Solar Trackers Explained: How It Works, Pros and Cons

Solar trackers can increase the efficiency of solar panels and reduce the payback time for solar owners to recoup their installation costs. While they are more common on commercial-scale and ground-mounted solar panels, some designs can also be installed on flat or low-slope rooftops. Whether they are worth the extra cost or not depends on a number of factors.

How Solar Trackers Work

Solar trackers are support structures that allow solar panels to follow the path of the sun and absorb more solar radiation. They can increase the efficiency of the panels by anywhere from 10% to 45%, depending on the type of tracker. Because of the cost of the hardware and installation, they are more commonly seen on large-scale solar projects like community solar farms than on individual residences. It is easier, safer, and more cost-effective to install trackers on ground-mounted arrays than on rooftops, and the scale of the project allows more return on the investment.

The challenge with installing a tracker on a roof is one of physics. While ground-mounted trackers are often sunk into the ground with concrete pillars, roof-mounted ones rely on the strength and integrity of the roof. Rooftop trackers raise the profile of the solar panels, which increases their exposure to strong winds—and that, in extreme weather, could pull the entire solar system off the roof. Rooftop trackers need to be of lighter weight and lower profile.

Types of Solar Trackers

Trackers follow the sun in one of two ways. Single-axis trackers rotate on an east-west axis, following the sun throughout the day. These are designed to increase solar absorption by 25% to 35%. Dual-axis trackers rotate on a north-south axis as well, following the sun throughout the year. Compared to a fixed-tilt system mounted on a roof, a ground-mounted system with a dual-axis tracker can produce up to 45% more electricity.

How the tracker follows the sun depends on the model and price. Some lower-cost trackers need to be shifted manually. Passive trackers are in the mid-cost range; they use no motor, but instead, use a liquid that tilts the system to the west as it heats up or tilts it back to the east when it cools. An active solar tracker uses a motor to automatically orient the panels for maximum exposure to the sun, and dual-axis systems can tilt to nearly any angle to face the sun. Many active trackers run their motors from energy produced by the solar panels themselves. They might also use GPS and software to maximize the panels' efficiency.

Pros and Cons of Investing in a Solar Tracker

Solar trackers are not cheap, so their benefits need to be weighed against their cost. Depending on the arrangement of the trackers and the size of the system, a single-axis tracking system can add $500 to $1,000 per panel to the entire system cost. A dual-axis system can double the cost of the entire project. The increased output of the solar system may or may not be worth the increased cost.

Many factors come into play. Using a tracking system means fewer panels can be installed. Consider the following back-of-the-napkin calculations: In the United States, the average American household consumes 11,000 kilowatt-hours (kWh) of electricity per year, or roughly 30 kWh/day. To provide that energy, a 5.1-kW solar system with 17 300-watt panels and no solar tracker could, in theory, produce 30.6 kWh of electricity in a 6-hour day, while a 3.9-kW solar system with thirteen 300-watt panels and a solar tracker could produce 31.2 kWh over an 8-hour day. Installing higher-efficiency solar panels can even further reduce the number of panels: Eleven 350-watt panels with a solar tracker can produce 30.8 kWh over 8 hours.

This simple math has a number of implications for overall system cost.

Where you live matters: Alaska receives on average 2-3 “peak sun hours” per day, when the sun shines at 1,000 watts per square meter, while Arizona receives an average of 7-8 peak sun hours. The lower the latitude (the closer to the equator), the less north-south seasonal change in the panels' relationship to the sun. A dual-axis tracker provides less of a return-on-investment in Arizona than adding more panels to capture those peak sun hours. In Alaska, however, where peak sun hours vary more widely depending on the time of year, a dual-axis tracker may provide more benefit.

In areas where electricity is billed depending on the time of day (called “time-of-use” billing, or TOU), trackers can increase the output of solar energy during times when electricity from the grid is most expensive, reducing the owner's energy costs.

States with net metering programs allow solar owners to get credit for any excess energy they send to the grid. Not every state, however, has such a program. Among those that do, some states give 100% credit for excess energy produced, while others give a smaller percentage. Solar trackers provide less of a benefit in states with 100% net metering programs, since homeowners can use more panels to produce more energy during peak sunlight hours, then essentially use the grid to store that electricity, getting full credit for it later when they use it.

In states with lower (or no) net metering programs, however, some or all of the credit for that peak energy will be lost when it is sent into the grid. By installing solar trackers, homeowners can install fewer panels, produce less electricity during peak hours (thereby losing less unused energy), yet extend the hours in which they produce electricity.

Especially in states without net metering, where the electricity grid cannot be used as a virtual battery, a solar tracker with solar battery storage can allow more energy to be stored with a smaller number of panels.

Your energy-use patterns may matter as well. If you live in a warm climate where you use far more electricity to cool your house in the summer than you do heating it in the winter, you can take fuller advantage of longer summer days by increasing your energy production with a solar tracker. The opposite may be true for colder climates: adding a third more panels to your array adds a third more energy output throughout the year, including winter, when you need it more.

As always, supply and demand matter. With the increasing demand for solar panels and supply-chain problems, solar module prices have begun rising in 2021, potentially making the installation of more panels less cost-effective than adding a solar tracker. The “learning curve” has also been an important factor in the solar industry; as the solar-tracker industry grows, its cost efficiencies may increase and its prices drop. Federal and state incentives for solar energy may change the equation as well.