We collected frequently asked questions about the solar thermal in our FAQ catalog. We devided the questions into different sections: general questions, installation and tubes. We are driven to
keep this site up to date at all time. If your specific question couldn't be answered, you can always message us personally via email or give us a call, whatever is more convenient for you. We
are happy to assist you in any way.
You can find general questions about our solar plants and AKOTEC products here. Before you buy a solar thermal plant, some questions occur, which have to be answered. Because of that, we have
collected those frequently asked questions and answered them beforehand. Nevertheless, we are happy to assist you personally, if you still need our help. If you have questions, which you couldn't
find down here, please feel free to contact us at any time. We are happy you are interested in our products.
Where can I purchase AKOTEC collectors?
Please do not hesitate to contact us and fill out the planning sheet. We will forward you to our partners.
Which different sizes are available?
We can offer Solar Keymark certificated collectors with 5, 10, 20 and 30 tubes.
Which medium flows through the collectors?
A water glycol mixture flows through the collectors and serves as a heat transfer medium. This fluid does not freeze up to a certain temperature.
Why should I use the antifreeze mixture by AKOTEC?
Our solar fluid VT51 contains corrosion inhibitors, which protect the plant. And because our sealing material is tested with that exact antrifreeze mixture, we guarantee a 20 years
manufacturer's warranty when using our solar fluid.
Is it possible to use a low-cost antifreeze fluid?
No, it is not possible because the AKOTEC antifreeze fluid is a highly temperature resistant glycol. The entitlement to the warranty would be cancelled when using another fluid.
Is it possible to operate the collectors with water?
When operating the collectors with water, the water must be prepared, decalcified and desalinated. Furthermore, a closed circuit must be existent and not an open drain back.
What is the freezing and faltering point of the ice regarding the antifreeze mixture.
Up to a temperature of -28°C, the heat transfer fluid is liquid. From the freezing point of -35°C, the antifreeze mixture changes to the solid state of aggregation.
What are direct flow and heat pipe collectors? Where is the difference?
The main difference is the tube. As the name suggests, the Direct Flow tube is flowed through directly by the heat transfer medium. Only the manifold of the Heat Pipe, however, is
flowed through by the fluid. The tube has its own circuit. The Direct Flow collector has various mounting options: pitched roof, flat roof, facade and balcony, elevation. When
mounting, the Heat Pipe mind an angle between 5 °-75 ° and vertical tube position. The collectors must be assembled elevated within that angle or on a pitched roof only.
How is the performance during the winter time?
The collectors produce yields even during the winter time and in diffuse light. This is due to the inner pipe system which is 100 % vacuum isolated. The vacuum tube has no heat loss
and does not cool down in contrary to common flat collectors.
Do AkoTec collectors overheat?
An overheating can be avoided through a professional system planning and a sufficiently dimensioned storage tank. We recommend for systems with an irregular heat consumption (regular
heat consumption: process heat, pool heating) and especially for private applications the Heat Pipe collectors. They possess an overheating protection, optionally at 100 °C or 160 °C
depending on the product version.
What happens with surplus energy?
Either you choose the Heat Pipe with the automatically shut down function or you have to plan a big dimensioned storage tank for saving the surplus energy.
Do building insurances include hail damages?
AKOTEC collectors are hail tested. Please contact your insurance agent.
How are the flow temperatures?
The collectors reach up to 120 °C under optimum sun radiation.
Do the tubes pollute?
No, the tubes are coated with a nano powder silicon dioxide and repel dirt.
When do the collectors begin to work?
The vacuum tube collectors produce yields even in diffuse sun light. Yields are generated from a sun radiation of 250 Watt.
Are vacuum tube collectors suitable for upgrading a single-family house?
AKOTEC collectors suite for upgrading existing heating systems as well as supporting conventional heating systems.
How is the efficiency factor of AkoTec full vacuum tube collectors in comparison to flat collectors?
At the zero point, the efficiency factors are almost equally. More important is a height of the efficiency factor at the operating point. At an average temperature of 80 °C the
efficiency factor of flat collectors amount 30 %. The AKOTEC full vacuum tube collectors have with 55 % a significantly higher performance. (Get to know more about this topic in our
comparison of the efficiency factors!)
Is it recommended to pump the chlorine water from a pool heater directly through the collectors?
No, the copper of the manifold may be damaged by chlorine content and corrodes faster. We recommend the use of swimming pool heat exchangers to prevent corrosion.
Our full vacuum tubes are unique in the market, regarding their system and the way they are manufactured. They are 100% made in Germany and our replacement tubes fit into almost every solar plant
from other manufacturers. We have collected the most important facts and information about our tubes, so that you get a perfect first overview. If you have any additional questions, or want to
talk about a specific solar plant right away, please feel free to contact us. We are happy to help you!
How is the performance of one tube?
The tubes with one side coating have a performance of 80 Watt (df) and 75 Watt (hp) (data from Narva). In connection with a reflecting area the double coated tubes can generate up to
110 Watt performance.
Which tube types are available?
