Solar tracker

Basic concept

Sunlight has two components, the “direct beam” that carries about 90% of the solar energy, ^[6] [7] and the “diffuse sunlight” that carries the remainder – the diffuse portion is the blue sky on a clear day, and is a larger proportion of the total on cloudy days. As the majority of the energy is in the direct beam, the maximizing collection requires the Sun to be visible to the panels for as long as possible.

The energy contributed by the direct beam drops with the cosine of the angle between the incoming light and the panel. In addition, the reflectance (averaged across all polarizations ) is approximately constant for angles of incidence up to around 50 °, beyond which reflectance degrades rapidly. ^[8]

Direct power lost (%) due to misalignment (angle i ) where Lost = 1 – cos ( i )

i	Lost	i	hours [9]	Lost
0 °	0%	15 °	1	3.4%
1	0.015%	30	2	13.4%
3	0.14%	45 °	3	30%
8 °	1%	60 °	4	> 50% [10]
23.4 ° [11]	8.3%	75 °	5	> 75% [10]

For example, trackers that have accuracies of ± 5 ° can deliver greater than 99.6% of the energy delivered by the direct beam plus 100% of the diffuse light. As a result, high accuracy tracking is not typically used in non-concentrating PV applications.

The purpose of a tracking mechanism is to follow the Sun as it moves across the sky. In the following sections, in which each of the main factors are described in a little more detail, the complex path of the Sun is simplified by its daily east-west motion of its annual north-south variation of the seasons of the year .

Solar energy intercepted

The amount of solar energy available for direct beam is the amount of light intercepted by the panel. This is given by the area of ​​the panel multiplied by the cosine of the angle of incidence of the direct beam (see illustration above). Or put another way, the energy intercepted is equivalent to the area of ​​the shadow cast by the panel onto a surface perpendicular to the direct beam.

This cosine relationship is very closely related to the observation formalized in 1760 by Lambert’s cosine law . This article is the subject of the light of an object of proportionality to the cosine of the angle of incidence of the light illuminating it.

Reflective losses

Not all of the light is Intercepted Transmitted into the panel – a little is reflected at ict surface. The amount reflected in the refractive index of the surface material and the angle of incidence of the incoming light. The amount of inflation is different depending on the polarization of the incoming light. Incoming sunlight is a mixture of all polarizations. Averaged over all polarizations, the reflective losses are approximately constant up to 50 ° beyond which it degrades rapidly. See for example the left graph.

Daily east-west motion of the Sun

The Sun travels through 360 degrees east to west by day, but from the perspective of the visible portion is 180 degrees during an average 1/2 day period (less, in fall and winter). Local horizon effects reduce this somewhat, making the effective motion about 150 degrees. A solar panel in a fixed orientation between the dawn and sunset extremes will see a motion of 75 degrees to one side, and thus, according to the table above, will be over 75% of the energy in the morning and evening. Rotating the panels to the east and west can help recapture those losses. A tracker that only attempts to compensate for the east-west movement of the Sun is known as a single-axis tracker.

Seasonal north-south motion of the Sun

Due to the tilt of the Earth’s axis , the Sun also moves through 46 degrees north and south during a year. The same set of panels set at the midpoint between the two extremes will thus see the Sun move 23 degrees on either side. THUS selon The Above table, an optimally aligned single-axis tracker (see polar aligned tracker below) will only lose 8.3% at the summer and winter seasonal extremes, or around 5% Averaged over a year. Conversely a vertically or horizontally aligned single-axis tracker. For example, a vertical tracker at a site at 60 ° latitude will lose up to 40% of the available energy in summer, while a horizontal tracker located at 25 ° latitude will lose up to 33% in winter.

A tracker that accounts for both the daily and seasonal motions is known as a dual-axis tracker. Generally speaking, the increase in the incidence of seasonal changes in the world, increasing in the summer in northern or southern latitudes. This biases collection towards the summer, so the panels are tilted closer to the average summer angles, the total annual losses are reduced compared to a system tilted at the spring / fall solstice angle (which is the same as the site’s latitude).

