Lesson 3: Tracking Systems

Overview

This lesson will introduce the concept of sun tracking and will discuss how it can improve the performance of solar energy systems. The sun is a light source that is not fixed, but rather is constantly moving relative to a solar receiver. This leads to significant variability of the available radiation and, as a result, variability of power output and efficiency of a solar energy conversion system. The idea of sun tracking was developed in attempt to mitigate that variability to some extent and in pursuit of higher efficiency and extending the solar power production over the course of the day. Tracking technology is more often associated with utility scale solar plants rather than small residential systems. Some examples of tracking include single-axis and two-axis tracking of PV panels, moving heliostats in solar tower thermal plants, variable tilt parabolic trough systems, and Stirling dish concentrators - systems whose operation heavily relies on the accuracy of tracking. In this lesson, we will first discuss when tracking is a viable idea, and what systems can benefit from it. Then, we will study the geometry of the solar motion through the sky and define the parameters that characterize the position of the sun relative to a solar receiver at a certain location and time. This background would be important in understanding any tracking algorithms. Some examples and activities within this lesson will involve geometric calculations that will help you to better understand how this technology works.

Learning Objectives

By the end of this lesson, you should be able to:

define the main parameters of the solar motion;
explain the types of tracking systems and principles of their operation;
calculate the position of the sun relative to the receiving surface at a locale at a particular time.

Readings

Kaligirou, A, Solar Energy Engineering, Chapter 2: Environmental Characteristics.

Brownson, J.R.S., Solar Energy Conversion Systems, Chapter 7. Applying the Angles to Shadows and Tracking, pp. 192-196.

Both books are available for reading online through the Penn State Library system. See the "Library Resources" / E-Reserves tab in Canvas.

3.1. Why tracking?

Solar tracking is a technology for orienting a solar collector, reflector, or photovoltaic panel towards the sun. As the sun moves across the sky, a tracking device makes sure that the solar collector automatically follows and maintains the optimum angle to receive the most of the solar radiation. Some solar concentrators hugely benefit from tracking, while some others do not. So, the tracking systems can be added with additional cost and certain trade-offs in system design only when it pays off.

The required accuracy of tracking varies with application. For example, concentrators, especially in solar cell applications, require a high degree of accuracy to ensure that the concentrated sunlight is directed precisely to the solar conversion element. Tracking the sun from east in the morning to west in the evening can increase the efficiency of a solar panel up to 45%, according to some manufacturers [Linak [1]]. Precise tracking of the sun is achieved through systems with single or dual axis tracking.

Watch this introductory video (5:33), which provides an illustration to the benefits of sun tracking:

DEGERenergie - Solar Tracking Systems (5:33)

Credit: messelive.tv. "DEGERenergie - Solar Tracking Systems [2]." YouTube. December 15, 2010.

Click here for a transcript of the DEGERenergie - Solar Tracking Systems video.

NARRATOR: During the last decade, photovoltaics have become an important source of energy. DEGERenergie has been the global pioneer for solar tracking systems, optimizing the efficiency of renewable energy for more than 12 years. DEGERenergie has been providing advanced technology to increase efficiency of solar plants. And, while having set the standard of today, DEGERenergie has new visions, ideas, and solutions which stretch beyond tomorrow.

MICHAEL HECK: Located in Germany, DEGERenergie is the leading manufacturers of the largest product portfolio worldwide for single and dual access solar attracting systems. As the market leader for solar power plants, with over 35,000 star systems worldwide, we offer a German technology product with the best price-performance ratio in the business.

NARRATOR: The Fraunhofer Institute for Solar Energy Systems calculated a 27% higher output of astronomically controlled systems compared to fixed systems. Spanish solar farm operator Picon de Solar reviewed its revenues of the last few years and discovered that they had achieved a 46% higher yield using DEGER trackers than with a comparable fixed system.

MICHAEL HECK: We have been consistently developing new ideas and concepts for the optimum use of solar energy through solar module tracking.

NARRATOR: DEGERenergie develops, produces, and provides individual service for intelligent solar tracking systems, energizing the global photovoltaic market.

ANDREAS SCHWEDHELM: The heart of this technology is a sensor, which is called the DEGERconecter. The advantage of using this technology is that we can also incorporate different weather conditions. For example, the eye of cloud effect, complete overcast days or also reflections, for example, if there is snow on the ground.

NARRATOR: All DEGER trackers use the patented maximum light detection technology, MLD. Unlike other systems, the DEGERconecter measures which direction most of the light is actually coming from. In doing so, each DEGER tracker finds its own ideal position and uses reflections to raise its output. In a similar way, the DEGERconecter takes the eye of cloud effect into account and, even on completely overcast days, each DEGER tracker moves individually into an ideal position for maximum yield. Within DEGER trackers there is no need for a computer that could crash, no need for calibration or extra wiring that costs money. The simple and individual control of a DEGER tracker provides for a calibration and maintenance-free long-term availability, and guarantees a sustainable operation, even with changing soil conditions. The optimized energy output of DEGER trackers will save an investor a 25% higher expenditure than equivalent fixed systems. Investing in DEGER trackers, customers will realize a profitable internal rate of return. DEGER's systems are guaranteed to have a good future. On average, the energy recovery of DEGER systems is complete after three years, including concrete, steel, and wiring. All steel and concrete parts are completely recyclable. DEGERenergie is an innovative technology with higher yields, low maintenance cost and optimal internal rate of return, emission-free energy production and eco-friendly manufacturing, with warranties extendable to 25 years.

MICHAEL HECK: You can't always rely on the weather, but you can count on your intelligent controlled system.

