Within the Flexnode Plus project the long-term degradation characteristics of a proton exchange membrane (PEM) electrolyzer (5.5 kW, AC, 1 Nm3/h H2) and fuel cell (1.0 kW, DC, 0.9 Nm3/h) was experimentally tested. The electrolyzer unit was operated at various loads and pressures for approximately 750 hours in total, while the fuel cell was operated at a constant load of 1 Ω resistance for approximately 1120 hours in total. The efficiency of the hydrogen production in the electrolyzer and the electricity production in the fuel cell was expressed using the hourly average system efficiency and average cell efficiency. Inorder to predict the state of health and remaining lifetime of the electrolyzer cell and fuel cell, the decay of the cell voltage over time was monitored and the direct mapping from aging data method was used.The electrolyzer cell showed a stable cell voltage and cell efficiency in the studied time period, with an average cell voltage decay rate of 0.5 μV/h. The average cell voltage of the fuel cell dropped with a rate of 2 μV/h during the studied time period.
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The European Union is striving for a high penetration of renewable energy production in the future energy grid. Currently, the EU energy directive is aiming for 20% renewable energy production in the year 2020. In future plans the EU strives for approximately 80% renewable energy production by the year 2050. However, high penetration of wind and solar PV energy production, both centrally and de-centrally, can possibly destabilize the electricity grid. The gas grid and the flexibility of gas, which can be transformed in both electricity and heat at different levels of scale, can help integrate and balance intermittent renewable production. One possible method of assisting the electricity grid in achieving and maintaining balance is by pre-balancing local decentralized energy grids. Adopting flexible gas based decentralized energy production can help integrate intermittent renewable electricity production, short lived by-products (e.g. heat) and at the same time minimize transport of energy carriers and fuel sources. Hence, decentralized energy grids can possibly improve the overall efficiency and sustainability of the energy distribution system. The flexibility aforementioned, can potentially give gas a pivotal role in future decentralized energy grids as load balancer. However, there are a lot of potentially variables which effect a successful integration of renewable intermittent production and load balancing within decentralized energy systems. The flexibility of gas in general opens up multiple fuel sources e.g., natural gas, biogas, syngas etc. and multiple possibilities of energy transformation pathways e.g. combined heat and power, fuel cells, high efficiency boilers etc. Intermittent renewable production is already increasing exponentially on the decentralized level where load balancing is still lacking.
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The intermittency of renewable energy technologies requires adequate storage technologies. Hydrogen systems consisting of electrolysers, storage tanks, and fuel cells can be implemented as well as batteries. The requirements of the hydrogen purification unit is missing from literature. We measured the same for a 4.5 kW PEM electrolyser to be 0.8 kW for 10 min.A simulation to hybridize the hydrogen system, including its purification unit, with lithium-ion batteries for energy storage is presented; the batteries also support the electrolyser. We simulated a scenario for operating a Dutch household off-electric-grid using solar and wind electricity to find the capacities and costs of the components of the system.Although the energy use of the purification unit is small, it influences the operation of the system, affecting the sizing of the components. The battery as a fast response efficient secondary storage system increases the ability of the electrolyser to start up.
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Bespreking van onderzoek van Rychard Bouwens in ‘Waar wij trots op zijn. De ontdekkingen van 2011’ van de Universiteit Leiden Faculteit der Wiskunde & Natuurwetenschappen. Het valt goed te begrijpen voor iedereen met een basale kennis van klassieke fotografie: bij weinig licht neem je een lange sluitertijd. En dat is wat Rychard Bouwens deed. Om naar de zogenaamde Dark Ages van het heelal te kijken, hield hij de Hubble-ruimtetelescoop maar liefst 87 uur lang op een plek gericht.
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Bespreking van onderzoek van Anton Akhmerov in ‘Waar wij trots op zijn. De ontdekkingen van 2011’ van de Universiteit Leiden Faculteit der Wiskunde & Natuurwetenschappen. De Leidse theoretisch natuurkundige Anton Akhmerov promoveerde in mei op een onderzoek naar functionele toepassingen van grafeen, een eenlaags koolstofmateriaal dat de afgelopen jaren volop in de belangstelling staat. Daarnaast werkte hij ook nog aan quantumcomputers, omdat hij tijd over had in zijn onderzoek.
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Bespreking van onderzoek van Erik Danen in ‘Waar wij trots op zijn. De ontdekkingen van 2011’ van de Universiteit Leiden Faculteit der Wiskunde & Natuurwetenschappen. Celbioloog Erik Danen doet onderzoek naar de verwoestende – maar in evolutionaire termen ook wonderlijke – strategieën van de kankercel. Met welke trucs verspreiden kankercellen zich door het lichaam? Hoe overleven ze een aanval van een chemokuur? En hoe wrang is het dat de één procent cellen die de therapie overleeft vervolgens dubbelhard terugslaat.
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