Hybrid photovoltaic-thermal(PV-T)collectors,which are capable of cogenerating useful thermal energy and electricity from the same aperture area,have a significantly higher overall efficiency and ability to displace em...Hybrid photovoltaic-thermal(PV-T)collectors,which are capable of cogenerating useful thermal energy and electricity from the same aperture area,have a significantly higher overall efficiency and ability to displace emissions compared to independent,separate photovoltaic panels,solar thermal collectors or combinations thereof.Spectral splitting has emerged as a promising route towards next-generation high-performance PV-T collectors,and nanotechnology plays an important role in meeting the optical and thermal requirements of advanced spectral splitting PV-T collector designs.This paper presents a comprehensive review of spectral splitting technologies based on nanomaterials for PV-T applications.Emerging nanomaterials(nanofluids,nanofilms and nanowires)suitable for achieving spectral splitting based on reflection,diffraction,refraction and/or absorption approaches in PV-T collectors are presented,along with the associated challenges and opportunities of these design approaches.The requirements from such materials in terms of optical properties,thermal properties,stability and cost are discussed with the aim of guiding future research and innovation,and developing this technology towards practical application.Nanofluids and nanofilms are currently the most common nanomaterials used for spectral splitting,with significant progress made in recent years in the development of these materials.Nevertheless,there still remains a considerable gap between the optical properties of currently-available filters and the desired properties of ideal filters.Aiming to instruct and guide the future development of filter materials,a simple generalized method is further proposed in this paper to identify optimal filters and efficiency limits of spectral splitting PV-T systems for different scenarios.It is found that the optimal filter of a spectral splitting PV-T system is highly sensitive to the value of thermal energy relative to that of electricity,which therefore depends strongly on the application and location.The efficiency limit of spectral splitting PV-T collectors is significantly higher than that of standalone PV panels.The stability of nanomaterial filters remains a critical challenge for their long-term employment and also for high-temperature operation in practical applications.展开更多
Spectral splitting is an approach to the design of hybrid photovoltaic-thermal(PVT)collectors that promises significant performance benefits.However,the ultimate efficiency limits,optimal PV cell materials and optical...Spectral splitting is an approach to the design of hybrid photovoltaic-thermal(PVT)collectors that promises significant performance benefits.However,the ultimate efficiency limits,optimal PV cell materials and optical filters of spectral-splitting PVT(SSPVT)collectors remain unclear,with a lack of consensus in the literature.We develop an idealized model of SSPVT collectors and use this to determine their electrical and thermal efficiency limits,and to uncover how these limits can be approached through the selection of optimal PV cell materials and spectral-splitting filters.Assuming that thermal losses can be minimized,the efficiency limit,optimal PV material and optimal filter all depend strongly on a coefficient w,which quantifies the value of the delivered thermal energy relative to that of the generated electricity.The total(electrical plus thermal)efficiency limit of SSPVT collectors increases at higher w and at higher optical concentrations.The optimal spectral-splitting filter is defined by sharp lower-and upper-bound energies;the former always coincides with the bandgap of the cell,whereas the latter decreases at higher w.The total effective efficiency limit of SSPVT collectors is over 20%higher than those of either standalone PV modules or standalone ST collectors when w is in the range from 0.35 to 0.50 and up to 30%higher at w~0.4.This study provides a method for identifying the efficiency limits of ideal SSPVT collectors and reports these limits,along with guidance for selecting optimal PV materials and spectral-splitting filters under different conditions and in different applications.展开更多
In this paper the provision of flexible generation is investigated by extracting steam from Rankine-cycle power stations during off-peak demand in order to charge thermal tanks that contain suitable phase-change mater...In this paper the provision of flexible generation is investigated by extracting steam from Rankine-cycle power stations during off-peak demand in order to charge thermal tanks that contain suitable phase-change materials(PCMs);at a later time when this is required and/or is economically effective,these thermal energy storage(TES)tanks can act as the heat sources of secondary thermal power plants in order to generate power,for example as evaporators of,e.g.,organic Rankine cycle(ORC)plants that are suitable for power generation at reduced temperatures and smaller scales.This type of solution offers greater flexibility than TES-only technologies that store thermal energy and release it back to the base power station,since it allows both derating but also over-generation compared to the base power-station capacity.The solution is applied in a case study of a 50-MW rated oil-fired power station unit at the autonomous system of Crete.The optimal operation of the TES system is investigated,by solving a modified Unit Commitment-Economic Dispatch optimization problem,which includes the TES operating constraints.The results indicate that for most of the scenarios the discounted payback period is lower than 12 years,while in few cases the payback period is 5 years.展开更多
基金the UK Engineering and Physical Sciences Research Council(EPSRC)[grant number EP/M025012/1]the Imperial College London EPSRC Impact Acceleration Account[grant number EP/R511547/1].
