Wolf-Peter Schill

Residual load, renewable surplus generation and storage requirements in Germany

I examine the effects of increasing amounts of fluctuating renewable energy on residual load, which is defined as the difference between actual power demand and the feed-in of non-dispatchable and inflexible generators. I draw on policy-relevant scenarios for Germany and make use of extensive sensitivity analyses. Whereas yearly renewable surplus energy is low in most scenarios analyzed, peak surplus power can become very high. Decreasing thermal must-run requirements and increasing biomass flexibility substantially reduce surpluses. I use an optimization model to determine the storage capacities required for taking up renewable surpluses. Allowing curtailment of 1% of the yearly feed-in of non-dispatchable renewables would render storage investments largely obsolete until 2032 under the assumption of a flexible power system. Further restrictions of curtailment as well as lower system flexibility strongly increase storage requirements. By 2050, at least 10GW of storage are required for surplus integration, of which a sizeable share is seasonal storage. Results suggest that policy makers should work toward avoiding surplus generation, in particular by decreasing the must-run of thermal generators. Concerns about surpluses should not be regarded as an obstacle to further renewable expansion. The findings are also relevant for other countries that shift toward fluctuating renewables.

Power system impacts of electric vehicles in Germany: Charging with coal or renewables?

We analyze the impacts of future scenarios of electric vehicles (EVs) on the German power system, drawing on different assumptions on the charging mode. We find that the impact on the load duration curve strongly differs between charging modes. In a fully user-driven mode, charging largely occurs during daytime and in the evening, when power demand is already high. User-driven charging may thus have to be restricted because of generation adequacy concerns. In contrast, cost-driven charging is carried out during night-time and at times of high PV availability. Using a novel model formulation that allows for simulating intermediate charging modes, we show that even a slight relaxation of fully user-driven charging results in much smoother load profiles. Further, cost-driven EV charging strongly increases the utilization of hard coal and lignite plants in 2030, whereas additional power in the user-driven mode is predominantly generated from natural gas and hard coal. Specific CO2 emissions of EVs are substantially higher than those of the overall power system, and highest under cost-driven charging. Only in additional model runs, in which we link the introduction of EVs to a respective deployment of additional renewables, electric vehicles become largely CO2-neutral.

Residual Load, Renewable Surplus Generation and Storage Requirements in Germany

We examine the effects of future renewable expansion in Germany on residual load and renewable surplus generation for policy-relevant scenarios for 2022, 2032 and 2050. We also determine the storage capacities required for taking up renewable surpluses for varying levels of accepted curtailment. Making use of extensive sensitivity analyses, our simulations show that the expansion of variable renewables leads to a strong decrease of the right-hand side of the residual load curve. Renewable surpluses generally have high peaks which only occur in very few hours of the year, whereas overall surplus energy is rather low in most scenarios analyzed. Surpluses increase substantially with growing thermal must-run requirements, decreasing biomass flexibility and decreasing load. On average, most surpluses occur around noon and in spring time. Whereas the energy of single surplus hours is often in the range of existing German pumped hydro capacities, the energy of connected surpluses is substantially larger. Using an optimization model, we find that no additional storage is required in the scenarios for 2022 and 2032 in case of free curtailment. Even restricting curtailment to only 1% of the yearly feed-in of non-dispatchable renewables would render storage investments largely obsolete under the assumption of a flexible system. In contrast, further restrictions of curtailment and a less flexible system would strongly increase storage requirements. In a flexible 2050 scenario, 10 GW of additional storage are optimal even in case of free curtailment due to larger surpluses. Importantly, minor renewable curtailment does not impede achieving the German governments renewable energy targets. We suggest avoiding renewable surpluses in the first place by making thermal generators more flexible. Afterwards, different flexibility options can be used for taking up remaining surpluses, including but not limited to power storage. Curtailment remains as a last resort. Full surplus integration by power storage will never be optimal because of the nature of surpluses shown in this paper. Future research should explore synergies and competition between different flexibility options, while not only covering the wholesale market, but also ancillary services.

Power System Transformation toward Renewables: Investment Scenarios for Germany

We analyze distinctive investment scenarios for the integration of fluctuating renewables in the German power system. Using a combined model for dispatch, transmission, and investment, three different investment options are considered, including gas-fired power plants, pumped hydro storage, and transmission lines. We find that geographically optimized power plant investments dominate in the reference scenarios for 2024 and 2034. In scenarios with decreased renewable curtailment, storage and transmission requirements significantly increase. In an alternative scenario with larger investments into storage, system costs are only slightly higher compared to the reference; thus, considering potential system values of pumped hydro storage facilities that are not included in the optimization, a moderate expansion of storage capacities appears to be a no-regret strategy from a system perspective. Additional transmission and storage investments may not only foster renewable integration, but also increase the utilization of emission-intensive plants. A comparison of results for 2024 and 2034 indicates that this is only a temporary effect. In the long run, infrastructure investments gain importance in the context of an ongoing energy transition from coal to renewables. Because of long lead times, planning and administrative procedures for large-scale projects should start early.

A Greenfield model to evaluate long-run power storage requirements for high shares of renewables

We develop a dispatch and investment model to study the role of power storage and other flexibility options in a greenfield setting with high shares of renewables. The model captures multiple system values of power storage related to arbitrage, dispatchable capacity, and reserves. In a baseline scenario, we find that power storage requirements remain moderate up to a renewable share of around 80%, as other options on both the supply side and demand side also offer flexibility at low cost. Yet storage plays an important role in the provision of reserves. If the renewable share increases to 100%, the required capacities of power storage and other technologies increase strongly. As long-run parameter assumptions are highly uncertain, we carry out a range of sensitivity analyses, for example, with respect to the costs and availabilities of storage and renewables. A common finding of these sensitivities is that – under very high renewable shares – the storage requirement strongly depends on the costs and availability of other flexibility options, particularly on biomass availability. We conclude that power storage becomes an increasingly important element of a transition towards a fully renewable-based power system. Power storage gains further relevance if other potential sources of flexibility are less developed. Supporting the development of power storage should thus be considered a useful component of policies designed to safeguard the transition towards renewables.

