Renewable energy sources have become very popular in the last years in electricity generation thanks to the technological developments, the increase in the price of fossil fuels and the environmental concerns. These factors have also prompted Turkey to utilize her very rich renewable energy sources to meet the demand increasing around 7% annually. In this study, solar and wind energy potential of Turkey is analyzed in terms of its economics to find out whether these sources are real alternatives to fossil fuels in electricity generation. Before this analysis, wind and solar energy technologies and costs and wind and solar energy potential of Turkey are discussed. Then, models are set up for five technologies which are onshore wind, offshore wind, solar PV, solar trough and solar tower technologies models to calculate cash flows which are used to calculate payback, NPV, IRR, LCE and shut-down price to conduct economic analysis. In addition to base case scenario, uncertainty analysis is done for the most promising technologies which are onshore wind and solar tower technologies by evaluating NPV and LCE under uncertain environment. The main finding of these analyses is that only onshore wind projects are attractive in Turkey; none of other technologies is attractive. However, with a minor increase in the regulated price for solar thermal electricity, tower plant projects will also be attractive. / text

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Στην παρούσα εργασία μελετήθηκαν βιβλιογραφικά οι ενεργειακές και αισθητικές παράμετροι που συμβάλλουν στην εξοικονόμηση ενέργειας στον κτιριακό τομέα. Παράλληλα έγινε πειραματική μελέτη μιας καινοτόμου προτεινόμενης διάταξης με φακούς Fresnel για τον έλεγχο του φωτισμού και της θερμοκρασίας των εσωτερικών χώρων των κτιρίων, καθώς και τριών πειραματικών διατάξεων θερμικών ηλιακών συλλεκτών με σκοπό την εκτίμηση της απόδοσης των συλλεκτών με πολύχρωμη απορροφητική επιφάνεια σε σχέση με αυτή των μαύρων συλλέκτων και σε σχέση με το πλεονέκτημα της αισθητικής ενσωμάτωσής τους στα κτίρια. / The abstract is not available.

These photographs offer illustrations of the people, places and resources in the 9 proposed solar energy zones (SEZs) visited during the Solar Programmatic Environmental Impact Statement.

Solar energy is the most abundant source of renewable energy available. The relatively high cost prevents solar photovoltaic (PV) from replacing fossil fuel on a larger scale. In solar PV power generation the cost is reduced with more efficient PV technologies. In this dissertation, methods to improve PV conversion efficiency with holographic optical components are discussed. The tandem multiple-junction approach has achieved very high conversion efficiency. However it is impossible to manufacture tandem PV cells at a low cost due to stringent fabrication standards and limited material types that satisfy lattice compatibility. Current produced by the tandem multi-junction PV cell is limited by the lowest junction due to series connection. Spectrum-splitting is a lateral multi-junction concept that is free of lattice and current matching constraints. Each PV cell can be optimized towards full absorption of a spectral band with tailored light-trapping schemes. Holographic optical components are designed to achieve spectrum-splitting PV energy conversion. The incident solar spectrum is separated onto multiple PV cells that are matched to the corresponding spectral band. Holographic spectrum-splitting can take advantage of existing and future low-cost technologies that produces high efficiency thin-film solar cells. Spectrum-splitting optical systems are designed and analyzed with both transmission and reflection holographic optical components. Prototype holograms are fabricated and high optical efficiency is achieved. Light-trapping in PV cells increases the effective optical path-length in the semiconductor material leading to improved absorption and conversion efficiency. It has been shown that the effective optical path length can be increased by a factor of 4n2 using diffusive surfaces. Ultra-light-trapping can be achieved with optical filters that limit the escape angle of the diffused light. Holographic reflection gratings have been shown to act as angle-wavelength selective filters that can function as ultra-light-trapping filters. Results from an experimental reflection hologram are used to model the absorption enhancement factor for a silicon solar cell and light-trapping filter. The result shows a significant improvement in current generation for thin-film silicon solar cells under typical operating conditions.

As a part of Fortum's vision of a future Solar Economy, a feasibility study of a Solar District Heating facility was conducted. The focus of this study was to determine the technical, economic and environmental potential of a Solar District Heating facility, combined with a seasonal thermal storage, in the district heating network in Stockholm. Three different cases have been studied. The cases differ on the size of the available land area, on what type of storage technology utilized and if excess heat from different production facilities in the network is included or not. The results indicate that it is technically possible to implement a Solar District Heating facility in Stockholm, no obvious limitations in the network has been identified. The thermal storage should preferably be charged throughout the year and be discharged during December to March. The economic results indicate that none of the studied cases are economically feasible without any subsidies, increased revenues or other reductions of initial investment costs. The most economically beneficial system configuration was to utilize a smaller land area for solar collector installations, include excess heat from local production facilities and to utilize existing rock caverns and infrastructure in the area. The Solar District Heating facility could decrease the climate impact and the net primary energy use compared to the production of a biofuel production facility, but a further study is needed.

