By Billy Anderson and Dr. Mack Grady
As part of its endeavor to conserve the usage of natural Texas resources, the Texas Parks and Wildlife Department (TWPD) recently installed eighteen solar panel arrays across Texas. They range from a 5kW array at Ft. Davis, 30kW at Cedar Hill State Park, 35 kW at Cooper Lake State Park, on up to the 92kW array on the Austin Headquarters (see Solar Power Parks ). The energy generated by these arrays typically supplies about 20% of facility power needs and supplements the Texas grid, but the department is unable to determine the efficiency of their photovoltaic systems. Consequently, the question is whether or not a higher level of energy production should be expected. Baylor University’s Solar Team, under the supervision of Prof. Mack Grady, is partnering with TPWD to develop a tool for evaluating actual photovoltaic system efficiency. The team is comparing the power generated by TPWD arrays to an idealized power output determined using Weather Analytics solar radiation data, and the structural characteristics specific to each array.
TPWD is not alone. Due to the lack of a standard for solar panel efficiency in Texas, every-day consumers across the state face the same dilemma. By establishing a standard for photovoltaic efficiency in TPWD solar arrays, the Solar Team will also provide a way for consumers within a reasonable distance from any TPWD array to benchmark their solar panel performance against a verified system. This standard, much like an MPG estimate for a car, would eliminate the guesswork involved in evaluating efficiency and alert consumers to solar panels that are either defective or in need of maintenance.
The 92kW photovoltaic array serving the TPWD headquarters in Austin, was selected as the pilot array for analysis. Using Sunny Portal, a data management site for the system monitoring TPWD’s Austin array, the Solar Team collected historical data and reviewed its daily kilowatt harvest beginning in April 2013. This provided a general understanding of past performance and patterns of fluctuation on hourly, daily, and monthly scales. On May 3, 2013, an ideal day, the Austin array generated nearly 70 kilowatts at its peak as illustrated by the figure below:
On the same day, an 80 kW array approximately 200 miles away in Athens at the Texas Freshwater Fisheries Center, generated a similar amount of power:
While the Solar Team’s general analysis on a daily scale is helpful in acquiring actual power outputs and revealing the role atmospheric conditions play on day-to-day power output variations, it is not sufficiently comprehensive. Determining the efficiency of the Austin array requires the careful analysis of actual power output. The development of an idealized power output based on the array’s tilt and azimuth angles, and solar radiation characteristics such as Global Horizontal, Diffuse Horizontal, and Direct Normal Irradiance in the Austin area is underway.
The photovoltaic array efficiency tool will be used to evaluate TPWD’s seventeen remaining sites once it is fully developed. This will mark the first step toward empowering TPWD and Texas residents alike to gauge the quality and efficiency of their effort to use clean, renewable energy.
Billy Anderson is a Sophomore in Electrical Engineering at Baylor University and a member of the school’s Solar Team.
Dr. Mack Grady has been a professor of Electrical and Computer Engineering specializing in electric power systems and renewable energy for 30 years, first at UT-Austin and now at Baylor University. He has a particular interest in solar array performance and can often be found in the field checking his installations. He is a member of the TXSES Board of Directors.