance
Given the growing uncertainty and changing dynamics of the power system, and recent FERC orders dictating performance standards and market rules, grid operators are seeing an increased need to monitor the performance of the grid and participating resources. In particular, as highlighted by PJM, the performance of regulation resources is key to understanding the current robustness of the system and future capacity needs.
Similarly, the grid operator in New England, ISO-NE, presented a new approach for assessing regulation performance in conjunction with the regulation market upgrade, compliant with the approved FERC Order No. 755. The goal is to encourage bid offers that match observed performance characteristics as well as fair compensation for participating units.
Other concerns raised by several ISOs address the erosion of inertia and governor response as thermal units retire and are replaced by inverter-based renewable generation, such as PV or wind. The available inertial and governor response on-line at any given moment is becoming increasingly volatile and the robustness of the system is harder to predict. These concerns point to a need for improved performance monitoring of the grid system as well as market participants in real-time in order to have a current understanding of system robustness and need for additional reserves or other measures.
Kermit is helping power system operators and planners on two continents to better understand factors driving the frequency performance of their systems and to make more informed decisions on system planning, operational measures, and ancillary service market design. The software is becoming an end-to-end modeling tool for integrated analysis of planning, operations and renewables production.
Filed Under: Renewable energy