By Brandon Wronski, Special To Solar Power World
Cost reduction is at the top of the priority list for manufacturers, installers, contractors and consumers alike. Especially is this true in renewable energy markets. Lowering installation costs decreases the overall cost of the project and means a more level playing field with fossil fuel competition.
This ultimately amounts to greater consumer growth and increased sustainability. Unfortunately many costs and variables are beyond the contractor’s control. For example, site conditions generally dictate roof or ground mounting options. Roof mounts can be limited by the size, angle and direction of the roof and the increased degree of danger usually means an increased cost in installation. On the other hand, if there is inadequate land area, ground mounted arrays are out of the question.
However, if sufficient and suitable land area is available, ground mounting can be the best option. While many developers agree that prime farmland should not be used for solar, in many cases solar arrays can be located on brownfields without environmental impact.
Some companies also produce mounting systems that can be set above grazing space for animals. Ground mounts are not restricted by the size, angle and direction as can be the case with roof mounting. And ground-mounted arrays can be easily maintained. So there are choices that are within the contractor’s control. Efficiency can be optimized and costs reduced by making the right decisions.
If the decision is ground mounting, next come choices in regards to anchoring the racking to support the solar arrays. A crucial step is to perform a geotechnical site investigation to confirm subsurface conditions and assess the site’s potential installation options. This ensures that time and money is not wasted through trial and error.
Racking manufacturers usually stipulate general specifications that must be met based on the site conditions, such as soil type. Anchoring options include drilled shaft piles (also called micropiles or caissons) where the borehole is filled with high-strength cement grout or concrete, driven piles, and helical piers or ground screws that are twisted into the soil and remain in the ground.
Some contractors bidding on solar field installations subcontract out the drilling or turn down certain projects altogether. So, does the contractor have any control in this scenario? Is there a way of reducing the installation costs?
The solution could be to bring the drilling in house, but is that really a feasible option? Solar fields often require the drilling of thousands of piles, but the piles are relatively shallow, and the drilling is reasonably straightforward. Capital otherwise spent on contracting drillers could be invested in equipment and drill training, boosting the contractor’s bottom line.
Here again there are choices to be made and some very economical options available. A drill rig can be obtained new, used or possibly even rented. Many contractors already own and operate compact equipment such as skid steers, excavators, and the like. In this case a cost effective solution can be a drilling mast attachment.
As the mast and rotation head are powered by the carrier machine, capital costs can be reduced substantially if a suitable carrier machine is already owned. It should be noted though that a dedicated drill rig will be more mobile and efficient – more on that a bit later. “Build your own equipment” kits are another cost effective alternative for acquiring new drilling rigs, saving up to 40 percent on the capital cost of the rig. All major components such as the rotation head, crawler tracks and engine are shipped as pre-assembled components ready to bolt onto the steel frame.
The drilling method is another area where productivity can be greatly improved. The most efficient method is largely determined by the depth required and ground conditions. Instead of being at the mercy of drilling subcontractors, with education and training in basic drilling methods, contractors can then select the most productive process for each installation.
For example, loose materials and overburden can be drilled effectively with augers. In stable soils, standard continuous flight augers can be used to drill the borehole after which they are removed and the open borehole is filled with cement/grout. In less stable soil, hollow stem augers can be used to keep the hole open. The auger is then slowly extracted as concrete or grout is pumped through the center bore of the rotation head, and down through the hollow stem of the augers. DTH (down-the-hole) hammer drilling is highly efficient in rock formations.
In suitable soils and with proper drilling equipment, helical piles offer substantial benefits including the exclusion of concrete, no curing time, immediate loading and even shorter installation depths – all of which can increase productivity considerably.
When it comes to drilling solar array anchors, versatility equals efficiency. A drill rig that has adequate torque to drill with augers or install helical piles, along with the ability to perform DTH hammer drilling, combined with the correct tooling means that the most efficient method can be employed. Additionally, as thousands of piles are often required, a compact, highly mobile rig is also important.
A lot of valuable time can be lost setting up and manoeuvring the rig for each hole. A rig with rubber tracks and lots mobility is crucial. Some drills have separate power units that can supply power up to 200 feet away, making the drill even more manoeuvrable. The choice of drill rig will directly affect the number of piles drilled per day, the cost of installation and therefore the overall cost of the entire project.
While some factors are out of the contractor’s hands, many are within reach. Reducing the installation costs of ground mounted solar arrays is possible with the right equipment and knowledge.