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37th European Photovoltaic Solar Energy Conference and Exhibition; 1923-1926, Vertical bifacial PV systems are becoming of great interest, also thanks to their adaptability to new PV systems integration options, such as on solar noise barriers. A substantial part of the extra yield of those systems comes from harvesting diffuse and reflected irradiance, therefore it is crucial to understand, quantify and optimise the effect of albedo on this type of PV systems. The goal of this work is to show that enhanced albedo can significantly contribute to improving the energy yield of vertical bifacial PV systems. The investigation of the albedo effect is performed both from an experimental and modelling point of view, using the case study of Solar Highways (SH), currently the largest bifacial solar noise barrier in the world. More than 1 year of measurements revealed that placing a high-albedo patch on the rear east side of a SH element led to a monthly energy gain of 3%. On sunny days the energy boost reached more than 6%. Simulations performed with the bifacial PV modelling tool BIGEYE showed that the gain associated with enhanced albedo can go up to 10%/year thanks to the optimisation of some configuration parameters such as albedo coefficient and ground slope.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1759-1762, Up to this point most floating PV projects have been installed on water bodies where relatively small waves occur. In the foreseeable future however, floating PV systems will be installed on large water bodies e.g. lakes or even on sea where medium to extreme waves can be formed. Therefore the aim of this study is to investigate the effect of waves on the performance of floating systems. The movement of PV panels, induced by wave-forces, makes that panels have different orientations, thus the Gpoa of the panels within a string varies. This causes mismatch losses within a single string. A model has been created to calculate these losses on an annual basis. Measured wave data of three different locations (extreme -, high - and medium wave intensity) together with GHI-data has been used as input for the model. It has been found that wave induced mismatch losses (WIML) can be significant. The loss in yield can be up to 9% for the location with extreme wave intensity, 7% for the location with high wave intensity and 3% for the location with medium wave intensity.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1437-1439, Floating solar systems can represent a serious alternative to ground mounted solar systems. At present, the international market for floating PV is small compared to the total PV market, but expected to become a multi-billion market in the coming years. A main driver for the growth of the market for floating PV is the mitigation of land cost. Other drivers are the potential added benefits of deploying photovoltaics on water such as a lower module temperature and reflections from the water, leading to higher energy output. Covering hydropower lakes or drinking water reservoirs will decrease evaporation rates. At present, Japan and China are the two driving markets, with Japan hosting a large number of projects and China being home to a number of very large systems, with the largest over 100MWp. In Europe, the UK hosts the largest systems. The yearly installed capacity shows a quickly increasing trend from 3MWp in 2013 to more than 400 MWp in 2017. Research projects are being executed in Singapore, Malta and the Netherlands. Of 20 different available floating PV systems we assessed different properties that affect the energy output, packing density, survivability, ease of maintenance and installation speed. We see large differences in design philosophy between the systems.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1375-1378, Two modular noise barrier test setups containing photovoltaic modules have been installed in the Netherlands, one in a North/South orientation, and the other in East/West orientation. Both setups contain one set of mono-facial c-Si panels, one set of bi-facial c-Si panels and two luminescent solar concentrator (LSC) panels, one red and one orange/yellow. The performance of all panels is monitored along with the irradiation and temperature data. Here we will focus on the performance of the two LSC panels and present the results of a ray-tracing model that mimics the situation at the demo site.

In this study, we present a new light absorption enhancement method for p-i-n thin film silicon solar cells using pyramidal surface structures, larger than the wavelength of visible light. Calculations show a maximum possible current enhancement of 45% compared with cells on a flat substrate. We deposited amorphous silicon (a-Si) thin film solar cells directly onto periodically pyramidal-structured polycarbonate (PC) substrates, which show a significant increase (30%) in short-circuit current over reference cells deposited on flat glass substrates. The current of the cells on our pyramidal structures on PC is only slightly lower than that of cells on Asahi U-type TCO glass (Asahi Glass Co., Tokyo, Japan), but suffer from a somewhat lower open circuit voltage and fill factor. Because the used substrates have a locally flat surface area due to the fabrication process, we believe that the current enhancement in the cells on structured PC can be increased using larger or more closely spaced pyramids, which can have a smaller flat surface area.