How to exploit and make use of natural gas hydrates in oceans will weigh much in the future researches. Unlike the oil or gas reservoirs, the distributions of natural gas hydrate are very complicated and don’t congregate massively in oceanic sediments. Besides, factors such as seafloor geohazards and climate must be taken into account, which makes it much more difficult and complicated to exploit oceanic gas hydrates than conventional oil or gas. Nowadays neither of such methods as thermal stimulation, depressurization, inhibitor injection, carbon dioxide replacement and mixing exploitation etc. is applied to exploit gas hydrates in marine sediments because of their disadvantages. This paper introduces a conception of combining solar and geothermal energy for gas hydrates exploitation. The model mainly includes five parts: solar energy transferring module, sea water circulating module, underground boiler module, platform and gas-liquid separating module. Solar cells and electric heaters are used to heat the formations containing hydrates. Because they become relatively more mature and cheaper, it’s the key of how to utilize the geothermy to exchange heat in developing this conception, which needs solution of fluid leakage, circulating passages and heat-exchange interface problems in building underground boiler. Probably it’s a feasible measure to use an effective hydraulic control system and hydraulic fracturing. The idea should be a good choice to exploit marine gas hydrates by combining solar and geothermal energy since this method has a great advantage either in terms of efficiency or cost.

This thesis is a study of the geometric design of solar concentrating collectors. In this work, a numerical optimization methodology was developed and applied to various problems in linear solar concentrator design, in order to examine overall optimization success as well as the effect of various strategies for improving computational efficiency. Optimization is performed with the goal of identifying the concentrator geometry that results in the greatest fraction of incoming solar radiation absorbed at the receiver surface, for a given collector configuration. Surfaces are parametrically represented in two-dimensions, and objective function evaluations are performed using various Monte Carlo ray-tracing techniques. Design optimization is performed using a gradient-based search scheme, with the gradient approximated through finite-difference estimation and updates based on the direction of steepest-descent. The developed geometric optimization methodology was found to perform with mixed success for the given test problems. In general, in every case a significant improvement in performance was achieved over that of the initial design guess, however, in certain cases, the quality of the identified optimal geometry depended on the quality of the initial guess. It was found that, through the use of randomized quasi-Monte Carlo, instead of traditional Monte Carlo, overall computational time to converge is reduced significantly, with times typically reduced by a factor of four to six for problems assuming perfect optics, and by a factor of about 2.5 for problems assuming realistic optical properties. It was concluded that the application of numerical optimization to the design of solar concentrating collectors merits additional research, especially given the improvements possible through quasi-Monte Carlo techniques.

Energetikos sistemos decentralizacija yra neišvengiamai susijusi su šiuolaikinės energetikos sistemos perėjimu prie tvarios ir ilgalaikės alternatyvos – atsinaujinantys energijos šaltiniai. Viena didžiausių perspektyvų – saulės energetika. Šiame darbe atlikta literatūros analizė apie fotovoltines sistemas ir jų komponentus. Remiantis vidutinio Lietuvos gyventojo elektros vartojimo įpročiais, atiktas modeliavimas sistemos, kuri tenkintų vidutinius poreikius. Optimizuojant elektros energijos vartojimą ir sistemos komponentus stebėta kaip tai veikia energijos suvartojimą, perteklinės energijos efektyvesnį panaudojimą, akumuliatorių darbo režimą. Įvertintas sistemos veikimas mažiausio ir didžiausio saulės spinduliuotės lygio Lietuvoje sąlygomis. / Decentralization of today‘s energy system is inevitability related to conversion to sustainable power system. Solar energy has the most potential to partially replace finite energy sources used today. A research on solar power systems and main components of the autonomous system was made in this paper. Autonomous photovoltaic system modelling was conducted. System size was chosen with reference to middle class user electric power consumption habbits in Lithuania. Consumption optimization and system load optimization were done and effects on consuption rate, excess electricity output and operating mode of batteries were observed and analysed. Optimized system‘s operation during the lowest and highest solar radiation conditions in Lithuania were evaluated.