Abstract: A pumping system comprising a pumping unit formed by a motor and a pump and adapted to raise a liquid from an underground level to a utilization level, a vaporizable fluid flowing in a closed circuit between a solar evaporator and a condenser, the said motor being disposed in the outgoing branch between the evaporator and the condenser, and a circulator being disposed in the return branch. The motor comprises a motor chamber which is connected by an internal bistable distributor either to the evaporator when said distributor is in an intake state, or to the condenser when said distributor is in an exhaust state, said motor chamber being partly limited by a flexible wall free to move between an intake stroke end position and an exhaust stroke end position, the flexible wall triggering the changes of state of the distributor by reaching its two end positions.