NARRATOR: DEGERenergie, not only simply brilliant, but brilliantly simple.

Systems that employ trackers

So, what types of systems should include tracking devices (a.k.a. trackers)?

First of all, the systems that specifically utilize the direct beam radiation benefit from tracking. In majority of concentrating solar power (CSP) systems, the optics accept only the beam radiation and therefore must be oriented appropriately to collect energy. Such systems will not produce power unless pointed at the sun. Tracking is required for heliostats in central receiver (solar tower) systems. CSP collectors require significant degree of accuracy of sun tracking.

In photovoltaic (PV) applications, tracking devices can be used to minimize the angle of incidence of incoming solar rays onto a PV panel. This increases the amount of energy produced per unit of installed power generating capacity. This increases the efficiency of the system and its cost-effectiveness, but, at the same time, tracking is not strictly required for regular flat panel PV as they accept both beam and diffuse radiation.

In concentrating photovoltaics (CPV), the optics requires beam radiation and therefore must be oriented appropriately to focus light on the PV collector to maximize the energy converted. 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 [Solar Tracker from Wikipedia.org [3]]. CPV modules require high degree of accuracy of sun tracking.

Single-axis and Dual-axis

There are many types of solar trackers, which are different in costs, design complexity, and performance. But we can distinguish two basic classes of systems:

Single axis trackers
The single axis solar trackers can either have a horizontal or a vertical axis. The horizontal axis is used in tropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in high latitudes, where the sun does not get very high, but summer days can be very long. In concentrated solar power applications, single axis trackers are used with parabolic and linear Fresnel mirror designs.
Dual axis trackers
The dual axis solar trackers have both a horizontal and a vertical axis, and thus they can track the sun's apparent motion at any location. Dual axis tracking is commonly used for CSP applications, such as solar power towers and dish (Stirling engine) systems. Dual axis tracking is extremely important in solar tower applications due to the angle errors resulting from longer distances between the mirror and the central receiver located in the tower structure.

In more detail, these types of trackers will be studied in Section 3.3. of this lesson.

Pros and Cons

With tracking incorporated in the system design, the cost of the system is understandably higher compared to fixed tilt systems. According to the US DOE report [Barbose et al., 2013], "among projects completed in 2012, the capacity-weighted average installed price in US dollars was 3.3/W for systems with crystalline modules and fixed tilt, compared to 3.6/W for crystalline systems with tracking and 3.2/W for thin-film, fixed-tilt systems." Efforts are constantly made by manufacturers to lower the cost of the tracking systems, making them less complex, more compact, reliable, and easier to maintain. In spite of the additional costs, use of trackers is often a preferred option for utility-scale installations due to the significant boost to the system performance. Figure 3-1 shows the trend of increasing use of tracking systems in the U.S. utility-scale PV installations over the 2007–2017 decade. Cumulative tracking system installation reached 79% in 2017 (meaning that only 21% of large PV installations opt not to use trackers). These data include both one-axis and dual-axis tracking systems cumulatively, however there are many more one-axis trackers deployed than dual-axis trackers.

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Figure 3.1: Percentage of U.S. utility-scale PV systems using tracking systems, 2007–2017

Source: NREL, U.S. Solar Photovoltaic System Cost Benchmark [4]: Q1 2018

3.2. Apparent daily path of the sun

For most solar tracking applications, we need a reasonably accurate knowledge of where the sun will be at a specific hour during each day in a year. Theory is well-developed to calculate the sun position with respect to the observation point on the earth surface, and it sets the background for design and modeling of both photovoltaic and concentrating solar power systems of various scale.

In order to discuss tracking or any other adjustments of solar receivers, it would be useful first to understand the sun's path across the sky dome. We are going to turn to the following reading, which describes the key parameters of the solar motion.

Reading Assignment

Book chapter: Kalogirou, A, Solar Energy Engineering [5], Chapter 2: "Environmental Characteristics." pp. 51-63. (See E-Reserves via the Library Resources tab.)

This reading explains a lot about the geometry of sun movement, provides the key equations and example calculations alongside with them. The objective here would be to learn how to estimate the sun position and draw its track for a particular location and time of the year.

The above materials provide the main tools for predicting the position of the sun at a location of choice at any specific time. Let us summarize a few key takeaways from this reading.

Solar Altitude and Solar Azimuth

The main parameters to determine are solar altitude (α) and solar azimuth (z). Here are the equations that are used to calculate these coordinates:

$\sin (α) = \sin (L) \sin (δ) + \cos (L) \cos (δ) \cos (h)$ (3.1)

where L is local latitude (GIS parameter defined as the angle between the line from the center of the earth to the site of interest and the equatorial plane), δ is the declination, and h is the hour angle for that location.

$\sin (z) = \cos (δ) s i n (h) / c o s (α)$ (3.2)

Let us consider an example showing how to use these equations.

Example

Calculate the solar position for Abu-Dhabi (UAE) on January 15 at 2 pm local time.

For this calculation, we will use equations (3.1) and (3.2) to find the solar altitude and solar azimuth, respectively. We will need to find the following parameters:

L - local latitude - Abu-Dhabi coordinates are: latitude 24.492^o N, and longitude 54.358^o E

You can use this website to get GIS data [6].

δ - declination - It is a function of the day of the year (N). For Jan 15, δ = -21.27^o

as found by Eq. (2.5), Kalogirou's text.

δ = 23.45 \sin [\frac{360}{365} (284 + N)]

h - hour angle - It is a function of the time of the day. For 2 pm, h = 22.04^o as found by Eq. (2.9), Kalogirou's text. For calculating hour angle, you need to determine the apparent solar time (AST), which is given by Eq. (2.3) of Kalogirou's text.

