Mediterranean Green Buildings & Renewable Energy pp 429-444 | Cite as

# Performance Analysis and Parametric Studies of a Bi-fluid Type Photovoltaic/Thermal (PV/T) Solar Collector in Simultaneous Mode Under Tropical Climate Conditions

## Abstract

Performance analysis of a photovoltaic/thermal solar collector with a bi-fluid configuration (air and water) was conducted under real sky conditions in the tropical climate of Perlis, Northern Peninsular Malaysia. In addition to the electricity generated, this type of collector has enabled three different modes of fluid operation: air mode, water mode and simultaneous (bi-fluid) mode. The third mode of fluid of operation is the primary focus in this chapter. This chapter highlights the performance of the collector outdoors, in terms of the experimental and two-dimensional theoretical analysis at steady state. For collector testing under real sky conditions, analyses of the collector for varying sets of mass flow rates under environmental conditions of an average wind speed of 3 m/s and average solar radiation of 700 W/m^{2} were conducted. To obtain suitable data, experiments were conducted for each of the mass flow rates on ten different days of testing. For the simultaneous mode, when air flow rate was fixed at 0.0262 kg/s, at a water mass flow rate that varied from 0.0017 to 0.010 kg/s, the electrical efficiency and total thermal efficiency ranged from 8.13 to 8.60 % and 44.36 to 47.45 % respectively. When the water flow rate was fixed at 0.0066 kg/s, at an air mass flow rate that varied from 0.0092 to 0.0753 kg/s, the efficiencies ranged from 8.10 to 8.56 % and 44.06 to 50.37 % respectively. Theoretical analysis was then conducted and compared with the experimental analysis by comparing the trend of the curves and using mean absolute percentage error (MAPE) analysis. The curves were found to be in good agreement, and the computed MAPE for the fluids’ output temperature was less than 2 %. Parametric studies were then conducted to investigate the performance of the collector with the change in air channel depth and performance with the change in collector length. The feasibility of incorporating two different types of working fluid into the same PV/T solar collector was demonstrated based on the thermal and electrical energy output of the collector under real sky conditions. Therefore, this research will serve as a starting point for further research into a bi-fluid type PV/T solar collector, both experimentally and theoretically.

## Keywords

Bi-fluid Photovoltaic thermal (PV/T) 2-D steady state Outdoor Parametric## Nomenclature

*A*_{PV}Collector aperture area’s subsegment, equal to area of PV module’s subsegment (m

^{2})*C*_{f}Conversion power factor

*C*_{pf1}Specific heat capacity of air

*C*_{pf2}Specific heat capacity of water

*D*_{i}Inner pipe diameter

*D*_{o}Outer pipe diameter

*f*A general subscript to denote a fluid

*f*_{r}A friction factor in a fluid’s channel

*G*Global radiation

*h*Heat transfer coefficient (W/m

^{2}K)*h*_{cvbs f1}Convection heat transfer coefficient from back surface of Tedlar to air flow (W/m

^{2}K)*h*_{cvbsf2}Convection heat transfer coefficient from back surface of Tedlar to water flow (W/m

^{2}K)*h*_{cvfin f1}Convection heat transfer coefficient from surface of a fin to flowing air (W/m

^{2}K)*h*_{cvw}Wind convection heat transfer coefficient (W/m

^{2}K)*h*_{i}Generalised notation for heat transfer coefficient of linear equations derived from developed energy balance equations for a general heat transfer coefficient

*i*(W/m^{2}K)*h*_{rbsbp}Radiation heat transfer coefficient between inner surfaces of collector (W/m

^{2}K)*h*_{rpvsky}Radiation heat transfer coefficient from PV cells to sky (W/m

^{2}K)*k*_{fin}Thermal conductivity of fin (W/mK)

*k*_{f1}Thermal conductivity of air (W/mK)

*k*_{f2}Thermal conductivity of water (W/mK)

*k*_{PV}Thermal conductivity of photovoltaic cells (W/mK)

*L*_{fin}Length of fin (m)

*m*Subsegment for each temperature node

- \( {\overset{.}{m}}_{f1} \)
Air mass flow rate (kg/s)

