• Energy Research

Abstract Feed-in tariffs (FIT) are among the most important policy instruments to promote renewable electricity production. The fixed-price FIT (FFIT), which guarantee a fixed price for every unit of produced electricity and the premium based FIT (PFIT), which pay a premium on top of the market price are commonly implemented in the EU. Costs for balancing intermittent electricity production may be significantly higher with FFIT than with PFIT, and FFIT do not provide any incentive to produce electricity when marginal production costs are high. In contrast, PFIT do provide strong incentives to better match renewable power output with marginal production costs in the system. The purpose of this article is to assess the effects of the two tariff schemes on the choice of wind turbine locations. In an analytical model, we show that both the covariance between wind power supply and demand as well as between the different wind power locations matter for investors in a PFIT scheme. High covariance with other intermittent producers causes a decrease in market prices and consequently in revenues for wind power investors. They are therefore incentivized to diversify the locations of wind turbines to decrease the covariance between different wind power production locations. In an empirical optimization model, we analyze the effects of these two different schemes in a policy experiment for Austria. The numerical results show that under a PFIT scheme, (1) spatial diversification is incentivized, (2) the covariance of wind power production with marginal electricity production costs increases, and (3) the variances of the wind power output and of residual load decrease if wind power deployment attains 10% of total national electricity consumption.

Abstract A high share of Brazilian power generation comes from hydropower sources and a further expansion of power generation is necessary due to high growth rates in electricity demand. As an alternative to the expansion of hydropower which shows high seasonal and annual variability with risks of load shedding due to droughts, windpower production may be increased. We assess the variability of potential windpower plants in the four most important windpower producing states Ceara (CE), Rio Grande do Norte (RN), Bahia (BA) and Rio Grande do Sul (RS) in comparison to adding new hydropower capacities in the North region. We assess seasonality and long-term deviations from seasonal production patterns. For that purpose, time series of windpower production from wind speeds derived from measurements and two global climate reanalysis models (NCAR and ECMWF) are generated and validated. Our results show that seasonal variability of windpower generation in the North-Eastern states is anticyclical to hydrological seasonality in the South-East, North-East, and North region of Brazil. Deviations of simulated windpower production from the monthly means are less correlated with current hydropower production than deviations of potential new hydropower projects. Adding windpower instead of hydropower to the system decreases significantly the risk of long periods of very low resource availability. The states Bahia and Rio Grande do Sul perform best with respect to that measure. Our validation procedure shows that ECMWF data may be the best source of long-term wind time series as it better reproduces ground measurements than NCAR.

Hydrogen produced from renewable electricity will play an important role in deep decarbonisation of industry. However, adding large electrolyser capacities to a low-carbon electricity system also increases the need for additional electricity generation from variable renewable energies. This will require hydrogen production to be variable unless other sources provide sufficient flexibility. Existing sources of flexibility in hydro-thermal systems are hydropower and thermal generation, which are both associated with sustainability concerns. In this work, we use a dispatch model for the case of Sweden to assess the power system operation with large-scale electrolysers, assuming that additional wind power generation matches the electricity demand of hydrogen production on average. We evaluate different scenarios for restricting the flexibility of hydropower and thermal generation and include 29 different weather years to test the impact of variable weather regimes. We show that (a) in all scenarios electrolyser utilisation is above 60% on average, (b) the inter-annual variability of hydrogen production is substantial if thermal power is not dispatched for electrolysis, and (c) this problem is aggravated if hydropower flexibility is also restricted. Therefore, either long-term storage of hydrogen or backup hydrogen sources may be necessary to guarantee continuous hydrogen flows. Large-scale dispatch of electrolysis capacity supported by wind power makes the system more stable, if electrolysers ramp down in rare hours of extreme events with low renewable generation. The need for additional backup capacities in a fully renewable electricity system will thus be reduced if wind power and electrolyser operation are combined in the system.