You can also use this helpful resource and embedded calculator [7] to find AST. (You may want to bookmark it to use in your homework!)

Applying it to the current location, we find that AST = 13.47 hr decimal time or 1:28 pm clock time. And the hour angle will be:

h = (A S T - 12) \times 15 = (13.47 - 12) \times 15 = 22.04

Now we can plug these L, δ, and h numbers into Eq. (3.1):

$\sin (α) = \sin (24.493) \sin (-21.27) + \cos (24.492) \cos (-21.27) \cos (22.04)= 0.6356$

α = 39.47^o

For solar azimuth, we use Eq. (3.2):

$\sin (z) = \cos (-21.27) s i n (22.04) / c o s (39.47)=0.453$

z = 26.93^o

This calculation can be essentially used for any location and any time in a year. The algorithms available help to produce detailed solar resource data for different settings. These data are available for reference and use, so you do not have to calculate all things from scratch, although it is useful to understand the theoretical background of it.

Sun Path Chart Tool

We can use the Sun Path Chart Program calculator [8] [8]at the University of Oregon's Solar Radiation Monitoring Laboratory website to obtain a complete picture of sun movement throughout the year. The calculator allows data to be plotted in either orthogonal or polar coordinates. For example, the diagram below (Figure 3.2) was obtained for the same location (Abu Dhabi).

graph of sun path adequately described in surrounding text

Figure 3.2. The orthogonal projection of the solar path for the location.

Credit: (Abu Dhabi, 24.5o N, 54.4o W) obtained by the SunChart calculator [UO SRML, 2007].

In this diagram, the solar altitude (elevation) is plotted versus solar azimuth, as shown by the blue curves for each date. There are a few representative dates shown, and January 21 is the closest to the calculation example previously given. Note that the solar azimuth is given on the 360^o scale, with 180^o corresponding to the south. Alternatively, Kalogirou uses the coordinate system and formulae to calculate solar parameters versus 0^o as true south, with negative azimuth values corresponding to morning and positive azimuth values corresponding to afternoon hours. So beware of that difference if you try to match data from both sources. On the Sun Path diagram, the hourly position of the sun is marked by the red curves. In this particular case, the local standard times are plotted, while a similar diagram can be made in terms of solar time.

Check Your Understanding - Questions 1-3

Check Your Understanding - Question 4

Is it possible for the sun to reach 90° altitude at any time in a year in the following states? Type "yes" or "no" for each location. Can you explain why?

Arizona

Pennsylvania

California

Hawaii

Problem 3-1: Solar path calculation

(This calculation will be submitted as part of Lesson 3 problem set).

Go to the Sun Path Chart Program calculator [8] and calculate the sun path for a location of your choice. Use the orthogonal projection. Save your diagram.
You may need to find geographical coordinates and time zone for your location as input. Here is one of the websites that can be conveniently used for that purpose: TimeandDate.com [9]. Just type in your location and get the data.
Using equations (3.1) and (3.2) in this lesson, perform a manual calculation of the sun position (solar altitude and solar azimuth) for the same location on February 20th, at 12 pm and 3 pm local time.
Mark your manual points on the diagram. Are you able to match your calculations with the plot?

The above materials and activity make sure that you can employ proper tools for defining solar position on the sky dome. Further on, the receiver positioning algorithms will use this information as the operational basis. Different types of tracking systems are discussed in the next section of the lesson.

Additional Reading

NREL Report: Reda, I.; Andreas, A. (2003). Solar Position Algorithm for Solar Radiation Applications. 55 pp.; NREL Report No. TP-560-34302, Revised January 2008. [10] (1.9 MB PDF Document)

3.3. Cosine Effect

In technical sense, sun tracking is a method to keep the surface of the solar panel or a collector perpendicular to the incident solar rays. This is the ideal condition, when maximum amount of solar energy is transmitted to the receiving surface.

When the incident ray is not perpendicular to the surface (which is often the case with fixed-tilt systems), the angle of incidence is not zero (q ¹ 0), and part of the incident energy will be lost due to so-called cosine effect. To maximize efficiency of the system, we should always seek ways to minimize the cosine effect at any particular moment of time.

The figure below shows two scenarios: the left image illustrates an ideal situation, when solar rays come down on the surface of solar collector (PV panel) at the 90^o angle; the right image shows what happens when the Sun moves across the sky while the panel remains fixed.

Figure 3.3: Orientation of the receiver plane perpendicular to the incident rays (left) and at an angle (right), which introduces cosine effect.

Mark Fedkin

In the second case, the sun rays come down to the surface at an angle q, which will decrease the amount of energy absorbed by the surface, and thus will lower the system efficiency. By how much?

We can try to estimate this reduction due to cosine effect if we break down the G vector into two components: one perpendicular to the surface ( $G_{⊥}$ ) – useful component that would be absorbed, and one - parallel to the surface ( $G_{| |}$ ) – non-useful component that would be reflected or somehow lost.

Figure 3.4: Evaluation of cosine effect on a horizonal surface based on the zenith angle.

Mark Fedkin

For example, if we assume incident irradiance to be 1000 W/m², and angle of incidence 30^o, then

G = 1000 \times \cos (30^{\circ}) = 866 W / m^{2}

Thus, without considering other inefficiencies, losses due to cosine effect are expected to be around 13.4% at this angle, which is quite substantial.

Tracking can be an effective solution to minimize these performance losses. Tilting the panel by the angle (b) equal to the zenith angle would set the panel perpendicular to the sun rays once again.