- \( {\overset{.}{m}}_{f2} \)
Water mass flow rate (kg/s)

*N*_{fin}Total number of fins

- \( {\displaystyle \sum }{Q}_{\mathrm{th},\mathrm{inst}} \)
Total instantaneous thermal energy produced by solar collector (J)

- \( {\displaystyle \sum }{Q}_{\mathrm{PVT},\mathrm{inst}} \)
Instantaneous primary energy saving (J)

*q*Rate of heat flux (W/m

^{2})*q*_{uf1, m}Rate of heat transfer per unit area for air nodes (W/m)

*q*_{uf2, m}Rate of heat transfer per unit area for air nodes (W/m)

- Re
Reynolds number

*S*_{PV}Total rate of solar energy absorbed by solar cells of PV module

*S*_{T}Total energy absorbed by Tedlar

*T*Temperature (K)

*T*_{a}Ambient temperature (K)

*T*_{bp, m}Temperature nodes of surface of back plate (K)

*T*_{bs, m}Temperature nodes of back surface of Tedlar (K)

*T*_{bp}Mean temperature of surface of back plate with fins (K)

*T*_{bs}Mean temperature of back surface of Tedlar (K)

*T*_{PV}Mean temperature of cell (K)

*T*_{f1, m}Temperature nodes of air flow in channel (K)

*T*_{f2, m}Temperature nodes of water flow in copper pipe (K)

*T*_{fin, m}Mean temperature of fin at subsegment

*m*(K)*T*_{PV, m}Temperature nodes of PV cells (at centre of cells) (K)

*T*_{ref}Temperature at reference point

*T*_{sky}Sky temperature (K)

*T*_{tin}Mean inner wall temperature of copper pipe (K)

*U*_{t, m}Overall top heat loss coefficient for subsegment

*m**v*_{f1}Maximum velocity of air (m/s)

*v*_{w}Wind speed (m/s)

*W*Tube spacing (m)

*α*_{c}Absorptance of PV cells

*β*_{c}PV module packing factor

*β*_{ref}Temperature coefficient at reference temperature

*δ*_{PV}Thickness of PV module

*δ*_{si}Thickness of Si-cells

*δ*_{T}Thickness of Tedlar layer

*δ*_{EVA}Thickness of ethylene-vinyl acetate (EVA) layer

*δ*_{fin}Fin thickness

- Δ
*y*_{PV}Δ*x* Area of subsegment of PV module

- Δ
*x* Distance between temperature nodes (\( \Delta x=1\kern0.5em \mathrm{cm} \))

*ε*_{sky}Emissivity of sky

*ε*_{g}Emissivity of glass cover

*γ*_{bsbp, m}Area correction factor for heat transfer from back surface of Tedlar to surface of back plate with fins

*γ*_{bs f1, m}Area correction factor for heat transfer from back surface of Tedlar to flowing air

*γ*_{bs f2, m}Area correction factor for heat transfer from back surface of Tedlar to flowing water

*γ*_{fin f1, m}Area correction factor for heat transfer from fin surfaces to flowing air

*γ*_{bp f1, m}Area correction factor for heat transfer from surface of back plate with fins to flowing air

*γ*_{bpa, m}Area correction factor for heat transfer from surface of back plate with fins to ambient

*τ*_{g}Transmittance factor of front cover glass of PV module

*η*Efficiency

*η*_{c}Electrical efficiency of PV cell

*η*_{ele}Electrical efficiency

*η*_{eth}Electrical efficiency converted to equivalent thermal efficiency

*η*_{fin}Fin efficiency

*η*_{p}Fin effectiveness

*η*_{Tref}Electrical efficiency at reference temperature

*η*_{th f1}Thermal efficiency of air

*η*_{th f2}Thermal efficiency of water

- \( {\displaystyle \sum }{\eta}_{\mathrm{th}} \)
Total thermal efficiency of solar collector

- \( {\displaystyle \sum }{\eta}_{\mathrm{PVT}} \)
Primary energy savings or equivalent thermal efficiency

- \( {\displaystyle \sum }{\eta}_{\mathrm{th},\mathrm{inst}} \)
Instantaneous total thermal efficiency of solar collector

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