The increasing global energy demand, which today is mainly supplied by energy sources with a fossil origin, is a severe threat to the environment and to the security of supply. In order to handle these problems, renewable energy sources are promoted globally as well as nationally in Sweden. Solar photovoltaic (PV) technology is one of the most mature and commercial renewable energy technologies and could play a vital role in phasing out fossil energy sources. In the emerging, promising concept of solar landfills, PV systems are installed on closed landfill sites in order to combine renewable electricity production with resource efficient use of land. In this study the legal, technical and financial aspects concerning a solar landfill project in a Swedish setting were investigated. Additionally, the potential of the concept on a regional level in Sweden was analysed. The methodology used in the study featured literature research, interviews, and a feasibility assessment of a solar landfill project on Visby landfill. Regarding the legal aspects linked to a solar landfill project, an inconsistency between Swedish municipalities concerning the need of a building permit for a ground mounted PV system was revealed in the study. While some municipalities demand a building permit, others do not. Additionally, the fact that a closed landfill usually is classified as an environmentally hazardous activity doesn’t result in any need for additional permissions for a PV system installation on a closed landfill. Therefore, such legal aspects are not likely to hinder a solar landfill project to any great extent. Considering the technical aspects, the choice of mounting system must be done carefully because of the special conditions which exist on a landfill site; such as ground penetration restrictions and risks of settlement. While a ballasted mounting system can avoid ground penetration, a driven pile mounting system generally features a lighter construction. Furthermore, a fixed tilt mounting system is preferred over a sun tracking mounting system due to the extra weight and sensitivity to settlement which comes with the latter choice. Regarding the choice of PV modules, thin film modules generally feature a lower weight and can therefore be advantageous in comparison with crystalline silicon modules. In the case of Visby landfill, where penetration was preferred to be avoided but where the risk of settlement was considered low, the PV system which was deemed most suitable for the site featured a ballasted fixed tilt mounting system with crystalline silicon PV modules. Considering the financial aspects, the study emphasises the importance of using the produced electricity to offset consumed electricity in order to enable a sound investment. This can be done by a wise choice of owning and financing structure where the produced electricity offsets consumed electricity for a large consumer, e.g. an industry or a grocery store, or for a number of residences in a community solar. The economic feasibility also heavily depends on the projects’ possibility to use policy incentives and tax exemptions. The feasibility assessment of Visby landfill showed that the most economically feasible investment was possible by founding a community solar which offsets the members’ consumed electricity. Such an investment would feature a 10 year payback time and an internal rate of return of 8.3 %. Finally, the potential of the solar landfill concept on a regional level was identified as significant. In a scenario where the PV system suggested for Visby landfill in the feasibility assessment is installed on all the suitable landfill sites on Gotland, the island has the possibility to produce 22 GWh of electricity from solar landfills, thereby meeting the regional energy goal set for 2020.

Abstract The Dlx genes play an important role in the differentiation and migration of gamma-aminobutyric acid (GABA) interneurons of mice. GABAergic interneurons are born in the proliferative zones of the ventral telencephalon and migrate to the cortex early during mouse development. Single Dlx mutant mice show only subtle phenotypes. However, the migration of immature interneurons is blocked in the ventral telencephalon of Dlx1/Dlx2 double mutant mice leading to reduction of GABAergic interneurons in the cortex. Also, Dlx5/Dlx6 expression is almost entirely absent in the forebrain, most probably due to cross-regulatory mechanisms. In zebrafish, the role of dlx genes in GABAergic interneuron development is unknown. By injecting Morpholino, we double knocked down dlx1 and dlx2 genes in wildtype zebrafish to investigate the function of the two genes in zebrafish GABAergic interneuron development. By comparing different subsets of GABAergic interneuron development in wildtype and dlx1/2 morphant zebrafish forebrain, we found out that at 3dpf, 4dpf and 7dpf, double knockdown of dlx1 and dlx2 genes in zebrafish remarkably reduced the number of Calbindin-, Somatostatin- and Parvalbumin-positive GABAergic neurons, whereas the development of Calretinin-positive neurons is slightly affected. These results suggest that in zebrafish, dlx1a and dlx2a genes are important for the development of certain subtypes of GABAergic interneurons (Calbindin-, Somatostatin- and Parvalbumin-positive neurons) and may have minor influence on Calretinin-positive neuron development. This also suggests that different regulatory mechanisms are involved in the development of the different subtypes of GABAergic interneurons.

