Smart Energy Technologies & Energy Storage
Aim/Objectives: Integration of intermittent renewable resources have presented challenges for grid stability especially as the penetration of solar and wind generation increases with falling costs and government mandates for zero carbon energy. Existing simple charge/discharge controls do not deliver maximum value to utilities building solar integrated with energy storage (PV+S) nor the deterministic output needed to reliably serve load. However, advanced controls built around common standards can enable intermittent PV+S to be dispatched much like a gas turbine/engine, but faster. This presentation will summarize two years of research and testing in creating a “dispatchable” PV+S plant using the MESA-ESS control mode specification. Specifically, we will discuss: 1. How MESA-ESS (Modular Energy Storage Association – Energy Storage System) controls (“control modes”) allow dispatchable and flexible operation of PV+S plants, 2. How a utility may achieve “value stacking” by performing multiple grid services and energy dispatch objectives simultaneously, and 3. How leveraging an accurate PV energy production forecast allows the utility to perform optimize battery utilization.
Methods: Our team has completed a three-step process for the last two years and we will be starting a two-year extended field trial starting in October of 2019. First, was to build a simulation environment that supports the MESA-ESS control modes as defined in DNP3 Application Note. Secondly, the controls simulation was transitioned to a time-accurate emulator, using 1-minute resolution solar production data test the controls in a more realistic environment. The extended field trial will utilize a 3MW solar inverter with a DC-coupled 1.5MW/1-hour BESS to implement the controls in a real power plant. Our presentation will focus on all of these steps and will clearly guide our audience through the MESA controls and our implementation methodology.
Results: Metrics for validating the performance of various control modes have been developed to evaluate the accuracy/performance of MESA-ESS control modes. The validation metric for most control modes is “Accuracy” which is calculated by dividing the number of seconds a control mode objective is not violated over the total number of seconds the control mode is enforced. Some control modes like the “Co-ordinated Charge-Discharge ” have specific metrics like “SOC miss ” which is the difference between target SOC and SOC achieved at the target time. When control modes and their objectives are stacked on top of each other in order of priority, these metrics can be used to evaluate the effectiveness of the individual control modes. For example, SOC management using Co-ordinated Charge-Discharge and Ramp-Rate control stacked with Active Power Smoothing + Frequency-Watt mode yields a 0.5 SOC miss %, 100% Ramp-rate control accuracy and 98% Frequency response accuracy.