#BetterCallPaul: Your Engineering Questions Answered (No. 8, September)

Better Call Paul

How does RPCS design the Array tracker to handle wind loading?

As we enter into the brunt of the hurricane season this September, we at RPCS think it may be apropos to give some insight as to how RPCS designs the Array tracker to handle wind loading at different degrees of severity throughout the country.

The first thing we need to do is pick a nationally accepted system of measurement for these hazard ratings. RPCS uses the ASCE 7-10 tables as the baseline for our data in structural design. However, it is worth noting, that the authority having jurisdiction (AHJ) in the area of the project has the right to prescribe to our customer a wind rating different than that which is stated by the ASCE 7-10 tables if they wish. This is especially common in areas with site-specific case study requirements, or in areas that have received more favorable results given by local permitting authorities. Another one of the most popular options today is to switch to the newer ASCE 7-16 tables, which also tend to be more favorable as they take further site-specific weather data into account which can yield better resulting foundation recommendations. RPCS is quite capable of using either data set and adjusting the tracker’s design to adhere to these codes.

After deciding on a wind rating, RPCS will assess the needs of the tracker to determine if any special considerations need to be followed. The most common remedy for medium-high wind loads is increasing the amount of bearing posts per row on exterior rows. Since the exterior rows often act as a sort of barrier for the interior rows, it is often appropriate to bolster the strength of the outer rows which will protect the other rows by taking the brunt of the wind event. Adding bearing posts to a module row can be an expensive prospect, but the cost benefits down the road often handsomely outweigh the negative initial price change. This is because with fewer posts, you will require larger and longer post sizes to account for the extra stress on the fewer foundations. Also, more bearings may alleviate the need for Heavy Duty (HD) Bearings which can be expensive if the project is able to be made structurally sound without them.


The last consideration, with respect to wind forces, that is worth highlighting is the effects of elevated tracker height. Increasing the height of the tracker will be a huge factor in heavy wind areas. There are times when this is simply unavoidable, like when there is a floodplain on site, but there are other times where, with minimal preparation/consideration, the taller tracker heights can be avoided altogether. The immediate benefits of grading a site with extreme topography, for instance, is the ease of installation and reduction of material complexity. By reducing the amount of undulation underneath, the tracker height is kept consistently closer to the ground- which reduces the size of the foundations needed and reduces the amount of specialized materials for the problem areas. This positively effects installation times, because the construction crew can get into a locked rhythm and not have to keep readjusting instruments/tools used to measure and install the tracker. All of this is especially beneficial on costs for high wind projects, as this mitigates the effects of wind events on the tracker and ensures a fast and effective build.

Intense wind forces are some of the most common design hazards encountered around the US by our customers. At RPCS, we make a point to take these wind ratings seriously when designing our projects so that we can confidently give to our customers a tracker that will stand the test of time.


Read more on the Array tracker’s wind mitigation strategy.


Meet Paul Towber
RPCS Manager of Project Design

In RPCS’s #BetterCallPaul segment, Paul answers your frequently asked engineering-related questions while offering unique insights into RPCS’s project design challenges, solutions, and expertise.


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