Starting with the three most important global energy flows (direct terrestrial solar radiation, earth rotation, geothermal energy of earth interior), the authors assess the technically usable potential of regenerative energies. This is shown on the background of the world energy demand of the next decades, expected to be in the range of 22 to 36 TWa/a for the year 2030. The potential of the following regenerative energy source is estimated: biomass, water power, wind power, geothermal energy, energy of the oceans, local (soft) solar energy. Further considerations touch on problems which occur on using regenerative energy sources, such as their low density of energy production and the ecological problems, especially on world-wide use of the biomass.