Figure 3.5: Tilting of the receiver plane to avoid the cosine effect losses.

Mark Fedkin

The early attempts to eliminate cosine effect would involve annual adjustment of panel angle throughout the day. But that would be tedious, inaccurate, and too discrete, while the Sun stays in constant motion on its daily path. Present-day automatic trackers use algorithms that are able to continuously track the Sun with accuracy of $\pm {0.0003}^{\circ}$ .

3.4. Types of tracking systems

Tracking systems are classified by the mode of their motion. We can define three axes for a moving surface (which represents a receiver): two horizontal axes and one vertical axis (Figure 3.3). The surface can be rotated around each axis (tilted) to achieve an appropriate angle with respect to the incident solar beam. When movement or adjustment of the surface is done by rotating around one axis (tilting), it is single-axis tracking. When rotation of the surface is done around two axes simultaneously, it is two-axis tracking. Two-axis tracking allows for the most precise orientation of the solar device, is reported to provide 40% gain in energy absorption, but it is more complex and costly. Such two-axis systems are also used for controlling astronomical telescopes.

Figure 3.3. Three axes of rotation of a hypothetical moving surface.

Credit: Mark Fedkin

In case of single-axis tracking, the axis of rotation is usually oriented in the N-S direction or E-W direction. Tilting is performed in a way to minimize the incidence angle. In case of two-axis tracking, ideally, the incidence angle is always zero, i.e., the surface is kept perpendicular to the solar beam.

Read about various tracking modes in the following sources.

Reading Assignment

Book chapter: Kalogirou, A, Solar Energy Engineering, Chapter 2: Environmental Characteristics. pp. 64-71. (See E-Reserves via the Library Resources tab.)

This reading is the continuation of the same chapter you read in the previous section of the lesson. It describes different types of single-axis and dual-axis tracking systems and compares their performance by the amount of received solar energy.

Book chapter: Brownson, J.R.S., Solar Energy Conversion Systems, Chapter 7. Applying the Angles to Shadows and Tracking, pp. 192-196. (See E-Reserves via the Library Resources tab.)

This reading gives a few more descriptions of tracking modes, some different from those listed in Kalogirou's book. You will also read here about specific advantages of particular types of tracking systems.

So, from reading these chapters, you now have quite complete list of different ways of tracking, and corresponding formulae to describe the relative position of the sun and inclined surface. The following activities will give you an opportunity to practice the basic calculations involved in two-axis and single-axis tracking. The first problem considers a simple case of two-axis tracking. As long as we know the solar coordinates, we can orient the receiver in that direction. But the tracking system that moves the plane needs precise input data, which we try to obtain here.

Problem 3-2: Dual-axis tracker data

The system is a heliostat with two-axis tracking: one vertical axis, and one horizontal (SN) axis. The goal is to determine the azimuth for the heliostat orientation and tilt angle for the horizontal axis at any time of the day to supply these data to the tracking system. A sketch of the collector is given below, and the blue line is the horizontal axis we want to tilt. The red line denotes the vertical axis, about which the collector can be rotated.

image adequately described in above text for more information contact instructor

Figure 3.4: Heliostat diagram

Calculate and tabulate a set of Z_s-β data for every hour during the daylight period on March 21 at your chosen location. Feel free to use any available resources (solar path diagrams or appropriate equations) to determine the position of the sun.

In this calculation, we can assume that incidence angle on the surface of the collector will be zero at any moment.
Please provide references and explanation to your work.

This calculation will be submitted as part of Lesson 3 problem set.

The second problem on this topic considers the single-axis tracking case - one with horizontal NS axis and EW tracking (see Kalogirou's chapter, p. 69). In this case, the receiver has only one degree of freedom, so its motion is limited. We will not be able to reach the zero incidence angle, but we will try to minimize it in order to maximize the solar radiation on the plane.

Problem 3-3: Single-axis tracker data

Consider a flat collector with a fixed horizontal NS axis and tilting EW axis (see sketch below, side view). Because the NS axis is fixed, the surface azimuth (Z_s) is either -90^o when it tilted east, or +90^o when it is tilted west. The β angle defines the tilt, which is applied to minimize the incidence angle on the surface.

image adequately discribed in above text

Figure 3.4: Flat Collector diagram

For your chosen location, determine and tabulate the surface position parameters (Z_s-β ) for every hour on March 21st. Feel free to use any available resource to determine the sun position. Make sure to provide references and explanation to your work.

This calculation will be submitted as part of Lesson 3 problem set.

3.5. Engineered devices for solar tracking

Image credit: Afloresm via Flickr [11]

The main elements of a tracking system include [Rockwell Automation, 2011]:

Sun tracking algorithm: This algorithm calculates the solar azimuth and zenith angles of the sun. These angles are then used to position the solar panel or reflector to point toward the sun. Some algorithms are purely mathematical based on astronomical references, while others utilize real-time light-intensity readings.
Control unit: The control unit executes the sun tracking algorithm and coordinates the movement of the positioning system.
Positioning system: The positioning system moves the panel or reflector to face the sun at the optimum angles. Some positioning systems are electrical and some are hydraulic. Electrical systems utilize encoders and variable frequency drives or linear actuators to monitor the current position of the panel and move to desired positions.
Drive mechanism/transmission: The drive mechanisms include linear actuators, linear drives, hydraulic cylinders, swivel drives, worm gears, planetary gears, and threaded spindles.
Sensing devices: For trackers that use light intensity in the tracking algorithm, pyranometers are needed to read the light intensity. Ambient condition monitoring for pressure, temperature, and humidity may also be needed to optimize efficiency and power output.
Limit switches are used to control speed and prevent over travels. The mechanical over travel limits are used to prevent tracker damage.
Elevation feedback is accomplished by either 1) a combination of limit switches and motor encoder counts, or 2) an inclinometer (a sensor that provides the tilt angle).
An anemometer is used to measure wind speed. If the wind conditions are too strong, the panels are usually driven to a safe horizontal position and remain in the safety position until the wind speed falls below the set point.

