The power unit could be realised with a small combustion engine, which burns low-polluting fuel and runs on just one frequency. In the following the commonly used "problematical" combustion engines are briefly explained before two alternative examples are shown in more detail.
Sources: Pictures are taken from the book :
"Das
will ich von der Technik wissen"
Author: Axel Rex
Südwest-Verlag
München
Information
are taken from BOMIN SOLAR, SIGNON SAN DIEGO, FUTURE DRIVE, WORLD WATCH.