Energy from solar ballons
Solar balloons are hot air balloons in which the air is heated directly by the sun, by means of a black absorber. The lift force of a tethered solar balloon can be used to produce energy by activating a generator during the ascending motion of the balloon. The hot air is then discharged when the balloon reaches a predefined maximum height. (...) The efficiency is lower than what can be achieved with conventional photovoltaic or thermal systems, due to the limited temperature difference that can be exploited. However, the system requires simple technologies and low cost materials, and the final cost per unit power output can be competitive.