Chasing the Sun. Siemens' latest controller technology helps Circadian Solar accelerate innovative renewable energy system towards commercial launch.
08/03/2011 Siemens Industry Automation & Drive Technologies
The IssueCircadian Solar is at the forefront of developing concentrator photovoltaic (CPV) systems, one of the most exciting emerging technologies in the renewable energy sector.
Like the more familiar photovoltaic (PV) systems used around the world, CPV converts the sun's light into energy. It differs significantly by concentrating sunlight onto its photovoltaic material via a Fresnel lens, guided by a solar tracker that follows the sun's path.
Combined with the use of advanced triple junction solar cells instead of the usual silicon-based single junction cells, this gives Circadian's CPV a conversion efficiency up to three times that of conventional PV in areas of high sunlight.
The accuracy of the solar tracker is fundamental. The Coventry, UK-based company set out to design "from a blank sheet of paper" a tracker that could meet its exacting requirements, explained Stuart Alexander, Senior Electronics Engineer.
Circadian set a goal of tracking the sun to +/- 0.1 degree accuracy. "Over a 30 metre square array in the wind that is a real challenge," said Alexander.
Accuracy was not the only design imperative. Its tracker must operate reliably in the hot, remote 'sunbelt' areas between the Tropics where CPV will be deployed. Its technology must also be scalable to support the distributed control systems needed to operate large-scale solar parks.
The Solution
Circadian selected the new SIMATIC S7-1200 series of controllers from Siemens Industry Automation and Drive Technologies (IA&DT) to form the heart of its tracker control system.
From summer 2009, Circadian worked closely with Siemens to develop a demonstrator system using the S7-1200 controller.
This process included application development carried out at Siemens in Germany by specialists with experience of working with the renewable energy industry. By that autumn, the system was ready for its first test and it exceeded Circadian's ambitious +/- 0.1 degree target.
Siemens' S7-1200 fitted Circadian's 'whole-system' design philosophy, which demands that all components play a part in meeting the overall goals of maximum efficiency and reliability at lowest cost.
For example, the tight margins of the energy industry mean issues such as warranty costs and component downtime will be key factors in commercial CPV deployment.
Alexander said Siemens' long track record in industrial controllers gave Circadian confidence that its system would perform to the standard required, reinforced by the company's open-handed approach. "Siemens provided us with all reliability and quality data that goes with their products, which not all suppliers seemed able to do."
By selecting the S7-1200 series of controllers, the newest on the market, Circadian set out to future-proof its tracker control system to the greatest extent possible.
Alexander explained that integrated TCP/IP networking through PROFINET makes the S7-1200 ideal for use as part of a distributed control system for a large-scale solar park. Here, each S7-1200 will carry out the main control functions for its own tracker while communicating with a master station that provides a supervisory control function, receiving diagnostic information from all the units and, for example, measuring wind speed to determine when the trackers should stow for safety reasons.
Native communication over TCP/IP networks gives Circadian visibility of its systems wherever they are in the world. "A simple VPN connection allows me to monitor and control any tracker from my desk in Coventry," said Alexander.
The Benefits
The S7-1200 played a key role in allowing Circadian Solar to quickly meet its highly demanding design target for its solar tracker. As a small company of around 20 people, it was also able to tap into Siemens' existing expertise in developing products specifically for the renewable energy sector. Both factors significantly accelerated product development.
Siemens' technology gave Circadian a level of operational control and visibility that would have been impossible with an off-the-shelf 'black box' controller, which would also have limited its future flexibility. "The S7-1200 is an open platform that we can use to develop new features as and when required," said Alexander.
Circadian also rejected the option taken by some others in the sector of developing its own custom control system. "We do not have the resources to deal with issues such as hardware obsolescence and international spares and service personnel," said Alexander. "With the S7-1200 we have all of these services provided, but we still have an open development platform to build our control IP into."
Circadian Solar's trackers are now undergoing testing in the Mediterranean and in the Middle East as the company prepares to move into a commercial phase that will see it bring clean, renewable energy to areas of the world where it is desperately needed.
Simon Fairbanks, Manufacturing Account Manager for Siemens IA&DT, said Circadian exemplifies the approach that will help renewable energy fulfil its potential. "It is driven by innovative technology and engineering excellence to achieve its goals in the hugely important tasks of supplying renewable energy and helping to combat climate change. Siemens is also at the forefront of meeting those goals and working with Circadian has been a true partnership."
For more information on Circadian Solar please visit www.circadiansolar.com or contact Richard Sammut on 02476 323 211 / richard.sammut@circadiansolar.com
For further information, please visit: www.siemens.co.uk/automation
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