| The development of renewable energy can contribute to the "carbon peak" and"carbon neutral" strategy.Solar energy is one of the most potential renewable energies.However,solar energy has some shortcomings such as low energy density and poor stability.Solar photochemical or thermochemical fuel production,can convert unstable and discontinuous solar energy into chemical energy of fuel.However,solar photochemical fuel production can only use a part of solar energy and solar photochemical efficiency is low;While in thermochemical fuel production process,the full spectrum of solar energy is converted to thermal energy,which is then converted into chemical energy,without considering the "quality" difference of solar energy in different bands.As there are many shortages in single photochemical or thermochemical fuel production,this dissertation focuses on the goal of efficient conversion and storage of solar full-spectrum energy.In light of the breakthrough point of the cross between different transformation methods and technical paths,the academic thought is changed from the emphasis on the "quantity" of solar energy traditionally into the "quality" difference of solar energy in different bands.The mechanism,method,system and experimental research is carried out from two research methods of solar full-spectrum energy cascade utilization and comprehensive utilization of photo energy and thermal energy respectively.The main contents and conclusions of this paper are as follows:(1)In view of the low efficiency of single photochemical and single thermochemical fuel production systems,the solar full-spectrum energy storage method with photoisomerism and methanol decomposition is proposed.The high-level solar energy is stored in the chemical bonds of the products by photoisomerism process,and the low-level solar energy is stored in the chemical energy of the products by methanol decomposition process.The annual average solar chemical efficiency can reach 49.78%on the off-design condition.(2)To solve the problem of large thermalization loss of the photovoltaic cell in existing photovoltaic-thermochemical systems,a cascade utilization method with chemical energy storage and photovoltaic cell is proposed for the utilization of the full spectrum of solar energy.The low-level solar energy which can not be used by the photovoltaic cell is recovered in the form of thermal energy,while the high-level solar energy whose photon energy is far higher than the band gap of the photovoltaic cell is utilized by photochemistry.In such a way,thermalization loss of the photovoltaic cell is reduced,and the utilization efficiency of high-level solar energy is improved.On the design condition,the solar energy utilization efficiency of the proposed system reaches up to 66.95%,which is higher than that of the photovoltaic-thermochemical systems.The superiority of the proposed system is more significant when solar irradiation is low.(3)For the large optical loss of solar thermochemical fuel production with single-axis tracking parabolic trough concentrated collectors and double-axis tracking parabolic trough concentrated collectors not applicable to large solar field,the distributed energy system integrated solar thermochemical fuel production with double-axis tracking parabolic trough concentrated collectors is proposed due to the smaller solar field needed by distributed energy systems.Solar chemical efficiency is improved in solar thermochemical fuel production unit,and it also solves the problem that the output of the distributed energy system does not match the user load due to the instability and discontinuity of the renewable energy.Thermodynamic analysis results show that the annual solar thermochemical efficiency is increased by 27%,the primary energy efficiency of the system is 74.74%on the design condition,and the exergic efficiency is 48.83%.It still has good performance under the off-design condition where solar irradiation and user loads change simultaneously.Solar thermochemical fuel production unit enhances the flexibility and stability of the distributed energy system.(4)Experimental study on photothermal hydrogen production from water is carried out,where the thermal energy is converted from the long-wavelength photo energy or the external heat source.The kinetic properties of photochemical,thermochemical,full-spectrum photothermal chemical and photothermal chemical with external heat source reactions are compared.Results show that when 10%triethylamine is added to water,photothermal chemical reaction rate with external heat source at 80? and 300W xenon lamp is 2.29 times of the sum of the single photochemical reaction and thermochemical reaction rate(80?),which is smaller than the photothermal chemical synergistic factor 3.03 under full spectrum light. |
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