The accumulation of soiling on photovoltaic (PV) modules affects PV systems worldwide. Soiling consists of mineral dust, soot particles, aerosols, pollen, fungi and/or other contaminants that deposit on the surface of PV modules. Soiling absorbs, scatters, and reflects a fraction of the incoming sunlight, reducing the intensity that reaches the active part of the solar cell. Here, we report on the comparison of naturally accumulated soiling on coupons of PV glass soiled at seven locations worldwide. The spectral hemispherical transmittance was measured. It was found that natural soiling disproportionately impacts the blue and ultraviolet (UV) portions of the spectrum compared to the visible and infrared (iR). Also, the general shape of the transmittance spectra was similar at all the studied sites and could adequately be described by a modified form of the Ångström turbidity equation. In addition, the distribution of particles sizes was found to follow the IEST-STD-CC 1246E cleanliness standard. The fractional coverage of the glass surface by particles could be determined directly or indirectly and, as expected, has a linear correlation with the transmittance. It thus becomes feasible to estimate the optical consequences of the soiling of pV modules from the particle size distribution and the cleanliness value. Soiling has a negative impact on the economic revenues of PV installations, not only because it reduces the amount of energy converted by the PV modules, but also because it introduces additional operating and maintenance costs and, at the same time, increases the uncertainty on the estimation of PV performance, leading to both higher financial risks and interest rates charged to plant developers. Power reductions greater than 50% have been reported in the literature because of soiling 1,2 ; it has been estimated that an average loss of 4% on the global annual energy yield of PV could cause losses in revenue on the order of 2 × 10 9 US$ annually 3. A careful monitoring of soiling is required to mitigate its effect 4. Soiling losses are generally quantified by using soiling stations. These systems are made of at least two PV devices, one of which is regularly cleaned while the other is left to soil naturally. By comparing the ratio of the electrical outputs of the two devices, it is possible to estimate the impact of soiling on the PV performance 5,6. The International Electrotechnical Commission's (IEC) metric to monitor and quantify the impact of soiling on PV modules is the soiling ratio, r s , which expresses the ratio of the electrical output of a soiled PV device to the output of the same device under clean conditions 7. Like the transmittance, a higher soiling ratio translates to less soiling deposited on the modules. A value of 1 indicates clean conditions, with no soiling. For a more detailed definition of r s , please refer to the Methodology section. The fractional loss of solar-generated power due to soiling is 1 − r s .

Perfect absorbers are indispensable components for energy harvesting applications. While many absorbers have been proposed, they encounter inevitable drawbacks including bulkiness or instability over time. The urge for CMOS compatible absorber that can be integrated for on chip applications requires further investigation. We theoretically demonstrate Silicon (Si) based mid IR super absorber with absorption (A) reaching 0.948. Our structure is composed of multilayered N-doped Si/ Si hyperbolic metamaterial (HMM) integrated with sub-hole Si grating. Our proposed structure has tunable absorption peak that can be tuned from 4.5 µm to 11 µm through changing the grating parameters. We also propose two grating designs integrated with N-doped Si/ Si HMM that can achieve wide band absorption. The first grating design is based on Si grating incorporating different holes’ height with (A) varying between 0.83 and 0.97 for wavelength from 5 µm to 7 µm. The second grating design is based on Si grating with variable holes’ diameter; the latter shows broad band absorption with the maximum (A) reaching 0.97. We also show that our structure is omnidirectional. We propose an all Si based absorber which demonstrates a good candidate for thermal harvesting application.

Graphene, as an optically transparent material, typically defies any attempt for mid-infrared (mid-IR) absorption, which limits its applications in mid-IR biosensing. Although remarkable evidence for mid-IR nanopatterned graphene plasmons has been reported via the induction of free charge carriers, no study so far has investigated plasmonic excitation in nanopatterned graphene without employing induced voltage, high chemical doping, or metallic reflectors. In this work, we show that localized plasmon resonance (LSPR) can be probed in metal-free, naturally doped, nanomembrane graphene (NMG) without induced voltage or using metallic layers. We rely on facile, lithography-free, fabrication methodology to pattern nanoscale holes in a single sheet of graphene using Au nanoislands with hole dimensions as small as 10 nm. We image the LSPR at the graphene membrane edges via scanning near-field optical microscopy. Our experimental findings are confirmed by theoretical electromagnetic field mapping at the graphene membrane edges leading to noticeable absorption. We demonstrate the dependence of this absorption wavelength on the hole diameter and interhole distance; hence, we present a new avenue to fundamentally boost light harvesting with naturally doped NMG which is pivotal for mid-IR sensors. We show that our designed NMG can be used as a mid-IR biosensor with theoretically calculated sensitivity of 825 nm/RIU.

Noble Metals such as Gold and Silver demonstrated for mid IR metamaterials have suffered many obstacles such as: high losses and lack of tunability. The application of doped semiconductors has allowed overcoming the tunability restriction, besides, possessing lower losses as compared to metals. In addition, doped semiconductors have small magnitude of negative real permittivity which is required to realize mid IR Hyperbolic Metamaterials (HMMs). We theoretically demonstrate super focusing based on an all Semiconductor planar HMM using InAs heterostructure. By applying a single slit integrated with doped InAs/InAs HMM, incident light can be coupled to high propagation wave vectors of the HMM modes leading to sub diffraction focusing within the mid IR wave length range. Our proposed structure shows a wide controllable/ tunable operation by changing the doping concentration of InAs. As a consequence, focusing resolution can be tuned over the mid IR ranging from 4.64 μm to 19.57 μm with the maximum achieved resolution is up to 0.045λ at an operating wavelength of 19.57 μm. In addition, we show the effect of substrate refractive index on tuning and enhancing the focusing resolution. Our proposed HMM is an all single based material in which it will not suffer lattice mismatch restrictions during fabrication.

No abstract