The Terrain Loss Of Solar Tracking Structure: a seemingly troublesome problem can be easily realized in the future

2021-09-01 19:43
Shadows between rows due to changes in terrain or construction tolerances are a particularly harmful source of losses in large solar power plants. Why? Because not only can the industry standard software be used to model the terrain shadow loss, but also most of the losses can be recovered using advanced system design and control strategies. This is undoubtedly an opportunity and a challenge for solar mounting system manufacturers such as CHIKO Solar.
 The Terrain Loss Of Solar Tracking Structure: a seemingly troublesome problem can be easily realized in the future
Not long ago, whether in the Mojave Desert or the St. Louis Valley in Colorado, industry stakeholders could use vast flat sunny land for solar bracket projects. Since these groundbreaking sites are basically free of complex terrain, performance models can characterize these sites by assuming standard backtracking on a flat surface. These basic assumptions no longer apply to the industry.
Today, utility-scale solar energy is increasingly appearing in places with complex terrain-these places did not seem to be suitable for the development of solar energy five years ago. In addition, "completely flat" websites have always been a myth rather than a reality. Scanning rows of drive piers on a solar construction site, the height of the piers varies significantly, even in adjacent rows on a relatively flat site. Even under the best of circumstances, certain topographical differences are inevitable, especially considering the scale of today's project sites.
A common theme at photovoltaic conferences is that the performance of deployed assets is below expectations, and no one really knows why. A reasonable explanation is that the problem is not the deployed assets, but our expectations. From your point of view, the tracker terrain loss is either an elephant in the room that no one talks about, or a low-hanging fruit that no one picks.
If the terrain loss of solar tracking bracket is not accurately modeled, the PVsyst production modeling simulation and the revenue models provided by these will tend to overestimate the performance of the photovoltaic power station. Always underestimating these effects may weaken investor returns and confidence. In addition, as long as these avoidable system losses have been underestimated during project development, design, and procurement, there is no urgency or motivation to recover the avoidable system losses.
Although terrain shadow loss is a real problem, the photovoltaic performance modeling community is facing this problem. As part of the 2021 IEEE Photovoltaic Expert Meeting (PVSC) meeting, a group of performance engineers from DNV presented the results of the ongoing terrain shadow loss research [1]. The author used DNV's SolarFarmer software to model a site with an average southwest slope of 4% in North Carolina. The author analyzed the difference between the output of trackers on level ground and the output on variable terrain, and found that the tracker’s terrain loss was -2%.
The recent work of Black & Veatch engineers produced similar results [2]. The author studied the proposed photovoltaic power plant in a site in the eastern United States with criss-cross wetlands and an east-west slope of about 3%. The author simulated a topographic yield loss of about -2.5%. Analyzing the influence of the terrain adaptive backtracking strategy, the author concludes that it can make up most of the terrain shadow loss.
Nextracker's own modeling results validated the rough order of magnitude of production loss estimates associated with sloping terrain. In locations with high diffuse irradiance content, using the standard backtracking method, depending on the ground coverage rate (GCR), a mild 3% level will result in a loss of 1% to 2.5% per year. Note that we modeled these results using the "Yin-resistant" half-cut battery module, as shown in Figure 1.
 The Terrain Loss Of Solar Tracking Structure: a seemingly troublesome problem can be easily realized in the future
Then, we extended this analysis to multiple locations based on the average PPA rate of a representative 100 MW single-axis solar tracking system plant and a specific area. As shown in Figure 2, the financial impact associated with the loss of tracker terrain shadows is far from trivial. The topographic shadow loss is about 100,000 to 200,000 US dollars per year. This is a huge gap between expectations and reality, especially for asset owners who closely track the financial status of the entire fleet project. Inferred over the entire life cycle of the project, the present value of revenue loss (discount rate of approximately 5%) for 30 years of operation can easily exceed US$2 million per 100 MW of power plant capacity.
 The Terrain Loss Of Solar Tracking Structure: a seemingly troublesome problem can be easily realized in the future
The importance of this underperforming risk deserves a more rigorous approach to terrain shadow loss modeling. The latest version of the de facto industry standard performance modeling software PVsyst 7 provides basic of the terrain shadow loss modeling function of solar tracking structure, for east-west slope changes.Combined with Nextracker's best practice guide for terrain modeling, engineers can import AutoCAD files of real plant layouts into PVsyst, cover detailed terrain from USGS or field surveys, and estimate the impact of east-west slope changes. This extra stringency benefits all stakeholders (developers, EPCs, IEs, insurance companies, and investors) because they increase transparency and trust in the key sources of output losses in large factories.
To compensate for the loss of terrain and construction tolerances, project stakeholders can deploy advanced tracking algorithms in the field system, such as Nextracker's TrueCapture technology. Supported by Nextracker's high-speed, high-precision, and high-granularity tracking hardware, the TrueCapture algorithm uses precise site and installation-specific information to calculate the optimal control strategy for each individual tracker row.
By minimizing row-level terrain shadow loss, Nextracker is able to maximize system-level output. Nextracker also has a proprietary modeling solution, TrueSim, which can not only estimate yield gains related to TrueCapture, but also provide a verification process for realized gains. Modeling and mitigating terrain shadow loss is just one of many ways Nextracker continues to optimize the performance of solar power plants through innovative technology and data analysis.
As the frequency and distribution of larger and larger solar mounting structure projects increase, the "simple" sites for solar development are increasingly becoming a thing of the past. Restricted sites with meaningful topographical changes are becoming the norm. The 4% average grade DNV modeled for its PVSC paper is not uncommon in today's market. If anything, this is a conservative average, as the local slope may be as high as 15%. The good news is that slope-aware backtracking reduces the shadow loss associated with complex terrain.
The general method to achieve slope perception backtracking is to cut and fill the site as needed to achieve a uniform slope. If the pier is then driven to a uniform height relative to the graded monoplane, the result is an in-plane tracker layout. Unfortunately, a perfect in-plane tracker layout is not realistic. Cutting and grading thousands of acres of land is not only impractical, it can also be counterproductive in terms of soil stability and habitat protection.
The intelligently controlled independent line tracker is ideal for capturing the full output of solar assets and maximizing its economic performance. In the real world, topographical changes at large utility-scale solar sites are inevitable. In real life, the top of the tracker pier rarely produces a perfect plane. In the context of this imperfect world, the most effective way to mitigate the tracker’s terrain loss is usually the most fine-grained.

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