There is a lot of difference between the two-axis tracker and the two-axis tracker. A recent review of actual production statistics from southern Ontario suggests that the difference is about 4% in total, which was more important than that of dual-axis systems. This compares unfavorably with the 24-32% improvement between a fixed-array and single-axis tracker. ^[12] [13]

Other factors

Clouds

The above models assumes uniform likelihood of cloud cover at different times of day or year. In different climate zones cloud cover can vary with seasons, affecting the experienced performance figures described above. Alternative, for example in an area where cloud cover on average builds up during the day.

Atmosphere

The distance that sunlight has the atmosphere, the sunlight has to the diagonally through the atmosphere. As the path reaches the atmosphere increases, the solar intensity reaches the collector decreases. This Increasing path length is Referred to as the mass air (AM) or air mass coefficient , Where AM0 is at the top of the atmosphere, AM1 Refers to the direct vertical path down to sea-level with Sun overhead, and AM Greater Than 1 The Sun approaches the horizon.

Interestingly, even though the sun may not be particularly important in the early morning or winter, the diagonal path through the atmosphere has not expected impact on the solar intensity. Even when the Sun is only 15 ° above the horizon it can be around 60% of its maximum value, around 50% at 10 ° and 25% at only 5 ° above the horizon. ^[14] Therefore, trackers can deliver benefit by collecting energy when the Sun is closed to the horizon.

Solar cell efficiency

Of course, the result of a photovoltaic cell has a major influence on the end result, regardless of whether it is employed or not. Of particular relevance to the benefits of tracking the following:

Molecular structure

Much research is being done to increase the size of the energy content.

Temperature

Photovoltaic solar cell efficiency decreases with increasing temperature, at the rate of about 0.4% / ° C. ^[15] For example, 20% higher efficiency at 10 ° C in early morning or as compared to 60 ° C in the heat of the day or summer. Therefore, trackers can deliver additional benefit by collecting early morning and winter energy when the cells are operating at their highest efficiency.

Summary

Trackers for concentrating collectors must employ high accuracy tracking to keep the collector at the focus point.

Trackers for non-concentrating flat-panel do not need high accuracy tracking:

• low power loss: under 10% loss even at 25 ° misalignment
• reflectance consist even to around 50 ° misalignment
• diffuse sunlight contributes 10% independent of orientation, and a larger proportion on cloudy days

The benefits of tracking non-concentrating flat-panel collectors flow from the following:

• power loss degrades soon after about 30 ° misalignment
• significant power is available even when the Sun is very close to the horizon, eg around 60% of full power at 15 ° above the horizon, around 50% at 10 °, and even 25% at only 5 ° above the horizon – of particular at high latitudes and / or during the winter months
• photovoltaic panels are around 20% more efficient in the cool of the early mornings as compared to the heat of the day; similarly more effective in winter than summer – and to effectively capture early morning and winter sun requires tracking.

Types of solar collector

Solar collectors may be:

• non-concentrating flat-panels, usually photovoltaic or hot-water,
• concentrating systems, of a variety of types.

Solar collector mounting systems may be fixed (manually aligned) or tracking. Different kinds of solar collector and Their rental ( latitude ) require different kinds of tracking mechanism. Tracking systems may be configured as:

• Fixed collector / moving mirror – ie Heliostat
• Moving collector

Non-tracking fixed mount

Residential and small-capacity commercial or industrial rooftop solar panels and solar water heaters are usually fixed, often flush-mounted on an appropriately facing pitched roof. Advantages of fixed mounts over trackers include the following:

• Mechanical Advantages: Simple to manufacture, lower installation and maintenance costs.
• Wind-loading : it is easier and cheaper to supply a sturdy mount; all mounts other than fixed flush-mounted panels must be carefully designed having a look to wind loading due to greater exposure.
• Indirect light : approximately 10% ^[6] [7] of the solar radiation incident is diffuse light, available at any angle of misalignment with the Sun.
• Tolerance to misalignment : effective collection area for a flat-panel is relatively insensitive to quite high levels of misalignment with the Sun – see table and diagram at Basic concept section above – for example even at 25 ° misalignment reduced the direct solar energy by less than 10%.

Fixed mounts are usually used in conjunction with non-concentrating systems, however an important class of non-tracking concentrating collectors, of particular value in the world, are portable solar cookers . These utilize relatively low levels of concentration, typically around 2 to 8 Suns and are manually aligned.