In the search for sustainable energy sources, solar energy can fulfil a large part of the growing demand. The biggest threshold for large-scale solar energy harvesting is the solar panel price. For drastic cost reductions, roll-to-roll fabrication of thin film silicon solar cells using plastic substrates can be a solution. In this thesis, we investigate the possibilities of depositing thin film solar cells directly onto cheap plastic substrates. Micro-textured glass and sheets, which have a wide range of applications, such as in green house, lighting etc, are applied in these solar cells for light trapping. Thin silicon films can be produced by decomposing silane gas, using a plasma process. In these types of processes, the temperature of the growing surface has a large influence on the quality of the grown films. Because plastic substrates limit the maximum tolerable substrate temperature, new methods have to be developed to produce device-grade silicon layers. At low temperature, polysilanes can form in the plasma, eventually forming dust particles, which can deteriorate device performance. By studying the spatially resolved optical emission from the plasma between the electrodes, we can identify whether we have a dusty plasma. Furthermore, we found an explanation for the temperature dependence of dust formation; Monitoring the formation of polysilanes as a function of temperature using a mass-spectrometer, we observed that the polymerization rate is indeed influenced by the substrate temperature. For solar cell substrate material, our choice was polycarbonate (PC), because of its low cost, its excellent transparency and its relatively high glass transition temperature of 130-140°C. At 130°C we searched for deposition recipes for device quality silicon, using a very high frequency plasma enhanced chemical deposition process. By diluting the feedstock silane with hydrogen gas, the silicon quality can be improved for amorphous silicon (a‑Si), until we reach the nanocrystalline silicon (nc‑Si) regime. In the nc‑Si regime, the crystalline fraction can be further controlled by changing the power input into the plasma. With these layers, a-Si thin film solar cells were fabricated, on glass and PC substrates. The adverse effect of the low temperature growth on the photoactive material is further mitigated by using thinner silicon layers, which can deliver a good current only with an adequate light trapping technique. We have simulated and experimentally tested three light trapping techniques, using embossed structures in PC substrates and random structures on glass: regular pyramid structures larger than the wavelength of light (micropyramids), regular pyramid structures comparable to the wavelength of light (nanopyramids) and random nano‑textures (Asahi U‑type). The use of nanostructured polycarbonate substrates results in initial conversion efficiencies of 7.4%, compared to 7.6% for cells deposited under identical conditions on Asahi U-type glass. The potential of manufacturing thin film solar cells at processing temperatures lower than 130oC is further illustrated by obtained results on texture‑etched aluminium doped zinc-oxide (ZnO:Al) on glass: we achieved 6.9% for nc-Si cells using a very thin absorber layer of only 750 nm, and by combining a-Si and nc-Si cells in tandem solar cells we reached an initial conversion efficiency of 9.5%.

The synthesis of metallic tungsten nanostructures and highly nanostructured thin films is presented. Crystalline tungsten oxide nanostructures are deposited on glassy carbon substrates kept at 700¿±¿100¿°C by oxidizing resistively heated tungsten filaments in an air flow under subatmospheric pressures. The internal morphology of the deposited tungsten oxide can be reproducibly controlled by the air pressure. After deposition, the tungsten oxides have been fully reduced to metallic tungsten by atomic hydrogen at a temperature of about 730¿°C. Polycrystalline metallic tungsten nanofibers, nanocrystallites, closed crystallite films, and nanogranular films are thus obtained in a single procedure involving deposition and subsequent reduction, at relatively low temperatures.

In this study, we present a new light absorption enhancement method for p-i-n thin film silicon solar cells using pyramidal surface structures, larger than the wavelength of visible light. Calculations show a maximum possible current enhancement of 45% compared with cells on a flat substrate. We deposited amorphous silicon (a-Si) thin film solar cells directly onto periodically pyramidal-structured polycarbonate (PC) substrates, which show a significant increase (30%) in short-circuit current over reference cells deposited on flat glass substrates. The current of the cells on our pyramidal structures on PC is only slightly lower than that of cells on Asahi U-type TCO glass (Asahi Glass Co., Tokyo, Japan), but suffer from a somewhat lower open circuit voltage and fill factor. Because the used substrates have a locally flat surface area due to the fabrication process, we believe that the current enhancement in the cells on structured PC can be increased using larger or more closely spaced pyramids, which can have a smaller flat surface area.

Control of the formation of dust particles in a silane deposition plasma is very important for avoiding electrical shunts in devices, such as thin film silicon solar cells. In this work we present a noninvasive in situ method for identification of the plasma regime, based on optical emission spectroscopy (OES), which can be applied to silane=hydrogen plasmas at low substrate temperatures. By monitoring the OES spectra as a function of the position perpendicular to the plasma electrodes we developed a method to identify the transition of a plasma from the dust free to a dusty regime, which was confirmed by TEM images of layers deposited in both regimes. Using this technique we mapped this transition as a function of applied forward very-high frequency (VHF) power and hydrogen dilution at different substrate temperatures. The advantage of this technique is that the experiment is insensitive to optical transmission loss at the viewport due to deposition of silicon films. As the transition from the dust free to the dusty regime is substrate temperature dependent and the transition from amorphous to nanocrystalline growth mainly depends on hydrogen dilution, a limited parameter window has been defined in which dust-free amorphous silicon can be deposited at low substrate temperatures. A single simple OES technique can be used for in situ monitoring of amorphous to nanocrystalline transition as well as the onset of the dusty regime in a thin film silicon cell fabrication process.

