The threat of severe weather during hurricane season keeps some solar asset owners and managers up at night wondering how much system damage and extra O&M cost will be incurred. While the choice of a solar tracker can’t stop a hurricane or flood, it may help to reduce downtime and O&M costs.
In this third part of my “Best Practices for Solar Tracker O&M” blog series based on our new white paper and recent GTM webinar, I’ll discuss the importance of your choice of a drive system and power requirements, as well as tracker fastener maintenance. I’d also like to share our own case study of how our NEXTracker systems fared during the flooding caused by Hurricane Matthew just this past fall.
Drive System and Power Requirements
NEXTracker’s mechanically simple yet elegant design reduces system O&M cost and increases energy yield throughout the life of the system. By having no row linkages, the greasing and inspection of joints and connections are eliminated. The systems are also mechanically self-balanced, so that the power required to move each row is very low, placing minimal stress on the internals of the motor. Each motor produces about 0.1 horsepower, requiring a mere 25 watts of power to rotate 90 panels on the row continuously. The design enables each row to rotate through a 120-degree range and capture up to two percent more energy per day. All of this is valuable from an O&M—and project owner’s—perspective.
Fastener maintenance is not a sexy topic and is an often-overlooked aspect of racking system maintenance. We’ve performed extensive cost analyses of the tracker portion of O&M budgets and have found that linked-row trackers typically use 85% more fasteners than are used on NX Horizon self-powered trackers. Now imagine how much stress all those nuts and bolts must bear during a severe weather event. The majority of our fasteners are permanent and “swaged” rather than torqued, can withstand inclement conditions, and require no maintenance over the entire solar project lifetime. This is an important concept, so let’s explore that a little further.
Torque vs. Tension
We’ve all heard about the advantages of tension over torqueing on mechanical systems. As the twisting force required to spin a nut up a bolt, torqueing is by nature inexact because of surface texture, debris, rust and other factors that can affect friction. Tension, on the other hand, involves the use of hydraulic tools to stretch screws and swage bolts to a structure. Did you know that the swaging of a lockbolt is five times stronger than its nut-and-bolt counterpart fastening system?
As you can imagine, maintaining system hardware can be tedious and costly. Dispatching crews to check the torque on screws or lubricate joints can add countless hours to an annual O&M budget, but centralized SAT operators don’t have a choice, since the failure of a single component can impact system performance dramatically.
As the diagram below illustrates, torque involves twisting the bolt, but with tension the swaged collar forms over the lock thread and eliminates the gap. Regular nuts and bolts have a gap, which can cause loosening by vibration. System hardware that does not require torqueing but instead relies on the tension between components will reduce the need for manual checks. We didn’t invent this concept, but adapted it from the aviation and aeronautics industries, which have been using tension-bolts and fasteners for strength and safety reasons in high-stress mechanical applications for years. There’s no need for periodic torque checking with NEXTracker’s highly durable, permanent fasteners that do not loosen over time and are more resilient during severe weather.
NEXTracker’s Flood-Zone Advantages
One advantage of ground-mount systems is that they can be built on flood-plain areas and other terrain unsuitable for development. But the racking and software solution must be designed to have longevity in the field and require minimal maintenance. The high clearance of the NEXTracker system and its components ensures that if flood waters rise, the system will be unaffected. Linked-row trackers are ill-prepared because most have mechanical and moving parts below the flood zone, endangering site operations until the flood waters recede and parts replaced.
The NEXTracker Flood Stow System (shown below) detects programmable flood depths through a self-powered ultrasonic sensor. Using our proprietary flood stow system, up to 2.75 feet of piers can be saved compared to a conventional 52.5-degree system, reducing steel costs.
You might be thinking that all of these resilient NX Horizon design features are great in theory or on a test field, but how do they work during a real hurricane?
Case Study: Hurricane Matthew Report Card
In fall 2016, the U.S and Caribbean experienced one of the worst hurricane seasons in 30 years. Destructive winds and torrential rains ravaged the southeastern United States. Because of NX Horizon’s robust design, component elevation and flood sensors, I’m proud to say that all our systems in the affected areas incurred zero damage. Before the storms, the trackers were rapidly placed into stow at 30 degrees within minutes. By contrast, most third-party trackers use a rectangular torque tube, which increases torsional load and slows the stowing procedure.
Even at the NEXTracker system sites in Virginia and North Carolina that were worst hit by flooding, none of the drive and mechanical components came into contact with rising waters due to their high clearance from ground level above high flood zones.
In short, our systems were designed with predictive O&M in mind so that costly corrective O&M was avoided. As a result, NEXTracker came through Hurricane Matthew with an A+ report card.
In the fourth and final installment of this series on solar tracker O&M best practices, I’ll discuss how to manage tracker assets intelligently, including the importance of corrective-based maintenance, as well as several key quality and reliability considerations.
(If you’re interested in reading the entire “Tracking Your Solar O&M Investment: Best Practices for Solar Tracker O&M” white paper, you can download it HERE, or watch the webinar with perspectives from several NEXTracker customers.)