Solar-thermal energy conversion

This term refers to the transformation of solar energy into heat. This primarily involves the use of solar collectors, which are available in two versions: flat collectors and vacuum tube collectors.

Dr. Laure Plasmatechnologie GmbH has been working on increasing the efficiency of vacuum tube collectors for years. Two concepts are being pursued here:

  • the application of anti-reflection coatings to reduce reflection losses
  • the improvement of corrosion protection for aluminium reflectors

Interior coating system for solar tubes

This system serves to apply an anti-reflection coating on the inner surface of the cladding tube of vacuum collector pipes for solar hot water production. The coating reduces the reflection of sunlight on the glass surfaces (similar to the conventional “de-reflection” of lenses for glasses and optical instruments), thus making the solar collectors more efficient.

How the inner suface coating system works:

Once the tubes have been inserted and the start button has been pushed, the tubes are contacted with a pneumatic coupling nozzle. Two inflatable gaskets seal off the tube to keep out ambient air. Once the air has been pumped out of the tube, oxygen and the silicon alcohol known as hexamethyldisiloxane (HMDSO, chemical empirical formula: C6H18OSi2) is fed in and then a plasma is ignited inside the glass tube using a high-frequency generator (see Figure 1 on the right). This reacts with the mixture of HMDSO and oxygen, creating a silicon dioxide coating on the inside of the tube. Oxygen and HMDSO are all the interior coating system consumes. And small quantities of carbon-hydrogen compounds and CO2 are all the waste it produces.

The interior coating system is equipped with a built-in quality assurance and labelling system. During the labelling process, the date, serial number and result of the online control measurement is embossed on the tube. If any flaws appear, the machine operator receives instructions on how to correct the problem.

The coating machine also has an internet connection. If a flaw is detected, an E-mail is automatically sent to a predefined address. The integrated hardware also enables remote maintenance. This way, the pilot series could be produced in China by Chinese personnel.

Inductive reflector plasma coating system

This system is used for applying coatings on complex three-dimensional components.

How the inductive reflector plasma coating system works:

The components are placed lot-by-lot into a special loading module and fed into the vacuum chamber with a lifting device. After the chamber has been evacuated, a proprietary Dr. Laure Plasmatechnologie GmbH transport system feeds the components through the plasma one-by-one and coats them.

Once they have been fed through the coating zone, the components are stacked in a storage module. The chamber is then ventilated and the module is automatically removed and unloaded on a special device. The loading module is then refilled and the coating cycle begins anew. The coating process takes place in plasma which is heated through induction over a large area. The layers are structured by the plasma gas reacting with a suitable precursor. This makes it possible to produce SiO2 coatings made of HMDSO in O2 plasma, to name but one example. Various test procedures have demonstrated that this SiO2 coating provides very good corrosion protection on sheet aluminium.

During a pilot production phase, roughly 2,500 metal sheets were coated with a 300nm thick layer of SiO2 at a feed rate of 50mm per second. This is equivalent to coating an area of 108m² per hour.
This process is currently being expanded for roll-to-roll coatings for aluminium coils.

Solar tube coating system

This system is used to apply an anti-reflection coating on the outside of vacuum collector pipes.

How the solar tube coating system works:

The tubes are placed in pairs upon the preprocessing module, where a proprietary Dr. Laure Plasmatechnologie GmbH transport system takes them to the prechamber.
The prechamber is then evacuated to the pressure level of the process chamber and the tubes run into the coating chamber once the process gate is opened. At the same time the tubes are undergoing the coating process, two new ones can already be fed in.

The coating is applied using Ar-O2-HMDSO plasma. An arc plasma generator is used to produce this kind of plasma. The plasma jet is used to transport the precursor to the Work piece. The coating process is permanently monitored by a plasma spectrometer.

An after chamber is used to discharge the tubes from the system, and a cleaning unit is located immediately on the other side of the afterchamber to clean off the loose SiO2 particles sticking to the tubes.
The system is currently capable of improving transmission by 2.5% points. The average tube throughput rate is 180 units per hour. More than 170,000 solar collector tubes have been coated at the Dr. Laure Plasmatechnologie GmbH development centre since June, 2012. This coating makes the resulting solar collector one of the most efficient ones on the market.