@techreport{RuhnauMuessel, type = {Working Paper}, author = {Ruhnau, Oliver and Muessel, Jarusch}, title = {Update and extension of the When2Heat dataset}, abstract = {The "When2Heat" dataset comprises synthetic national time series for heat demand and heat pumps' coefficient of performance (COP) in hourly resolution. Heat demands for space and water heating are computed by combining gas standard load profiles with spatial temperature reanalysis data and population geodata. With this update, we extend the dataset to 28 European countries and the period from 2008 to 2019, including new, state-of-the-art data sources. For the geographical extension, we propose a novel approach, shifting established German heat demand curves based on country-specific heating thresholds to account for regional differences in thermal insulation and user behavior. Using the example of Italy, we illustrate the effect of shifting heat demand curves. The dataset, scripts, and input parameters are publicly available under an open-source license on the Open Power System Data platform.}, language = {en} } @article{Ruhnau, author = {Ruhnau, Oliver}, title = {How flexible electricity demand stabilizes wind and solar market values: the case of hydrogen electrolyzers}, series = {Applied Energy, Elsevier}, volume = {307}, journal = {Applied Energy, Elsevier}, doi = {10.1016/j.apenergy.2021.118194}, abstract = {Wind and solar energy are often expected to fall victim to their own success: the higher their share in electricity production, the more their revenue on electricity markets (their "market value") declines. While in conventional power systems, the market value may converge to zero, this study demonstrates that "green" hydrogen production, through adding electricity demand in low-price hours, can effectively and permanently halt the decline. With an analytical derivation, a Monte Carlo simulation, and a numerical electricity market model, I find that - due to flexible hydrogen production alone - market values across Europe likely converge above €19 ± 9 MWh-1 for solar energy and above €27 ± 8 MWh-1 for wind energy in 2050 (annual mean estimate ± standard deviation). This lower boundary is in the range of the projected levelized costs of renewables and has profound implications. Market-based renewables may hence be within reach. simulation, and a numerical electricity market model, I find that - due to flexible hydrogen production alone - market values across Europe likely converge above €19 ± 9 MWh-1 for solar energy and above €27 ± 8 MWh-1 for wind energy in 2050 (annual mean estimate ± standard deviation). This lower boundary is in the range of the projected levelized costs of renewables and has profound implications. Market-based renewables may hence be within reach.}, language = {en} } @article{RuhnauQvist, author = {Ruhnau, Oliver and Qvist, Staffan}, title = {Storage requirements in a 100\% renewable electricity system: Extreme events and inter-annual variability}, series = {Environmental Research Letters}, journal = {Environmental Research Letters}, publisher = {IOP Publishing}, doi = {10.1088/1748-9326/ac4dc8}, abstract = {In the context of 100\% renewable electricity systems, prolonged periods with persistently scarce supply from wind and solar resources have received increasing academic and political attention. This article explores how such scarcity periods relate to energy storage requirements. To this end, we contrast results from a time series analysis with those from a system cost optimization model, based on a German 100\% renewable case study using 35 years of hourly time series data. While our time series analysis supports previous findings that periods with persistently scarce supply last no longer than two weeks, we find that the maximum energy deficit occurs over a much longer period of nine weeks. This is because multiple scarce periods can closely follow each other. When considering storage losses and charging limitations, the period defining storage requirements extends over as much as 12 weeks. For this longer period, the cost-optimal storage capacity is about three times larger compared to the energy deficit of the scarcest two weeks. Adding other sources of flexibility for the example of bioenergy, the duration of period that defines storage requirements lengthens to more than one year. When optimizing system costs based on single years rather than a multi-year time series, we find substantial inter-annual variation in storage requirements with the most extreme year needing more than twice as much storage as the average year. We conclude that focusing on short-duration extreme events or single years can lead to an underestimation of storage requirements and costs of a 100 \% renewable system.