Aspects of plane waves and Taub-NUT as exact string theory solutions

This thesis is a study of some aspects of string theory solutions that are exact in the inverse string tension ɑ', and thus are valid beyond the low-energy limit. I investigate D-brane interactions in the maximally supersymmetric plane wave solution of type IIb string theory, and study the fate of the stringy halo surrounding D-branes. I find that the halo is like in flat space for Lorentzian D-branes, while it receives a non-trivial modification for Euclidean D-branes. I also comment on the connection between Hagedorn temperature and T-duality, which motivates a more general study of T-duality in null directions. I consider such transformations in a spinning D-brane solution of supergravity, and find that divergences in the field components associated with null T-dualities are invisible to string and brane probes. I also observe that there are closed timelike curves in all the T-dual solutions, but that none of them are geodesies. The second half of the theses is an investigation of the fate of closed tirnelike curves and of cosmological singularities in an exact stringy Taub-NUT solution of heterotic string theory, and in a rotating generalisation of it. I compute the exact spacetime fields, using a description in terms of a gauged Wess-Zumino-Novikov-Witten model and find that the ɑ' corrections are mild. The key features of the Taub-NUT geometry persist, together with the emergence of a new region of space with Euclidean signature. Closed timelike curves are still present, which is inter-preted as a sign that they might be a natural ingredient in string theory, for instance in pre-Big-Bang cosmological scenarios

Quantifying the Market Value of Wave Power compared to Wind&Solar - a case study

This study discusses the market value of electricity production by different sustainable sources, and shows how it is influenced by the correlation between electricity market price and energy production. The generic discussion is accompanied by a case study comparing the value of wave, wind and solar power using time series data for production and prices generated by grid and market simulations. The study has shown that simplified common-practise approaches (which do not consider correlation) fail to correctly reveal the market value of electricity production. It has also been shown that wave power can achieve a market value that is significantly higher than wind and slightly higher than solar. These differences in market value have been explained through correlation between electricity production and price, which is different for different energy sources. The study has identified competitive advantages of wave power towards the dominant sustainable energy sources, that need to be taken into account when competitiveness and profitability are to be assessed.acceptedVersio

The Low Emission Oil and Gas Open reference platform—An off-grid energy system for renewable integration studies

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo (7373223)This article introduces and describes the integrated energy system of the Low Emission Oil and Gas Open reference platform. It is a hypothetical case meant to represent a typical oil and gas installation in the North Sea. The aim of this detailed specification is to serve as an open reference case where all the information about it can be publicly shared, facilitating benchmarking and collaboration. The relevance of this reference case of an off-grid energy system is not limited to the oil and gas industry, since it can also be seen as a special kind of electrical micro grid. The remote offshore location makes it especially relevant for studying offshore wind power and ocean energy sources like wave power. The specification has an emphasis on the energy system and electrical configuration, but also includes a basic description of the oil field and processing system. The intention is that it will serve as a basis for energy system studies and relating power system stability analyses regarding the integration of renewable energy sources. This allows for comparisons of a base case with different design modifications, new operational planning methods, power management strategies and control concepts. Examples of possible modifications are the replacement of gas turbines by wind turbines, addition of energy storage systems, a more variable operation of loads etc. The last part of the article demonstrates the behaviour of the reference platform implemented in two software tools: one for operational planning and one for dynamic power system analyses.publishedVersio

Operational Planning and Power Management System for Offshore Platform With Wind Energy Supply – Impacts on CO2 Reduction and Power Quality

publishedVersio

Validation study of an approximate 2014 European power-flow model using PowerGAMA

This study presents a validation study of an approximated model of the European power system in 2014. A lightweight and open-source power-flow tool is used for this study. The tool and the model are publicly available and can be adapted to study future impact of large investments in the power system, specifically large-scale integration of renewable energy. The input dataset is based on a prior work, but it has been substantially updated for 2014. To maintain all aspects of the model open-source, only publicly available data was implemented. The modelling approach and simplifications are explained. Comparison of the simulation results with actual data on cross -border flows and energy mix for 2014 shows acceptable correlation. The model is able to capture main characteristics of the power system, such as reservoir handling, hydro pump pattern, and seasonal variation on cross -border flows.acceptedVersio

Modelling and analysis of offshore energy hubs

publishedVersio

Improving wind power market value with various aspects of diversification

The wind generation share in many European bidding zones is now large enough to affect the market value of wind power, and wind energy is getting less-than-average market price in day-ahead markets. As alternatives to investing in dedicated energy storage, there are two main ways to mitigate the decreasing market value trend. The first is employing different diversification measures (geographical spread, alternative wind turbine technologies, integration with solar). The second is implementing demand flexibility measures. Examples of these measures from some European and USA studies are given in this article, which stems from the international collaboration under IEA Wind TCP Tasks 25 and 53.Improving wind power market value with various aspects of diversificationacceptedVersio

Planning tool for clustering and optimised grid connection of offshore wind farms

A planning tool for clustering and optimised grid connection of offshore wind farms is presented and described in some detail. This tool is suitable for high level, strategic planning of clustering and grid connection of future offshore wind farms that are planned in the proximity of each other. This tool is an upgraded version of a previously developed tool for offshore grid expansion planning. The use of the upgraded tool is demonstrated with an example that considers the Kriegers Flak area, with results indicating benefits of interconnecting wind farms across country borders and using a hybrid AC and DC transmission system to shore.publishedVersio

Hourly wind and solar energy time series from Reanalysis dataset

This document gives a brief description of a method to generate hourly time series for wind power and solar power production for a number specified locations, using publicly available numerical weather model reanalysis data covering the period from 1950 until today.publishedVersio