NOVELTY - The plant has a fluid that is circulated from a surface (S) through a supply hole (20) and returned to the surface through a return hole (1). A pipe (5) separates return flow in the supply and a return hole (22). A seal (66) seals an annulus space by surrounding the pipe. The supply and return hole forms a lower return hole (1'). A first manifold zone (8) is connected with an end of a production hole (3,4,3',4',P) formed in a rock and other end of that hole is connected with the lower return hole in a second manifold zone (9), to form a closed-loop to circulate working fluid.    USE - Geothermal energy plant for extracting energy from rock through combined supply and return hole.    ADVANTAGE - The formation of vertical production holes in the rock formation leads to achieve a simple design of the plant, in rock formations with higher temperature gradients. The heat is efficiently extracted from the rock formation by optimized spacing of production holes. The geothermal energy plant design is provided by combining the supply and return holes, hence allowing a significant reduction of drilling cost and risk related to plant manufacture. The cost reduction allows drilling patterns to be optimized with respect to energy output versus drilling costs. The energy output is optimized and total cost is reduced by making production holes essentially horizontal, in rock formations with lower temperature gradients. The fracturing is employed to enhance circulation and simplify plant completion. The diameter of the lower portion of the return hole is made smaller than that of the combined supply and return hole, hence the drilling costs are reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for establishing geothermal energy.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of the geothermal energy plant.    Return hole (1)    Lower return hole (1')    Production hole (3,3',4,4',P)    Pipe (5)    First manifold zone (8)    Second manifold zone (9)    Supply hole (20)    Return hole (22)    Seal (66)