A solar chimney PV/T power plant (SCPVTPP) is proposed. Mathematical models are established for the PV/T solar collector, the chimney, and the power conversion unit, respectively. Performances of the designed SCPVTPP are then simulated. The SCPVTPPs with different PV module areas are finally discussed. It is found that the PV cells hold the highest temperature in the solar collector. Temperature rise of the PV module has significant influences to its power generation. Without cooling, the PV power capacity has an average decrease of 28.71%. The contradictory influences of temperature rise and airflow cooling lead to an 11.81% decrease of the average power capacity. By adding the power generated by PVT, the total PV-related power contribution increases by 4.72%. With the increase of the solar collector ratio, the temperature rise and the wind velocity both first decrease then increase, the SCPP power productivity decreases linearly, and the PV power productivity increases linearly, whereas the PVT power productivity first increases linearly then increases superlinearly. There is a reversed solar collector ratio, exceeding which the PV generates most power. In this study, solar thermal power takes the major role when the solar PV area ratio is smaller than 0.055.
The solar chimney power plant (SCPP) consists of three essential parts: a solar collector, a chimney, and a power conversion unit. The schematic of a SCPP is shown in Figure
(a) Schematic of a conventional solar chimney power plant (SCPP). (b) Schematic of a SCPVTPP.
Theoretical, experimental, and case studies of the SCPPs all around the world have concluded that the SCPP is with low power efficiency [
Parameters of some case studies of SCPPs.
Year | Location | Weather condition | SCPP parameters | Power efficiency | ||
---|---|---|---|---|---|---|
Solar radiation | Collector radius | Chimney height | Power capacity | |||
1983 | Manzanares, Spain [ |
1000 W/m2 | 122 m | 194.6 m | 50 kW | 0.11% |
2003 | Yinchuan, China [ |
600 W/m2 | 250 m | 200 m | 110–190 kW | 0.09% |
2010 | Adrar, Algeria [ |
800 W/m2 | 250 m | 200 m | 140–200 kW | 0.09% |
2010 | Qinghai-Tibet Plateau [ |
807 W/m2 | 2825 m | 1000 m | 92.4 MW | 0.89% |
2012 | 7 cities in Iran [ |
640 W/m2 | 122 m | 194.6 m | 75.9 kW | 0.08% |
1The authors of [
A mathematical model is built for the SCPVTPP. The mathematical model can be divided into three parts, namely, the PVT solar collector model, the chimney model, and the power conversion unit (PCU) model. Practically, the SCPVTPP has a large solar collection area, high chimney height, high PV surface temperature, and high airflow velocity, compared with the collector height, the collector cover thickness, and the temperature rise in the solar collector are much smaller. Correspondingly, the next assumptions can be made: (a) temperature rises linearly along the airflow direction in the solar collector; (b) ignore the velocity and temperature gradient on the vertical direction in the solar collector; (c) ignore the velocity and temperature gradient on the cross section of the chimney; (d) ignore the temperature difference between the collector upper and back surface; (e) airflow is under adiabatic condition in the chimney; and (f) PV lower surface and ground up surface are connected together.
Energy balance of a representative elemental volume in the solar collector and PV is established (Figure
Energy balance of a representative elemental volume in the solar collector and PV: (a) full view and (b) enlarged view of the PVT section.
Continuity equation:
Momentum equation:
Energy equation:
Considering the energy balance of a representative elemental volume, as shown in Figure
Taking a depth of
And taking a depth of
Continuity equation:
Momentum equation:
Energy equation:
For a vertical adiabatic chimney, the pressure difference created in the chimney is
And the pressure difference between the inlet and outlet of the solar collector is calculated as
According to Boussinesq assumption and (
As the connection section of the PCU is irregular, a randomized coordinate along the power generator surface is built for this area (Figure
Cross-section of the PCU.
Continuity equation:
Momentum equation:
Energy equation:
As
Consequently, the momentum equation can be simplified as
The generated pressure is consumed by four parts, that is, the friction losses in the collector and the chimney
The power generated by the turbine
Equations to calculate the coefficients, namely, the heat transfer coefficients, the loss coefficients, the friction loss, and turbine efficiency, follow the previous studies [
Flowchart of the simulation process.
The configuration sizes of the SCPVTPP are shown in Table
Configuration sizes and coefficients of the SCPVTPP.
Component | Value | |
---|---|---|
Solar collector | Collector radius | 625 m |
Collector inlet height | 3 m | |
Collector cover emittance | 0.87 | |
Glass extinction coefficient | 32 m−1 | |
Glass thickness | 5 mm | |
Refractive index | 1.526 | |
PV module | Percentage of PV area over whole solar collector area | 30% |
Emittance | 0.9 | |
Density | 2330 kg/m3 | |
Specific heat capacity | 677 J/(kg·K) | |
PV cover transmittance | 0.912 | |
PV efficiency under standard conditions | 0.115 | |
Temperature coefficient (Br) | 0.0045 K−1 | |
PV standard testing temperature | 298 K | |
Chimney | Height | 550 m |
Radius | 22.5 m | |
Ground | Material | Granite |
Density | 2640 kg/m3 | |
Specific heat capacity | 820 J/(kg·K) | |
Thermal conductivity | 1.73 W/(m·K) | |
Normal emittance | 0.92 | |
Reflectance | 0.25 | |
Turbine | Efficiency | 0.8 |
Inlet loss coefficient | 0.056 |
Photovoltaic layer properties.
Layer | Glass | ARC | PV cell | EVA | TPL |
---|---|---|---|---|---|
Thickness |
0.003 | 100 × 10−9 | 225 × 10−6 | 500 × 10−6 | 0.0001 |
Thermal conductivity |
1.8 | 32 | 148 | 0.35 | 0.2 |
As the SCPP is dominated by the buoyancy effect, temperature rise in the solar collector is of high significance. Moreover, two contradictory phenomena occur concerning the temperature rise in the PV/T solar collector. On one side, the PV modules are sensitive to the temperature rise. The PV power generation would decrease with the rise of temperature. On the other hand, the updraft wind would enhance with the temperature rising and the generated wind would reduce the temperature of the PV modules. Considering this, the meteorological data, temperatures, and wind velocity inside the SCPVTPP are calculated and the results are shown in Figure
(a) Solar radiation and ambient temperature of the SCPVTPP. (b) Temperatures of the glass cover, airflow, PV module, and ground and temperature increase inside the chimney during different months in the year.
Solar radiation and ambient temperature of Lanzhou is shown in Figure
There are three parts contributing to the power generation in the SCPVTPP, namely, the PV power capacity, the SCPP power capacity, and the PVT power capacity, which, respectively, refers to the power generation directly from the PV modules, the power contribution by the airflow from the solar collector without PV modules, and the power contribution by the airflow heated by the PV modules. Power generations from the PV, the PVT, and the SCPP are shown in Figure
Power capacity of the PV, SCPP, and PVT.
As mentioned above, the temperature takes contradictory effect on the PV power generation. The temperature influences on the PV power generation is thus analysed. By taking the PV power generation under ambient temperature as a reference, the PV model power, the PVT power contribution, and the total PV-related power contribution (PV + PVT) in the present study and the PV power generation without airflow cooling are then compared in Table
Comparison of PV model power, PVT power contribution, and total PV-related power contribution (PV + PVT) in the present study and the PV power generation without airflow cooling by taking PV power generation under ambient temperature as a reference.
