In this study, a small flat plate solar collector (FPSC) was fabricated and tested for the effects of different nano particles concentration of TiO_2 in water as base fluid. Three flow rates (i.e. 36, 72 and 108 lit/m2.hr) and four particles concentrations ratios (i.e. 0, 0.1, 0.2 and 0.3 % wt) were investigated. Experimental testing method was according to EUROPEAN STANDARD EN 12975-2 as a quasi-dynamic test method (QDT). Adding the nano particles to water improved the initial efficiency of FPSC between 3.5 and 10.5% and the index of collector whole efficiency between 2.6 and 7% relative to base fluid, respectively. Also the results indicate that the initial efficiencies ( η_0) for 36, 72 and 108 lit/m2.hr mass flow rates of base fluid were 0.4712, 0.4998 and 0.5457, that have grown for 72 and 108 lit/m2.hr mass flow rates by 6.1 and 15.8%, respectively relevant to 36 lit/m2.hr mass flow rate. The index of collector whole efficiency for 72 and 108 lit/m2.hr mass flow rates has increased by 6.7 and 15.7%, respectively in comparison with 36 lit/m2.hr mass flow rate.

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