How can I evaluate mounting systems for solar electric panels, and choose the best one for my site?

If you are considering an investment in photovoltaics, you can maximize the value of your investment by choosing the mounting system which will give you the most energy for the lowest installed cost.

You can choose from five ways to mount your PV panels:

  • Fixed racks
  • A horizontal one-axis tracking system
  • A tilted one-axis tracking system
  • An upright-pole two-axis tracking system
  • A rail tracking system

The amount of energy which will be produced by your system can be estimated using a calculator known as PVWatts.  PVWatts was developed by the United States National Renewable Energy Lab;  version 2 is available here at no cost.

You can use PVWatts if you know the approximate location of your system, the number of panels and the rated watts of each.  PVWatts allows you to choose fixed, or one-axis tracking, or two-axis tracking.  (But note the diagrams below to make sure the hardware you are considering matches the PVWatts configuration you input!)

At the left is an example from PVWatts.

You will also want to consider operating and maintenance costs, and the reliability of each option.  Usually simpler technologies cost less to maintain, and last longer.

Here is a summary of the options, advantages and disadvantages:

Fixed racks are simple, inexpensive, and reliable, and are available from most PV installers.  They can be tilted upward toward the south, at an angle approximately equal to the latitude, to capture more energy through the year.

In very low latitudes – below 10° – fixed-rack PV systems produce nearly as much energy as tracking systems, so fixed racks may be cost-effective.

The biggest disadvantage of fixed rack systems, ironically, is cost:  more panels and other system components are needed, so while the cost of the mounting equipment is low, the overall system cost is high.

In estimating the energy production for a fixed-rack system, make sure to enter the right tilt.  The box below shows the drop-down selection (“Fixed Tilt”) and tilt (40.02°).  You can vary the tilt, to find the highest production, generally equal to your latitude or a few degrees lower.

Most one-axis tracking systems are horizontal one-axis tracking systems;  that is, systems that track the sun east/west through the day, but keep the panels at a tilt of zero degrees.

Horizontal one-axis tracking systems can be reliable, though they have some moving parts which may fail.  They track the sun east/west during the day, but not north/south through the seasons.  Since the panels are horizontal in the north/south direction, these systems perform well during the summer, but poorly during the winter.

One-axis tracking systems produce more energy than fixed-rack systems, so fewer panels are needed, and the total system cost may be less than the cost of a fixed-rack system at some latitudes.

To get an energy estimate for a horizontal one-axis tracking system, make sure to enter 0 degrees in the “array tilt” field as shown here.

Tilted one-axis tracking systems are more complex than horizontal one-axis trackers, and generally require a concrete foundation.  They are tilted upward and toward the south (in the northern hemisphere), and rotate the panels east/west through the day to follow the sun.

Because they are more complex, tilted one-axis tracking systems may be expensive.  They may also require a concrete foundation, which adds cost.  They are generally not scalable;  that is, mechanical components are not shared between units, so cost per panel may not be much lower in larger arrays.

Estimated energy production for tilted one-axis tracking systems can be obtained from PVWatts, by choosing “1-Axis Tracking”.

Production is much higher than fixed-rack systems, but the expense of these systems, the added cost of a foundation, and maintenance costs, may keep them from being cost-effective.

Upright-pole two-axis tracking systems track the sun east/west through the day, and north/south through the seasons, so they are very productive.

Upright-pole two-axis systems may be expensive, and generally require concrete foundations which add to the initial cost.  They are complex, which can add to maintenance costs and down-time.  Like tilted one-axis tracking systems, upright-pole two-axis systems are generally not scalable.

The weight of the panels is concentrated at the top of the pole, so stresses there are high.  Panels at the edges of the array are unsupported, so wind can be a problem;  these systems are generally given wind ratings of only 90 miles per hour.

Rail tracking systems track the sun east/west through the day, and north/south through the seasons, so they produce about the same amount of energy as upright-pole two-axis tracking systems.  (Rail tracking systems may be slightly less productive due to “back-tracking” – panels returning to a horizontal position early in the day and late in the day, in order to keep the panels from casting shadows on each other.)

But rail tracking systems spread the weight of the panels over the area of the array, so stresses are not concentrated in one spot, and they have only two moving parts, so maintenance cost and down-time are minimize.

The weight of each panel is supported, so rail tracking systems can be rated for winds up to 150 miles per hour.

Rail tracking systems can be mounted without a concrete foundation, which saves cost.  Because they are very productive – 25% to 50% more energy from each panel, compared with fixed-rack systems – fewer panels and other system components are needed, making rail tracking systems very cost-effective.

Rail tracking systems are also scalable:  frames which hold a few panels each can be mechanically coupled, sharing a single controller and set of actuators, so cost per panel is further reduced in larger arrays.

Rail tracking system

To find out more about rail tracking systems and whether an InteliTrack system can save you money, go to the “Request Information” bar to the right and provide us with your contact information.  A Sedona engineer will contact you soon.

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