Camino Real Mobile Estates

A tight project footprint and challenging soils required the project team at the Camino Real Mobile Estates in Lathrop, California, to find an innovative solution to drive piles to install a 419 kW solar array.

Sansome Skyline Development wanted to bring solar energy to its residents at the mobile home park. However, mobile homes don’t have enough rooftop space to make the economics of solar work, so the only feasible option was using a narrow but steep retention basin located next to the park that already served an important role in diverting the area’s heavy rains.

Developer and EPC Solar Gain brought its long-term racking partner to the Camino Real project. Terrasmart designed, engineered, and manufactured the 419 kW racking system, using its GLIDE Wave fixed-tilt racks to adapt to the terrain’s contours. They were able to use continuous rows to reduce foundation material and labor. At 180 ft long and 200 ft wide, the narrow stormwater management pond presented thorny logistical issues, and the site’s topography demanded unusually high elevation to keep the solar equipment safe above the retention pond.

The site offered little access space for materials. And because the site was located right next to the mobile homes, work could only take place during standard business hours to avoid disturbing the community.

Other challenges included a geotech soil report that detected extremely soft soils, requiring a 28-ft pile length, which was not doable. The construction team was able to adapt to the extremely muddy conditions, laying construction matting on-site for all equipment to install safely and efficiently in 6 in. of water.

The solar array will help the property owners improve the mobile home park, according to Roman Black, president of Solar Gain.

“It reduces the operating cost of the park for the owners,” Black says, “helping them to have more resources available for their community to provide improvements and give back to the residents.”

Developing the project

Solar Gain became involved in the Camino Real project prior to the current property owners purchasing the mobile home park, Black says.

“We had a relationship with the owners, and they were interested in exploring how they could have a more affordable mobile home park by using solar energy to power the park,” says Black, adding that the facility is a master metered property in the PG&E district. “They were in the acquisition process right at the NEM 2 deadline, and so there was a big scramble to figure out how to apply for a project with the new owner right as they were taking ownership of the facility.”

Siting the project

The Camino Real solar project was originally supposed to be a solar canopy covering a parking lot that was going to be built over a retention basin, Black says. However, acquiring approvals turned out to be a challenge.

“The owners went through about a year of planning, conditional planning, approvals, civil engineering drawings to figure out if they could put retention tanks underneath the parking lot,” Black explains. “The plan was to do carports to provide covered parking storage for the residents there. After going through extensive public hearings with the county, they declined their request for the opportunity to build the carports because the use didn’t match the function of the property, and the cost of the underground retention basins made the project unfeasible.”

Because Solar Gain had its applications under NEM 2, the company had to keep its existing system sizes.

“We couldn’t change those very much,” Black says. “But we’re able to redesign the system through the help of Terrasmart to still use this retention basin. That was a very tight space for the capacity of the system we needed, and we were able to squeeze it all in there and work within these steep banks that were sandy and get all of our zoning clearances from the neighboring properties.”

Siting the project over the retention basin created a challenge for driving piles. Not only was it a tight space with soft soil, but Black adds the steep terrain also posed an obstacle with 10- to 12-degree slopes. The project team had to re-evaluate the project design to better suit the terrain, according to Adam Brescia, national account manager at Terrasmart, which installed the mounting system.

“We were trying to design a flat plane system so that the leading edge of the modules would always maintain a certain clearance height over the max flood height of the retention basin,” Brescia says. “As the name implies, it’s a retention basin, so water collects in the bottom. During construction we had to apply construction matting to the bottom of the basin to allow our equipment to move around without sinking or getting stuck in the soils.”

Other challenges included the foundation design.

“Typically, we can utilize a geotech report to design the foundations for a project like this, but the soil conditions were problematic within their capacities, where we were initially thinking that we were going to need concrete,” Brescia says. “But we were able to go back to the site and do an on-site pull test with our installation equipment and our engineers reviewing the data. We were able to make a driven pile solution work, which really benefited the cost of the project overall.”

Water, water everywhere

As Brescia mentioned, working in the retention basin posed a challenge for the project team. However, initial surveys of the site indicated that water wouldn’t be a problem.

“Famous last words of the facility manager. Oh, that basin has never had water standing in it. You’ll be fine,” Black jokes. “In 30 years of working here, I’ve never seen water actually stay in that for more than a day or two. So don’t worry about it.”

Black explains that when Solar Gain performed its geotech survey of the site prior to the project commencing, the water table was at 13 ft below grade. However, the conditions would change.

“When we went to start construction, there was about 6 in. of water standing in the basin,” Black says. “We worked to do some pumping to try to evacuate the water and it kept coming back. Ultimately, we were working within the retention water, which made it challenging. We couldn’t get our standard scissor lifts in there. We couldn’t get our standard forklifts in there. We ended up having to provide proper lift options that were different than what we would normally use. It was a lot of creative ingenuity in order to build this project.”

The reason why the usually dry retention basin had standing water was because of an especially rainy season and a heavy snowpack, something that “never really occurs in our area,” according to John Reusche, commercial project manager at Solar Gain.

“It’s always a matter of the fact that the aquifer is actually going down and we’re losing water,” Reusche says. “Where here, of all times, they had a huge snowpack, and so the aquifer kept filling up more. In December and January, where you might have expected to have some water down there, there wasn’t any when they did the pull test. And then when we started construction, all of a sudden the water started percolating up. Normally, there would not be very much water, but there was quite a bit more than we expected.”