Trackers

Even though a flat-panel can be set to collect a high proportion of available noon-time energy, it is also available in the early mornings and late afternoons ^[14] when the misalignment with a fixed panel becomes excessive to collect a reasonable proportion of the available energy. For example, even when the Sun is only 10 ° above the horizon the energy can be around the noon-time energy levels (or even greater depending on the latitude, season, and atmospheric conditions).

Thus the primary benefit of a tracking system is to collect solar energy for the longest period of the day, and with the most accurate alignment in the Sun’s position shifts with the seasons.

In addition, the greater concentration of the concentration of the substance is more important, because the proportion of energy derived from direct radiation is higher, and the region where the energy is focused becomes smaller.

Fixed collector / moving mirror

Many collectors can not be moved, for example high-temperature collectors where the energy is recovered as hot liquid or gas (eg steam). Other examples include direct heating and lighting of buildings and fixed in-built solar cookers, such as Scheffler reflectors . In such cases it is necessary to employ a moving mirror so that, regardless of where the Sun is located in the sky, the Sun’s rays are redirected to the collector.

To to to,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. In different applications, mirrors may be flat or concave.

Moving collector

Trackers can be grouped by the number and orientation of the tracker’s axes. Compared to a fixed mount, a single axis tracker increases annual output by approximately 30%, and a dual axis tracker an additional 10-20%. ^[16] [17]

Photovoltaic trackers can be classified into two types: standard photovoltaic (PV) trackers and concentrated photovoltaic (CPV) trackers. Each of these tracker types can be further categorized by the number and orientation of their axes, their actuation architecture and drive type, their intended applications, their vertical supports and foundation.

Floating ground mount

Solar trackers can be built using a “floating” foundation, which can be used for invasive concrete foundations. Instead of placing the tracker on concrete foundations, the tracker is placed on a gravel pan that can be filled with a variety of materials, such as sand or gravel, to secure the tracker to the ground. These “floating” trackers can sustain the same wind load as a traditional fixed mounted tracker. The use of floating trackers Increases the number of potential locations for solar projects since trade They Can Be Placed on top of capped Landfills gold in areas Where excavated foundations are not feasible.

Non-concentrating photovoltaic (PV) trackers

Photovoltaic panels accept both direct and diffuse light from the sky. The panels on standard photovoltaic trackers are available both direct and diffuse light. The tracking functionality in standard photovoltaic trackers is used to minimize the angle of incidence between incoming light and the photovoltaic panel. This increases the amount of energy collected from the direct component of the incoming sunlight.

The physicists behind standard photovoltaic (PV) trackers works with all standard photovoltaic module technologies. These include all types of crystalline silicon panels (either mono-Si , or multi-Si ) and all types of thin film panels(amorphous silicon, CdTe, CIGS, microcrystalline).

Concentrator photovoltaic (CPV) trackers

The optics in CPV modules accept the direct component of the incoming light and should be oriented appropriately to maximize the energy collected. In low concentration applications of light scattered light from the sky can also be captured. The tracking functionality in CPV modules is used to orient the optics such that the incoming light is focused on a photovoltaic collector.

CPV modules that concentrate in one dimension must be tracked normal to the Sun in one axis. CPV modules that concentrate in two dimensions must be tracked normal to the Sun in two axes.

Accuracy requirements

The physics behind CPV optics requires that tracking accuracy increase as the systems concentration ratio increases. However, for a given concentration, nonimaging optics provide the widest possible acceptance angles , which may be used to reduce tracking accuracy. ^[20] [21]

In typical high concentration tracking systems must be in the ± 0.1 ° range to deliver approximately 90% of the rated power output. In low concentration systems, tracking accuracy must be in the 2.0 ° range to deliver 90% of the rated power output. As a result, high accuracy tracking systems are typical.

Supported technologies

Concentrated photovoltaic trackers are used with refractive and reflective based concentrator systems. There are a range of emerging photovoltaic cell technologies used in these systems. These range from crystalline silicon- based photovoltaic receivers to germanium-based triple junction receivers.

