Safety and Efficiency of Daytime Operation of Solar Hot Water System

   During the operation of evacuated tubular collectors in cold climates, pure propylene glycol or its mixture with water is used as the coolant. The upper permissible heating temperature of pure propylene glycol is 187 °C, and the freezing point is –60 °C. However, the heated mixture, which does not freeze at –40 °C, boils when heated to 108 °C, decomposing into acids and toxic substances. The safety and efficiency of such solar collectors during the day can be ensured by managing their temperature regimes.

   Purpose: The aim of the work is to develop a method of temperature control of solar collectors and hardware and software complex for its implementation to ensure a safe operation and improve the efficiency of solar hot water supply systems during the daytime.

   Methodology: For the full-scale testing of the proposed method, pilot-industrial combined solar hot water supply systems with two and four evacuated tubular collectors are used in Kaftanchikovo village of the Tomsk region, in the production workshop of NPO VEST.

   Research findings: Full-scale experiments allow to obtain and analyze thermal modes of collectors, ensuring a safe operation of combined solar hot water supply systems during the daytime with increased efficiency of converting solar energy into thermal energy.

   Value: It is shown that the best collector temperature can be adjusted with the collector temperature exceeding 5 to 10 °C. This gives the maximum energy efficiency in converting solar energy into thermal energy.

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