Testsing and development of components and systems for commercial solar thermal power plants. The aim is to make solar thermal power plants more efficient. They also test processes for solar water splitting, the production of solar fuels and the use of solar heat in industrial processes.
More than 2,000 movable mirrors (heliostats) cover an area of around ten hectares in front of Jülich's two solar towers. They catch the sunlight, concentrate it and direct it onto the two solar towers.
In the solar tower power plant, a volumetric receiver at the top of the tower absorbs the concentrated sunlight and uses it to heat the surrounding air to up to 700 degrees Celsius. A steam generator inside the tower uses this to heat water into steam, which drives a turbine that produces electricity via a generator.
https://www.dlr.de/en/research-and-transfer/research-infrastructure/solar-towers-juelich
It doesn't really need to be tall i guess. Its only for the mirrors to be able to reflect the sunlight to the receptor.
Maybe it needs to be taller if there were more mirrors though. This is still experimental
I have no concept of how tall it should be for effectiveness, i just meant that from the pictures i thought it looked like 50 stories tall