Abstract US wind power generation has grown significantly over the last decades, in line with the number and average size of operating turbines. However, wind power density has declined, both measured in terms of wind power output per rotor swept area as well as per spacing area. To study this effect, we present a decomposition of US wind power generation data for the period 2001–2021 and examine how changes in input power density and system efficiency affected output power density. Here, input power density refers to the amount of wind available to turbines, system efficiency refers to the share of power in the wind flowing through rotor swept areas which is converted to electricity and output power density refers to the amount of wind power generated per rotor swept area. We show that, while power input available to turbines has increased in the period 2001–2021, system efficiency has decreased. In total, this has caused a decline in output power density in the last 10 years, explaining higher land-use requirements. The decrease in system efficiency is linked to the decrease in specific power, i.e. the ratio between the nameplate capacity of a turbine and its rotor swept area. Furthermore, we show that the wind available to turbines has increased substantially due to increases in the average hub height of turbines since 2001. However, site quality has slightly decreased in this period.

Austria aims to meet 100% of its electricity demand from domestic renewable sources by 2030 which means, that an additional 27 TWh/a of renewable electricity generation are required, thereof 11 TWh/a from photovoltaic. While some federal states and municipalities released a solar rooftop cadastre, there is lacking knowledge on the estimation of the potential of both, ground mounted installations and rooftop modules, on a national level with a high spatial resolution. As a first, in this work data on agricultural land-use is combined with highly resolved data on buildings on a national level. Our results show significant differences between urban and rural areas, as well as between the Alpine regions and the Prealpine- and Easter Plain areas. Rooftop potential concentrates in the big urban areas, but also in densely populated areas in Lower- and Upper Austria, Styria and the Rhine valley of Vorarlberg. The ground mounted photovoltaic potential is highest in Eastern Austria. This potential is geographically consistent with the demand and allows for a production close to the consumer. In theory, the goal of meeting 11 TWh/a in 2030 can be achieved solely with the rooftop PV potential. However, considering the necessary installation efforts, the associated costs of small and dispersed production units and finally the inherent uncertainty with respect to the willingness of tens of thousands of individual households to install PV systems, installing the necessary solar PV on buildings alone is constrained.

The current EU regulatory framework for CO2 emissions of cars is based on tank-to-wheel (TtW) emissions. In an exploratory study we have analysed what-if-scenarios within this regulatory framework to quantify the costs in attaining the TtW emission targets and possible impacts on the well-to-wheel (WtW) emissions of the EU’s new vehicle portfolio. In particular, we analysed the introduction of electric drive vehicles (EDV) and shifts between car segments. We performed the what-if-scenarios on the basis of the monitoring data for CO2 emissions from new passenger cars in the EU that was further reprocessed to achieve a break-down per vehicle segment, enriched with cost information and well-to-tank (WtT) emission data. Our calculations show that under the assumption that there are no significant segment shifts towards smaller vehicles, a minimum share of 11% of EDV would be needed to comply with a stricter CO2 target of 70 g/km, as improvements on conventional cars cannot provide sufficient savings. Deploying the EDV allows a cost effective achievement of the regulatory TtW targets, but also leads to higher WtW emissions than the baseline under the assumption that the TtW targets are not overachieved. Public incentives would be necessary to increase the share of EDV in the portfolio. We calculated that the order of magnitude of these incentives would be in the range of scrappage schemes that have been recently witnessed in European countries.

