Apparatus and method for generating useful energy

An apparatus for useful energy, comprising:

• a first chamber which contains a draw solution which comprises an osmotic agent and a second chamber which contains a feed solution;
• a semi-permeable membrane which is arranged such that feed solution can move across the semi-permeable membrane by osmosis, from the second chamber to the first chamber, to form a diluted draw solution;
• a pressurising means, which is operable to apply a pressure to the diluted draw solution in the first chamber;
• an energy conversion means, which is configured such that it can convert mechanical energy into electrical energy, wherein the energy conversion means is arranged such that it can convert mechanical energy in the diluted draw solution, which is generated due to the movement of the feed solution from the second chamber to the first chamber across the semi-permeable membrane by osmosis, into useful energy,
• wherein the osmotic agent comprises particles with a diameter (d) in the range 0.5 nm-5 mm and wherein the semi-permeable membrane comprises pores which have a diameter which are at most equal to the diameter of the particles of the osmotic agent, so as to improve the amount of power or useful energy which can be generated by the apparatus,
• wherein the particles comprise thermoresponsive material which causes the osmotic agent to aggregate in the draw solution or diluted draw solution at a predefined temperature, to facilitate recovery of the osmotic agent.