Increasing Solar Power Yield by 20 to 40%
Software positioning solar panels for utmost efficiency.
Reliance on foreign energy sources and the drive to reduce greenhouse gas emissions are combining to make solar energy a viable, attractive energy source in the US. Due to federal and state government mandates to achieve significantly higher levels of energy from renewable energy sources, solar energy is expected to achieve rapid growth rates in the coming years. Critical to maximizing efficiencies with solar panels, and thus making solar economical when compared to traditional fossil fuels, is the positioning of the panels. Since the sun moves across the sky through the day the panels need to follow the sun and be optimally positioned throughout the day. When properly positioned efficiencies can increase dramatically allowing solar to reach parity for electrical generation as far as cost.
Solar is an increasingly attractive source of clean energy since it is renewable, pollution free, and in certain technologies, requires no water source. There are 2 primary types of solar power being considered for mass deployment, photovoltaic (PV) and concentrated solar power (CSP). Photovoltaic technology is expected to be the major technology deployed because, as opposed to CSP, the panels can be placed anywhere and as mentioned require no water. CSP requires significant amounts of water. Since water sources are not abundant in the large solar fields that are required to make CSP viable, this is a significant issue for this technology.
PV solar plants range in sizes as far as output. Some are as large as 25 Megawatt requiring thousands of large solar panels. Tracking systems are deployed to move the huge arrays so the cells can gather the most sunlight. The benefits of precise positioning are substantial, ranging from a 20 to 40% improvement over fixed array structures. The reflective heads on the huge panels tilt towards the sky maintaining 90 degrees to the sun’s rays as they track the sun through its 240 degrees of movement every day. The tracking systems utilize a software algorithm inside an automation controller to know where to position the panels. The level of precision is extremely tight, most programs account for minute changes in the earth’s rotation. The programs must also account for the time of year since the sun changes its position in the sky as the seasons change. The software accommodates these variables with remarkable precision.
The algorithm for solar tracking was completed by the National Renewable Energy Laboratory (NREL) written for the U.S. Department of Energy. It calculates the solar zenith and azimuth angles with precision of greater than ±0.0003 degrees/ inch. These calculations include values for longitude, latitude, elevation, pressure, temperature, time and atmospheric refraction. The latter having a typical value of 0.5667° for the atmospheric refraction at sunrise and sunset times.
Though the solar positioning calculations are complex and exacting, Siemens has implemented a solar tracking control library that has a small software footprint to reduce processing requirements as well as memory costs. The implemented NREL calculation software requires a scant 13.6 Kbytes of working memory and a required load memory of only 187 Kbytes.
The mechanical controls constantly adjust the panels’ position to account for the minute changes that occur in 24 hours. Systems designed around Siemens Automation hardware let engineers meet these exacting demands while meeting the stringent economic factors needed for this emerging technology to compete with conventional power sources.
In a typical configuration, each solar tracker is controlled by a SIMATIC S7-1200. This automation platform provides the 64-bit arithmetic accuracy needed by the NREL astronomical algorithm. The Siemens solar tracking control blocks implementing the NREL SPA algorithm are executed with a cycle time of approximately 170 milliseconds.
These controllers provide output signals to support a number of different types of motors. Brushless DC motors and Induction AC motors, in both a native mode and with frequency converters, are common. Servomotor drive applications also provide the accuracy needed to respond to the minute changes in the sun’s relative position. Gear drives like the TD 30 from Siemens Gear Motors also address the requirements of this field.
In a large solar plant field networks, typically Ethernet, are put in to monitor the many panels and report on issues or problems to a central control room. They carry feedback for the many signals that determine proper positioning along with diagnostics that constantly check the components that make up the arrays. With a built-in Ethernet port, the S7-1200 supports hardwired (cable and/or fiber optics) or wireless field networking to allow for Ethernet deployment throughout a solar farm, maintaining a single technology to simplify communications, operation and maintenance over the long lifetime of a power plant.
The human machine interface is another critical aspect of the design. Solar farms can cover several hundred acres. Operators must be able to quickly and easily determine what is going on and where issues may be arising. The HMI also provides a way for operators to examine subsystems when necessary, letting them drill down with layered menus. The diagnostic system that works with the HMI constantly monitors motors, solar cells and other equipment. Diagnostic systems are critical in large solar farms for quickly diagnosing problems and hopefully preventing issues designed to minimize the false positives that push maintenance costs skywards.
With each individual solar tracker being controlled by a local S7-1200, each tracker is constantly positioned to maximize the power from the sun. Using the ubiquitous Ethernet scheme also makes it simpler to maintain time synchronization, react to weather conditions, such as high winds, and provide diagnostics and alarming for efficient operation and field maintenance. This allows for the optimal farming of solar energy to be fed into utility companies’ systems for distribution of power throughout the grid.
There’s enormous potential for companies that provide components and install and maintain solar systems. Global installations of solar photovoltaic reached a record high of 5.95 Gigawatts in 2008, representing growth of 110% over the previous year. The growth is further emphasized by a comparison to 2001, when just under 350 Megawatts of solar equipment was sold.
The photovoltaic solar industry generates around $10 billion in revenues that include the sale of solar modules, related equipment and installation. Europe accounted for 82% of global demand in 2008, when the U.S. market grew to 357 Megawatts. However with renewed commitment to use this abundant renewable energy source growth rates in the US will likely exceed that in Europe and might eventually displace Europe as the leading producer of solar energy.
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Closed form solutions are fine, but isn’t it sufficient to continuously adjust azimuth and elevation angles for max output?
Já não esta na hora de as autoridades brasileiras desenvolverem normas e leis incentivando a utilização das energias limpas , verdes , como a solar e a eólica?
Em uma usina hidroelétrica e uma usina nuclear os custos de manutenção e operação são imensos , quando comparados aos custos de projeto e execução de uma usina eólica e solar .Então porque as autoridades não se mexem ?
Atenciosamente ,
Eng.Ricardo Pantoja