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ispartof: Energy Journal vol:43 issue:4 pages:69-100 status: published

Clustered unit commitment (CUC) formulations have been proposed to provide accurate and fast approximations to the unit commitment (UC) problem. In these formulations, identical or similar plants are grouped into clusters. This way, the binary commitment variables of all the plants within a cluster can be replaced by a single integer variable. This approach has recently been mainly used for tractably integrating flexibility constraints in generation expansion planning problems. However, a thorough general validation is still missing. In addition, these formulations do not provide commitment schedules on a plant-by-plant level and hence cannot be used directly for operating actual systems or markets. A first contribution of this paper is to show that errors can be introduced both due to the problem formulation and the grouping of non-identical units. A case study is presented in which these errors are quantified under different conditions. Overall, the error in approximating the total cost does not exceed 0.06%. A second contribution of this paper is the development of a hybrid approach which sequentially uses a CUC and a traditional UC model. This approach allows to reduce the computational cost of solving the UC problem while providing a guaranteed feasible and near optimal solution. ispartof: IEEE Transactions on Power Systems vol:33 issue:2 pages:2195-2204 status: published

The deployment of renewable cooperation mechanisms within the European Union (via statistical transfers,joint support schemes and joint projects) is expected to increase in the near future. Such cooperation mechanisms can significantly reduce the compliance cost for meeting renewable energy targets. Nevertheless,as it is known that ill-designed national support instruments distort renewable investment and production decisions, it can also be expected that these impact the performance of cooperation mechanisms. In this paper, we develop a bi-level two-country competitive equilibrium model that analyzes the impact of national RES-E support instruments on the performance of renewable cooperation mechanisms. Further-more, we assess the efficiency of two international cooperation mechanisms (statistical transfers and joint support schemes) and compare it to the situation without renewable cooperation. Based on an analytical derivation and a numerical example, we first confirm that fixed feed-in premiums are the globally most efficient instrument, given production-based quotas (in MWh). Other national instruments (feed-in tariffs and capacity-based subsidies) can distort renewable investment decisions, and are sub-optimal. Second, the employment of statistical transfers always outperforms the no-renewable cooperation case, independent of the national support instruments. Third, statistical transfers are preferred over joint support schemes when employing sub-optimal national policy instruments. In fact, it even is possible that sub-optimal joint sup-port schemes (i.e. not based on the fixed feed-in premium) perform worse than no renewable cooperation at all. Finally, we also consider the country-level distributional effects and conclude that country-level incentives for renewable cooperation may not align with the global optimum, i.e. national policy makers might be incentivized to constrain their cooperation levels. ispartof: ENERGY ECONOMICS vol:81 pages:859-873 status: published

We aim to provide an overview of renewable subsidy schemes, thereby focusing on renewable investment incentives and cost effects in a uniformly-priced market zone. Specifically, we develop a deterministic short-term market equilibrium model that allows to investigate both siting and technological distortions in onshore wind turbine deployment. This paper includes five support instruments: the feed-in tariff, sliding feed-in premium, fixed feed-in premium, investment-based subsidies and capacity-based subsidies. Investment decisions under these instruments are analyzed using an extensive German case study. Apart from providing a general overview, our contribution is threefold. First, we show that investment- and capacity-based subsidies generally are not equivalent, despite being used interchangeably in literature. Generators granted investment offsets opt for the most system-friendly technologies, whilst those granted capacity-based subsidies tend to select the least system-friendly ones. As these two generation-independent subsidy instruments promote very different technologies, we question the prevailing belief that learning-by-doing externalities must be related to capacity. Second, sliding feed-in premiums yield very similar outcomes as fixed feed-in premiums for both investment and cost effects, and can substitute fixed premiums to mitigate investment risks. This conclusion holds for technology-specific support within a uniformly-priced market zone, but might not hold over multiple pricing zones or for technology-neutral support. Finally, we show that most of these effects arise from technological distortions, whilst locational incentives are roughly the same under all instruments.