Single axis trackers

Single axis trackers have one degree of freedom that acts as an axis of rotation . North meridian is the true axis of rotation. It is possible to align in any cardinal direction with advanced tracking algorithms. There are several common implementations of single axis trackers. These include horizontal single axis trackers (HSAT), horizontal single axis trackers with tilted modules (HTSAT), vertical single axis trackers (VSATs), tilted single axis trackers (TSATs) and polar aligned single axis trackers (PSAT). The orientation of the module is important when modeling performance.

Horizontal

Horizontal single axis tracker (HSAT)

The axis of rotation for a single horizontal axis tracker is horizontal with respect to the ground. The posts at the end of the axis of rotation of a horizontal single axis tracker can be shared between trackers to lower the installation cost. Field layouts with horizontal single axis trackers are very flexible. The simple geometry means that all of the axes of rotation are in line with each other. Appropriate spacing can maximize the ratio of energy production to cost, this being dependent on local terrain and shading conditions and the time-of-day value of the energy produced. backtrackingis one way of computing the disposition of panels. Horizontal trackers typically have the face of the module oriented parallel to the axis of rotation. As a module tracks, it sweeps a cylinder that is rotationally symmetric around the axis of rotation. In single axis horizontal trackers, a long horizontal tube is supported by Pylons or frames. The axis of the tube is on a north-south line. Panels are moving upon the tube, and the tube will be rotating on its axis to the apparent motion of the Sun through the day.

Horizontal single axis tracker with tilted modules (HTSAT)

In HSAT, the modules are mounted flat at 0 degrees, while in HTSAT, the modules are installed at a certain tilt. It works on the same principle as HSAT, keeping the axis of the horizontal tube in the north-south and the solar modules east to west throughout the day. These trackers are usually suitable for use in the United States. Vertical single axis tracker (VSAT). Therefore, it has the advantages of VSAT in a horizontal tracker and minimizes the overall cost of solar project. ^[23] [24]

Vertical

Vertical single axis tracker (VSAT)

The axis of rotation for vertical single axis trackers is vertical with respect to the ground. These trackers rotate from East to West over the course of the day. Such trackers are more effective at high latitudes than are horizontal axis trackers. Field layouts must consider to avoid unnecessary energy losses and to optimize the use of land. Also optimization for dense packing is limited to the nature of the shading over the course of a year. Vertical single axis trackers typically have the face of the module oriented at an angle with respect to the axis of rotation. As a module tracks, it sweeps that it is rotationally symmetric around the axis of rotation.

Tilted

Tilted single axis tracker (TSAT)

All trackers with axes of rotation between horizontal and vertical are considered tilted single axis trackers. Tracker tilt angles are often limited to reduce the wind and decrease the elevated end height. With backtracking, they can be packed without shading perpendicular to their axis of rotation at any density. However, the packing parallel to their axes of rotation is limited by the tilt angle and the latitude. Tilted single axis trackers typically have the face of the module oriented parallel to the axis of rotation. As a module tracks, it sweeps a cylinder that is rotationally symmetric around the axis of rotation.

Dual axis trackers

Dual axis trackers have two degrees of freedom that act as axes of rotation. These axes are typically normal to one another. The axis that is fixed with respect to the ground can be considered a primary axis. The axis that is referenced to the primary axis can be considered a secondary axis. There are several common implementations of dual axis trackers. They are classified by the orientation of their primary axes with respect to the ground. Two common implementations are dual axis trackers (TTDAT) and azimuth-altitude dual axis trackers (AADAT). The orientation of the module is important when modeling performance. Dual axis trackers typically have parallel oriented modules to the secondary axis of rotation. Dual axis trackers allow for optimum solar energy levels due to their ability to follow the Sun vertically and horizontally. No matter where the Sun is in the sky, they are able to get in touch with the Sun.

Tip-tilt

A tip-tilt dual axis tracker (TTDAT) is so-named because the panel array is mounted on the top of a pole. Normally the east-west movement is driven by rotating the array around the top of the pole. The top bearing is a T-or H-shaped mechanism that provides vertical rotation of the panels and provides the main mounting points for the array. The position at the end of the primary axis of rotation of a dual tracker may be shared between trackers to lower installation costs.

