Hawaiian Electric State of the System Summary Hawaiian Electric Company State of the System Summary for ESS RFP April 23, 2014 HECO-Transmission Planning Page 1 Hawaiian Electric State of the System Summary (This page is intentionally left blank) HECO-Transmission Planning Page 2 Hawaiian Electric State of the System Summary HECO Electrical System The Hawaiian Electric Company (HECO) electric utility system serves the island of Oahu. The system load has a daytime peak of approximately 1100MW and a daytime minimum load of approximately 800MW. The evening peak is roughly 1200MW. Historically, the system load has been served primarily by conventional generation including baseload steam reheat units, cycling steam units, and peaking combustion turbine units. Within the past five years the HECO system has experienced a large growth in variable renewable generation from photovoltaic (PV) and wind generation. By the end of 2013 there were roughly 250MW of PV capacity (primarily rooftop PV systems) and 100MW of wind capacity. The forecast for renewable generation on Oahu is expected to continue to grow at a high rate. The total PV and wind energy forecast for the next 10 years is shown in Figure 1, which shows how the forecasted renewable generation compares with the projected system loading. 1 Figure 1 HECO Forecasts 1400 1200 Power (Net MW) 1000 Total Renewables 800 Total PV Total Wind 600 Eve Peak Day Peak w/o PV 400 2011 Day Min 200 0 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 Forecast Year 1 The ‘2011 Day Min’ is based on historical loading. There is currently no forecast for daytime minimum loading for future years. HECO-Transmission Planning Page 3 Hawaiian Electric State of the System Summary Generator Minimum Operating Limits The amount of renewable generation that can be accepted on the system is limited by how low our conventional generation can go down in total MW output and still provide the required downward regulation required for the loss of a feeder, transformer or an increase in variable generation. Each generator has a minimum MW output rating including downward regulation. In general, by subtracting the total minimum operating limits from the forecasted system loading, we can get a rough “ceiling” of the amount of renewable generation that can be accepted with minimal curtailment. In order to accommodate more renewable generation additional conventional generators must be turned off. System Impact As renewable generation increasingly displaces conventional generation, the system’s ability to respond to contingencies such as loss of a generating unit, line faults, or rapid changes in system loading due to the variability of the renewable generation becomes compromised. At some point the amount of renewable generation that the system can accept reaches a point where the reliability of the system becomes unacceptable without some form of mitigation. System Stability Conventional generators provide ancillary services such as inertia and quick load pickup which provide instant response to help maintain system frequency and system stability for contingencies such as loss of generation or system faults. HECO’s load shed scheme is also designed to help maintain system stability by reducing system load during contingency events. As more renewable generation displaces conventional generators, the system loses inertial and quick load pickup response which results in more loads shed for common contingencies and ultimately could lead to system collapse. This has already been seen in an April 2013 event in which the loss of the largest generator (AES) on HECO’s system resulted in the system frequency dipping down to 58.35Hz initiating three blocks of under-frequency load shed. Approximately 79,000 customers experienced an outage. Exacerbating the event was the loss roughly 60MW of rooftop PV generation that tripped at 59.3Hz following the IEEE 1547 under-frequency trip setting. In addition, simulation of various transmission line faults led to frequency exceeding 60.5 Hz for over 10 cycles due mainly to the high-speed reclosing action. Most rooftop PVs will trip on over-frequency under IEEE 1547 settings. The loss of significant amounts of generation during line faults can lead to system instability. To allow for greater amounts of renewable generation, more conventional generating units must be taken off the system, reducing system inertia and making the system less stiff to frequency excursions. For transmission line faults with delayed clearing, simulations showed rooftop PVs tripping on undervoltage protection under IEEE 1547 settings for voltage below 50%. The loss of PV generation on undervoltage results in system frequency decay initiating multiple blocks of under-frequency load shed. HECO-Transmission Planning Page 4 Hawaiian Electric State of the System Summary Not all PV on the system will trip due to under-voltage since voltage is a local quantity and is not the same everywhere for the same fault. PV tripping due to under-voltage depends on the severity of the voltage depression and is sensitive to PV location relative to the fault location. Ramp Rate Capabilities Conventional generators like the ones in HECO’s fleet have ramp rate capabilities/limitations. Historically, the HECO generator dispatch has been well-capable of following the normal variation in system load. However as the amount of renewable generation increases on the system, the conventional generators must try to accommodate the additional variability of system load due to the variability of the renewable generation which relies on highly variable sources such as sun and wind. The down ramping capability for renewables is limited by the total on-line generator up ramping capability. When the ramping of renewables exceeds the capability of the on-line generators, system frequency will drop and in extreme cases load shedding may occur. As conventional units are turned off, the available generator ramping capability is reduced which adversely impacts the system’s ability to load follow the growing variability from renewable generation. Figure 2 shows the estimated ramping rates of total renewables at different MW levels compared to the available ramping capability of HECO’s conventional generators for different generation dispatch scenarios. HECO-Transmission Planning Page 5 Hawaiian Electric State of the System Summary Figure 2 1 Minute Day Ramping Rates Ramping Rate (MW/1 minute) 35 30 All Baseload Units On K1,K2 or K3,K4 Off K5,K6 Off K1,K2,K3,K4 Off 25 K1,K2,K5,K6 Off W7,W8 Off AES Off AES,K1,K2 or AES,K3,K4 Off 20 AES,K5,K6 Off Total Renewables 15 300 400 500 600 700 Total Renewables (MW) END OF ATTACHMENT G HECO-Transmission Planning Page 6