}, language = {en} } @techreport{RuhnauStieweMuesseletal., type = {Working Paper}, author = {Ruhnau, Oliver and Stiewe, Clemens and Muessel, Jarusch and Hirth, Lion}, title = {Gas demand in times of crisis. The response of German households and industry to the 2021/22 energy crisis}, pages = {8}, abstract = {Europe is in the midst of the most severe energy crisis in a generation, at the core of which is the continuously plummeting supply of Russian natural gas. With alternative supply options being limited, natural gas prices have surged. This paper empirically estimates the response of natural gas demand to the price increase, using data from Germany—the so far largest consumer of Russian natural gas. We identify the crisis response of small and large consumers separately, controlling for temperature, gas-fired power generation, and economic activity. For small consumers, including mostly households, we find a substantial demand reduction of 6\% from March onwards—most likely due to political and ethical considerations after the start of Russia's invasion of Ukraine. For industrial consumers, demand reductions started much earlier in August 2021, when wholesale prices for natural gas started to surge, with an average reduction of 11\%. We conclude that voluntary industrial demand response has played a significant role in coping with the energy crisis so far.}, language = {en} } @techreport{RuhnauSchiele, type = {Working Paper}, author = {Ruhnau, Oliver and Schiele, Johanna}, title = {Flexible green hydrogen: economic benefits without increasing power sector emissions}, pages = {25}, abstract = {Electrolytic hydrogen complements renewable energy in many net-zero energy scenarios. In these long-term scenarios with full decarbonization, the "greenness" of hydrogen is without question. In current energy systems, however, the ramp-up of hydrogen production may cause additional emissions. To avoid this potential adverse effect, recently proposed EU regulation defines strict requirements for electrolytic hydrogen to qualify as green: electrolyzers must run on additional renewable generation, which is produced in a temporally and geographically congruent manner. Focusing on the temporal dimension, this paper argues in favor of a more flexible definition of green hydrogen, which keeps the additionality criterion on a yearly basis but allows for dispatch optimization on a market basis within that period. We develop a model that optimizes dispatch and investment of a wind-hydrogen system—including wind turbines, hydrogen electrolysis, and hydrogen storage—and apply the model to a German case study based on data from 2017-2021. Contrasting different regulatory conditions, we show that a flexible definition of green hydrogen can reduce costs without additional power sector emissions. By contrast, requiring simultaneity implies that a rational investor would build a much larger wind turbine, hydrogen electrolyzer, and hydrogen storage than needed. This leads to additional costs, underutilized resources, and a potential slow-down of green hydrogen deployment. We discuss that current trends in the energy transition are likely to amplify the economic and environmental benefits of a flexible definition of green hydrogen and recommend this as the way forward for a sustainable hydrogen policy.}, language = {en} } @phdthesis{Ruhnau, author = {Ruhnau, Oliver}, title = {The Economics of Flexible Electricity Demand}, school = {Hertie School}, abstract = {In electricity systems, supply traditionally follows demand. Consequently, economists have focused on analyzing supply while assuming perfectly inelastic demand. Demand flexibility, if at all, occurred in deterministic patterns, such as during peak and off-peak periods, incentivized by static time-of-use tariffs. Nowadays, the role of electricity demand is changing fundamentally: growing shares of fluctuating wind and solar energy require flexibility in a larger quantity and on a stochastic basis; increasing loads of electric vehicles, heat pumps, and hydrogen electrolyzers could provide flexibility through battery, thermal, and gas storage; and the introduction of smart meters enables dynamic real-time tariffs and an automated response of distributed loads. This cumulative dissertation contributes to the economic understanding of flexible electricity demand with five scientific articles. Article 1 starts with reviewing the role of electrification in decarbonization scenarios for heating and road transport in Germany. The article finds that decarbonization drives electrification, leading to an increase in electricity demand by a factor of roughly two. Direct and indirect electrification options are contrasted with respect to their distinct flexibility potential. Articles 2 and 3 explore the implications of decentralized electric heat pumps and centralized electrolytic hydrogen, respectively, for the market value of renewables. Both use the same numerical electricity market model. Article 2 finds that the volatility of the heat pump's electricity demand challenges the electricity system, which becomes apparent in increasing load cost. A flexible operation of heat pumps may reduce this challenge, but potential benefits for the market value of wind energy are minor. By contrast, Article 3 shows that hydrogen electrolyzers have the potential to stabilize renewable market values at high renewable market shares effectively and permanently, because additional renewable supply can trigger investment in additional hydrogen electrolyzers with additional demand. Articles 4 and 5 investigate the flexibility of the current electricity demand using econometric models with instrumental variables. Article 4 reveals that, at an hourly temporal resolution, the aggregated electricity demand in Germany is indeed price-elastic; it decreases by 70 MW for every € 1 per MWh increase in the day-ahead wholesale price. Article 5 finds that demand is also price-responsive in the very short term: the demand for imbalance energy responds to the imbalance price—despite the legal obligation in Germany to minimize imbalances independent of prices.