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tracking array

Contributor(s): Kate Brush

A tracking array is a collection of solar panels that turn to follow the path of the sun in order to maximize the solar radiation on the photovoltaic (PV) surface and convert light into electrical current. The tracking array creates solar power, a form of renewable energy.

A tracking array is considered a PV system because its most essential element is the PV cell, or solar cell. The word photovoltaic basically means the voltage of light and is used to describe the conversion of light energy into an electrical current.

How a tracking array works

A solar array refers to a grouping of solar panels. The tracking array is comprised of this collection of solar panels and placed on an axis so it can follow the path of the sun. Each panel is comprised of PV cells linked together that work to use particles of light (photons) to knock electrons free from their atoms, creating a flow of electricity. The solar panels create a direct current (DC). However, appliances and electronics require an alternating current (AC). The balance of system (BOS) components, everything besides the solar panels, converts the initial DC into AC, making it functional for domestic and commercial use.

Tracking arrays use both direct and indirect sunlight. There are two common orientations for tracking arrays: single axis and dual axis.

Single axis tracking allows the solar array to move back and forth in one direction. The axis can be vertical, horizontal, tilted or polar aligned. Usually, the single axis tracker follows the sun from east to west.

A dual axis tracker moves in a more direct, circular path. It can travel in two different directions and changes position seasonally and daily so the panels directly face the sun at all times of the year. As a result of its flexibility and direct path, the dual axis tracker captures the maximum possible energy from the sun.

When deciding what type of tracker to install, it is important to consider the local climate, system size, degree of latitude, land constraints, government incentive and electrical rates and requirements. Tracking arrays are designed for warmer climates with little or no snow. Fixed racks better accommodate harsher climates.

Horizontal single-axis trackers are commonly used by utility-scale and large projects. Smaller residential applications and locations with high taxes on renewable electricity (Feed-In-Tariffs) tend to install dual-axis trackers. Vertical single-axis trackers are best used in high latitudes.

Types of tracking arrays

Three types of single or dual axis tracking arrays can be found: passive, active and chronological trackers.

Passive trackers are driven to move by a compressed gas fluid that directs the array form one side to the other.

Active trackers are propelled by motors and gears that react to a controller's response to the sun's direction.

Chronological trackers counteract Earth's rotation by turning in the opposite direction.

Pros

The biggest difference between a tracking array and a stationary mount, or fixed rack, which holds panels in a permanent position, is the tracking array can maximize the creation of solar energy due to its ability to follow the sun throughout the day. The productivity of stationary mounts can be compromised if the sun passes to a less optimal angle, a problem tracking arrays solve by moving with the sun. As a result, tracking arrays can experience as much as a 10 to 25% increase in productivity, depending on geographic location.

Furthermore, tracking arrays require about the same amount of space as a fixed rack, but produce more electricity, making them perfect for increasing land usage.

Time of Use (TOU) rate plans are offered by utilities, organizations supplying gas, water, electricity or sewage, in some states for solar power. With this plan, the utility will purchase the power that is generated by the array during the peak time of day at a higher rate. Therefore, it becomes beneficial to produce a higher amount of electricity during peak times of the day. The tracking array helps optimize energy production during peak times.

Cons

Since tracking arrays are a more complex system than fixed racks, they usually require more site preparation, making the installation process longer and more expensive. In general, tracking arrays are more expensive than their stationary counterparts due to their moving parts and more complex technology. Since solar panels have decreased in cost, it can be hard to rationalize the extra cost of maintenance and installation over adding extra panels to a fixed system.

Tracking arrays are more easily damaged in storms than fixed racks. If the tracking array breaks down when the panels are at a severe angle, then the loss of production until it is fixed can be extreme. Maintenance for the tracking array systems can be more difficult than it is for fixed racks, especially as the tracking array ages.

Fixed racks usually last up to 30 years and provide a 25-year performance guarantee. A tracking array only comes with a 5 to 10-year warranty.

Considerations

When deciding whether or not to install a tracking array, it is necessary to complete a detailed cost analysis and return on investment; these results will be specific to location and case.

Recent advancements in technology and reliability in electronics and mechanics have significantly reduced long-term maintenance concerns for tracking arrays. However, even with these advancements, the tracking array will generally require more maintenance than a fixed rack. The amount of extra maintenance will depend on the quality of the tracking array.

Single axis tracking arrays are more difficult to finance because they are more complex and are seen as a higher risk. Therefore, they demand an extra focus on company stability, cash flow, assurances and promise of success.

The future of tracking arrays

The use of tracking arrays is expected to grow, especially in utility-scale projects where the tracking arrays present major benefits. The solar industry is seeing a decrease in equipment prices while installation and operations and maintenance (O&M) efficiencies are improving. This development is expected to continue through the next few years. As demand for the tracking array increases, new manufacturers enter the market. The crowded landscape makes companies strive to gain market share, creating a driving force for innovation within the industry.

The levelized cost of energy (LCOE) also motivates innovation in solar. The LCOE measures the lifetime expenses of a product and divides it by the energy production. Reducing the LCOE but maintaining system reliability, structural integrity and quality is the main challenge facing manufacturers in the future.

Risk assessment will continue to become an increasingly important consideration. Bankability -- or funds that are accepted by the bank and guaranteed to bring profit -- experience and proven reliability will hold greater power in the decision making process. Simplification of the tracking array's system will become a trend as its strength and ability to last 30 years at a utility-scale site gains importance.

The solar industry's goal for the future is to make tracking arrays completely independent and eliminate the necessity of personnel to operate the systems. The industry hopes to continue to lower the total cost of ownership (TCO) by building systems that can maintain themselves but are sturdy, reliable and can be completely forgotten about after the initial set up.

To succeed in the solar industry, tracking array manufacturers must create products that increase efficiency and optimize the system in order to lower the LCOE and inspire widespread adoption of solar technology.

This was last updated in June 2019

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