NOVELTY - The unit has a closed loop fluid channel (101) e.g. pipe, containing lumen for conducting working fluid e.g. water, from a connectable opening (102) to another connectable opening (103). An energy collecting element (104) e.g. Fresnel lens, is mounted in front of the fluid channel for concentrating radiation onto the fluid channel. An inverted and truncated pyramid shaped air evacuated chamber contains low atmospheric pressure between the energy collecting element and the fluid channel, where walls of the chamber are covered with mirrors to concentrate the radiation onto the fluid channel.    USE - Energy collecting unit for use in an energy collecting module to assemble an open and closed loop energy collecting modular system utilizing solar energy and installed in an energy collecting area to preheat working fluid e.g. water and oil, and heat and steam working fluid for an industrial process to feed a mixture of a target fluid stream heated by a heat exchanger and an additional fluid stream from an independent heating system to an energy consumption unit e.g. steam turbine of electricity generating system, steam engine and steam accumulator (all claimed), an absorption chiller and an absorption refrigerator for processing heat, electricity generation and air conditioning and for promoting chemical reaction and organic reaction e.g. encouraging bacteria and algae growth in the working fluid.    ADVANTAGE - The energy collecting module optionally not includes moving and active parts such as pumps, such that the energy collecting module is inexpensive to manufacture and maintain. The unit is designed such that atmospheric pressure in an intermediate space between the fluid channel and the energy collecting element is decreased so as to reduce heat loss by convection. The unit enhances chemical reaction and suppresses biological processes. The energy collecting module reduces maintenance fees as defective and checked energy collecting module can be replaced separately without disassembling other collecting module. The energy collecting module allows setting fluid conducting tubular bodies in different lengths so as to cover energy collecting areas having different dimensions.    DETAILED DESCRIPTION - The fluid channel is made of transparent material selected from a group consisting of glass, borosilicate glass, quartz glass, fused silica and PTFE. INDEPENDENT CLAIMS are also included for the following:    (1) an energy collecting module comprising a heat exchanger    (2) a method for installing an energy collecting modular system    (3) an energy collecting modular system comprising a pump.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of an energy collecting module having a closed loop fluid circulation channel.    Closed loop fluid channel (101)    Connectable openings (102, 103)    Energy collecting element (104)    Support structure (106)    Fluid channel segment (151)