ElectrolysisHybrid hydrogen-battery energy storage Renewable storage a b s t r a c t Off-grid hybrid systems, based on the integration of hydrogen technologies (electrolysers, hydrogen stores and fuel cells) with battery and wind/solar power technologies, are proposed for satisfying the continuous power demands of telecom remote base stations. A model was developed to investigate the preferred role for electrolytic hydrogen within a hybrid system; the analysis focused on powering a 1 kW telecom load in three locations of distinct wind and solar resource availability. When compared with otherwise equivalent off-grid renewable energy systems employing only battery energy storage, the results show that the integration of a 1 kW fuel cell and a 1.6 kW electrolyser at each location is sufficient, in combination with a hydrogen storage capacity of between 13 and 31 kg, to reduce the required battery capacity by 54e77%, to increase the minimum state-of-charge from 37 to 55% to >81.5% year-round despite considerable seasonal variation in supply, and to reduce the amount of wasted renewable power by 55e79%. For the growing telecom sector, the proposed hybrid system provides a 'green' solution, which is preferable to shipping hydrogen or diesel to remote base stations.
Off-grid autonomous hydrogen system PEM electrolysis Solar PV capture Maximum power point tracking Thermal management a b s t r a c t A novel embodiment of a polymer electrolyte membrane (PEM) electrolyser is presented as a means for producing hydrogen off-grid by the efficient absorption of the time-varying power output of a solar photovoltaic (PV) panel or array. The balance-of-plant powerload was minimised using passive design principles to ensure efficient operation under cloudy, sunset and wintry conditions. Heat generated during the electrolysis process is stored when appropriate to significantly enhance the efficiency of hydrogen production after a period of darkness. A prototype field trial demonstrated the electrolyser's ability to track closely the highly variable output of the PV year-round under a wide range of operating conditions. Hydrogen yields for various geographical locations were estimated to vary from 25 to 65 kg p.a. for a 1.6 kW electrolyser with fixed-tilt PV panels depending on local levels of solar insolation. This could be increased to over 100 kg p.a. by employing a PV panel of greater capacity and a battery for absorbing the peak generation and then discharging it overnight to the electrolyser. IntroductionIn order to meet an energy demand, individual wind or solar power sources need to be connected to an electricity grid, or to an energy converter and store, due to their time-varying availability characteristics. It is conventional for such renewable energy converters to be configured to supply AC power to the electricity grid, and for the power industry to accommodate the weather-dependent nature of these inputs by managing the operation of thermal power plant. As the renewable power penetration increases in the grid this accommodation becomes more difficult e several concerns emerge including the need to curtail wind/solar power sources at times of low demand, greater requirements for reserve power plant for grid balancing, and the negative impact of increased cycling upon thermal power plant. The alternative of converting this renewable electricity to another form of energy and storing it for later use is technically challenging, but it is a principal pathway for decarbonising the energy system [1].Electricity can be converted to gaseous hydrogen by electrolysis and stored indefinitely, thereby providing a 'green' fuel source for meeting any time-varying requirement for energy. The inherent applications flexibility of hydrogen (e.g. as a transport/heating/cooking fuel, or if desired for reconversion to electricity) invites the development of distributed renewable-hydrogen energy systems, which can be designed to meet a given demand requirement for fuel or electricity. Applications of interest include: zero-carbon homes [2], ScienceDirect j o urn al h om epa ge: www.elsev ier.com/locate/he i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 9 ( 2 0 1 4 ) 1 9 8 5 5 e1 9 8 6 8 http://dx.hydrogen refuelling stations for fuel cell cars [3], refuellers for unmanned...
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