Other such TTDAT trackers have a horizontal primary axis and a dependent orthogonal axis. The vertical azimuth axis is fixed. This allows for greater flexibility in the cost of connecting to the pole.

Field layouts with dual track-tip dual trackers are very flexible. The simple geometry means that it is necessary to keep track of one another. Normally the trackers would have to be at least one of the trackers in the world. Tip-tilt trackers can make up for this by tilting closer to horizontal to minimize up-Sun shading and managing the total power being collected. ^[26]

The axes of rotation of many types of symmetry are usually aligned along the east or west line of latitude.

Given the unique capabilities of the Tip-Tilt configuration and the appropriate controller fully automatic tracking is possible for use on portable platforms. The orientation of the tracker is of no importance and can be placed as needed. ^[27]

Azimuth-altitude

An azimuth-altitude (or alt-azimuth)Dual axis tracker (AADAT) has its primary axis (the azimuth axis) vertical to the ground. The secondary axis, often called elevation axis, is then typically normal to the primary axis. They are similar to tip-tilt systems in operation, but they are different in the way the array is rotated for daily tracking. Instead of rotating the array around the top of the pole, AADAT can use a large ring mounted on the ground with the array mounted on a series of rollers. The advantage of this arrangement is the weight of the array is distributed over a portion of the ring, as opposed to the single loading point of the pole in the TTDAT. This allows AADAT to support much larger arrays. Unlike the TTDAT, however, the AADAT system can not be placed closer to the diameter of the ring,

Construction and (Self-) Build

As described later, the economic balance between cost of panel and tracker is not trivial. The steep drop in cost for solar panels in the early 2010s made it more difficult to find a sensible solution. As can be seen in the attached media files, Even commercial offers like “Complete-Kit-1KW-Single-Axis-Solar-Panel-Tracking-System-Linear-Actuator-Electric-Controller-For-Sunlight-Solar / 1279440_2037007138” have rather unsuitable solutions (a big rock) for stabilization . For a small (amateur / enthusiast) construct following criteria have to be met: economy, stability of endproduct against elemental hazards, ease of handling materials and joinery. ^[28]

Tracker type selection

The selection of tracker type, location, latitude, and local weather.

Horizontal single axis trackers are typically used for large distributed generation projects and utility scale projects. The combination of energy improvement and lower cost computing in compiling economics in large deployments. In addition the strong performance is favored for large grid-tied photovoltaic systems so that production will match the peak demand time. Horizontal single axis trackers also add a substantial amount of productivity during the spring and summer seasons when the Sun is high in the sky. The inherent robustness of their supporting structure and the simplicity of the mechanism also results in low reliability. Since the panels are horizontal,

A vertical axis tracker pivots only about a vertical axis, with the panels either vertical, at a fixed, adjustable, or tracked elevation angle. Such trackers with fixed or (seasonally) adjustable angles are suitable for high latitudes, where the apparent solar path is not particularly high, but which leads to a long arc.

Dual axis trackers are typically used in smaller cities and services.

Multi-mirror concentrating PV

This device uses multiple mirrors in a horizontal plane to reflect sunlight upward to a high temperature photovoltaic or other system. Structural problems and expenses are greatly reduced since they are not significantly exposed to wind loads. Through the employment of a patented mechanism, only two systems are required for each device. Because of the configuration of the device it is especially suited for use on flat roofs and at lower latitudes. Approximately 200 peak DC watts.

A multiple mirror reflective system combined with a central power tower is employed at the Sierra SunTower , located in Lancaster, California. This generation is operated by eSolar is scheduled to begin operations on August 5, 2009. This system, which uses multiple heliostats in a north-south alignment, uses pre-fabricated parts and construction as a way of decreasing startup and operating costs.

Drive types

Active tracker

Active trackers use motors and gear trains to direct the tracker by a controller responding to the solar direction. In order to control and manage the movement of these massive structures, they are designed and rigorously tested. The technologies used to date have been constantly evolving and have recently been improved. ^{[ quote needed ]}

Counter rotating slewing drives sandwiching a fixed angle bracket can be applied to create a “multi-axis” tracking method which eliminates relative rotation to longitudinal alignment. This method will be used in conjunction with a PV array and will not rotate in a parking lot. It will also allow for maximum solar generation in any parking lot lot lane / row orientation, including circular or curvilinear.

