Economic and regulatory uncertainty in renewable energy system design: a review

Renewable energy is increasingly mobilizing more investment around the globe. However, there has been little attention to evaluating economic and regulatory (E&R) uncertainties, despite their enormous impact on the project cashflows. Consequently, this review analyzes, classifies, and discusses 130 articles dealing with the design of renewable energy projects under E&R uncertainties. After performing a survey and identifying the selected manuscripts, and the few previous reviews on the matter, the following innovative categorization is designed: sources of uncertainty, uncertainty characterization methods, problem formulations, solution methods, and regulatory frameworks. The classification reveals that electricity price is the most considered source of uncertainty, often alone, despite the existence of six other equally influential groups of E&R uncertainties. In addition, real options and optimization arise as the two main approaches researchers use to solve problems in energy system design. Subsequently, the following aspects of interest are discussed in depth: how modeling can be improved, which are the most influential variables, and potential lines of research. Conclusions show the necessity of modeling E&R uncertainties with currently underrepresented methods, suggest several policy recommendations, and encourage the integration of prevailing approaches.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantPostprint (published version

A comprehensive methodology for the statistical characterization of solar irradiation: application to the case of Morocco

The prediction and characterization of solar irradiation relies mostly on either the use of complex models or on complicated mathematical techniques, such as artificial neural network (ANN)-based algorithms. This mathematical complexity might hamper their use by businesses and project developers when assessing the solar resource. In this study, a simple but comprehensive methodology for characterizing the solar resource for a project is presented. It is based on the determination of the best probability distribution function (PDF) of the solar irradiation for a specific location, assuming that the knowledge of statistical techniques may be more widely extended than other more complex mathematical methods. The presented methodology was tested on 23 cities across Morocco, given the high interest in solar investments in the country. As a result, a new database for solar irradiation values depending on historical data is provided for Morocco. The results show the great existing variety of PDFs for the solar irradiation data at the different months and cities, which demonstrates the need for undertaking a proper characterization of the irradiation when the assessment of solar energy projects is involved. When it is simply needed to embed the radiation uncertainty in the analysis, as is the case of the techno-economic valuation of solar energy assets, the presented methodology can reach this objective with much less complexity and less demanding input data. Moreover, its application is not limited to solar resource assessment, but can also be easily used in other fields, such as meteorology and climate change studies.Peer ReviewedPostprint (published version

Contribution to the PV-to-inverter sizing ratio determination using a custom flexible experimental setup

This work presents a novel approach to the experimental validation of the optimal PV-to-inverter sizing ratio value for the energy yield maximization of a GCPVS by means the implementation of a custom workbench using a solar array simulator which has allowed to replicate a wide variety of technical configurations and environmental data. The compliance between the experimental setup and the mathematical model developed to simulate the optimal PV-to-inverter sizing ratio value was demonstrated by the specific tests carried out on its two main subsystems (the PV generator and the inverter), thus the subsequent simulations were made on a firm basis. Likewise, the evaluation of the overall system also showed a good agreement between the experimental and the simulated energy yield and optimal PV-to-inverter sizing ratio results, rendering relative errors below 3% for both magnitudes. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author’s final draft

Power calculation algorithm for single-phase droop-operated inverters considering nonlinear loads and unsing n-order SOGI filtering

The average active and reactive powers, P and Q, are crucial parameters that have to be calculated when sharing common loads between parallelized droop-operated single-phase inverters. However, the droop method algorithm should employ low-pass filters (LPF) with very low cut-off frequency to minimize the distortion impact in the provide droop amplitude and frequency references. This situation forces the droop control to operate at a very low dynamic velocity, degrading the stability of the parallelized system. For this reason, different solutions had been proposed in literature to increase the droop velocity, but the issues derived from the sharing of nonlinear loads had not been properly considered. This work proposes a novel method to calculate P and Q based on the fundamental components of the inverter's output voltage and current and using the measured phase angle between the output voltage and current. The method is used under normal and highly distorting conditions due to the sharing non-linear loads. The fundamental components are obtained by means of the highly filtering capability provided by norder cascaded second order generalized integrators (nSOGI). The proposed method leads to faster and more accurate P and Q calculations that enhances the droop-method dynamic performance. Simulations are provided to validate the proposal.Peer ReviewedPostprint (published version

Power sizing factor design of central inverter PV grid-connected systems: a simulation approach.

This paper presents a simulation approach which can help in the preliminary power sizing design of a gridconnected PV system based on a single inverter configuration. Given a nominal peak power of the PV array, this simulation procedure leads to the PV inverter maximum rated power which maximizes the yearly injected energy to the grid.Peer ReviewedPostprint (published version

Reactive current injection protocol for low-power rating distributed generation sources under voltage sags

Voltage sags are one of the main problems in transmission and distribution networks. This study proposes a voltage support control scheme for grid-connected low-power rating inverters under voltage sags. Voltage support capability is provided thanks to reactive current injection. The main objective is to inject the maximum rated reactive current during the voltage sag. Second, to raise the higher phase voltage to a predefined maximum boundary, thus preventing over-voltage. Moreover, with this strategy the phase voltages can be equalised. The first objective can be always accomplished during voltage sags. Achieving the second objective depends on the grid characteristics, the sag profile and the power rating of the inverter. Selected experimental results are reported to validate the effectiveness of the proposed control.Preprin

