Slope analysis case study

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Unique use cases is the best way to showcase the capabilities of the software. Our slope case study will help you see how our software solves complex solar engineering issues. This time we are going to look into the solar plant project situated between two hills with the potential shading issues.

The challenge for this site is the location in the valley between two hills with the potential for horizon shading issues. The site is located in the TOU territory, therefore the tracker system would be an ideal option for higher production. However, the initial assessment shows the conformity of the site to be challenging to construct a tracker system. So, we should look at the differences between trackers and fixed-tilt to present an alternative solution.

The project we will be looking at in this case study is in the early stage of development. The land available for development is 171.45 acres (7468705 sq. ft). The goal is to find out if the size and the production of the solar system are economical to develop and whether this site is feasible to construct.

Another aim is to calculate if this site is buildable and what type of system is more suitable to build on a site like this by comparing the key values below between single-axis trackers and fixed-tilt systems.

First of all, it is necessary to have topography data, and know the limitations of each racking system that will be built on this site. In this case, we have our preferred racking vendor and the following slope limitation parameters — 10 degrees for a single-axis tracker and 17 degrees for the fixed-tilt system.

To achieve the goal of this study, we are going to begin with using the terrain mesh feature in PVcase. This tool allows us to generate the 3D ground surface from the topographic data. This will help us visualize the site for a more efficient slope study. If the topographic information is not available for you to generate the terrain mesh, you can utilize PVcase Online Terrain Import feature (step-by-step instructions here).

First, we generate the 3D terrain mesh (step-by-step instructions here). We are going to utilize the Slope setup table, where you can control how detailed the terrain mesh should be and what slope direction you want to study for a particular system: north-south for single-axis trackers, east-west for fixed-tilt. To break down the slope changes, we start both systems at a 0-degree slope. The ending value is set higher at 20 degrees for the fixed-tilt system compared to 15 degrees for the single-axis tracker system due to each system’s limitations. This value is also slightly higher than their limitation to maximize the capacity and later utilize the ground grading tool (step-by-step instructions here) to determine the civil work necessary for this site once the capacity is optimized.

Single-axis trackers system:

Slope table interpretation:

You can see that 35.36% of this site is over a 15-degree slope. It is unlikely that the tracker system is inappropriate to use for this particular site. Since the tolerance is 10 degrees, we will set the slope limit for this site at 12 and later use the grading tool to determine the appropriate site preparation method. This means there is 49.28% of usable land that is appropriate for this type of tracker at this site.

We can see that terrain in the east-west direction is flatter and more appropriate for a fixed-tilt system. With the same testing conditions with the tracker system, in the east-west direction 31.11% of the site has slopes over 15 degrees. However, considering the higher slope tolerance of the fixed-tilt system of 17 degrees, there is 65.7% of appropriate land to generate a fixed-tilt layout here, which is 16.42% more than the tracker system.

With a similar frame preset, we have 2 types of frames: 26 modules, and 13 modules. Each frame has 1 module in portrait for both fixed-tilt and tracker sites to maximize the capacity. The sites are set up with the sun angle at 25.63 degrees on December 21 at noon.

At this point, we can export the layout to PVcase Yield or PVsyst (step-by-step here) for production simulation to compare the 2 systems.

Production results:

Table 1 outlines the key performance between the 2 sites. Due to the single-axis tracker system having a low slope tolerance, compared to the fixed-tilt system, the fixed-tilt layout has a higher capacity. Despite having a higher specific production and GCR, the tracker layout for this site is particularly challenging. The site limits tracker layout to 14.405 MW, which is 32.25 % less in comparison to a traditional fixed-tilt system. The fixed-tilt layout experiences lower near shading, compared to the tracker layout with backtracking resulting in a 2.88% higher performance ratio and 25.15% overall produced energy. In addition, the fixed-tilt site requires 27.96% less land to achieve a higher capacity, and therefore cheaper in terms of land leasing/purchasing prices.

With the production indicators above, it is more beneficial for owners to utilize the fixed-tilt layout at this particular site because of the higher capacity fit on the site, and the energy export back to the grid. In terms of mechanical, fixed-tilt frames handle higher slope deviation better, which is a better fit for this particular site. On the contrary, the tracker layout falls short for this type of terrain because of its slope limitation. The tracker layout experiences significantly less capacity, and even with 27.97% higher in GCR, the overall production is 25.15% less than the fixed-tilt layout.

So, let’s see which system is suitable and whether the site is buildable. The results of the key values show us that a fixed-tilt system is a better approach for high level development at sites with higher slope variance. With the initial evaluation, using the fixed-tilt approach makes this site a possible buildable site.

The terrain mesh tool could be used along with other features within PVcase to make decisions at the early stage of project development. In this slope study we used the terrain mesh, terrain-based site generation, and PVcase Yield or PVsyst export features to help the users understand the best fit system for the given site, and therefore maximize capacity, and production while eliminating unfavorable or unnecessary risk options.