A giant engine with a tethered balloon for a “piston” could generate cheap, renewable electricity (Image: Chad Ehlers/Stock Connection/Rex)

For those who dislike the sight of wind turbines on the horizon, would a spectacular hot-air balloon farm be more acceptable?

Ian Edmonds, an environmental consultant with Solartran in Brisbane, Australia, has designed a giant engine with a balloon as its “piston”. A greenhouse traps solar energy, providing hot air to fill the balloon. As the balloon rises, it pulls a tether, which turns a generator on the ground. Once the balloon has reached 3 kilometres, air is released through …