Performance of a hybrid solar collector system in days with stable and less stable radiative regime

Figures & data

Figure 1. Details of HSC design (all dimensions are in m).

Figure 2. Heat transfer mechanisms through the HSC (all dimensions are in cm).

Figure 3. Forced circulation HSC system with water storage tank

Table 1. Design parameters.

Parameter	Value
HSC
Number of glass covers	1
Insulation thermal conductivity	0.04 W/(m K)
Material of the absorber plate	Copper
Thickness of glass cover	4
Thickness of thermal insulation	5 cm
Thickness of absorber plate	1 mm
Emissivity of glass cover	0.88
Emissivity of absorber plate	0.1
Gross collector area	1.94 × 0.94 m^2
Water pipe diameter	0.003−0.01 m
Air channel high	0.03−0.1 m
Collector tilt angle	30^0
Tank
Type	Fully mixed
Thickness of thermal insulation	5 cm
Volume	0.4 m^3
Working fluids (water and air)
Maximum water mass flow rate per collector unit area	0.077 kg/(s m^2)
Maximum air mass flow rate per collector unit area	0.077 kg/(s m^2)

Figure 4. Simulation flow chart

Figure 5. Air temperature rise (T_a,out− T_a,in, see Figure 3) simulated by the present model and measured by Assari, Basirat Tabrizi, and Jafari (2011).

Table 2. Selected days during 2009 at Timisoara. The daily average values of the sunshine number (SSN) and sunshine stability number (SSSN) are also shown.

Day type	Sunshine class σ	Radiative regime	Summer	Spring	Autumn	Winter
Clear sky	1.0	Fully stable	NA	April, 3	October, 8	January, 6
Overcast sky	0.0	Fully stable	July, 11	May, 28	October, 13	January, 28
Low cloudiness	0.8–1.0	More stable	July, 15	April, 10	November, 14	February, 25
		Less stable	July, 26	April, 5	November, 25	NA
Medium cloudiness	0.4–0.7	More stable	July, 3	April, 30	October, 16	January, 17
		Less stable	July, 12	May, 4	October, 17	January, 19
High cloudiness	0.0–0.3	More stable	July, 2	May, 30	October, 29	December, 17
		Less stable	NA	May, 31	October, 28	December, 24

Figure 6. Time variation of (a) solar global irradiance, G, and ambient air temperature, T_amb, for four different days in winter, spring, summer and autumn; (b) water temperature in the storage tank, T_w,s; (c) water mass flow rate, m w; (d) dependence of the collector total daily efficiency, , on water mass flow rate.

Figure 7. (a) Time variation of solar global irradiance, G, and ambient air temperature, T_amb, for a fully stable day with clear sky (6 January) and a less stable day with medium cloudiness (4 May); (b) total daily efficiency, , for several values of the water pipe diameter (in m) and air channel height.

Figure 8. (a) Time variation of solar global irradiance and ambient air temperature for a more stable day with low cloudiness (15 July) and a fully stable day with overcast sky (13 October); (b) total daily efficiency, , for several values of the water pipe diameter (in m) and air channel height.

Figure 9. Effect of storage tank volume on efficiency and water temperature for different water mass flow rate on 26 July 2009. A constant air mass flow rate 0.06 kg/s (0.033 kg/(s m²)) has been considered.

Assari, M. R., H. Basirat Tabrizi, and I. Jafari. 2011. “Experimental and Theoretical Investigation of Dual Purpose Solar Collector.” Solar Energy 85: 601–608.10.1016/j.solener.2011.01.006

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