“The plant for Thelen Sand and Gravel was not one of these large off-the-shelf projects,” said Fabian Huber, head of technical advisory for ground-mounted systems at Schletter, who planned and supervised the project. “The soil in the gravel pit is extremely compressed and stony, and at the same time, plants in this region have to withstand high snow and wind loads in winter. We therefore had to come up with a special solution.”
Because of the difficult ground conditions Schletter carried out test pile-driving during the planning phase. “Our tests showed that the pile-driving profiles we normally use with a material thickness of 3mm were not strong enough to be reliably inserted into the ground, as the ground is riddled with stones and highly compact,” Huber, who supervised the pile-driving on site, explained.
In order to solve this problem and to ensure the structures were safely anchored in the ground, extra-strong pile foundations with a material thickness of 4mm were used. They also have a special profile geometry that prevents deformation when rammed into hard ground.
Although systems with only one support are often used for ground-mounted installations in the U.S., this customer decided in favor of the FS Duo two-support structure, as this system is capable of supporting heavy snow and wind loads. “For this situation, a two-support structure was the more economical solution,” Huber elaborated. “The benefit of additional stability clearly outweighs the slightly higher costs of material. In particular in light of the fact the system is designed to last 20 to 30 years under tough conditions.” In winter, the area south of Lake Michigan is regularly hit by heavy snowfall and storms.
Thelen Sand & Gravel is using all of the solar power generated by the plant, thus covering around 30 percent of its energy consumption. The company installed the system to save energy costs, but more importantly to improve its carbon dioxide footprint.
Schletter Group has worked with SunPeak, the project developer, for several years. The two companies have collaborated on several other projects, with total installed capacity of more than 20 MWp.