Avec l'augmentation de la part des énergies renouvelables variables dans les systèmes électriques, de nombreuses études ont été développées afin de déterminer leur mix technologique et spatial optimal. La théorie du portefeuille moderne (MPT) a été fréquemment appliquée dans ce contexte. Cependant, certains aspects cruciaux, importants dans la planification énergétique, ne sont pas abordés par ces analyses. Nous proposons donc plusieurs améliorations et évaluons l'impact de chaque changement de formulation sur les résultats. Plus précisément, nous utilisons le coût de production au lieu de la capacité installée comme l'un des objectifs ; nous considérons la corrélation entre la demande et les profils de production ; et nous limitons les risques de pénurie via l'inclusion d'une mesure CVaR. Ces modifications sont présentées dans un modèle formel qui est également appliqué au cas du Brésil. Nous avons constaté que, après avoir inclus nos modifications proposées, la frontière efficace résultante diffère fortement de celle obtenue dans la formulation originale. La principale différence est que la nouvelle frontière efficace a une plage beaucoup plus courte de valeurs d'écart type acceptables. Par conséquent, de nombreux portefeuilles obtenus à partir de la formulation traditionnelle ont une probabilité beaucoup plus élevée de sous-production, en particulier les portefeuilles situés dans des régions où l'écart type est trop faible ou trop élevé. En outre, nous montrons que la diversification joue un rôle important dans le lissage de la production des portefeuilles de sources renouvelables variables. Con el aumento de la participación de las energías renovables variables en los sistemas eléctricos, se desarrollaron muchos estudios con el fin de determinar su combinación tecnológica y espacial óptima. La teoría moderna de la cartera (MPT) se ha aplicado con frecuencia en este contexto. Sin embargo, algunos aspectos cruciales, importantes en la planificación energética, no se abordan en estos análisis. Por lo tanto, proponemos varias mejoras y evaluamos cómo cada cambio en la formulación afecta los resultados. Más específicamente, utilizamos el costo de generación en lugar de la capacidad instalada como uno de los objetivos; consideramos la correlación entre los perfiles de demanda y generación; y limitamos los riesgos de escasez mediante la inclusión de una medida CVaR. Estas modificaciones se presentan en un modelo formal que también se aplica al caso de Brasil. Encontramos que, después de incluir nuestras modificaciones propuestas, la frontera eficiente resultante difiere fuertemente de la obtenida en la formulación original. La principal diferencia es que la nueva frontera eficiente tiene un rango mucho más corto de valores de desviación estándar aceptables. Por lo tanto, muchas de las carteras obtenidas de la formulación tradicional tienen una probabilidad mucho mayor de subproducción, especialmente las carteras ubicadas en regiones con una desviación estándar demasiado baja o demasiado alta. Además, mostramos que la diversificación juega un papel importante para suavizar la producción de las carteras de fuentes renovables variables. With the increase of the share of variable renewable energies in electricity systems, many studies were developed in order to determine their optimal technological and spatial mix. Modern Portfolio Theory (MPT) has been frequently applied in this context. However, some crucial aspects, important in energy planning, are not addressed by these analyses. We, therefore, propose several improvements and evaluate how each change in formulation impacts results. More specifically, we use generation cost instead of installed capacity as one of the objectives; we consider the correlation between demand and generation profiles; and we limit shortage risks via the inclusion of a CVaR measure. These modifications are presented in a formal model which is also applied to the case of Brazil. We found that, after including our proposed modifications, the resulting efficient frontier differs strongly from the one obtained in the original formulation. The main difference is that the new efficient frontier has a much shorter range of acceptable standard deviation values. Therefore, many of the portfolios obtained from the traditional formulation have a much higher probability of under-production, especially portfolios located at regions with standard deviation either too low or too high. Furthermore, we show that diversification plays an important role in smoothing output from portfolios of variable renewable sources. مع زيادة حصة الطاقات المتجددة المتغيرة في أنظمة الكهرباء، تم تطوير العديد من الدراسات من أجل تحديد مزيجها التكنولوجي والمكاني الأمثل. تم تطبيق نظرية المحفظة الحديثة (MPT) بشكل متكرر في هذا السياق. ومع ذلك، فإن بعض الجوانب الحاسمة، المهمة في تخطيط الطاقة، لا تتناولها هذه التحليلات. لذلك، نقترح العديد من التحسينات ونقيم كيفية تأثير كل تغيير في الصياغة على النتائج. وبشكل أكثر تحديدًا، نستخدم تكلفة التوليد بدلاً من السعة المركبة كأحد الأهداف ؛ وننظر في العلاقة بين الطلب وملفات تعريف التوليد ؛ ونحد من مخاطر النقص من خلال تضمين مقياس CVaR. يتم تقديم هذه التعديلات في نموذج رسمي يتم تطبيقه أيضًا على حالة البرازيل. وجدنا أنه بعد تضمين تعديلاتنا المقترحة، تختلف الحدود الفعالة الناتجة اختلافًا كبيرًا عن تلك التي تم الحصول عليها في الصيغة الأصلية. والفرق الرئيسي هو أن الحدود الفعالة الجديدة لديها نطاق أقصر بكثير من قيم الانحراف المعياري المقبولة. لذلك، فإن العديد من المحافظ التي تم الحصول عليها من التركيبة التقليدية لديها احتمال أعلى بكثير لنقص الإنتاج، وخاصة المحافظ الموجودة في المناطق ذات الانحراف المعياري إما منخفض جدًا أو مرتفع جدًا. علاوة على ذلك، نظهر أن التنويع يلعب دورًا مهمًا في تسهيل الإنتاج من محافظ المصادر المتجددة المتغيرة.