A novel approach to the design of multi-junction solar cells on silicon substrates for 1-sun applications is described. Models for device simulation including porous silicon layers are presented. A silicon bottom subcell is formed by diffusion of dopants into a silicon wafer. The top of the wafer is porosified to create a compliant layer, and a III-V buffer layer is then grown epitaxially, followed by middle and top subcells. Due to the resistivity of the porous material, these designs are best suited to high efficiency 1-sun applications. Numerical simulations of a multi-junction solar cell incorporating a porous silicon compliant membrane indicate an efficiency of 30.7% under AM1.5G, 1-sun for low threading dislocation densities (TDD), decreasing to 23.7% for a TDD of 10^7 cm^-2.

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

This Master of Applied Science thesis presents a single phase grid connected DC/AC inverter with reactive power (VAR) control for residential photovoltaic (PV) applications. The inverter, utilizing the voltage sourced inverter (VSI) configuration, allows the local residential PV generation to actively supply reactive power to the utility grid. A low complexity grid synchronization method was introduced to generate the parallel and orthogonal components of the grid voltage in a highly computationally efficient manner in order to create a synchronized current reference to the current control loop. In addition, the inverter is able to use a small long life film type capacitor on the DC-link by utilizing a notch filter on the voltage control loop. Simulations were performed on PSCAD/EMTDC platform and a prototype was also developed in the lab to prove the effectiveness of the controllers and the grid synchronization method.

Increasing penetration of stochastic photovoltaic (PV) generation into the electric power system poses significant challenges to system operators. In the thesis, we evaluate the spatial and temporal correlations of stochastic PV generation at multiple sites. Given the unique spatial and temporal correlation of PV generation, an optimal data-driven forecast model for short-term PV power is proposed. This model leverages both spatial and temporal correlations among neighboring solar sites, and is shown to have improved performance compared with conventional persistent model. The tradeoff between communication cost and improved forecast quality is studied using realistic data sets collected from California and Colorado. n IEEE 14 bus system test case is used to quantify the value of improved forecast quality through the reduction of system dispatch cost. The Modified spatio-temporal forecast model which has the least forecast PV overestimate percentage shows the best performance in the dispatch cost reduction.

Current Source Inverter (CSI) topology is gaining acceptance as a competitive alternative for grid interface of renewable energy systems due to its unique and advantageous features. Merits of CSI over the more popular Voltage Source Inverter (VSI) topology have been elaborated on by a number of researchers. However, there is a dearth of quality work in modeling and control of CSI topology interfacing renewable energy resources to the grid. To enrich the study focussing on application of CSI for renewable energy interface, this thesis develops a multilevel structure based on CSI for three-phase grid-connected Photovoltaic (PV) application. In the first part of research, a single-stage CSI interfacing to PV array is developed. The CSI-based PV system is equipped with Maximum Power Point Tracker (MPPT), DC-link current controller, and AC-side current controller. To eliminate the nonlinearity introduced by the PV array, a feed-forward control is introduced in the DC-link current controller. The AC-side current controller is responsible for maintaining unity power factor at the Point of Common Coupling (PCC). To verify the performance of the developed CSI-based PV system, a number of simulation studies are carried out in PSCAD/EMTDC environment. To illustrate the performance of the CSI-based PV system during transients on the grid side, simulation studies are carried out for four kinds of faults. Results obtained from fault studies are highly in favor of CSI topology and provide illustrative evidence for short-circuit current protection capability of the CSI. On the other hand, the VSI-based PV system performs poorly when subjected to similar grid transients. To extend the research on CSI-based PV system further, a multilevel structure based on CSI is developed. The multilevel structure is a parallel combination of $n$ CSI units and capable of producing $2n+1$ levels of current at the terminal of the inverter. Each unit in the multilevel structure has its own MPPT, DC-link current controller. However, on the AC-side a combined current controller is proposed. The design results in a high power rating with reduced number of filters, sensors and controllers. The developed multilevel structure can operate with PV arrays exposed to equal and unequal insolation level. However, when the PV arrays are operating under unequal insolation level, low order harmonics are generated in the sinusoidal current that is injected into the grid. Elimination of these harmonics is performed by implementing a modified control strategy in stationary reference frame that corresponds to the harmonic component that needs to be minimized. The modified control strategy operates in coordination with the existing DC-side and AC-side current controllers, and MPPTs. Therefore, real-time suppression of current harmonics can be ensured. Performance of the multilevel structure is verified by different transient studies.