Practicalities of individual producer responsibility under the WEEE directive: experiences in Germany

In theory, individual producer responsibility (IPR) creates incentives for ‘design-for-recycling’. Yet in practice, implementing IPR is challenging, particularly if applied to waste electric and electronic equipment. This article discusses different options for implementing IPR schemes under German WEEE legislation. In addition, practical aspects of a German ‘return share’ brand sampling scheme are examined. Concerning ‘new’ WEEE put on the market after 13 August 2006, producers in Germany can choose between two different methods of calculating take-back obligations. These can be determined on the basis of ‘return shares’ or ‘market shares’. While market shares are regularly monitored by a national clearing house, the ‘return share’ option requires sampling and sorting of WEEE. Herein it is shown that the specifics of the German WEEE take-back scheme require high sample sizes and multi-step test procedures to ensure a statistically sound sampling approach. Since the market share allocation continues to apply for historic waste, producers lack incentives for choosing the costly brand sampling option. However, even return share allocation might not imply a decisive step towards IPR, as it merely represents an alternative calculation of market shares. Yet the fundamental characteristics of the German take-back system remain unchanged: the same anonymous mix of WEEE goes to the same treatment operations.

The Effect of Market Power on Electricity Storage Utilization: The Case of Pumped Hydro Storage in Germany

In this paper, we develop the game-theoretic electricity market model ElStorM that includes the possibility of strategic electricity storage. We apply the model to the German electricity market and analyze different realistic and counterfactual cases of strategic and non-strategic pumped hydro storage utilization by different players. We find that the utilization of storage capacities depends on the operator and its ability to exert market power both regarding storage and conventional generation capacities. The distribution of storage capacities among players also matters. A general finding is that strategic operators tend to under-utilize their storage capacities. This affects generation patterns of conventional technologies and market outcomes. Strategic under-utilization of storage capacities might also diminish their potential for renewable energy integration. Accordingly, economic regulation of existing and future storage capacities may be necessary, depending on policy objectives. We also find that the introduction of electricity storage generally increases overall welfare, while outcomes vary between different cases. Strategic storage utilization decreases consumer rent compared to non-strategic storage utilization. However, this effect is less pronounced if storage capacities are distributed among several players.

Power System Transformation towards Renewables: An Evaluation of Regulatory Approaches for Network Expansion

We analyze various regulatory regimes for electricity transmission investment in the context of a transformation of the power system towards renewable energy. We study distinctive developments of the generation mix with different implications on network congestion, assuming that a shift from conventional power plants towards renewables may go along with exogenous shocks on transmission requirements, which may be either of temporary or permanent nature. We specifically analyze the relative performance of a combined merchant-regulatory price-cap mechanism, a cost-based rule, and a non-regulated approach in dynamic generation settings. Through application in a stylized two-node network, we find that incentive regulation may perform satisfactorily only when appropriate weights are used. While quasi-ideal weights generally restore the beneficial properties that incentive regulatory mechanisms are well-known for in static settings, pure Laspeyres weights may either lead to overinvestment (stranded investments) or delayed investments as compared to the welfare optimum benchmark. Stranded investments could then be avoided through proper handling of weights. Model results indicate that using average Laspeyres-Paasche weights appears to be an appropriate strategy in the context of permanently or temporarily increasing network congestion. Our analysis motivates further research aimed to characterize optimal regulation for transmission expansion in the context of renewable integration.

On Start-Up Costs of Thermal Power Plants in Markets with Increasing Shares of Fluctuating Renewables

The emerging literature on power markets with high shares of fluctuating renewables suggests that more frequent start-up procedures of thermal power plants may become an increasing concern, both for costs and possibly also for market design. Based on official scenario assumptions, we investigate how start-ups and related costs develop in Germany, where the share of fluctuating renewables quadruples between 2010 and 2030. We find that the overall number of start-ups decreases by a third, while related costs increase by half. The relative share of start-up costs in overall variable costs of thermal plants grows only slightly and remains below 1%. Several overlapping effects drive these results. The expansion of fluctuating renewables alone would strongly increase start-up costs. In contrast, increased flexibility of biomass power plants, additional power storage and larger block sizes have opposite effects. While the relevance of start-up costs grows only moderately under baseline assumptions, it may increase further under alternative developments of system flexibility. Future power market design reforms should thus aim to ensure proper remuneration of quasi-fixed start-up costs. Our findings are also relevant for many other countries with thermal power systems that plan to undergo comparable transitions toward fluctuating renewables.

A Coordinated Strategic Reserve to Safeguard the European Energy Transition

In Germany and beyond, various capacity mechanisms are currently being discussed with a view to improving the security of electricity supply. One of these mechanisms is a strategic reserve that retains generation capacity for use in times of critical supply shortage. We argue that strategic reserves have specific advantages compared to other capacity mechanisms in the context of the European energy transition. To date, however, the debate on capacity mechanisms has largely been restricted to national contexts. Against this background, we discuss the feasibility and potential benefits of coordinated cross-border strategic reserves to safeguard electricity supply and aid the energy transition in Germany and neighboring countries at large. Setting aside strategic reserve capacity which is deployed only in the event of extreme supply shortages could improve the security of electricity supply without distorting the EU’s internal electricity market. In addition, overall costs may decrease when reserve procurement and activation are coordinated among countries, particularly if combined with flow-based market coupling.