Design and Analysis of a Large Solar Industrial Heat Plant for Frito Lay in Modesto California

Industry-specific technology demonstration projects are key to facilitating deployment of solar industrial process heat technologies. Frito Lay North America (FLNA) is pursuing installation of a solar industrial process heat plant at the manufacturing plant in Modesto CA. FLNA contracted with Industrial Solar Technology Corp. for design and installation of the system and with National Renewable Energy Lab for technical assistance. The US Department of Energy and California Energy Commission both facilitate private companies implementation of technology demonstration projects with incentives, tax policy, and technical assistance. The solar plant would include: 5,387 m2 (57,969 sf) of parabolic trough solar collectors; pipe from solar array to unfired steam generator; unfired steam generator (USG); hot water heat exchanger (HWHX); pipe from hot water heat exchanger back to array field; and associated pumps, bypass piping, and controls. Performance of each component of the solar heating system varies with changing conditions of intensity of the sunlight, position of the sun, and ambient temperature. Since each of these parameters change throughout the day and throughout the seasons an hourly simulation of one year’s performance is performed. The simulation is used to estimate annual energy delivery as well as to inform design recommendations. The solar array inlet temperature is solved for iteratively for each hour of the year based on an energy balance of the entire loop including all components. Nested within this iteration are iterations for the operating temperature of each of the 16 modules in series. Hourly direct beam solar radiation (W/m2) data for Modesto CA for 8 years from 1998–2005 was provided by the National Renewable Energy Laboratory Renewable Resource Data Center and the minimum year, average year, and maximum year were used in the analysis. Results indicate that the system would deliver between 3,898 MWh and 4,308 MWh per year (13.3 and 14.7 billion Btu/year) with an average of 4,044 MWh/year (13.8 billion Btu/year). This average estimate of 13.8 billion Btu/year agrees with the contractors proposal and also with methods described in the Industrial Process Heat Handbook published by NREL. The simulation is able to model more detail and inform design recommendations, such as bypassing the steam generator and only making hot water on winter days.