In designing any power generation system that incorporates photovoltaics (PV) there is a basic requirement to accurately estimate the output from the proposed PV array under operating conditions. PV modules are given a power rating at standard test conditions(STC) of 1000Wm-2, AM1.5 and a module temperature of 25 °C, but these conditions do not represent what is typically experienced under outdoor operation. It is well known that different PV technologies have different seasonal patterns of behaviour. These differences are due to the variations in spectral response, the different temperature coefficients of voltage and current and, in the case of amorphous silicon (a-Si) modules, the extra effect of photo-degradation and thermal annealing. In this study a novel method has been used to obtain highly accurate energy output data from six different PV modules representing five different technologies: Single crystal silicon (c-Si). Poly-crystalline silicon (p-Si) (2 modules). Triple junction amorphous silicon (3j, a-Si). Copper indium diselenide (CIS). Laser grooved buried contact (LGBC, c-Si) crystalline silicon. This data set includes all the associated meteorological parameters and back-of-module temperatures. The monitoring system allows the simultaneous measurement of six different modules under long-term outdoor operation, which in turn allows a direct comparison of the performance of the modules. Each of the modules has been deployed for at least one year, which provides useful information about the seasonal behaviour of each technology. This data set ultimately provides system designers and consumers with valuable information on the expected output of these different module types in climates like that of Perth, Western Australia. The second part of the study uses the output data collected to assess and compare output predictions made by some currently available photovoltaic performance prediction tools or methods. These range from a generalised approach, as used in the Australian Standards, to the commercially available software packages that employ radiation, thermal and PV models of varying complexities. The results of these evaluations provide very valuable information, to PV consumers, about how complex PV output prediction tools need to be to give acceptable results.

The application and efficiency of optoelectronic devices depends on the ability to control the absorption and emission processes of photons in semiconductors. This thesis looks at three different applications of spectral management across a broad range of optoelectronic devices: photovoltaics (PVs), luminescent solar concentrators (LSCs) and light-emitting diodes (LEDs). Multiple excitation generation (MEG) – a process in which multiple charge-carrier pairs are generated from a single optical excitation - is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley-Queisser limit. Here we present solar cells fabricated from PbSe nanorods which show external quantum efficiencies exceeding 100 %. This demonstrates the potential for substantial improvements in PV device performance due to MEG. Through spatial and spectral concentration, LSCs have the potential to reduce the cost of photovoltaic energy production and are attractive prospects for photobioreactors and building-integrated applications. Here we introduce versatile star-shaped donor-acceptor molecules based on a central BODIPY acceptor with oligofluorene donor side units. We perform comprehensive device measurements and Monte Carlo ray tracing simulations of LSCs. We find that the measured structures permit waveguide propagation lengths on a par with state-of-the-art nanocrystalline emitters, while proposed hypothetical structures can be seen as viable candidates for photobioreactor and energy production roles and should be synthesized. The efficiency of nanocrystal-based LEDs is inherently limited by the types of crystals used. Cesium lead halide perovskite nanocrystals exhibit photoluminescence quantum efficiencies approaching 100%. However, due to the large surface areas and anion mobility halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, limiting applications. Here, we report significantly reduced halide exchange between chloride and iodide CsPbX3 (X= Cl, I) perovskite nanocrystals. We investigate perovskite-based multi-crystal component samples and their resulting optical and electrical interactions in bulk heterojunction LEDs. Efficient photon reabsorption from CsPbCl3 to CsPbI3 nanocrystals was found to improve LED device performance.

The consequences of over-reliance on fossil fuels for energy supply, namely climate change and security of supply, are pushing for the use of local, renewable energy sources which are usually variable in nature, prompting the need for energy storage. Today, there is a trend towards distributed energy storage, justified by the distributed nature of renewable energy sources and the important share of energy consumption in buildings. Important information on such small scale energy storage installations, however, is still missing and the results of the existing literature vary widely. To account for these research gaps, a thorough characterisation of energy storage technologies is performed, together with the dimensioning and optimisation of such installations in buildings, as well as some aspects of their impact on the grid.It is found that storage is still far from grid parity and expensive when compared to other solutions, although necessary for a high share of renewables. Also, energy storage is subject to important economies of scale and technical limitations that counter the reasoning for a distributed approach. There is an important lack of practical information on several energy storage technologies, and many studies on distributed storage use downsized values from large-scale installations that do not correctly depict smaller installations, leading to biased results. Nevertheless, today, lithium-ion batteries seem to be the most appropriate electrical energy storage technology for buildings, being well adapted to short term storage. On the other hand, a very high share of renewables will push for long term storage, itself a challenge given the high cost brought by a low utilisation factor. A high share of distributed generation also impacts the grid, a problem which most final consumers have no economic incentive to mitigate. Storage by itself, without a sound control strategy, does not help as it tends to increase the load variability while the peak load remains the same. Specific control algorithms could change that but incentives must be present, namely through the adaptation of current grid tariffs that do not correctly allocate existing costs. These findings are essential in the future planning of energy systems as well as in energy policy. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished