【Author】: Guoliang Xu, Tingzhen Ming, Yuan Pan, Fanlong Meng, Cheng Zhou

Energy Conversion and Management 52 (2011) 876–883

School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Power generating technology based on renewable energy resources will definitely become a new trend of future energy utilization. Numerical simulations on air flow, heat transfer and power output characteristics of a solar chimney power plant model with energy storage layer and turbine similar to the Spanish prototype were carried out in this paper, and mathematical model of flow and heat transfer for the solar chimney power plant system was established. The influences of solar radiation and pressure drop across the turbine on the flow and heat transfer, output power and energy loss of the solar chimney power plant system were analyzed. The numerical simulation results reveal that: when the solar radiation and the turbine efficiency are 600 W/m2 and 80%, respectively, the output power of the system can reach 120 kW. In addition, large mass flow rate of air flowing through the chimney outlet become the main cause of energy loss in the system, and the collector canopy also results in large energy loss.

Energy Conversion and Management, In Press, Corrected Proof, 2011

Fei Cao, Liang Zhao, Liejin Guo

Solar chimney power system is one large-scale utilization style of solar energy, which has drawn high attentions worldwide. Though scholars all over the world have made many researches on the solar chimney power system, reports of sloped solar chimney power system are still few. A sloped solar chimney power plant, which is expected to provide electric power for remote villages in Northwest China, has been designed for Lanzhou City in this paper. The designed plant, in which the height and radius of the chimney are 252.2 m and 14 m respectively, the radius and angle of the solar collector are 607.2 m and 31° respectively, is designed to produce 5 MW electric power on a monthly average all year. The performances, such as the airflow temperature increase, pressure, the airflow speed, system efficiency and solar collector efficiency, of the built sloped solar chimney power plant are simulated and presented. Simulation results show that parameters of the sloped solar chimney power plant are symmetrical and stable; the power plant has better performances in spring and autumn days; the overall efficiency of the power plant is low. Considering the abundant solar radiation, environmental friendliness, easy management and low population density, the sloped solar chimney power system is of high value to Northwest China.

Article Outline

Nomenclature

1. Introduction

2. System description

3. Mathematical model

3.1. Solar collector

3.2. Chimney

3.3. Power generation and thermal efficiency

4. Configuration sizes of the SSCPP

5. Results and discussion

5.1. SSCPP performances in different months

5.2. Efficiency of the SSCPP

5.3. Discussions

6. Conclusions

Acknowledgements

References

Research highlights

► A sloped solar chimney power plant in Lanzhou, China is investigated. ► The configuration sizes are designed separately. ► The system has high periodicity and stability but low efficiency. ► The sloped solar chimney power system is of high value for Northwest China.

Solar Energy, In Press, Corrected Proof, 2011

Roozbeh Sangi, Majid Amidpour, Behzad Hosseinizadeh

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to conduct a more detailed numerical analysis of a solar chimney power plant. A mathematical model based on the Navier–Stokes, continuity and energy equations was developed to describe the solar chimney power plant mechanism in detail. Two different numerical simulations were performed for the geometry of the prototype in Manzanares, Spain. First, the governing equations were solved numerically using an iterative technique. Then, the numerical simulation was performed using the CFD software FLUENT that can simulate a two-dimensional axisymmetric model of a solar chimney power plant with the standard k-epsilon turbulence model. Both the predictions were compared with the available experimental data to assess the validity of the model. The temperature, velocity and pressure distributions in the solar collector are illustrated for three different solar radiations. Reasonably good quantitative agreement was obtained between the experimental data of the Manzanares prototype and both the numerical results.

Article Outline

Nomenclature

1. Introduction

2. System description

3. Modeling

3.1. Basic equations

3.1.1. Navier–Stokes equations

3.1.2. Continuity equation

3.1.3. Energy equation

3.1.4. k– equations

3.2. Mathematical model of the collector

3.2.1. Heat balance of the glass roof

3.2.2. Heat balance of the earth

3.2.3. Heat transfer coefficients

3.2.4. Pressure equation of the collector

3.3. Turbine model

3.4. Mathematical model in the chimney

3.4.1. Pressure equation in the chimney

3.5. Pressure equation of the whole model

4. Results and discussion

4.1. Model results

4.2. FLUENT results

4.3. Validation of the numerical results with the experimental data

4.4. Comparison between the model and FLUENT results

4.5. Comparison of the model and the results of Pastohr et al.

5. Conclusions

Acknowledgements

References

Energy Conversion and Management, Volume 52, Issue 2, February 2011, Pages 876-883

Guoliang Xu, Tingzhen Ming, Yuan Pan, Fanlong Meng, Cheng Zhou

Power generating technology based on renewable energy resources will definitely become a new trend of future energy utilization. Numerical simulations on air flow, heat transfer and power output characteristics of a solar chimney power plant model with energy storage layer and turbine similar to the Spanish prototype were carried out in this paper, and mathematical model of flow and heat transfer for the solar chimney power plant system was established. The influences of solar radiation and pressure drop across the turbine on the flow and heat transfer, output power and energy loss of the solar chimney power plant system were analyzed. The numerical simulation results reveal that: when the solar radiation and the turbine efficiency are 600 W/m2 and 80%, respectively, the output power of the system can reach 120 kW. In addition, large mass flow rate of air flowing through the chimney outlet become the main cause of energy loss in the system, and the collector canopy also results in large energy loss.

