Session: 18-03 HelioCon Solar Field

Paper Number: 142397

142397 - Forecasting Soiling-Related O&m Costs for Concentrating Solar Power Tower Plants 

Abstract: 

Concentrating solar power (CSP) plants require ongoing operations and maintenance (O&M) oversight to maintain production over specific thresholds set in place to meet contractual obligations, and as the plant ages the required O&M is expected to increase.  Soiling, or the deposition of particulate matter on the heliostats which redirect sunlight to a central receiver in CSP plants, is a significant source of efficiency loss at plants and its mitigation is one of the predominant sources of O&M cost.  Currently deployed plants utilize a wide range of methods, including dry-wiping the heliostats with mounted wipers, hand-cleaning the heliostats, and deploying vehicles which operate water sprayers of varying pressures, with or without mounted brushes.  The impact of soiling on efficiency losses varies widely by site, and in turn, so do the O&M costs associated with soiling and the method employed to mitigate its impacts.  However, existing performance models offer user-specified values for both heliostat performance and O&M cost with limited guidance on the interaction between the two factors. 

In this study, we present an overview of existing mirror-washing optimization models that can be used to estimate the required O&M cost of a CSP plant depending on site characteristics and capital and labor costs for vehicles.  Specifically, we compare a seasonal mirror-washing optimization model in which the cleaning schedule varies seasonally but cleaning frequency is consistent in each month to a stochastic soiling model with a threshold cleaning policy in which cleaning is performed in response to a level of degradation which we optimize.  We develop a collection of case studies in which the soiling rate and costs vary by location, and we show that the key decisions of staffing and/or vehicle procurement are consistent across the models that we choose from prior work.  We then propose a site-specific approach that forecasts expected costs of soiling-related O&M as a function of (i) the available cleaning technologies, (ii) the costs of vehicles and/or robots, (iii) fuel and water costs, (iv) labor costs, and (v) a measure of the revenue lost as a function of the average field reflectance weighted by each heliostat field section’s productivity. The study illustrates the importance of site characterization on selection of cleaning methods, staffing methods, and planned water consumption. Additionally, the study provides perspective on the thresholds for cost and performance that making automated vehicles, which are currently under development and deployed on a limited basis, cost-competitive with the various methods employed at operating CSP plants today.

Presenting Author: Alexander Zolan National Renewable Energy Laboratory

Presenting Author Biography: Alex Zolan is a researcher in the Thermal Sciences Group at NREL. His recent work involves the development of models that seek optimal design, dispatch, and operations of concentrating solar power and hybrid energy systems. He currently co-leads the Field Deployment task of the NREL-led Heliostat Consortium.

Authors:

Alexander Zolan National Renewable Energy Laboratory
Michael Cholette Queensland University of Technology