We present a novel method to achieve light trapping in thin film silicon solar cells. Unlike the commonly used surface textures, such as Asahi U-type TCO, that rely on light scattering phenomena, we employ embossed periodically arranged micro-pyramidal structures with feature sizes much larger than the wavelength of visible light. Angular resolved transmission of light through these substrates indeed showed diffraction patterns. unlike in the case of Asahi U-type substrates, which show angular resolved scattering. Single junction amorphous silicon (a-Si) solar cells made at 125 degrees C on the embossed structured polycarbonate (PC) substrates showed an increase in current density by 24% compared to a similar solar cell on a flat substrate. The band gap and thickness of the i-layer made by VHF PECVD are 1.9 eV and 270 nm respectively. A double p-layer (nc-Si:H/a-Si:H) was used to make proper contact with ZnO:Al TCO. Numerical modeling, called DokterDEP was performed to fit the dark and light current-voltage parameters and understand the characteristics of the cell. The output parameters from the modeling suggest that the cells have excellent built-in potential (V-bi). However, a rather high recombination voltage, V-mu affects the FF and short circuit current density (J(sc)) for the cells on Asahi as well as for the cells on PC. A rather high parallel resistance >> M Omega cm(2) (obtained from the modeling) infers that there is no significant shunt leakage, which is often observed for solar cells made at low temperatures on rough substrates. An efficiency of more than 6% for a cell on PC shows enormous potential of this type of light trapping structures.

26th European Photovoltaic Solar Energy Conference and Exhibition; 370-372, In this work we propose and study a light trapping scheme for thin film silicon solar cells that is based on geometrical light trapping (instead of textures optimized for light scattering), using periodically arranged pyramidal structures with dimensions larger than the effective wavelength of light. We studied the absorption behavior of amorphous silicon (a-Si) layers on such a pyramidal structured substrate using ray tracing calculations. According to the calculations, for pyramids on a square base, the maximum relative light absorption enhancement for normal incident light occurs at pyramid angles between 40° to 45°, which results in an increase of the weighted absorption of 45%. For diffuse light a maximum in light trapping yields an absorption increase of 40% compared to a flat structure. a-Si solar cells in a p-i-n configuration deposited at low temperature (125°C) on a micro-pyramidal structured polycarbonate substrate were used as proof-of-concept of this new light trapping scheme for the current enhancement. The cells deposited on the structured substrates showed an increase in short-circuit current density of 24% compared to the reference solar cell structures on flat glass substrates.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3149-3151, In this work we present a non disturbing method for in situ identification of the plasma regime of low substrate temperature silane/hydrogen plasmas based on Optical Emission Spectroscopy (OES). Producing solar cells directly on plastics would drastically reduce manufacturing costs for flexible cells. As inexpensive plastics cannot withstand temperatures above ~125°C, we need to develop deposition methods of which the substrate temperature does not exceed this temperature. A major problem in low temperature depositions is the formation of dust particles, which can cause electrical shunts when incorporated in the silicon layers. By recording OES spectra as a function of the position perpendicular to the electrodes, we can identify the transition from the dust free alpha-regime to the dusty gamma’-regime. In this way we can map the transition as a function of the deposition parameters. Because the amorphous to nanocrystalline transition occurs at lower power for higher hydrogen dilution and the alpha to gamma’ transition occurs at higher power at increased dilutions, these two transitions define a limited parameter window in the dilution-power space in which we can grow amorphous silicon in a dust-free plasma at low temperature. Using this technique we gain accurate control over the plasma regime, so that dusty plasmas may also be effectively used to create layers, e.g., for nanocrystal (quantum dot) based photovoltaic devices.

Texture etching of ZnO:1%Al layers using diluted HCl solution provides excellent TCOs with crater type surface features for the front contact of superstrate type of thin film silicon solar cells. The texture etched ZnO:Al definitely gives superior performance than Asahi SnO2:F TCO in case of nanocrystalline silicon (nc-Si) type of solar cells. The stress of the ZnO:Al film changes from tensile to compressive with the increase in substrate temperature of sputter deposition and the rms roughness and the haze of the film seem to have a correlation with the stress of the film prior to etching; the sample made at 150 °C is most tensile and the etching rate and the evolved roughness is least at this condition whereas the sample made at 350 °C with a compressive stress character gives a high roughness. At present the ZnO:Al made at room temperature provides the best combination of the electrical property and the scattering property of the texture etched layer. A current density of 24 mA/cm2 has been obtained for a nc-Si cell of 2200 nm thick. To apply such a texturing technique to make rough ZnO:Al TCO layers on PET and PEN substrates for solar cells on plastics, an additional step of embossing the plastics prior to the sputter deposition of the ZnO:Al layers was employed to release the undue stress. The texture etching of such layers on plastics showed excellent scattering properties in addition to the good electrical properties. As far as ZnO:Al as back reflector is concerned, use of a thick, low doped ZnO:Al in combination with white reflectors, instead of metals, will be a possible solution to avoid surface plasmon absorption loss. We have successfully applied this concept using 0.5% Al doped ZnO to a superstrate type a-Si solar cell using upconversion material at the back of the solar cell. In case of substrate type solar cells on plastics, the ZnO:Al layers that are used as the Ag/ZnO:Al back reflector as well as barrier layers, have to be thin and made at a low stress condition. Such a process resulted in 6% efficiency of n-i-p a-Si solar cells on PET and PEN substrates.