Article Outline

Nomenclature

1. Introduction

2. Theoretical models

2.1. Physics model

2.2. Mathematical model

2.3. Boundary conditions and solution method

3. Validity

4. Results and discussion

5. Conclusion

References

Solar Energy, In Press, Corrected Proof, 2011

Ian Edmonds

This article outlines the concept, theory and performance of an engine for converting the heat in warm, saturated air to electrical energy. The engine comprises a drive balloon and a support balloon both connected to an electric generator by a rope. Warm, saturated air from a source such as a solar pond or the cooling tower of a power station is used to charge the larger drive balloon. The two balloons ascend several kilometers while performing work on the electric generator. At some maximum height the larger drive balloon discharges all its air into the cold upper atmosphere and, with the smaller balloon providing support for the larger balloon envelope, the two balloons are hauled back to ground by switching the electric generator to electric motor operation. The work done by the system on the electric generator during ascent exceeds the work done on the system by the electric motor during descent resulting in a positive work output. Condensation of water vapor in the drive balloon maintains the internal saturated air temperature above ambient temperature and provides an increasing lift force with height. Recycling the condensate adds to the work output of the engine and conserves water. The ideal thermal efficiency of the engine approaches 15%, corresponding to the large temperature difference available within the 10 km height of the troposphere. The engine power scales as the cube of the drive balloon diameter. Scaling by a factor of four up from the diameter of commercially available balloons provides power outputs in the MW range.

Article Outline

Nomenclature

1. Introduction

2. The upper atmosphere as a low temperature heat sink

3. Balloon engines operating between ground level and the upper atmosphere

3.1. A balloon engine operating with warm, saturated air

4. Theory of a saturated air balloon engine

4.1. Ideal efficiency of an unfilled balloon engine

4.1.1. Unfilled engine, no water recycling

4.1.2. Unfilled engine with water recycling

4.2. Ideal efficiency of a filled balloon engine

4.2.1. Filled engine, no water recycling

4.2.2. Filled engine with water recycling

4.3. The efficiency of balloon engines with different ambient air and input air parameters

4.4. Engine efficiency for dry air input

5. Predicted performance of a practical saturated air balloon engine

5.1. Validity of the assumption of adiabatic change

6. Discussion

6.1. Factors determining the average power output of balloon engines

6.2. Percentage increase in power station output when using balloon engines

6.3. Scaling factors for the cost of balloon engines

6.4. The effect of wind in increasing the power output of balloon engines

7. Conclusions

References

Energy, Volume 36, Issue 2, February 2011, Pages 1236-1242

Sandro Nizetic

The instability and unpredictability of future global energy markets necessitate the development of new alternative technical solutions to meet our continuously increasing energy demands. This rapid development has permanent consequences for the environment. This paper analyses several technical solutions and theoretical ideas concerning energy utilisation, i.e. for carbon-free electricity production. The ideas are discussed from theoretical and experimental perspectives. This review focuses on methods of production of an artificial vortex column in the surrounding atmosphere. Namely, convective vortices can be used as heat engines to convert available solar energy into mechanical work. Some of the proposed technical solutions deal with the ability to capture the mechanical energy and produce electricity. The discussion focuses on theoretical models and experimental results. The main aim of this study was to identify the state of the art. The conclusions presented herein may form a basis for further development of this alternative carbon-free concept of energy utilisation.

Article Outline

Nomenclature

1. Introduction

2. Available mechanical work from convective vortices: a theoretical overview

2.1. Working potential of the convective vortices

2.2. Heat-to-work efficiency of convective vortices

2.3. Idealised standard air cycles in the atmosphere

2.4. The impact of air humidity on the working potential

3. Experimental attempts to produce artificial convective vortices

3.1. Atmospheric vortex engine

3.2. Meteotron experiment

3.3. Large tornado simulation chamber experiment

3.4. Solar power plant with a short diffuser

4. Possible development trends

5. Conclusions

Acknowledgements

References

Research highlights

► Detailed review of the previous research that deals with possibility of the convective vortices utilisation for carbon-free electricity production which was not done before in any previously published papers. ► Introduced new analytical approach for estimating heat-to-work efficiency of the convective vortices apprehended as heat engines, and detailed analysis of heat-to-work efficiency. ► Detail air cycle analysis with introduction of the modificated Brayton air cycle as one that is close to the real air cycle and comparison with other standard cycles. ► Impact analysis of air humidity on the working potential of the air. ► Proposed alternative concept for convective vortices utilisation, i.e. "Solar power plant with a short diffuser". ► Review of the experimental attempts to produce artificial convective vortices.