1/9/2012, Düsseldorf / Germany

 

Terostat MS from Henkel as an adhesive solution for collectors in solar thermal power plants

 
 
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New ideas from Novatec Solar for the CSP industry

Fossil fuels are finite, but the sun’s energy is inexhaustible – all of our planet’s energy resources in the form of oil, coal and natural gas add up to just 20 days of sunlight. Energy from the sun is not only a dependable long-term option but clean as well, and that is why it makes sense as an alternative to fossil fuels. This is the credo of Novatec Solar. Headquartered in Karlsruhe, Germany, this company uses its own patented concentrated solar thermal technology to operate the first commercial power plant of this kind. Since 2006, Novatec and Henkel have been jointly developing a high-tech adhesive solution for this application. 

In the south of Spain, covering a total area of 18,000 square meters, two rows of mirrors, each with 16 units arranged in parallel, stretch across the plain: The pilot plant Puerto Errado 1 (PE1) is the first commercial solar power facility to use the solar-thermal steam generator Nova-1 from Novatec Solar. A further large-scale solar farm, Puerto Errado 2 (PE2), has been under construction since 2010.

The innovative design of Nova-1 is based on linear Fresnel collector technology. Sheet glass mirrors – bonded to steel frames with Henkel’s Terostat MS adhesive – are positioned so that the reflected sunlight is concentrated into a single beam. Above the banks of mirrors is a linear receiver installed at a height of 7.4 meters. In this receiver, the concentrated solar radiation is used to heat water, turning it instantaneously into steam that drives a turbine. The steam is then cooled back to the liquid state and the water is recirculated through the receiver to generate more steam. The electricity produced in this way has been fed into the local grid since March 2009. Puerto Errado 1 was thus the first solar-thermal power plant in the world with direct steam generation. Unlike other existing power plants of this kind, this facility is used almost exclusively for commercial purposes.

Good sunlight capturing efficiency is an essential prerequisite in such a plant. The mirrors are therefore continuously repositioned, tracking the sun's course so that the beams of all mirror elements will be concentrated in the receiver at all times. Maintaining the curvature of the mirrors on their steel frames demands an adhesive whose elasticity is capable of compensating for the different temperature expansion rates of the substrates – steel and mirror glass – without in any way affecting the accurate alignment of the mirrors with the receiver. The product Terostat MS from Henkel meets this requirement.
 
Fast production with Terostat MS
“We explained to Henkel exactly what we wanted to do and they teamed up with us to find a way of putting this into practice. The chosen solution was the Terostat MS adhesive – which delivers truly outstanding performance,” says Gerhard Hautmann, management board member and co-founder of Novatec Solar, who designed the entire supply chain and the automated manufacturing process for the mirrors. The ideas for building such solar-thermal power plants were first discussed in 2005 on the basis of a dissertation by Max Mertins, board member for research and development at Novatec Solar. During a cycling tour through the Black Forest in 2005, Gerhard Hautmann and Martin Selig, board member for market and product development at Novatec Solar, developed the initial approaches that ultimately led to the founding of Novatec Solar in 2006.
 
Terostat MS, based on modified silane polymers, has a crucial role to play during the manufacturing process, since the adhesive must maintain the curvature of the mirror. The bonding process takes ten minutes per module. Within this short time span, the adhesive is first applied to the steel frame automatically. Then the sheet glass mirrors are fed into the production line and pressed into the adhesive. Terostat MS has to develop its full bonding strength as fast as possible in order to hold the mirrors on the steel frames with the correct curvature. “We knew right from the beginning that the success of our design depended critically on the choice of adhesive,” says Hautmann.

Silane-modified polymers last the longest
In addition to fast processing, aging resistance was another major challenge, “because these bonds have to hold for twenty-five years. That was a key factor in our requirements profile for the adhesive,” explains Hautmann. “Replacing the mirrors more frequently than that would simply not be economical.”

In a study on the long-term behavior of adhesives, which Hautmann had undertaken jointly with the Münster University of Applied Sciences and published in 2007, modified silane polymers scored highly in terms of durability of the bond and resistance to corrosion creep. These adhesives also showed the best performance in climate cycling tests. The two-component version of Terostat MS is one of this class of adhesives. It features a high initial tack and rapidly reaches full bonding strength. The adhesive is used to build the steam generators.

Elastic and heat resistant
The non-hazardous Terostat MS adhesives also show excellent weathering performance and withstand extreme temperatures in both summer and winter, making them perfect for use in regions like southern Spain where temperatures can range between minus 20 and plus 45 degrees Celsius. “A new challenge is use in areas close to the sea, where the adhesive will have to demonstrate that it can also withstand the higher salt levels in the air,” says Hautmann.

Solar thermal power contributes to sustainable development
The very low water consumption of these solar power plants is a huge advantage in areas such as the dry steppes of southern Spain. The use of air condensers means that no cooling water is required. This reduces the burden on natural resources and also speeds up permit approval procedures in regions where water is scarce.  “In the meantime, we can compete with oil as an energy source,” says Hautmann, championing the use of solar thermal technology. Plans are already in the pipeline to build more of these solar power plants that help to conserve our planet’s natural resources, especially in hot and arid regions such as exist in South Africa, Australia and the USA.

By the end of 2011, construction of the second power plant, PE2, will have been completed. The 30-megawatt plant will be the world’s largest linear Fresnel solar thermal power plant and will cover an area of 500,000 square meters. PE2 will produce around 50 gigawatt hours of electricity per year, enough to meet the needs of approximately 12,000 households. And its 28 rows of mirrors will also be bonded to their steel frames using Terostat MS adhesives from Henkel as a result of their excellent performance in the first commercial solar thermal plant PE1.

At the SolarPACES conference, Novatec Solar was honored with the Technical Achievement Award for its development and implementation of Fresnel technology in solar power plants.

Henkel AG & Co. KGaA