Reducing the Impact of Irradiance Ramps on PV Power Production – A Techno-Economic Analysis of Nowcasting

Abstract

Electricity grids experience an increasing amount of volatile renewable energy integration. This introduces new challenges for the stable operation of the grid and the matching of supply and demand. One of the technical challenges relates to unforeseen short-term power ramps being transmitted to the electrical grids. Such ramps in power production can disrupt grid stability, leading to imbalances, fluctuations in frequency and voltage, potential equipment failures and power outages. Furthermore, they can affect electricity market dynamics, causing price fluctuations. For photovoltaic (PV) power plants the primary source of short-term variability are irradiance ramps caused by clouds. All-sky imagers offer the potential to analyse the current sky conditions and produce shortest-term forecasts (nowcasts) of the irradiance up to 20 minutes into the future. This work investigates the potential of nowcasts for mitigating power ramps through preventive curtailment and analyses the associated economic consequences. For this purpose, irradiance nowcasts for a time frame of one year are fed into a virtual PV plant model located in southern Spain. The model simulates the power output of the plant and thereby processes the irradiance nowcasts into power nowcasts. Several ramp mitigation strategies based on the power nowcasts are developed and assessed. These nowcasting strategies are benchmarked against battery storage strategies, as well as hybrid strategies combining nowcasting and battery storage. The economic performance of the configurations is analysed and compared. For this, an incentive for power smoothing in the form of a monetary penalty for missed ramps is introduced. A simplified simulation of the marketing of the produced electricity determines yearly profits for every configuration which are then used in combination with the overall system costs to calculate the net present values. Using the net present value as a benchmark, a hybrid configuration is found to be the optimal solution for the power control under the applied regulatory framework. It is able to reduce the number of ramps by 93 % while reducing the required battery size by 40 % in comparison to a standalone storage solution. However, the analysis also shows that the introduction of ramp rate regulation and the consequent investment in ramp mitigation and curtailment of energy leads to overall higher levelized costs of energy and lower net present values.