تجزیه و تحلیل سیستم انرژی استفاده از هیدروژن به عنوان ناقل انرژی برای انرژی باد در بخش حمل و نقل در غرب دانمارک

Hydrogen is an energy carrier that can potentially be used for introducing renewably generated electricity into the transportation sector. This paper presents a methodology for an overall energy system analysis of a hydrogen infrastructure, which meets a transportation hydrogen demand profile. The methodology starts by building a mathematical model for optimizing the economic operation of electrolyzers on the electricity market by use of Genetic Algorithms. Demand profiles from the optimization are then included in an overall energy system analysis model studying the electricity market and power balance system effects. A sample 2030 scenario analysis of Western Denmark is presented to demonstrate the applicability of the devised methodology. It is shown that Genetic Algorithms is a flexible tool that can be adapted to optimization problems involving energy storage. On the other hand, it is found that the ability of Genetic Algorithms to find a solution is highly dependent on initial variables and the storage constraint. Further analysis is required in order to test and expand the methodology and scenario results.

Wind energy provided 22% of the electricity consumption in Western Denmark in 2006. The installed wind turbine capacity of 2400 MW already exceeds the local demand at certain hours of the year (Energinet.dk, 2007). On the other hand, transportation has almost entirely relied on products derived from oil (DEA, 2005). The operational costs of a thermally dominated electricity system (such as in Denmark) are expected to increase with an increasing share of fluctuating wind power (Meibom et al., 2007a). While foreign exchange can contribute to balancing fluctuating power, having local flexible technologies is essential for the development of a renewable energy market (Hvelplund, 2006). Various technological alternatives have been analyzed for increasing the system flexibility and economically allowing the integration of higher shares of wind power in the Danish electricity system (Andersen and Lund, 2007, Lund and Münster, 2006, Meibom et al., 2007b and Østergaard, 2005). A transportation fleet based on electricity is expected to have a positive technical influence on the electricity system flexibility and stability at high wind power penetration (Lund, 2007 and Mathiesen and Lund, 2008). The introduction of renewable energy into the transportation sector requires an energy carrier that meets the performance characteristics demanded by modern societies. Electrolytic hydrogen produced from wind and solar power is a potential carrier that has received considerable research attention during the previous decade (EHFCTP (European Hydrogen and Fuel Cell Technology Platform), 2006, EC (European Commission), 2004, USDOE (U.S. Department of Energy), 2007 and IEA (International Energy Agency), 2004). Several studies have analyzed various aspects of a future energy system with hydrogen as an energy carrier in the transportation sector in Denmark. Sørensen et al. (2004) constructed 2030 scenarios for Denmark with centralized and decentralized hydrogen production. The scenarios sought to maximize the utilization of wind power and study the impact on the storage size and hydrogen transportation problem. The study concluded that both centralized and decentralized scenarios are technically feasible, and that the mismatch between intermittent renewable energy sources and electricity demand can be offset by using hydrogen storage. The study, however, did not address the interaction between electricity prices and hydrogen electrolyzer operation. One of the studies of the operational system effects of electrolytic hydrogen production in Western Denmark was performed by Pedersen and Eriksen (2005). In the mentioned study, a futuristic hydrogen scenario is simulated. The electrolyzer operation strategy is based on a fixed maximum electricity purchase price on the spot market. The study concludes that electricity prices are highly unlikely to fluctuate enough to allow for the utilization of the produced hydrogen in stationary applications. This is due to the fact that the Danish system is interconnected with the Scandinavian system, which is characterized by relatively high hydropower capacities. It is thus recommended to utilize the produced hydrogen in the transportation sector where tax benefits could potentially allow hydrogen to compete with oil on an energy unit basis. The study, however, puts no restraints on the hydrogen storage capacity or hydrogen demand, and this gives a relatively large storage capacity and has a minor impact on electricity system prices. The problem of optimizing the operation of energy storage on the day ahead spot market such as the NordPool market poses a modeling challenge. In his work, Korpås models a hydrogen system with a limited grid connection and local wind power generation (Korpås, 2004). An economic optimization method considering wind speed and electricity market prices is presented. The study, however, assumes a deterministic electricity price time series. On a large scale, the hydrogen system would inevitably influence the operation of the electricity market itself.

The paper has presented a methodology for simulating the operational and market system effects of a scenario in which electrolytic hydrogen meets a fixed transportation demand profile. A mathematical model for optimizing the electrolyzers' economic operation was constructed. The model makes it possible to prioritize the utilization of wind power for hydrogen generation. GAs constituted the tool used for performing the optimization. It was shown that GAs can be tailored to optimize the electrolyzer operation for a period of up to one day based on hourly time series. Special algorithm factors were devised in the application to avoid local conversion and ensure a wide search space of potential solutions. The ability of GAs to find a solution is seen as highly sensitive and dependent on the chosen factors and the storage content during the simulated periods (day). Other optimization methods were not compared to GAs in this study. The results of the hydrogen electrolyzer model were incorporated in the SIVAEL overall energy system model. A Western Denmark 2030 scenario was presented in which an expanded offshore wind power capacity contributes to generating around 32% of the transportation energy demand. A limited storage of two days demand capacity is introduced in the scenario. It was found that iterating between the two models does not converge to a final solution. Two suggestions for convergence were given but not tested further. General conclusions from the scenario models could still be derived. The two main scenario conclusions were: – The average annual market price increases and becomes more volatile with higher peaks and lower troughs than a similar scenario with unlimited storage. – The limited storage leads to a large number of hours with power deficit during periods with a lack of wind power. These above results support the assumptions specified in the scenario, in particular regarding the absence of demand elasticity and extra generation investments.