As the name suggests, the Direct Flow tube is flowed through directly by the heat transfer medium. Only the manifold of the Heat Pipe, however, is flowed through by the fluid. The
tube has its own circuit. The Direct Flow collector is very versatile in relation to its mounting options. Everything is possible – from pitched roof, to flat roof mounting, to facade
or balcony mounting up to elevation. Please mind that the Heat Pipe must be elevated between an angle of 5 ° – 75 °. Therefore the collectors can only be assembled elevated in that
angle or on a pitched roof. The tubes are available on request in the following lengths: 0,8 m, 1,5 m and 1,75 m. The standard length is 2m.
Does the tube lose its vacuum?
No, as long as the tube is not damaged it does not lose its vacuum and 25 years of stable energy yields are ensured.
What is the difference between Standard and Power Tubes?
In contrary to standard tubes, power tubes are double coated and used for reflector collectors or if the collector is mounted on a reflecting area such as a bright facade or a tin. It
is possible to generate up to 40 % more energy yields by using the reflections of the sunlight.
What is the absorber and the coating made of?
The absorber plate is made of copper and coated with Titan-Nitrit-Oxyd. In fact there are multiple layers. See (TINOX energy Cu):
How is it ensured that the vacuum stays durably?
This is ensured by the innovative and sturdy NARVA glass-to-metal connection which does not punish the glass through movements. Therefore the glass-to-metal connection resists to
powerful axial and transverse forces effortlessly. The NARVA solution is protected by patent law: http://www.narva-solar.de/de/technologie/glas_metall.html
What is the difference between Sydney tubes and full vacuum tubes?
The Sydney tubes have a glass tube as protection of the inner tubing. Therefore the tubing system is in the atmosphere and ages. The Power decreases already after 2 years. The tubing
system of the NARVA tube is vacuum isolated. Materials do not age inside of vacuum. This is why our collectors generate stable energy yields over 25 years.
Is a reflector included in the scope of delivery of collectors and power tubes?
Reflectors are not included in the scope of delivery, because the reflection of a white wall, a glaced tiled roof or a zinc tin roof are enough. The reflector has to be installed on
We get a lot of questions regarding the installation of our solar plants. And even though we try to find a solution for every problem, when it comes to the installation, we have to clarify some
questions and information beforehand. We have collected every important point and question regarding the installation of our solar plants. If you can't find your question down below, you can send
us an email or give us a call. We are happy to assist you any time!
Are the mounting options of heat pipe and direct flow identic?
No, the Heat Pipe collector needs to be assembled between an angle of 5° – 75° and with vertical tubes to ensure that the condensed fluid flows back in the tube. In contrary the
Direct Flow collector can be assembled on a flat roof, facade/balcony and elevated. Even the position of the tube is freely selectable.
Which collector is suitable for facade and balcony mounting?
The Direct Flow collectors are perfectly suitable for balcony and facade mounting because they can be assembled flat on a wall with horizontal tubes. The Heat Pipe collectors can be
assembled on a facade/balcony too, but they have to be elevated to an angle between 5° – 75° with vertical tubes.
How is the flow ensured when mounting the collector horizontally?
The flow works despite horizontal mounting because the fluid is pumped through the collector with a pump.
How long does it take to remove air inclusions completely with a flushing and filling pump?
This depends on the flushing and filling pump. We recommend a flushing time of 30 – 45 minutes in a single-family house.
The heat pipe collectors can be elevated up to an angle of 5 °, is this sufficient?
In theory it is sufficient, but on construction site it must be planned 10 ° because the tolerances are larger and with that the 5 ° can be fulfilled.
How do I change the tubes?
Direct flow system: It is particularly important to empty the whole system because the tube is tethered wet. Afterwards take off the housing cover and remove the spring clips. Now you
can dismount the tube easily. Heat pipe system: Remove the housing and pull the tube 10 cm back. Take out the tube backwards. It is not necessary to empty the system, because the tube
is dry tethered.
Where is the flow and where the return?
From the heat generator the flow is always hotter side and the return the colder side. The collector is the heat generator in a solar system. The installation of flow and return is
What does the reflector consist of?
It consists of a white coated plastic aluminium plate.
Which mounting options are possible with the direct flow collector?
The Direct Flow collector is mountable on a flat roof, facade, balcony and elevated. Even the position of the tube is freely selectable.
How need fittings to be sealed, teflon tape or hemp?
We recommend the use of Solar-Fermit with hemp to seal the fittings properly. Teflon tape is not suitable, because of the high thermal load.
Is it possible to use the collectors as an in-roof system or brick replacement?
Yes, we can offer an in-roof solution for our collectors, that are mounted like a roof window.
How close to a boarder can I mount the collector on a flat roof?
Please mind a minimum distance of 1m (100cm).
What is the maximum pressure for the collectors?
The collector can be perfused with a maximum pressure of 10 Bar.
Where has the sensor pocket to be mounted?
The sensor must be mounted at the flow.
What type of mounting is recommended in snow areas?
We recommend the facade mounting.
Is it necessary to mount the air vent on the highest position in the solar system?
It is not necessary to mount the air vent on the highest point of the system when the system is filled with a filling pump. The filling pump flushes air inclusions out of the system.
We recommend installing air vents on large systems (more than 15 KW/120 tubes). The solar fluid gases a bit out on heating because it can absorb less air in hot state than in a cold
state. The air vent is used as an air buffer container and the solar fluid includes the air again in cold state. The air vent must not be provided with automatical air vents.