Main Reserves for Increasing the Efficiency of Solar Thermal Energy in Heat Supply Systems (Review)

The main reserves for increasing the efficiency of solar energy utilization in heat supply systems are considered in this paper. This is of particular relevance under the conditions of market stagnation of modern solar collectors with parameters close to their limiting values, and forcing out traditional solar water heating plants with photovoltaic systems, whose cost becomes commensurate with thermal ones. The research objective is revealing and estimating the main reserves and determining promising directions and rational ways of improving the efficiency of the solar heat supply systems, based on minimizing the loss of temperature voltage during the transfer of thermal energy from solar collector to heat accumulator and further to consumer. It is shown that the main reserves of improvement of efficiency of solar heat supply systems is the improvement of their schematics, auxiliary equipment and operating parameters using the simplest self-regulating active elements, that can significantly influence the hydrodynamics of non-isothermal fluid flow in the system and its thermal efficiency when low specific flow rates of heat carrier through solar collector. The main ways of implementing the assigned task are revealed, which are: decreasing the heating temperature of heat carrier in the solar collector by 5–10°C, due to exclusion of the intermediate heat exchanger between the solar collector and accumulator and replacement of a multi-contour system with antifreeze to a single-contour self-draining unit; increasing the energy efficiency of known self-draining plants up to 65–80% by mutual transformation of potential and kinetic energy of a fluid in the Venturi tube and thereby eliminating the loss of hydrostatic pressure due to jet rupture; decreasing the temperature difference by 5—10°С when charging and discharging the heat accumulator using high-efficient temperature stratification of water; reducing the loss of temperature voltage and stabilization of water heating temperature in thermosiphon solar hot water supply systems due to its single heating in solar collectors; reducing the average operating temperature by 5–10°C of the solar collector and of the helio field of solar collectors by increasing the uniformity of fluid flow distribution by individual collector channels and the helio field as a whole.