Trolleybuses are electric buses than run on electric power from overhead electric power lines (catenary) like trams do. Although is a service that dates all the way back to 1882, it has managed to regain interest in the recent years due to the constant electrification of various aspects of the world. This comes as a response towards environmental challenges as, even today, the majority of the energy necessary to cover our need comes from fossil fuels, making the transition to renewable energy sources more vital. One promising form of renewable energy source is solar energy and its use with photovoltaic (PV) systems. An interesting implementation of such systems is in catenary grids like trolleybus grids. Nevertheless, their integration has a low potential as the gaps in the trolleybus schedule and the intermittent behavior of the PV electric power leave a lot of excess PV electric energy unused. Possible solutions to this problem could be either the storage of this excess energy in on-board energy storage systems (OESS) or stationary energy storage systems (SESS). Besides that, in preparation for the future, more attention is given every day to the multifunctionality of trolleybus grids. This is related to parameters such as voltage drops, that have important role in rendering the trolleybus grid capable of being expanded with components other than trolleybuses, such as electric vehicle chargers.

The objective of this thesis work is to find out which energy storage systems (on-board or stationary) are most favorable for a PV-powered multifunctional trolleybus grid for increasing the PV system utilization and improving its multifunctionality. Parameters related to the multifunctionality of trolleybus grids can be the yearly electric energy consumption and the voltage drops.

For the conduction of this work is used an existing, verified trolleybus grid model of Arnhem in MATLAB that has realistic trolleybus electric power profiles as an input. By using the backward-forward sweep method are determined precise values such as the total electric power needed, voltage drops, ohmic losses and more. Also, is used as an existing, verified PV system model that provides the PV electric power as an output based on measured data. Then is developed a model for the on-board energy storage system which with the help of a constraint checking algorithm, that simulates the energy storage technologies, it provides new, adjusted trolleybus electric power profiles that are used as input to the trolleybus grid model. Finally, for the stationary energy storage system, the main trolleybus grid model is expanded with storage capabilities based on voltage control and a similar constraint checking algorithm for the storage technologies.

The results show that the impact of stationary energy storage systems on the PV system utilization and on parameters of the trolleybus grid in general is heavily correlated to the control strategy used. The technology, the PV system size, the trolleybus grid section, and the targeted outcome (improve the PV system utilization or reduce the voltage drops) have key role to the selection of the control strategy. The comparison of stationary energy storage systems to other energy storage systems cannot be straightforward. Besides that, on-board energy storage systems can perform better on parameters regarding the multifunctionality of the trolleybus grid such as the total yearly electric energy consumption and the mitigation of the severity of the voltage drops. On the other hand, stationary energy storage systems can perform well on a wide range of parameters according to their control strategy. For the one used in this work, they perform better on parameters regarding the PV system utilization, managing to have a positive impact.

Thin-film silicon solar cells make use of relatively thin layers of active material compared to wafer based solar cells. The main advantage of thin absorber layers is the possibility to fabricate flexible solar cells. However, due to limited absorber layer thickness and weak absorption coefficients at long wavelengths, light management techniques need to be implemented in order to increase the
device performance. Advanced substrate texturisation is one of the promising light management techniques that have drawn much attention recently. In state-of-the-art devices, randomly textured interfaces are often used to increase the optical performance. However, the introduction of periodic diffraction gratings resulted in world record conversion efficiencies for hydrogenated amorphous/nanocrystalline silicon (a-Si:H/nc-Si:H) tandem solar cells.

A different method of advanced texturisation is introducing modulated surface textures (MST). These MST structures combine various surface morphologies (random and/or periodic) to reach higher levels of light scattering over a broader wavelength range. Modulated surface textures based on large periodic gratings and small random textures have been successfully employed in single junction
nc-Si:H solar cells, resulting in a world record efficiency of 11.8 %. An MST structure based on large random features and small periodic gratings, however, has not been reported yet.

The aim of this work is to investigate the possibility of fabricating MST structures based on micro-textured glass with superimposed periodic gratings, and to obtain a functioning n-i-p nc-Si:H solar cell, based on an MST substrate. An optical and morphological analysis of randomly textured substrates, periodic gratings, and modulated surface textures was carried out. It was found that MST substrates can be fabricated using ITO induced, wet-etched glass substrates, and a photolithography process. MST structures resulted in light scattering into greater, less distinct angles, when compared to either one of the individual surface morphologies. Therefore, these structures show promising light scattering behaviour for application in nc-Si:H solar cells.

Hydrogenated nanocrystalline silicon solar cells were fabricated on randomly textured glass substrates and MST structures. Two-dimensional (2D) periodic gratings, with square and hexagonal lattice structures, were superimposed on randomly textured glass to obtain MST substrates. nc-Si:H solar cells based on hexagonal MST structures seemed to outperform their square lattice counterparts. A functioning device with an active area efficiency of 6.46 % and short-circuit current density (Jsc) of 19.74 mA/cm2 was fabricated. This work reports the first functioning nc-Si:H solar cell, based on a periodic-random modulated surface texture substrate. The best performing solar cell on randomly textured glass, however, exceeded this performance with an active area efficiency of 7.67 % and JSC of 23.2 mA/cm2. It can be concluded that functioning nc-Si:H solar cells can be fabricated on 2D MST substrates. Further research focused on the morphological optimisation of MST substrates could help to prevent defective material growth, to improve the electrical properties of future devices.