Business Green: An engineering student claims to have found a way to store solar energy — the Holy Grail of solar technology. Claus Volkening, 23, of the University of Portsmouth, has designed and laboratory-tested a solar updraft tower that uses water storage tanks to solve the problem of existing solar power plants which only generate electricity when the sun shines. Existing solar updraft towers work by collecting heat energy from the sun and sending the warm air up through a tower which …