The demand for energy services (which must not be mistaken for the demand for energy itself) is proportional to the world's wealth, which, as monitored for the past 1000 years, still increases exponentially. Current efforts in controlling the resulting rise in energy demand mainly focus on efficiency improvement and sustainable conversion technologies. This paper demonstrates that these technological efforts most likely cannot provide long-term alternatives. At best, they can buy some time during which long-term sustainable solutions can be developed.
There are two effective long-term solutions to energy related problems. The first would be the discovery of a sustainable energy source with an unlimited potential that can cater for an exponentially growing demand. The second is to limit economic growth, which would also stop the corresponding demand for energy services. In this case, sustainable energy sources with limited potential or resources can provide sufficient energy.
As a first crucial step, research efforts should focus on quantifying the demand for energy services and estimate how much energy man, at his thermodynamical limits, will still need. This knowledge can further on establish the timeframe for implementing an effective longterm solution.