German coating manufacturer Almeco Solar has designed a new absorber tube: Small in size with a working temperature around 200 °C and no vacuum. The company wants to beat both the performance and the current price of black chrome absorber tubes. The solution is called Tinox tube 2.0 and has been designed for temperatures around 200 °C. Almeco Solar presented the non-evacuated tube at the Intersolar Europe in Munich, Germany, in the middle of June.
Almeco Solar has developed an absorber tube for linear concentrating process heat collectors, e.g., parabolic troughs or Fresnel collectors with a standard diameter of 35 mm and a maximum tube length of 6 m. The tube is extruded from a special alloy of aluminium by German supplier Standard Metallwerke. The alloy is resistant to corrosion in combination with water- and oil-based heat transfer fluids. Almeco Solar is using standard coating processes, as the coating is not done on the tube, but on a flat aluminium sheet, which is then wrapped around the tube. The edges of the sheet are attached by laser welding, but Almeco does not reveal how it achieves the close bond between the sheet and the tube – the bond necessary to transfer the heat.
Thermal emission at 200 °C is 6 % +/- 2 %. “This is significantly better than the black chrome tubes,” says Rudi Gleich, International Business Manager at Almeco Solar. Because the tube has no vacuum insulation, costs can be kept fairly low. Gleich does not say a number, but prefers to put it this way: “We can offer our tubes cheaper than the current prices of black chrome tubes.”
Currently, Almeco is testing the tube at their production sites in Atlanta, USA, Bernburg, Germany, and Milano, Italy. Official tests are still running at the SPF Institute for Solar Technology, Switzerland, and the German Institute for Thermodynamics and Thermal Process Engineering (ITW). “So far, the results have corresponded well to our own tests, but we have not had enough sun this year for any definite data.”
Still, there are some improvements left to be done. For example, the tube currently needs to be welded to the pipes. “Of course, this is only a preliminary solution. In the end, the parts will be joined using either screws or plug connections,” Gleich says.
As the process heat market is still in its infancy, customer preferences have not been revealed yet. As a consequence, Almeco Solar is going after both standardised and customised solutions, searching for cost advantages and flexibility at the same time. “We will offer the tube as a standardised product, but customer-specific lengths will be available as well,” the International Business Manager says.
Almeco’s mid-term aim is to develop and produce more and more components for solar process heat collectors. In addition to the mirrors, which have already been part of the company’s product range under the brand name Vega, this might also include complete collectors and even support structures and other components. “When it comes to the collector, the first model would probably be a parabolic trough, but Fresnel collectors might be possible, too,” Gleich says.
But while the products are still subject to modifications and will depend on customer demand, the mission is clear. “Our goal is a high degree of standardisation and automation,” Gleich says. “Of course, this depends on the market. But to overcome the chicken-and-egg dilemma, we are willing to take the first step, as we can see a realistic market potential.”
This year, Tinox celebrates its 20th anniversary: In 1993, a group of students had developed the Tinox coating at the Technical University of Munich and measured a temperature of 350 °C in a flat plate collector with a Tinox-coated absorber. One year later, they founded Tinox. In 2008, the company started producing mirrors for concentrating solar plants in Bernburg, in cooperation with Italian company Almeco, under the name Almeco-Tinox. In 2010, the Almeco Group bought all shares of Almeco-Tinox and since 2012, the name of the solar business has been Almeco Solar.
Almeco Solar’s new absorber tube:
Almeco Solar’s mirror products:
Absorbers based on black chrome by Energie Solaire, Switzerland: