By Joshua Marriott, senior VDC field engineer for McCarthy Building Companies
Global demand for solar energy has increased tenfold since the early 2000s. As demand has increased, the construction industry has been required to keep pace by improving methods, efficiency and technology all while reducing the project expenses and delivery cost to remain competitive.
McCarthy Building Companies, one of the top 10 utility-scale solar contractors in the United States, has teamed up with Trimble, a global provider of GPS and advanced positioning systems, to develop a focused solution that reduces labor needs, improves production tracking, provides better civil and equipment installation design and automates aspects of steel pile installation on utility-scale solar projects (with more than 10,000 piles per site).
By piloting the use of Trimble’s GPS Machine Guidance System on solar pile installation, McCarthy has been able to make changes to workflows that significantly reduce manpower needs and provide for highly accurate field data.
“Our Training Within Industries solar program has been instrumental in training local workforces in solar construction techniques involving pile installation and beyond, but we are constantly looking to improve our processes,” said Scott Canada, senior vice president of the renewable energy team at McCarthy Building Companies. “GPS technology crossed our radar as a method to reduce manpower on jobsites and potentially increase efficiencies and the accuracy of our survey data, while reducing costs.”
Traditional method of pile installation
In order to better understand the pilot program, one must understand the traditional method that is used to install piles on utility-scale solar projects. Typically, a team of seven to eight people are involved in the process beginning with a surveyor who marks end points of a tracker where end piles need to be installed. Depending on the solar tracker equipment, this can represent more than 250 ft end-to-end.
A layout crew then utilizes a string line marked at different dimensions pulled between two predetermined tracker end points, and colored markings are placed to identify the pile type and location. Next, the shakeout crew places the appropriate pile next to the ground marker, so the pile machine crew can then install it into the ground.
Finally, quality control makes sure piles are installed in the correct spot and at the appropriate height. With this process, which is largely reliant on human calculations and performance, the margin of error can be significant.
Testing out a new solution using GPS technology
Working closely with McCarthy’s renewable energy team, the virtual design and construction (VDC) group at McCarthy has been closely monitoring improvements in GPS technology that could potentially benefit the solar construction industry.
McCarthy approached SITECH Tri-Rivers, an authorized Trimble dealer based in Memphis, to see if it would be interested in piloting a GPS solution for pile installation on a utility-scale solar project in Tennessee.
After a series of meetings and site visits, a solution was designed that involved installing a GPS unit on the pile machine along with a small tablet so survey data could be inputted and displayed for the installers to follow.
McCarthy’s VDC group plays an integral role in creating terrain layouts for the solar sites, which often represent 400 to 500 acres. The layout pinpoints GPS locations for every single pile (many times this means upwards of 30,000 to 40,000 piles). The tablet mounted to the machine with the GPS tracker identifies precise pile locations for the installation crew, who then pound the pile into the ground and know when the top of the pile has reached the appropriate elevation based on the survey data from the tablet.
Analyzing benefits and challenges
McCarthy and Trimble’s pilot project has already demonstrated numerous benefits including: 1) a significant reduction in jobsite manpower (what used to take eight people now only takes three; 2) cost savings in the form of surveying expenses and employee salaries; 3) more accurate and useful data on location and drive times, which can be used to track production; and 4) a reduction in the areas where quality control needs to focus due to the ability to “red flag” any piles deviating from tolerance.
“Having the GPS technology on pile machines enables McCarthy to follow the path of the machine throughout the work day, giving their team greater control over the production process,” said Jon Wieneke, software and sUAS technology solutions and support with SITECH Tri-Rivers. “It provides them with a wealth of information at their fingertips, which can be used to streamline processes and increase efficiencies for the duration of a project.”
As with any pilot project, the lessons learned were not all favorable. The team discovered that longer and heavier piles are not ideal for this process because it increases the margin of data error. The team also learned that smaller piles (8 to 15 ft in length; weighing 50 to 150 lbs) and smaller pile machines produce more reliable GPS data. Additionally, accurate, existing and post-grading topography is essential. McCarthy is now implementing advanced lidar technology and infrared drones to capture sophisticated mapping data representing millions of points over large areas of terrain.
“We know the field technology is there,” Canada said. “We just need to work with Trimble to continue to refine the integration of the software component, so it’s more flexible and can meet the varying requirements of utility-scale solar sites across the U.S.”
Josh Marriott is a senior VDC field engineer for McCarthy’s renewable energy team, which has completed or is in the process of constructing more than 30 utility-scale solar projects across the United States, representing a combined capacity of more than 1.3 GW of clean energy production.