Three classes of tracker drive types to operate the moving receiver:

Passive trackers use the sun's heat to expand the compressed gas, which is used to move the panel. Selective heating of some cylinders versus others create more expansion on one side of the panel and make it tilt. These systems are relatively simple and low-cost, although may lack due precision necessary for the solar conversion systems using concentrated sunlight.
Active trackers use hydraulic or electric and an actuator to move the panel based on sensor response. Light sensors are positioned on the tracker at different locations for higher precision. These systems work best with the direct sunlight and are less efficient with cloudy skies.
Open-loop trackers use pre-recorded data on the sun position for a particular site. Simple timed trackers move the panel at discrete intervals to follow the sun position, but do not take into account the seasonal variations of the sun's altitude. The altitude/azimuth trackers employ astronomical data to determine the position of the sun for any given time and location.

Actuators

Linear actuators are common technical tools that proved to be effective solution for moving the solar receivers. An electric linear actuator is a device that converts the rotational motion of an electric motor into linear motion. With linear actuators you can lift, slide, adjust, tilt, push or pull objects of various mass, and they are easy to implement in many different applications. Mechanically, linear actuators are quite simple devices that have been extensively deployed in 2-axis and 1-axis trackers due to their precision and service reliabilty.

The following video provides a rather detailed overview of the design, principle of operation, and specifications of electric linear actuators:

Video: Linear Actuators 101 (19:43)

Credit: Robert Cowan. "Linear Actuators 101 [12]." YouTube. June 24, 2018.

Click here for a transcript of the Linear Actuators 101 video.

Hello, everyone. In this video, I'm going to be talking about linear actuators. Linear actuators are really cool. And in this video, I want to explain what they are, how to use them, how to drive them, and how to pick them based on the various specs for your application. So, let's get started.

So, first off, what is a linear actuator? Well, really, linear actuators are just motors, but instead of moving around in a rotational direction, they move in and out along a linear plane. So, a normal motor would spin around like this. It just kind of spins, and it spins indefinitely. If you apply voltage one way, it goes this way.

If you apply it the other way, it goes the other way. Whereas linear actuators, when you apply voltage to the motor, the shaft here either goes out this way, or if you reverse it, it goes back the other way. Ultimately, you drive them in the same way that you would a standard DC motor. If you go positive to positive, negative to negative, it will go usually out. And if you flip the polarity of those around, it will go the other way.

I will be taking one of these apart later so that you can kind of see how it works. But as you can see, each one of these basically has this big motor on the end of it. Right there, right there and right there. And that motor spins around, essentially a lead screw, which pushes that lead screw out or pushes it back in. Now, with standard rotational motion, there are no end stops.

It kind of just keeps spinning indefinitely. But when you have something like this, there is an end stop to where it can hit the end on the extended travel, or it can come all the way back in. And there's a couple of little mechanisms that stop that from basically causing damage to the actuator. But that's really all there is to it. You can use these in any application where you want linear motion rather than rotational motion, like lifting up forks on something.

They're used a lot of times in combat robots for lifting up, clamping down. Or I used it in my little wheelchair snowblower thing for actually lifting the blade up and down. They are really good for any kind of linear motion. Just like with standard DC motors, there's a lot of various sizes and configuration to linear actuators, but ultimately, they all pretty much do the same thing. They provide linear movement.

There are a couple different variations that you need to look out for when purchasing a linear actuator for your application. If we look at the end of this service city one, we see that there are five wires coming off the end of it. And if we look at these two that I salvaged from the wheelchairs, there are two wires and two wires. Now, the difference is all of these can be driven just like a standard motor. You apply voltage, it goes out, you switch the voltage, it goes back in.

However, this one actually has a feedback mechanism inside of it. What I was saying earlier about the shaft reaching the end of travel, on either extreme, all of these have some sort of protection mechanism or some sort of electronics inside that stop them from overextending themselves. It's usually in the form of just a diode, so that when it goes out to the far end of its reach, the diode will stop current from flowing in that direction, and then you can only reverse it back the other way. Almost every linear actuator has that. There's probably some exceptions.

I'm sure there's some really cheap ones out there that don't have that, but generally speaking, that's a feature of a linear actuator. So, what does the servo city one have that is different? And this isn't unique to servo city, by the way. It's just the one that I have here that has the feedback mechanism inside of the base of this. When I open up, you'll see it in better detail.

There is essentially just a potentiometer that is connected to this output shaft, and it is, I guess, wired proportionately so that when this shaft is all the way in, that potentiometer is at one end of its range. And then when this shaft is all the way out, it is at the other end of the range. And this happens to be a ten k potentiometer. So here it's going to read zero, and all the way out there it's going to read ten kilo ohms. So this is very useful when hooking up to a motor controller or something else to determine pretty much where this is in the travel.

Now, with both of these, they were for a wheelchair, I think this was like the power lift for the seat, and this was like a tilt for the seat, something like that. You're less concerned with where that is. And in some applications, you might not really care where this shaft is. You just kind of want to move it forward and backward, much like a standard motor. You just want to move it at a certain speed in a certain direction.

