Social indicators show that an annual energy consumption of 2 t of oil equivalent per capita (toe pc) should be enough to ensure a sufficient global average level of welfare and happiness. Hence, rich countries with currently up to 8 toe pc should reduce and poor should legitimately increase their energy demand until 2 toe pc are reached. At today's global energy mix with 80 % fossil fuels, even this optimistic scenario will inevitably lead to a conflict between welfare and stable ecosystems. The population will be 9 billion by 2050 and the ecological footprint would rise from today 1.5 in 2010 to 2 planet Earths. The only option to reach the desired footprint of one planet Earth is a complete shift from fossil fuels to renewables, presumably to solar power. One option is a technology based on four steps: separation of CO2 from flue gases (in the long run from air), H2 production by water electrolysis driven by solar power or other renewables, CO production by reverse water gas shift, and finally synthesis of renewable liquid fuels (gasoline and diesel oil) by Fischer-Tropsch synthesis.