Month | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | Average | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PV power generation under ambient temperature, |
Value/MW | 17.15 | 17.51 | 23.13 | 24.36 | 25.91 | 26.64 | 25.46 | 24.25 | 23.14 | 19.48 | 15.46 | 15.17 | 21.47 |
Percentage to |
100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | |
PV model power in the present study | Value/MW | 17.15 | 17.09 | 21.00 | 21.07 | 21.50 | 21.50 | 20.48 | 19.85 | 19.70 | 17.70 | 15.03 | 15.17 | 18.94 |
Percentage to |
100.00 | 97.60 | 90.79 | 86.49 | 82.98 | 80.71 | 80.44 | 81.86 | 85.13 | 90.86 | 97.22 | 100.00 | 88.19 | |
PVT power contribution in the present study | Value/MW | 0.85 | 0.85 | 1.13 | 1.16 | 1.22 | 1.23 | 1.16 | 1.10 | 1.08 | 0.91 | 0.72 | 0.73 | 1.01 |
Percentage to |
4.96 | 4.85 | 4.89 | 4.76 | 4.71 | 4.62 | 4.56 | 4.54 | 4.67 | 4.67 | 4.66 | 4.81 | 4.72 | |
Total PV-related power contribution (PV + PVT) | Value/MW | 18.00 | 17.94 | 22.13 | 22.23 | 22.72 | 22.73 | 21.64 | 20.95 | 20.78 | 18.61 | 15.75 | 15.90 | 19.95 |
Percentage to |
104.96 | 102.46 | 95.68 | 91.26 | 87.69 | 85.32 | 85.00 | 86.39 | 89.80 | 95.53 | 101.88 | 104.81 | 92.91 | |
PV power generation without airflow cooling | Value/MW | 12.27 | 12.77 | 15.56 | 16.67 | 17.68 | 18.29 | 18.17 | 17.62 | 16.69 | 14.57 | 12.00 | 11.39 | 15.31 |
Percentage to |
71.55 | 72.93 | 67.27 | 68.43 | 68.24 | 68.66 | 71.37 | 72.66 | 72.13 | 74.79 | 77.62 | 75.08 | 71.29 |
The performances of the SCPVTPP is discussed in Figures
(a) Temperature increase and wind velocity in the SCPVTPP under different solar collector ratios. (b) Power generation from PVT, PV, and ground and the total power generation under different solar collector ratios.
The SCPP has a large solar collector area, which can be used to lay the PV modules. A SCPVTPP is proposed and studied in this study. A mathematical model is established for the proposed system. The SCPVTPP performances and the power productivities under different solar collector ratios are then discussed. It can be concluded from this study that
The PV cells hold the highest temperature in the solar collector throughout the year, followed by the ground temperature, the glass cover temperature, and the airflow temperature. The temperature rise of the PV module has significant influences to its power generation. Without cooling, the PV power capacity has an average decrease of 28.71%. The contradictory influences of temperature rise and airflow cooling lead to an 11.81% decrease of the average power capacity. By adding the power generated by PVT, the total PV-related power contribution increases by 4.72%. With the increase of the solar collector ratio, the temperature rise and the wind velocity both first decrease then increase. The lowest temperature rise is located at the solar collector ratio of 0.4, whereas the lowest wind velocity is located at the solar collector ratio of 0.6. With the increase of the solar collector ratio, the SCPP power productivity decreases linearly and the PV power productivity increases linearly, whereas the PVT power productivity first increases linearly then increases superlinearly. There is a reversed solar collector ratio, exceeding the PV which generates most of the power. In this study, solar thermal power takes the major role when the solar PV area ratio is smaller than 0.055.
Area (m2)
Specific heat (J·m−2·K−1)
PV power (W)
Friction loss coefficient (−)
Acceleration of gravity (m·s−2)
Heat transfer coefficient (W·m−2·K−1)
Height (m); solar radiation (W·m−2)
Extinction coefficient (m−1)
Length (m); channel length (m)
Pressure (Pa); electrical power generation (W)
Energy flux (J·hr−1)
Direction (−)
Radius (m)
Solar radiation absorb by glass (W/m2)
Solar radiation absorb by PV (W/m2)
Temperature (K)
Compound heat coefficient (W·m−2·K−1)
Air velocity (m·s−1)
Total pressure difference (Pa).
Difference (−)
Air density (kg·m−3); reflectance (−)
Angle (°); direction (−)
Turbine inlet loss coefficient (−)
Dynamic viscosity (kg·m−1·s−1)
Turbine efficiency.
Ambient
Collector cover
Collector
Chimney
Airflow
Ground
Turbine inlet
Outlet of the solar collector
Outlet of the chimney
Photovoltaic.
The authors declare that they have no conflicts of interest.
This research was supported by the National Natural Science Foundation of China (Grant no. 51506043), the Natural Science Foundation of Jiangsu Province (Grant no. BK20141153), the “Dayu Scholar” Foundation of Hohai University, and the China Scholarship Council (Grant no. 201706715058).