文摘Hybrid photovoltaic-thermal(PV-T)collectors,which are capable of cogenerating useful thermal energy and electricity from the same aperture area,have a significantly higher overall efficiency and ability to displace emissions compared to independent,separate photovoltaic panels,solar thermal collectors or combinations thereof.Spectral splitting has emerged as a promising route towards next-generation high-performance PV-T collectors,and nanotechnology plays an important role in meeting the optical and thermal requirements of advanced spectral splitting PV-T collector designs.This paper presents a comprehensive review of spectral splitting technologies based on nanomaterials for PV-T applications.Emerging nanomaterials(nanofluids,nanofilms and nanowires)suitable for achieving spectral splitting based on reflection,diffraction,refraction and/or absorption approaches in PV-T collectors are presented,along with the associated challenges and opportunities of these design approaches.The requirements from such materials in terms of optical properties,thermal properties,stability and cost are discussed with the aim of guiding future research and innovation,and developing this technology towards practical application.Nanofluids and nanofilms are currently the most common nanomaterials used for spectral splitting,with significant progress made in recent years in the development of these materials.Nevertheless,there still remains a considerable gap between the optical properties of currently-available filters and the desired properties of ideal filters.Aiming to instruct and guide the future development of filter materials,a simple generalized method is further proposed in this paper to identify optimal filters and efficiency limits of spectral splitting PV-T systems for different scenarios.It is found that the optimal filter of a spectral splitting PV-T system is highly sensitive to the value of thermal energy relative to that of electricity,which therefore depends strongly on the application and location.The efficiency limit of spectral splitting PV-T collectors is significantly higher than that of standalone PV panels.The stability of nanomaterial filters remains a critical challenge for their long-term employment and also for high-temperature operation in practical applications.
基金supported by the UK Engineering and Physical Sciences Research Council(EPSRC)(grant numbers EP/M025012/1 and EP/R045518/1)supported by the Imperial College London EPSRC Impact Acceleration Account(grant number EP/R511547/1).We thank UK company Solar Flow Ltd(www.solar-flow.co.uk).
文摘Spectral splitting is an approach to the design of hybrid photovoltaic-thermal(PVT)collectors that promises significant performance benefits.However,the ultimate efficiency limits,optimal PV cell materials and optical filters of spectral-splitting PVT(SSPVT)collectors remain unclear,with a lack of consensus in the literature.We develop an idealized model of SSPVT collectors and use this to determine their electrical and thermal efficiency limits,and to uncover how these limits can be approached through the selection of optimal PV cell materials and spectral-splitting filters.Assuming that thermal losses can be minimized,the efficiency limit,optimal PV material and optimal filter all depend strongly on a coefficient w,which quantifies the value of the delivered thermal energy relative to that of the generated electricity.The total(electrical plus thermal)efficiency limit of SSPVT collectors increases at higher w and at higher optical concentrations.The optimal spectral-splitting filter is defined by sharp lower-and upper-bound energies;the former always coincides with the bandgap of the cell,whereas the latter decreases at higher w.The total effective efficiency limit of SSPVT collectors is over 20%higher than those of either standalone PV modules or standalone ST collectors when w is in the range from 0.35 to 0.50 and up to 30%higher at w~0.4.This study provides a method for identifying the efficiency limits of ideal SSPVT collectors and reports these limits,along with guidance for selecting optimal PV materials and spectral-splitting filters under different conditions and in different applications.
文摘In this paper the provision of flexible generation is investigated by extracting steam from Rankine-cycle power stations during off-peak demand in order to charge thermal tanks that contain suitable phase-change materials(PCMs);at a later time when this is required and/or is economically effective,these thermal energy storage(TES)tanks can act as the heat sources of secondary thermal power plants in order to generate power,for example as evaporators of,e.g.,organic Rankine cycle(ORC)plants that are suitable for power generation at reduced temperatures and smaller scales.This type of solution offers greater flexibility than TES-only technologies that store thermal energy and release it back to the base power station,since it allows both derating but also over-generation compared to the base power-station capacity.The solution is applied in a case study of a 50-MW rated oil-fired power station unit at the autonomous system of Crete.The optimal operation of the TES system is investigated,by solving a modified Unit Commitment-Economic Dispatch optimization problem,which includes the TES operating constraints.The results indicate that for most of the scenarios the discounted payback period is lower than 12 years,while in few cases the payback period is 5 years.