So that is something to look out for, is some of them do have some kind of feedback mechanism, and others do not. You might not need it, or you might need it. The other thing to look out for is some of these are actually linear servos. So, they take it one step further, and they actually take the motor controller and put it directly inside. So, you control it much the same way you would with a servo.

You just send it a pulse command, and then it travels wherever you dictate. So if you say, I'm going to give it this pulse, then it would go halfway, or you can go like 80%, 20%, whatever it is. And so linear servos are very different. Servo city does have a very good video that shows you the difference between a standard linear actuator, one with feedback, and a linear servo. So that's worth checking out.

And that is linked below. But that is something that you might want to look at, because not all of these have the exact same features inside of them. Driving linear actuators is pretty straightforward because they are just motors. So, you drive them the same way you would a standard motor. I have these leads connected up to my benchtop power supply over there, and this has 12 volts on it.

So if I connect one lead down here and then the other one up there, this will just start moving. There we go. So, it's moving in. And if I switch these around, this one up here, it will move out once I clip it in. Right?

And now it moves out the other way. As you can see, linear actuators are not the fastest thing in the world. There's a lot of power. There is absolutely no way I could stop this from moving, but they are relatively slow, and I will get into that a little bit later. But the speed at which these move is one of the things that you should factor in when you are picking these out.

So if we look over at the Servo city, we have all these five wires coming out. We can just ignore these three for now, and then we can connect it and control it the exact same way. I'm just going to go red to red and black to black. This one is a little bit zippier, and then we can reverse it and it will go the opposite direction. So, it's really that simple.

And some of these actually do come with a little toggle switch that is pre wired for these. But if you don't have that, or if you want to make your own, you can use any dual pole, dual throw switch. Basically one that has six connections like this. You wire a power supply into the middle. One side is one polarity, and then the other side is a different polarity.

So let's say this is red from the supply, this is black from the supply. You would just go red and black directly to the motor, but in this side, you would actually flip them to the other side. And I will have a link to a wiring description down below if that's confusing. But you're going to want a motor that is not latching like this one. You're going to want kind of a toggle that goes like a normal toggle switch.

This isn't the right one to use, and I didn't have one on me, so I won't show that. In addition to using just a simple switch, which will just go full speed one direction or full speed the other direction, you can use a motor controller. The main difference between using just a switch directly up to a power supply and a motor controller is with a motor controller like this, Roboclaw is, you can actually vary not only the speed, but the direction on the fly. This you can connect to a microcontroller. You can connect it to all sorts of other things.

And this is what I'll be using for my application. But the real big difference is controlling the speed and other parameters. This can actually also accept the encoder feedback, and we can do all sorts of fun things. But for basic control, you really don't need anything, really, beyond a switch and a power supply. So they're pretty easy to drive.

Now it's time to disassemble this, dissect it, and show you what's going on inside the linear actuator. I'm using the servo city one only because it's actually the most well laid out and the easiest to get into. So let's just start taking it apart. There's three screws at the bottom of this, so I'm just going to go ahead and take those out.

You can see we've got some plastic gears around here, and at the very bottom, you can see that is our potentiometer. Now, don't fear, these plastic gears actually have nothing to do with the driving of the actuator. This is just for the feedback side. So I'm going to take this off, take this shell off, and then we can actually see the gears that are driven by the motor directly. But this is, I want to say, maybe probably a five turn or ten turn potentiometer.

And it spins directly with the output shaft, and that gives you the feedback that ends up going on these main wires. So, it's a pretty simple little mechanism that as this main output shaft turns, it also turns the potentiometer. And then you just read the potentiometer. So, nice and simple. All it.

So, now that we've got this open, there's yet another gasket here. And then you can see all the output gears. Let me see if I can get a little bit better shot of that. So you've got the motor right there, and that is a plastic pinion gear. And then it moves into all the metal gears right here.

So this particular motor comes in a couple of different configurations. And ultimately, the difference between the stroke or how far this travels out is really just going to be the gear reduction here, because the pitch of the linear rail inside here, all of that good stuff. But this is just the gear train that slows down the motor and drives the linear actuator inside this shell. And you can see you've got a lot of decent gears in here. There's a lot of nice oil.

So awesome. That is pretty cool. So that's really all there is to it inside, it's just basically a really simple gearbox that drives a linear shaft over here. So, let's take this outer shell off, and then you can see what's inside of here. It.

So there you go. There's a little gasket that goes all the way at the bottom down here. Let's get that out of the way. And then you can see we've got two little micro switches. One here and then one here.

And then we have a couple of diodes in place. Now, this one does not appear to have adjustable end of travel. So, basically, as this comes down, it will hit against there. And as it goes out to this side, it will hit against there. So, it's just this little nub or this little piece right there that travels up and down and is hitting your end stop.

So, pretty cool. Some of the higher end ones actually do have adjustments. So, where you can kind of slide these along and you can have different end stops. However, this one does not have that. So you would need to rely on software to do that.

And if you do use something like the roboclaw, which I misplaced, if you use something like this roboclaw, you can actually put that into the software in here and configure that separately. And then right here, you can see we just have a simple lead screw right there, and it's all nice and greased up. And then this just simply slides along the lead screw. So when the motor turns, it turns these gears, it turns this and that, either presses this out or brings it back in. It is really that simple.

There's not a whole lot to it. And then this is just a cover to protect the whole thing. So, yeah, that's all there is to a linear actuator. Let's put this back together. Okay, so we've talked a little bit about what a linear actuator is, how it functions.