}, language = {en} } @techreport{MuesselRuhnauMadlener, type = {Working Paper}, author = {Muessel, Jarusch and Ruhnau, Oliver and Madlener, Reinhard}, title = {Simulating charging behavior of electric vehicles: review and comparison with empirical data}, series = {19th International Conference on the European Energy Market (EEM), Lappeenranta, Finland, 2023}, journal = {19th International Conference on the European Energy Market (EEM), Lappeenranta, Finland, 2023}, doi = {10.1109/EEM58374.2023.10161947}, pages = {1 -- 7}, abstract = {Electric vehicles (EVs) are an important option to decarbonize the passenger transport sector and, therefore, critical to be adequately represented in energy system models. One of the main challenges is to model the volatility associated with charging EVs. We provide an overview of existing modeling approaches for this. We especially compare methods for simulating charging profiles and discuss their advantages and disadvantages, depending on the application. On that basis, we pick one simulation approach and generate time series for a case study of Germany in 2030. We assess the results and compare them with a large empirical dataset on EV charging in the UK. We derive recommendations for the future modeling of EVs.}, language = {en} } @article{MuesselRuhnauMadlener, author = {Muessel, Jarusch and Ruhnau, Oliver and Madlener, Reinhard}, title = {Accurate and scalable representation of electric vehicles in energy system models: A virtual storage-based aggregation approach}, series = {iScience}, volume = {26}, journal = {iScience}, number = {10}, doi = {10.1016/j.isci.2023.107816}, abstract = {The growing number of electric vehicles (EVs) will challenge the power system, but EVs may also support system balancing via smart charging. Modeling EVs' system-level impact while respecting computational constraints requires the aggregation of individual profiles. We show that studies typically rely on too few profiles to accurately model EVs' system-level impact and that a na{\"i}ve aggregation of individual profiles leads to an overestimation of the fleet's flexibility potential. To overcome this problem, we introduce a scalable and accurate aggregation approach based on the idea of modeling deviations from an uncontrolled charging strategy as virtual energy storage. We apply this to a German case study and estimate an average flexibility potential of 6.2 kWh/EV, only 10\% of the result of a na{\"i}ve aggregation. We conclude that our approach allows for a more realistic representation of EVs in energy system models and suggest applying it to other flexible assets.}, language = {en} } @article{RuhnauSchiele, author = {Ruhnau, Oliver and Schiele, Johanna}, title = {Flexible green hydrogen: The effect of relaxing simultaneity requirements on project design, economics, and power sector emissions}, series = {Energy Policy}, volume = {182}, journal = {Energy Policy}, doi = {10.1016/j.enpol.2023.113763}, abstract = {In many net-zero energy scenarios, electrolytic hydrogen is a key component to decarbonize hard-to-abate sectors and to provide flexibility to the power sector. In current energy systems that are not yet fully decarbonized, however, the hydrogen ramp-up raises the concern of increasing power sector emissions. To avoid such additional emissions, recent EU regulation defines requirements for electrolytic hydrogen to qualify as green along three dimensions: the additionality, the proximity, and the simultaneity of renewable electricity generation. Focusing on the temporal dimension, this article investigates the effects of a strict hourly simultaneity requirement, full temporal flexibility, as well as simultaneity exemptions in the current EU regulation. We develop a model of a renewables-hydrogen project, consisting of individual wind turbines, solar panels, hydrogen electrolysis, and hydrogen storage. As a novelty, the model optimizes not only dispatch but also investment decisions, and we expose it to different regulatory conditions. We show that a flexible definition of green hydrogen does not necessarily increase power sector emissions. By contrast, requiring hourly simultaneity implies that rational investors build much larger wind turbines, hydrogen electrolyzers, and hydrogen storage than needed—meaning additional costs and embedded carbon, underutilized assets, and a potential slow-down of green hydrogen deployment. These adverse effects can only partially be mitigated by including solar panels and by the EU simultaneity exceptions. We argue that current energy transition trends further lower the risk of increasing power sector emissions under a flexible definition of green hydrogen and recommend this as the way forward for a sustainable hydrogen policy.}, language = {en} }