Solar panels that follow the sun: are solar trackers right for you?
Sun tracking systems are common with large solar panel installations, but usually don't make sense for residential solar. Here's why.
If you live in the Northern Hemisphere, the sun rises in the east, spends a bunch of time in the southern sky, and then sets in the west.
Some plants have developed an ability, called heliotropism, to track the sun as it makes this daily trip across the sky. A young sunflower will point east in the morning, track the sun until it sets in the west, and then reorient themselves so they’re ready for the sun again in the morning. (Mature sunflowers stop doing this tracking behavior.)
Solar panels can do this too! Ground-mounted arrays can incorporate tracking systems that automatically move the panels in one or more directions so that they stay pointed at the sun. By keeping the panels directly facing the sun for as long as possible during the day, solar trackers can increase the output of an array by as much as 40%.
This means that you can generate more electricity with fewer panels. While this is a good thing, the tradeoff is higher cost, and for small residential systems the payoff often isn’t there. However, there are cases where it might make sense for a homeowner to add a tracker to their system. That’s what we’ll discuss in this article.
What is a solar tracker?
I have a more indepth description in my article on ground-mounted solar, but a short explanation is there are two types of solar trackers.
Dual- or two-axis trackers can change the horizontal orientation (azimuth) or vertical orientation (elevation) of a set of solar panels. Dual-axis trackers work with pole mounts, an example of which you can see at the top of this article. A pole mount is needed with a dual-axis tracker to give the system the freedom to rotate side-to-side or tilt up and down.
Single-axis trackers can tilt solar panels up and down as the sun moves higher and lower in the sky over the course of a day. This means that a single-axis tracker can’t follow the sun as it moves from east to west, but despite that limitation you can still expect a 15-25% increase in power generation with a single-axis tracker according to the NREL (pdf).
Both types of trackers utilize an electric motor to drive gears that move the panels, and include an electronics package that continuously calculates the ideal tilt. Usually the tracker will be powered by the solar panels themselves, so they don’t need an external power supply.
Advantages of solar trackers
The main advantage of a sun tracker is that it allows you to get more electricity production with fewer solar panels. Not only does this save you money on the panels themselves, but it also reduces the number of related components such as inverters and racking, which also means lower installation costs.
Where land costs are a limiting factor, reducing the footprint of the solar array can be a significant savings as well.
This works best when you can spread the additional cost of a tracker over a large number of panels. In the photo above of the solar array mounted on a single-axis tracker, you can see that a large row of panels is being controlled by one tracker.
Because of this, trackers are quite common on large solar arrays. According to Berkeley Lab, about 12% of large non-residential solar arrays included a tracking system.
Disadvantages of solar trackers
The main disadvantages of a solar tracker are higher costs and maintainance.
While trackers may reduce your other component costs, usually the high upfront and long term maintainance costs of trackers outweighs those savings.
A pole-mounted solar array that a homeowner would have in their backyard might fit only 6 panels. This means that a typical residential installation will need between two and four mounts and dual-axis trackers, resulting in a high cost on a per-panel basis.
An array on a linear mount controlled by a single-axis tracker will usually be able to fit more panels than a pole mount, reducing the number of trackers needed. Even so, the smaller size of residential systems means that the per-panel cost of a tracker is still relatively high even with a single-axis system.
Maintenance and durability are also concerns. Wind is a particular concern: the array can act like a sail, so the mechanism must be very strong to survive high winds. Some trackers can access real-time wind speed data and can tilt the array into a safe mode when wind speeds are high, but even so, abuse from the elements and the daily wear-and-tear from moving the array means that you can’t expect a tracking system to last as long as the other components in the system.
For example, a tracking system will often only have a 5 year warranty. This is very short compared to the 25 year warranty that many panels and inverters have.
Price of solar trackers for homeowners
Costs vary significantly, but ground mounts without a tracker will add about 15% to the cost of a system. This means that for a system that costs $14,000, adding ground mounts will increase the price by about $2,100 on average.
The cost of adding a tracking system on top of that? A couple thousand dollars at least, with dual-axis trackers being the most expensive.
A home solar array might have only 15-20 panels, so adding thousands of dollar to optimize the output of a small number of panels usually doesn’t make financial sense. Instead, it’s usually more cost effective to simply add more panels.
Should homeowners use a solar tracker?
Many large commercial solar installations are ground-mounted, but few residential systems are. Because of this, most homeowners aren’t considering trackers as part of their system. However, there are a couple cases where a tracker might make sense for a residential solar installation:
- You have a small yard, and want to maximize the output of your ground-mounted system within the available space.
- Your local authority has a cap on system size, and you want to maximize your electricity production within that cap.
For example, in Massachusetts there is a simplified interconnection process for solar arrays that are 15 kW or smaller in size. Larger systems must go through a more extensive application process, resulting in a longer and more costly project timeline. Adding a tracker can be a way to obtain the same output as a larger system while staying within the 15 kW limit.
Other local authorities might have similar limits, in which case a solar tracking system might be a smart option.
Bifacial panels are another way to maximize output but with less complexity
With the relatively short warranty that solar trackers come with, you should budget for tracker repairs or replacement during the expected 25 year lifespan of your solar panels. On top of the high upfront cost, this starts to look even worse financially.
A better alternative? Bifacial solar panels, which generate electricity from sunlight hitting both the front and rear of the panels.
With a ground-mounted system that allows reflected light to hit the rear of the panels, bifacial panels generate something in the range of 6-9% more electricity than conventional panels. While that’s less than the gain from a tracker, they use the same mounting systems as conventional panels and don’t rely on mechnical systems that can break, making them a more cost-effective way to increase your electricity output without increasing the size of your system.