Real World Suntracking Solar Arrays

While this is certainly a specialty area related to solar arrays, sun tracking systems do represent a significant investment in engineering and cost. The intended return of "more consistent" electrical power during daylight hours as compared with a fixed solar array must be worthwhile.

Like their solar cell counterpart, sun tracking system's initial development dates back to the 1950s where satellites needed to keep their solar panels pointed at the sun while they orbited the earth. It was only by this means that the satellite could maintain its electronic systems in an uninterrupted manner.

Figure 4-1:

Satellite Sun Panel Solar Tracking Array

Image Courtesy NASA/JPL-Caltech

Figure 4-1:

Satellite Sun Panel Solar Tracking Array

Image Courtesy NASA/JPL-Caltech

With our country's space program fully funded at the time, little thought was given to the expense involved in developing and deploying such systems. This is still true today when it comes to purely scientific or military space-based systems, including the international space station, which continues to be built at the time of this writing.

The International Space Station's eight-part solar arrays will be 112 ft long by 39 ft wide. With all of the arrays installed, the complete Space Station will be large enough to cover a football field. Because the International Space Station (ISS) needs very high power levels, the solar arrays will require more than 250,000 silicon solar cells. The solar cells provide the ISS with 120 VDC which will generate 110 kW (kilowatts) total power, about as much as 55 houses would typically use. The solar hardware is provided by the U.S. and Russia.

Figure 4-2: The International Space Station

Photo Courtesy of NASA

Military and government spending for the development of high-risk experimental systems such as a sun tracker often pays off, both economically and scientifically, when commercial systems begin to use the same technology. Essentially, the government pays up front for the development of systems and technology that are beyond the budgets of even the most profitable commercial companies. The payback comes when commercial companies get enough technology from government research and development to continue to advance the technology on their own. Here the cycle becomes complete with commercial companies selling back their much-improved technology to the government and military. This was certainly the case in terms of government-funded programs such as the transistor, the laser and early communications satellites. And it is also the case for commercial sun trackers.

Figure 4-3: Sun Trackers - 1 kW system (Canary Islands)

Photo Courtesy of Poulek-Solar, Co. Ltd.

Many commercial companies now manufacture sun tracking systems for medium to large solar arrays, and they come in a wide variety of configurations. By adding single-axis tracking to a solar array, electrical output is increased by about 20 percent as compared to a non-tracking solar array. By moving to two-axis tracking, an increase of 10 percent over a single-axis tracker and about 30 percent over a fixed array can be achieved.

Single-Axis Tracking Systems

These have a single left-right axis on which the solar array rotates. This is the axis. This is the least complicated tracking system with a fairly simple motor and control system that turns the solar array from east to west each day. This keeps the array pointed in a close approximation to the sun.

Dual-Axis Tracking Systems

These use both left-right and up-down axes to position the solar array. Over the course of a year, the dual axis system will produce the most power, since the elevation of the sun changes with the seasons. At the same time, the tradeoff is that it is far more expensive and complicated to design, construct and maintain.

Passive Trackers

These trackers follow the sun without having any motors to drive them. The trackers are carefully balanced. The tubes on each side of the tracker are filled with a gas. As the sun heats the gas on one side, the gas expands and flows into the other side of the tracker. This shifts the delicate balance, and the solar panels automatically tilt toward the sun.

The Zomeworks tracker has no motor. It is a passive tracker in which the shifting weight of DuPont FreonĀ® refrigerant tips the tracker to follow the sun. The Freon moves to the cooler of two side canisters, which because of the position of the shades, causes the rack to follow the sun. This simple yet elegant and cost-effective system demonstrates that even modest solar panel installations can benefit from commercial sun trackers, as long as the increased efficiencies justify the added cost.

Figure 4-4:

Zomeworks Corp. Sun Tracker

Figure 4-4:

Zomeworks Corp. Sun Tracker

Photo Courtesy of Zomeworks

Trackers with Parabolic Panels

Pictured below are two examples of sun trackers with parabolic panels that keep the sun's rays concentrated at a central point. Figure 4-5 shows the SHEC solar concentrator unit that uses a system of mirrors to concentrate the sun's energy much like a satellite dish concentrates data frequencies to a central receiver. Called the SHEC-Labs Hydrogen Generator, this device uses a proprietary catalyst, a new solar collection technology and solar tracking plus process software developed by the company to produce hydrogen from natural gas, or by electrolyzing water at temperatures of 800 degrees Celsius (1472 degrees Fahrenheit). The solar technology shown here allows for virtually pollution-free manufacturing of hydrogen.

Figure 4-5:

SHEC-Labs Hydrogen Generator

Image Courtesy SolarAcess.com

Figure 4-5:

SHEC-Labs Hydrogen Generator

Image Courtesy SolarAcess.com

However, SHEC isn't the only company with the same goal in mind either. The Stirling Energy Systems (SES) 25 kW solar energy concentrator dish in Figure 4-6 also uses sun tracking as a means to keep its solar array always aimed directly at the sun. So whether the answer to mass-produced hydrogen from the sun is solved by SHEC, the SES dish, or some other approach altogether, it's clear that hydrogen has become the next major frontier for energy experimentation. Sun trackers will be at the heart of any such system.

Figure 4-6:

The Stirling Energy Systems Solar Dish

Image Courtesy SolarAcess.com

Figure 4-6:

The Stirling Energy Systems Solar Dish

Image Courtesy SolarAcess.com

Detriments to Tracking

Tracking adds cost and mechanical fallibility. On larger commercial systems, the increased energy output more than offsets the added costs. However, on small rooftop systems the added costs typically outweigh the benefits. Fixed panel systems can be the best solution for some applications, like the one pictured below.

Figure 4-7 uses two solar panels, rather than using a tracking device, to power a signal light in Folsom, CA. The smaller panel faces south where the sun's energy is strongest, and the larger panel faces west. As the understanding of solar panels increases we will continue to see more and more real world applications, some simple and some complex, but each designed to meet the economic realities of the situation.

Figure 4-7

Fixed-panel solar system for a traffic light.

Photo by Rich Allred

Figure 4-7 uses two solar panels, rather than using a tracking device, to power a signal light in Folsom, CA. The smaller panel faces south where the sun's energy is strongest, and the larger panel faces west. As the understanding of solar panels increases we will continue to see more and more real world applications, some simple and some complex, but each designed to meet the economic realities of the situation.

Making the Decision

The final question is usually "What is the cost of adding a sun-tracking device to my solar panel?" There are actually two costs to consider - one is the monetary cost and the other involves an energy-related cost.

The monetary cost involves the money needed to design, build and maintain the sun-tracking device. In a commercial installation these costs must be justified by a greater return on investment in the solar panel "system," meaning the solar panel itself plus the sun-tracker. If the added cost of a sun-tracker cannot be justified by a better return on investment (ROI) as compared to a fixed solar panel installation, the sun-tracker will not be constructed.

Then there are the energy related costs. Since the sun-tracking equipment must get its power from somewhere, it makes sense to first determine if the additional power derived from the solar panels tracking the sun will actually provide MORE power than is used by the sun tracking device itself. If not, the sun-tracker will still not be considered.

These last two paragraphs point out a fundamental fact of "engineering" life. That is, if you're working for a company that is in business to make a profit (as most are) then any project, large or small, done by the company must take into account both engineering AND economic considerations. So if you're thinking about a technical career you should bear this in mind, since you will most likely be asked from time to time to justify why you should, or shouldn't, be engaged in certain technical activities.

But since this experiment is "not for profit" and "all for fun and enlightenment", let's get going with building our servo-driven sun tracker, and "hang the costs!"

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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