Efficiency limits of concentrating spectral-splitting hybrid photovoltaic-thermal (PV-T) solar collectors and systems

Abstract

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.

Selective Solar Harvesting Windows for Full‐Spectrum Utilization

“…Figure 3e shows that the generated electrical power is around 6 W m −2 and the thermal power is around 150 W m −2 , which is 25 times of the generated electrical power, suggesting that the harvesting thermal power is of primary importance for building‐integrated solar energy harvesting windows. Here, we consider the equivalence of the thermal power and electrical power and provide an overall estimation to the SSH window's solar energy conversion efficiency with a total effective efficiency, [ 16 ] i.e., η tot = η ele + w • η th , where w is a weight coefficient that ranges from 0 to 1 and represents the worth of thermal energy relative to that of electricity. The value of w can be based on a thermodynamic value (e.g., via the second‐law arguments or heat engine conversion efficiencies), a cost value (e.g., through a price ratio of heat/electricity), or a ratio of environmental benefits (e.g., displaced or mitigated emissions).…”

“…The η tot of the SSH window drops to 15.8% and 6.8% when the weight coefficient w = 0.5 and 0.2, respectively. Note that when w is >0.36, which is the conversion factor of the thermal power plant, [ 16 ] the SSH window would outperform the most efficient TPV ever reported [ 19 ] ( η tot = η ele = 12.6%, T v = 21.5%). We believe, in most scenarios, our SSH window will serve as one of the most efficient candidates for building‐integrated solar harvesting devices.…”

Reassessment of different flat TCO integrated reflectors for the crystalline silicon solar PV module in view of its longer operational life

“…In the literature, different fluids were analysed for selective wavelength absorption between collector and concentrator, such as water, inorganic aqueous salts, silicone oil, glycol, synthetic and mineral oils, ethylene, propylene and ZnO nanofluid. [32][33][34]. The thin-film-based spectrally selective filters consist of single or multilayer interference of different materials in order of their refractive index value [35,36].…”

Evaluation of the potential of nanofluids containing different Ag nanoparticle size distributions for enhanced solar energy conversion in hybrid photovoltaic-thermal (PVT) applications

“…These types of HTFs originally allowed PVT systems to progress in terms of the efficiencies achieved and reduced the costs involved in the unification process [17,18]. An alternative solution is to place the HTF in front of the PVT [19], however, for this configuration to yield a positive exergetic merit for the system the spectral properties of these HTF needs to be carefully assessed before their integration in PVT applications [20]. This stems from the fact that in order to efficiently partition the solar spectrum into its respective thermal and electrical components, the optical properties of the HTF must also be spectrally matched to the responsivity of the PV element [21,22].…”