There are two main reasons why most utility-scale solar projects use tracking systems: 15-25% more energy production by following the sun, as well as a broadening of the power generation profile by maximizing energy production in the mornings and afternoons.
Below are a few of the design principles that provide big benefits to solar farms in Australia and around the world.
Fewer components = higher reliability, less maintenance
Maintenance considerations in Australia are paramount. The country is vast, with many town centers hundreds or thousands of kilometers away from the largest solar sites. This, coupled with some of the highest-cost labor rates in the world, means that operators can’t afford to be trapped in a constant battle to fix trackers that may fail over time.
Electronics and components drive solar tracker maintenance, as these are the items that will fail and have to be replaced over the 30-year life of the asset. It comes down to simple probabilities: the more motors, electronics, or batteries a solar tracker relies on, the greater the rates of failure that will occur over time.
Take a 100 MW solar farm: Array’s DuraTrack® HZ v3 system has only 149 motors and controllers vs. over 25,000 electromechanical components for battery-powered, independent-row tracker designs. It doesn’t take an advanced degree in statistics to realize what the implications are: more money and time spent diagnosing and fixing each component that fails over time.
In a study published by independent engineering firm TUV Rheinland, the difference between these tracker architectures was about a 7% lower LCOE, or ~USD$.04/watt NPV difference. Another way to think about it: if you take an average of the expected repairs of both systems over 30 years, you will have 1 repair per year per 100 MW for Array’s tracker architecture vs. 2 repairs per day for battery-powered, distributed-type trackers.
You can download the full report and LCOE spreadsheet model here.
While some may think of Australia as fairly flat, the reality is that many sites have undulating hills or sloping terrain that make adaptability a key requirement for solar trackers. Unlike many other linked-row systems, Array’s DuraTrack HZ v3 system provides row-to-row terrain flexibility of up to 40 degrees in the East/West direction and up to 15 degrees in the North/South. Rotating drivelines sit about 30 cm above the ground and can be easily stepped over in the field if needed. Additionally, the drivelines feature a quick-disconnect release and are installed at the end of the build leaving space between rows clear for construction.
By design, the DuraTrack HZ v3 follows site boundaries or undulating terrain while driving approximately a megawatt of power with a single motor. This reduces the cost and complexity of the project by of avoiding the need to proliferate the same components at each and every row, in addition to ancillary electronic devices like wireless communication, batteries and inclinometers required for independent-row tracking systems.
Speed of Installation
Simplicity by design also means faster installation. Adjustable slots engineered in the DuraTrack HZ v3 system provide greater tolerances and a more forgiving build, should a pile not go perfectly into the ground. The tracker has less than half the number of fasteners than the closest competitor, and pre-kitting of every nut-and-bolt assembly in the factory to the highest-level possible means time and money are saved in the field.
Array can commission 12 MW per day with a 2-man crew, and the unique mechanical calibration of the system eliminates the need to level out each row at the end of the install. As with most things in life, construction schedules have many – often unpredictable – variables, and the ability to commission a site in a matter of days instead of weeks is a valuable tool to use when one needs to meet an interconnect date.
No-Stow Approach: reduced risk of catastrophic failure or torsional galloping
One of the least understood yet biggest risks of solar trackers today is the fact that most manufacturers use what is called active electrical stow – moving the tracking system into a “stow” position during wind events.
In effect, this is a byproduct of the manufacturers’ taking steel out of the structure to be more cost-competitive upfront, meaning that the tracking system can structurally fail in windspeeds above 40 or 60 km, unless it can get to a stow position before the wind reaches that threshold. Should one link in the stow chain fail: backup power goes out, the anemometer stops working, or wireless communications fail, these actively-stowed tracking systems can place the entire site at risk of catastrophic failure.
Even for trackers that do get to stow, there is a chance of torsional galloping that can occur even at relatively low windspeeds. Essentially, harmonic wind forces and dynamic interactions along the row can lead to a “galloping effect” or resonant frequency that builds up, causing twist along a row. Lightweight, flexible trackers that stow can experience a fluttering effect in the wind, which can lead to microcracking of modules or other interactions that are detrimental to long-term power production.
Array’s DuraTrack HZ v3 system eliminates this risk through a fully-passive, mechanical wind relief mechanism that doesn’t rely on electrical stow to survive a windstorm. Able to survive the maximum site windspeed at any tracker angle, torsion limiting devices build into each row allow the affected rows to automatically relieve torsion forces by moving in a controlled way in the direction the wind wants to move the row. Mechanical stops located at each column at and the center gear of the array allow the rows to lock into place – eliminating the possibility of vibrations or torsional galloping along the entire row span. An additional benefit of this feature is that all of the system’s piles are the same size and embedment depth across the entire site, as the wind loads are distributed equally across every foundation. Most trackers spec different-sized posts and embedment depths along a row and throughout a site which increases complexity and cost during install.
Increased Production: density is king
This final aspect that is important to solar farms, not just in Australia but everywhere, is maximizing energy production to the highest level possible. A tracking system has a few variables that affect production: space between the rows, range of rotation that the modules move, and the power density along a row.
The greatest level of production often comes in the power density per square meter of a tracker. For example, a half a meter of dead space can accumulate due to gaps along a row, extrapolated over a 100 MW solar farm, which adds up to a substantial amount of wasted space!
Density of tracking systems are driven primarily by the spacing along a row, regardless of whether you have a single or multiple-module configuration. Array has designed the DuraTrack HZ v3 system to be a continuous row without gaps or protrusions, and a minimal 7 mm space between modules. This enables the system to be 6% denser than the closest competitor, meaning that you can pack more power into the same site or spread the rows out more to reduce backtracking losses at the twilight hours of the day.
In effect, all of these aspects play into the ultimate goal of a solar tracker: to deliver the lowest levelized cost of energy (LCOE) to the project over the 30-year life of the asset. The tracking system is the foundation of the power plant, and much like a house, if the foundation does not stand the test of time, neither will the solar farm it is built on.