A renewable energy turbine generator comprising: a rotor, a generator and a hydraulic transmission which transmits rotational energy from the rotor to the generator, the hydraulic transmission comprising a variable displacement hydraulic pump which is driven by the rotor, a variable displacement hydraulic motor which is coupled to the generator, and an oil circuit comprising a high pressure oil line which is arranged between a discharge side of the hydraulic pump and an intake side of the hydraulic motor, and a low pressure line which is arranged between an intake side of the hydraulic pump and a discharge side of the hydraulic motor, each of the hydraulic pump and the hydraulic motor comprising: a plurality of working chambers each of which is defined by a cylinder and a piston slidably mounted in the cylinder, a rotatable shaft coupled to a cam, the cam having a cam surface in engagement with the said pistons, the cycles of working chamber volume being coupled to rotation of the rotatable shaft, bearings in engagement with the rotatable shaft, and a plurality of valves for regulating the net displacement of working fluid between each working chamber and the high and low pressure lines, at least one valve associated with each working chamber being an electronically controlled valve, said electronically controlled valves being operable by the controller to select the volume of working fluid displaced by each said working chamber on each cycle of working chamber volume and thereby regulate the net rate of displacement of working fluid by the hydraulic pump and the hydraulic motor respectively, wherein the hydraulic pump and/or the hydraulic motor comprise a reduced temperature oil feed (107, 128) configured to introduce oil to the bearings, wherein the renewable energy turbine generator comprises at least one first temperature regulator (110, 130) for regulating the temperature of oil to the reduced temperature oil feed such that the oil supplied by the reduced temperature oil feed is cooler than the oil supplied from the oil circuit to the working chambers of the hydraulic pump and/or hydraulic motor respectively. a rotor, a generator and a hydraulic transmission which transmits rotational energy from the rotor to the generator, the hydraulic transmission comprising a variable displacement hydraulic pump which is driven by the rotor, a variable displacement hydraulic motor which is coupled to the generator, and an oil circuit comprising a high pressure oil line which is arranged between a discharge side of the hydraulic pump and an intake side of the hydraulic motor, and a low pressure line which is arranged between an intake side of the hydraulic pump and a discharge side of the hydraulic motor, each of the hydraulic pump and the hydraulic motor comprising: a plurality of working chambers each of which is defined by a cylinder and a piston slidably mounted in the cylinder, a rotatable shaft coupled to a cam, the cam having a cam surface in engagement with the said pistons, the cycles of working chamber volume being coupled to rotation of the rotatable shaft, bearings in engagement with the rotatable shaft, and a plurality of valves for regulating the net displacement of working fluid between each working chamber and the high and low pressure lines, at least one valve associated with each working chamber being an electronically controlled valve, said electronically controlled valves being operable by the controller to select the volume of working fluid displaced by each said working chamber on each cycle of working chamber volume and thereby regulate the net rate of displacement of working fluid by the hydraulic pump and the hydraulic motor respectively, wherein the hydraulic pump and/or the hydraulic motor comprise a reduced temperature oil feed (107, 128) configured to introduce oil to the bearings, wherein the renewable energy turbine generator comprises at least one first temperature regulator (110, 130) for regulating the temperature of oil to the reduced temperature oil feed such that the oil supplied by the reduced temperature oil feed is cooler than the oil supplied from the oil circuit to the working chambers of the hydraulic pump and/or hydraulic motor respectively.