Taken a look inside and I've kind of covered the very basics on how to control them, either directly with a power supply or just wiring them up to a switch. If you want to take this further, I will be doing another video as a supplement to this that shows you some of the more, I guess, advanced parts of controlling these with something like the roboclaw or another type of motor controller. That's a little bit beyond the scope of this video, but I will be coming out with that separately because I am working on my own project using a couple of these linear actuators. So, the next thing that we need to talk about is how to spec them for your project. As I discussed earlier, linear actuators are essentially just motors, and you can treat them the same way in terms of specking them out.

For your project, you're going to need to pay attention to the voltage that the motor runs at and the current requirements behind that. And really you can run these at different voltages and that's a larger discussion. But essentially the amount of voltage that you put into a DC motor is going to proportionately relate to how fast it spins. However, if you over voltage, a DC motor apply more voltage than it is speced at, you will lessen the lifespan of that motor. So keep that in mind.

And a lot of these have a duty cycle rating that is only like 25%. I. E. This is not meant to run 100% of the time. It is spec to run 25% of the time.

Now, the big difference in driving these motors with just a power supply directly and driving them with a motor controller like, let's say the roboclaw is going to be being able to vary the speed. If you put 12 volts into this motor, it's always going to run at that exact same speed, either forward or backwards. It's always going to be the same. If you use a motor controller, that gives you the opportunity to control it at different speeds. And that's really the only reason why you would want to use a motor controller, is to vary that speed of how fast the shaft moves.

There are a couple specifications for linear actuators that are unique to them, and you won't find them on a normal DC motor like the voltage and the current. You're going to want to pay attention to the stroke. The stroke is probably the most important part of the linear actuator. And it basically means how far the shaft can travel. It's a total travel, not necessarily the total size of it, but just how much it can travel.

This one is a twelve inch, meaning when this is all the way in to all the way extended, it moves twelve inches. These are somewhere around like six inches. So definitely pay attention to the stroke. The other spec that you're going to want to pay attention to with a linear actuator is going to be the load rating. There's going to be two load ratings.

Usually there's going to be the dynamic load and the static load. The static load is quite simply how much force can you put against this before it will fail statically? So let's say it was just sitting there like that and it had a load on top of this. This one's rate, I think like a 500 pound static load. It means it can just sit there with 500 pounds resting on it without failing.

The dynamic load is how much force it can actually exert on the thing that you're trying to use it with. I want to say this one's rated like 100 and 5175 pounds. So that means it can actually press or exert a force of 175 pounds. So that is the difference between a static and a dynamic load. The last thing that you want to look at is the speed at which these things move.

Usually it's some kind of like inches per minute or something like that, and it's going to be how fast it can move. That's something that you really want to pay attention to because this has a twelve inch stroke. Let's say it was one inch per hour. That means it's going to take 12 hours to fully extend from fully non extended. So that is something you really want to pay attention to.

Now, when you look at these linear actuators, you will see that there's usually multiple variations of the same thing. For Instance, with this model, there are, I think, three different versions of it, and they're all the exact same price. One of them has like a 50-pound loan rating. One's like 100 and 5175, and the other is like 500. Let's say.

Why are they all the same price? Why wouldn't I go with the one that's like rated 500 pounds? Well, there's no free lunch here. These all have a fixed amount of power that they contain, and power is equal to work done over time. So guess what?

That one that has the really high load rating is also going to be incredibly slow because it is the amount of work done over time. You're doing it in a lot longer time, so then the work can be a lot higher. And likewise, on the other side of the spectrum, a really fast one just can't do as much work because it's doing it in a much shorter period of time. So that's something you want to pay attention to when you're specking. These is not only the stroke, which is how much they can move, but how fast they can move.

And then of course, you want to pay attention to the static load rating because if you're trying to lift something really heavy, but something's pushing against it, you want to make sure that it can handle those static forces as well as the dynamic ones. So I think that's about all I wanted to talk about with linear actuators. I think the last point to talk about is where to find them. These two were salvaged from an electric wheelchair. I do a lot of electric wheelchair salvaging because there's a lot of good parts in there.

Look for some that have a dead battery, dead charger, dead controller, and you can usually find a linear actuator in there. If they have some kind of tilting seat mechanism, usually the fancier ones do. Just keep in mind the voltage is almost always going to be 24 volts and they are going to be a weird form factor that might be really difficult to use. And typically, they have a very short stroke and they are very, very slow. So there's a lot of caveats to getting them free out of a wheelchair or really inexpensive out of a wheelchair.

But you can find them on eBay. There's a lot of sellers that have them on eBay, and there's a lot on Amazon. Just keep in mind, the ones on Amazon and eBay tend to not have any feedback. They're just two wires. Some of them do have feedback, but they tend to start getting kind of pricey.

And sometimes the load ratings are not really exactly what you're looking for and they have limited strokes, stuff like that. Also, you might want to check out Servo City. Servo City has a really nice selection of them, and I'm not just simply plugging them. They really do have a nice selection of linear actuators in all shapes and sizes. So it's at least worth a look to see what's available for your project.

As always, thanks for watching this very long and informative video on linear actuators. You can check out my Facebook page for all my little project updates and such. And down below there's a lot of links that you can check out. There's an Amazon link down below that. If you use and shop with Amazon using that link, you can give a little bit of a kickback to my channel to help support my projects and my videos.

As always, thanks for watching. See you next time.

The technical details of all the components of tracking systems would be beyond the scope of this course. It is important to understand though that additional components and more complexity, while improving efficiency of the solar panels and reflectors, add to the cost of the whole system and consume additional energy.

