Because fossil resources are finite, we need new possibilities for the production of energy. Silphium and Sida are two flowering energy crops from North America with a high potential as an energy crop in Europe. These two crops were be tested as an alternative biogas substrate and for the production of bioethanol. To do this, Silphium was planted 2012 at four locations and Sida was planted once in 2010 in Großweikersdorf and once in 2014 in Grabenegg. The aim of this work was to test the potential of Silphium as a biogas and bioethanol substrate and do the first tests of Sida for the biogas process. The different locations and varieties of fertilisation have a significant influence of the methane yield of Silphium. The locations Grabenegg and Schönfeld deliver higher methane yields then Hirschstetten and Strem. The harvest date has an effect of the methane yield. The methane yield varied between 304 Nl/kg oDM at the earlier harvest date and 158 Nl/kg oDM at the later harvest date. Because of the low methane yield at the later harvest dates, different pre-treatment methods to enhance the methane yield were tested. Although the thermochemical pre-treatment has an influence on the sugar amount and the thermal by-products, no higher methane yields were achieved with the mechanical or thermochemical pre-treatment. Silphium has a low potential for the production of ethanol. The plant achieved only fifty percent of the ethanol yield of maize straw after a pre-treatment temperature of 200 C. The utilization of Sida as a biogas substrate has a higher potential than Silphium. The plant delivers higher methane yields and can be an alternative in the future instead of maize. However, these are preliminary results based on few samples.