Solar Water Heating @ -40° C & Super Hot
The highest mountain in Germany is called the Zugspitze and in the late 1990s a hotel called the Schneefernerhaus closed down and its premises were adapted to use as an Environmental Research Station. Its main task is to measure accurately and carefully changes in atmospheric pollution. There are many places doing this work throughout the world and the sum of their research adds greatly to our knowledge about global warming and climate change.
If you went skiing on the Zugspitze, around noon you would see on the south side high on the wall of the environmental research station, a large mass of dark black solar water heating panels. A few hours later, this wall will appear to be silver. However, you would not be looking at a wall in the conventional sense, but a wall of vacuum thermal solar panels some 100 square meters in area, designed and installed by Thermosolar, based in Bavaria. These panels provide spacing heating & hot water for the environmental research centre all year round.
At these latitudes, we normally recommend mounting the panels at an angle of between 40 and 45 degrees. The Zugspitze’s panels are mounted vertically, and thus do not receive the maximum amount of solar radiation. The reason for this is snow. In normal conditions, snow will melt from a well – designed solar thermal panel first – usually before it melts from evacuated tubes – but these are not normal conditions.
The panels are mounted on a mountain side some 2,650 metres above sea level. In these conditions snow is usually present ten out of twelve months each year, and so mounting the panels as a vertical wall prevents the snow collecting on them and enables the panels to collect light bouncing off the surrounding snow fields. The low winter sun makes the vertical angel more efficient in winter, because the sun’s rays strike at a better angle.
On good days, the panels achieve the solar constant which is 1.4kWm2; the yearly energy gain is 1950kWh/m2. For eight months of the year the panels provide a solar fraction of 100%. I have to admit that there some advantages in mounting panels on a building 2,600 meters above sea level. There are very good light levels so high; clouds and fogs often shroud the base of the mountains but leave the peak in bright light.
The 100 square meters of panels are evacuated to around 3mbars of pressure. This is about 3% of atmospheric pressure at sea level. Although it is not a perfect vacuum (does such a vacuum exist?) it is reinforced with krypton gas, just like installations we have completed in United Kingdom, Norway, Canada and numerous European Union Countries. For our technically minded readers, filling the panels with 30mbar krypton increases the insulation tremendously. The heat transition coefficient is 2.6W/m2K, which keeps heat losses to a minimum even in a place where temperature drops to -40 degrees c.
The heat that the panels create from light is stored in a 100 m3 insulated fire tank. Because of the tremendous heat potential, Thermosolar had to design safeguards to ensure that the water stored would never be hotter than 60 degrees Celsius, otherwise fire fighters would be endangered in the event of fighting a fire.
The station also specified the TS400 vacuum panels, they do not contain insulation as a vacuum is the best form of insulation, The panels are evacuated on-site once installed. Over time the panels will lose their vacuum but the TS400 panels can be re-evacuated keeping the insulation at a maximum throughout the lifetime of the panel which should be in excess of 35+ years.
As a result the important work of measuring atmospheric pollution is still being carried on in conditions unpolluted by the energy requirements that are needed to keep the researchers warm.