This following video (4:25) demonstrates some technical features of a single-axis tracking system:

Video: Renewable Energy: Single-Axis Tracker (4:24)

Credit: Snmsuaces. "Renewable Energy: Single-Axis Tracker [13]." YouTube. February 14, 2012.

Click here for a transcript of the Renewable Energy: Single-Axis Tracker video.

THOMAS JENKINS: Here we have an example of something that might be at more of a commercial application of photovoltaic systems. We have several photovoltaic panels. We have two sets, we have one type on this structure, we have another type on the structure behind it. Both are mounted on what's called one-axis trackers, in that there are electric motors which turn these panels such that they track the sun as it goes from the east to the west.

With this type of tracker, it's fairly sophisticated in that it's a computer-controlled tracker. There is a little computer in here that runs some very sort of mid-complexity algorithm that knows the latitude of your location, where you are-- Las Cruces, New Mexico, 32 degrees latitude-- and it knows the day of the year-- for example, January 28, day 28-- and it knows the time of the day-- 2:00.

With that information, it can predict exactly the angle of the sun, relative to east and west, and it knows to turn the tracker exactly that many degrees every day to point directly to the sun. This increases the efficiency or the amount of electricity that comes from the solar panels, but you have some additional complexity in your system. These are what's called active trackers, in that it requires electrical motors, it requires some mechanical components, some electrical components, and it tracks the sun, but you get more electricity from this type of system.

This system is a German design, and it's being tested here at SWTDI. Right next to it, we have a good bit of data collection that is brand new, very sophisticated, and it's connected via cell phone and land lines such that all the data-- which is being collected real time-- can be accessed through a cell phone from anywhere in the world. For example, at the headquarters of the German company, who's looking at the system design and the system components and seeing how they're interacting.

You can see on this structure here that we have a couple of instruments that are being used to characterize the sun's energy. These are called pyranometers. They are reading the amount of sunlight so we know how much energy is striking the surface. And, from that, we can see how much energy the panels are delivering to us and determine the efficiency of the panels. So a lot of instrumentation is going in this because this is an evaluation system, but this might be a system that might go into, for example, a desert environment over several acres that might be a large scale electrical production.

Tracking the sun, in some cases, is very important, especially on systems that use a new type of system with lenses, called Fresnel lenses that are used to concentrate the sun onto a smaller section of photovoltaic, so the total amount of photovoltaics that you need is smaller, but they produce the same amount of energy because you're concentrating the sunlight onto the cell. So we're looking at two different types of modules on the same structures, under the same ambient conditions, the same location, the same amount of sunlight, and we're comparing those, seeing how efficient they are relative to one another and relative to traditional solar photovoltaic systems.

PRESENTER: The preceding was a production of New Mexico State University. The views and opinions in this program are those of the author and do not necessarily represent the views and opinions of the NMSU Board of Regents.

Additional Reading

Journal paper: Mousazadeh, H. et al., A review of principle and sun-tracking methods for maximizing solar systems output, [14] Renewable and Sustainable Energy Reviews 13 (2009) 1800–1818.

Summary and Activities

In Lesson 3, we discussed the benefits of sun tracking for performance of the solar energy conversion systems. It is clear that although tracking helps to collect more solar radiation per square unit of solar receiver, the tracking systems may be complex and costly, and hence should be used only when benefits in terms of efficiency outweigh the expenses for extra energy and equipment. We reviewed the fundamentals of solar motion, and you should now be comfortable using the key equations to calculate the sun position at any time at any location on the earth. This lesson included description of different modes of tracking - single-axis and two axis - and gave you an opportunity to perform some basic calculations and work with available data on solar path. I hope you found the resources in this lesson useful and that, in the future, you will feel confident applying those calculation methods to the systems of your choice. Tracking certainly is a worthy technology when we look at the utility scale solar systems, as this technology provides an even more significant boost when scaled up. A number of companies are currently specialized in tracking technologies, constantly innovating and creating more and more robust systems for future solar plants.

The table below summarizes all activities that are due for this lesson. Some of those have been included in the body of the lesson, and this list simply repeats them for your reference.

Lesson 3 Assignments
Type	Description/Instructions
Reading	Complete all assigned reading for this lesson.
Yellowdig Discussion	Discussion "Tracking systems": Lesson 3 Search the Internet for commercially available tracking systems. If you are to choose such systems for your project (consider utility scale), which manufacturers / models would be your top 3 choices? Express your opinion in the Yellowdig community and check what other people find. Provide some technical justification to support your choice. Comment on other posts and provide your advice as you see fit.
Written Assignment	Problem set on sun position and tracking Please complete the Problem Set posted within this lesson (you can also download this problem set as a single document from Canvas module): Problem 3-1: Sun path calculation Problem 3-2: Two-axis tracker data Problem 3-3: Single-axis tracker data You can type your solutions or hand-write them and scan to a PDF file (just make sure that all is legible). Submit your work to the respective Dropbox in Lesson 3 Module.

References for Lesson 3

Barbose, G., Darghouth, N., Weaver, S., and Wiser, R., Tracking the Sun VI. An Historical Summary of the Installed Price of Photovoltaics in the United States from 1998 to 2012. US Department of Energy, July 2013.

Brownson, J.R.S., Solar Energy Conversion Systems, Elsevier, 2014.

Kaligirou, A, Solar Energy Engineering, Elsevier, 2014.

LINAK Group Inc., We Catch the Sun [15]. 2015.

Rockwell Automation, Solar Tracking Application [16], White Paper. 2011.

UO SRML - University of Oregon, Sun Radiation Monitoring Laboratory, Sun Path Chart Program, 2007.

Wikipedia [3]