Assessing the 2014 retroactive regulatory framework applied to the concentrating solar power systems in Spain

The RD 413/2014 new economic and regulatory framework applied to the concentrating solar power plants (CSPP) in Spain has been here analysed and its new remuneration scheme has been formulated, becoming evident its high complexity and the great number of regulatory parameters involved. Next, a new model focused on determining its impact on the economic results of the existing CSPP has been proposed. Due to the complexity of the system, a methodology comprising a set of different stages of analysis has been developed. The new model has proven to be a useful tool to analyse the economic impact of the new regulatory scheme on the facilities and to identify its most influential regulatory parameters. One of the most representative facilities has been chosen as a case study to undertake the analysis. The results of the analysis, which have shown a substantial profitability reduction, have been consistent with the appreciations and data provided by the claimants of the last arbitral Award concerning the Kingdom of Spain and investors of CSPP in this country.Peer ReviewedPreprin

Renewable energy auction prices: near subsidy-free?

The latest trend of low record bid prices in renewable energy auctions has raised concerns on the effective deployment of the winning projects. A survey of recent auction data from several countries, technologies and remuneration designs is analysed and compared with the corresponding levelised costs of energy (LCOEs) to draw first insights on their viability. A critical assessment of the ability of the LCOE for determining the adequate bid level is then performed and the preliminary unviable results of selected mature technologies are further investigated using improved profitability metrics as the project and equity net present value (NPV) and internal rate of return (IRR). As representative examples, the analysed Danish 2019 onshore wind and photovoltaics (PV) auctions require very specific scenarios to become viable, which cast doubts on their effective implementation. Under the assumptions of a realistic base case, the sensitivity analysis revealed that either 59% of decrease in the weighted average cost of capital (WACC), or 37% of discount on the investment cost or a 3.6% annual increment in the mean market price is needed for achieving the NPV break-even in the onshore wind case. Likewise, the PV case is unprofitable whatever the WACC may be, and either a 60% discount on the investment cost or a 6.8% annual increment in the mean market price is needed for the NPV to break-even. Although some projects could be relying on indirect revenues or additional sources of incomes beyond the auction support, it remains to see if they are finally materialised.Peer ReviewedPostprint (published version

Methodology for obtaining simplified models for the long-term energy management of renewable assets under a high degree of uncertainty

This paper addresses the attainment of a methodology aimed at obtaining simplified models embedding the regulatory constraints imposed by the country-specific remuneration mechanisms in the energy management system of long operating life renewable assets under a high degree of uncertainty. This methodology, composed of different steps in which sensitivity analysis as well as Monte Carlo simulation play a key role, is focused on a significant case study that has implemented two of the most widely used worldwide remuneration mechanisms in the promotion of renewable energies, i.e., feed-in tariffs and auctions. The earnings before interest, tax, depreciation and amortization have been used as the output variable of the energy management model, as it is essential to take into account both revenues and operating costs of these renewable assets to manage them optimally. Some valid simplified models have been achieved by applying the proposed methodology to the case study with generalized errors below 5%. Specifically, one simplified energy management system model has been obtained under the feed-in tariff scheme, which involves acting on almost 40% of the equations of the original model and reducing the initial input parameters by 22%. Meanwhile, two simplified energy management system models have been obtained under the auction scheme. The most conservative simplified model involves acting on almost 50% of the equations of the original model and reducing the initial input parameters by 35%, while in the less conservative case it involves acting on more than 50% of the equations of the original model and reducing the initial input parameters by 42%. In short, although the uncertainty on the energy assets cannot be completely eliminated, it can be considerably reduced by facilitating the assessment of its prospective financial results. The validity of the achieved simplified models demonstrates the suitability and usefulness of the proposed simplifying methodology, providing a touch of quality in the long-term judgement and decision-making of the stakeholders when optimally managing renewable energy facilities under any type of remuneration scheme.Peer ReviewedPostprint (author's final draft

Adaptación de la metodología PBL a la enseñanza de las energías renovables

La asignatura de libre elección “Energías renovables” se imparte en “l’Escola Universitária d’Enginyeria Tècnica Industrial de Barcelona”, “Campus d’Urgell” de la Universidad Politécnica de Cataluña. La asignatura pretende acercar el campo de las energías renovables a los estudiantes de ingeniería de la EUETIB, así como dar una visión genérica de este tipo de energías en la actualidad. Es también objeto de esta asignatura profundizar en el campo de la energía solar, sea térmica o fotovoltaica, para ello se hace hincapié en los principales aspectos conceptuales de dichas instalaciones, en sus procesos de cálculo adaptados a la legislación vigente, y en como legalizar dichas instalaciones. La metodología utilizada, desde el año 2003, para impartir esta asignatura se basa en la metodología PBL. En este artículo describiremos las motivaciones que nos indujeron a introducir dicha metodología, y cómo la utilización de dicha metodología ha incidido en la definición y desarrollo de los objetivos de la asignatura.Eje: Educación universitaria: Experiencias educativasRed de Universidades con Carreras en Informática (RedUNCI