Session: 08-14-03: Emerging Technologies in Solar Energy

Paper Number: 99860

99860 - The Influence of Seasonal Cloud Cover, Ambient Temperature and Seasonal Variations in Daylight Hours on the Optimal Pv Panel Tilt Angle in the United States 

With growing interest in solar energy, multiple studies have been conducted to find the optimal tilt for PV (photovoltaic) arrays. While previous studies have found optimal tilt using different methodology for various locations around the world, few studies have considered the optimal PV tilt angle for locations within the United States. Likewise, a variety of variables influence the optimal tilt angle of a PV panel, including the characteristics of the panel, the local seasonal weather variations, the number of daylight hours the panel is exposed to and the ambient temperature of the surroundings. In this study, the optimal PV tilt angle and maximum energy output of PV arrays is calculated for every county in the United States and compared against the practice of setting the PV tilt angle to be equivalent to the latitude angle of the PV geographic location. A PVWatts API, implemented through Python, is used in conjunction with the SciPy optimization package to find the optimal tilt angle for each county using a direct line search algorithm. The results are then used to explore the influence of seasonal cloud cover, number of daylight hours and ambient temperature on PV panel performance. The results show that states in the southwestern region of the United States produce the most amount of energy annually and have the lowest optimal tilt angles. Tilt angles in this region can be as low as 24º, while states in the northern region of the United States had the highest optimal tilt angles, which could be as high as 42º.   All counties analyzed showed a difference between the location latitude and the optimal tilt, specifically 2,987 counties of a total 3,115 counties have optimal tilt angles that differ from their latitude by more than one degree. Most counties showed a deviation of 2º – 6º lower than the location latitude. The results also show that the optimal tilt depends on weather conditions, specifically cloud cover and ambient temperature, as well as the location latitude due to the seasonal variation in daylight hours with location latitude. The number of daylight hours is shown to have the largest influence, decreasing the tilt angle below latitude values due to the higher number of daylight hours in summer months. Seasonal cloud cover and ambient temperature have varying levels of influence, depending on the county. Generally, winter cloud cover decreases the optimal tilt angle whereas high summer temperatures increase the tilt angle, although the influence is less consequential than number of sunlight hours. 

Presenting Author: Rydge Mulford University of Dayton

Presenting Author Biography: Dr. Rydge Mulford is an assistant professor of Mechanical and Aerospace Engineering at the University of Dayton

Authors:

Essa Al-Hamer University of Dayton
Addison Grigsby University of Dayton
Rydge Mulford University of Dayton