Active two-axis trackers are also used to orient heliostats – movable mirrors that reflect sunlight toward the absorptive of a central power station . These methods are controlled by a central computer system, which also allows the system to be shut down when necessary.

Light-sensing trackers typically have two or more photosensors , such as photodiodes , configured differentially so that they output a null when receiving the same light flux. Mechanically, they should be omnidirectional (ie flat) and are intended 90 degrees apart. This will cause the steepest share, which translates into maximum sensitivity. For more information about controllers see active daylighting .

Since the motors consume energy, one wants to use them only as necessary. So instead of a continuous motion, the heliostat is moved in discrete steps. Also, if there is enough power generated to warrant reorientation. This is also true when there is not enough difference in light of one direction to another, such as when clouds are passing overhead. Consideration must be made to keep the tracker from wasting energy during cloudy periods.

Passive tracker

The most common Passive trackersUse a low boiling point compressed gas that is driven to one side or the other (by solar heat creating gas pressure) to the tracker to move in response to an imbalance. As this is a non-precision orientation it is unsuitable for certain types of concentrating photovoltaic collectors but fine works for common PV panel types. These will have viscous dampers to prevent excessive motion in response to wind gusts. Shader / reflectors are used to reflect early morning sunlight to “wake up” the panel and tilt it to the Sun, which can take nearly an hour. The time to do this by adding a self-releasing tiedown to the position of the panelist.

A newly emerging type of passive tracker for photovoltaic solar panels uses a hologram behind stripes of photovoltaic cells so that sunlight passes through the transparent part of the module and reflects on the hologram. This allows sunlight to hit the cell from behind, which increases the module’s efficiency. Also, the panel does not have to go to the hologram always reflects the correct angle towards the cells.

Manual tracking

In some developing nations, the trackers. This has the benefits of robustness, having staff available for maintenance and creating employment for the population in the vicinity of the site.

Rotating buildings

In Freiburg im Breisgau, Germany, Rolf Disch built the Heliotrop in 1996, a residential building that is rotating with the sun. It’s producing four times the amount of energy building consumes.

The Gemini House is a unique example of a vertical axis tracker. This cylindrical house in Austria (latitude above 45 degrees north ) rotates in its entirety to track the Sun, with vertical solar panels on one side of the building, rotating independently, allowing control of the natural heating from the Sun.

ReVolt House is a rotating, floating house designed by TU Delft students for the Solar Decathlon Europe competition in Madrid . The closed facade turns itself towards the Sun in summer to prevent the interior space from direct heat gains. In winter, the glass facade faces the Sun to get direct sunlight in the house.

Disadvantages

Trackers add cost and maintenance to the system – if they add 25% to the cost, and improve the output by 25%, the same performance can be achieved by making the system 25% larger, eliminating the additional maintenance. ^[30]Tracking was very cost effective in the past when photovoltaic modules were expensive compared to today. Because they have been expensive, it has been important to use a number of panels in a system with a given power output. But as panels get cheaper, the cost effectiveness of tracking vs. a greater number of panels decreases.

Tracking is also not suitable for typical residential rooftop photovoltaic installations. Since tracking requires that panels tilt or move otherwise, provisions must be made to allow this. This requires that panels be offset to a significant distance from the roof, which requires expensive racking and increases wind load. Also, such a setup would be made for a very attractive installation on residential rooftops. Because of this (and the high cost of such a system), tracking is not used on residential rooftop installations, and is unlikely to be used in such facilities. This is especially true as the cost of photovoltaic modules continues to decrease, which makes increasing the cost-effective option. Tracking can (and sometimes is) used for residential ground mount installations,

Tracking can also cause shading problems. As the panels move during the course of the day, it is possible that, if the panels are located too close to one another, they may shade one another due to profile angle effects. As an example, if you have several panels in a row from east to west, there will be no shading during solar noon. But in the afternoon, they could be closed. This means that panels must be spaced far beyond the limits of sun hours. This is not a big problem if it is sufficient land area to the general public. But it will reduce the output during certain days of the day compared to a fixed array.

See also

• Air mass coefficient
• heliostat
• Solar energy
• Sun path

Notes and references