Study On The Characteristics Of Combined Photovoltaic And Thermoelectric Power Generation Via Nanofluid Spectral Splitting

Photovoltaic power generation relieves the pressure on the traditional energy supply and provides an effective way to achieve the goal of " carbon emissions peak and carbon neutrality ".However,the accumulation of photon energy on the surface of photovoltaic cells will lead to cell efficiency reduction or irreversible thermal damage.Therefore,the effective heat dissipation of photovoltaic cells is very important for the efficient operation of solar power stations.The spectrum splitting technology,an active cooling technology based on the utilization of solar energy,realizes the decoupling operation of photovoltaic and photothermal modules.It is one of the effective ways to prevent photovoltaic cells from overheating.However,the performance evaluation method of the photovoltaic/thermal（PV/T）system is still imperfect and the conversion efficiency of solar energy to high-grade electric energy is still low.In this paper,the performance of PV–thermoelectric combined power generation was investigated,and the technical feasibility of further improving the stable power output in PV/T system by nanofluid splitter was explored.Based on the finite difference time domain method,the absorption,scattering,and extinction cross sections of the nanoparticle were calculated,and the influence of particle size on photon absorption capacity was analyzed.The decrease in particle size strengthened the photon absorption ratio,and when the particle size was 10 nm,the absorption ratio was close to 1.Therefore,a 10 nm nanoparticle can improve the PT conversion performance while maintaining spectral characteristics.Meanwhile,Au nanofluid was prepared by the sodium citrate reduction method,and its particle size was about 10 nm.Moreover,it had a wide absorption band in the visible range,with the characteristic peak corresponding to the wavelength of ～524 nm,which matched well with the response band of the Si-PV cell.Besides,the electromagnetic distribution of particles indicated that along the direction of incident polarization and perpendicular to the direction of incident polarization,there was an electromagnetic enhancement effect on the surface of particles,and then heat the base liquid around the particles to increase the fluid temperature.Based on the above research,the results verify the spectral absorption characteristics and PT conversion ability of plasmon nanofluids in PV/T technology.The performance test platform of the thermal decoupled PV/T system was built,and the photon energy outside the spectral response band of the Si-PV cell was pre-absorbed by the front absorption single-channel structure.By adjusting the nanofluid concentration and the splitter thickness,the regulation law of PV efficiency and PT efficiency was analyzed,and the influence of nanoparticle concentration and splitter thickness on energy distribution was explored.Considering heat loss to introduce exergy efficiency,the influence of energy distribution on output energy grade was expounded,while combining energy conversion efficiency.The results show that the increase of nanofluid concentration and the splitter thickness can strengthen the thermal energy output and promote energy conversion efficiency.The energy efficiency of the PV/T system reached 88.5%,and the improved PT efficiency can make up for the loss of electrical energy output.However,the increase in heat loss led to a gradual increase in the efficiency and then a downward trend.When the thickness reached 18 mm,the equilibrium temperature was 49.9 ℃ and the efficiency was 12.8%.Considering the thermal recovery of the PV/T system,a hybrid power generation system is constructed by coupling a thermoelectric generator（TEG）and the heat storage module.The TEG is driven to generate electricity by the thermal energy output of nanofluid.The influences of energy distribution,nanofluid flow rate,TEG cold-junction temperature on TEG and PV output current density,and heat storage temperature are analyzed.Further,the nanofluid concentration is optimized to improve the energy output grade of the system.Moreover,adjust the heat storage and power generation performance of the nanofluid flow rate balance hybrid system.Last to explore the ability of thermal recovery technology to alleviate the fluctuation of output energy and discuss the low-temperature applicability of the system.The results show that higher thermal energy output strengthened the output current density of the hybrid power generation system,and TEG output current density accounts for 51.0% of the total electric energy.Based on the changing trend of PV and TEG electrical properties with cooling temperature,when the cooling temperature was reduced to 5 ℃,the current density increased by ～2.55 times.Moreover,the flow exothermic characteristic of nanofluids alleviated the fluctuation of energy output.