Design and sizing of stand-alone photovoltaic hydrogen system for HCNG production
Introduction
At the beginning of the twenty-first century global energy consumption has reached an alarming threshold, with 11,164 million tones oil equivalents (Mtoe) in 2009 [1]. That is because the great portion of energy requirements is supplied by conventional fossil fuels such as oil, natural gas and coal responsible for both global warming and climate change, and at the same time are in a quick depletion [2], [3], [4], [5], [6], [7]. The transportation sector is one of the most affected sectors by this situation since it is the second largest energy consuming sector after the industrial sector with 30% of the world's total delivered energy [8]. Hydrogen (H2) from renewable energy sources is a clean and sustainable option as a fuel and is seen as a potential alternative to gasoline in the future [9]. The use of hydrogen in the transportation sector is more known in the fuel cell electric vehicles, where they have been widely investigated around the world over the past decades [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. These vehicles use the hydrogen as an energy carrier to power electric motors through fuel cells. Furthermore, hydrogen as a fuel can be used in internal combustion engines in mixture with compressed natural gas (HCNG) [20], [21], [22] which is used as a transition to hydrogen technology. Many research related to HCNG have been conducted during the last 15 years. Some of these works use the HCNG mixture at different hydrogen fractions to characterise: i) emission of polluting exhaust gases HC, CO, CO2 and NOx [23], [24], [25]; ii) engine power performance and efficiency [26], [27], [28]; iii) combustion [29], [30].
Hydrogen can be produced by different technologies such as: i) electrolysis of water using fossil, nuclear or renewable energy sources; ii) gasification of biomass and coal; iii) reforming of hydrocarbons which include gasoline, liquefied petroleum gas, natural gas; iv) photo-electrochemical/photo-catalytic splitting of water; v) thermolysis and thermochemical cycles [31]. Currently, hydrogen production is dominated by the reforming process with more than 90% of world hydrogen production [32], and hydrogen produced by electrolysis represents only 4–5% of the world production [33], [34]. Despite this, the use of energy from the photovoltaic (PV) array generator is one of the most promising technologies for water electrolysis hydrogen production from a clean renewable energy, because of the relatively high efficiency (70–80%) and high purity of produced hydrogen [31]. Stand-alone photovoltaic systems with hydrogen storage have been widely investigated around the world over the past decades [35], [36], [37], [38], [39], [40], [41], [42], [43], with proposed modelling, optimal sizing and energy management strategies models. In all of these studies, hydrogen is used only as an energy carrier for producing electricity with fuel cells. At the best author's knowledge, no study is conducted on the photovoltaic hydrogen production system (PV/H2Fuel) where hydrogen gas is used as a fuel. Nevertheless, intermittences of both the solar source and the hydrogen demand which depend significantly on seasons and locations, make challenging the optimal sizing of the PV/H2Fuel system components for achieving high energy efficiency with rational system cost. The objective of the present article is to develop a sizing method for a clean photovoltaic hydrogen production used in the preparation of the HCNG mixture. Case studies are provided to verify the validity of the proposed methodology.
Section snippets
System description
In this paper we illustrate the developed method for an optimal design and sizing of a stand-alone photovoltaic hydrogen system for electrolytic hydrogen gas production (PV/H2Fuel). In this study, the produced hydrogen is especially used in mixture with compressed natural gas as a fuel in internal combustion engines.
As Fig. 1 shows, the PV/H2Fuel system does not include an electricity energy buffer. However, this system contains two PV array generators to provide separately the electrical
System sizing
As Fig. 1 shows, the PV/H2Fuel system consists of two sub-systems where the hydrogen production sub-system (sub-system 1) is electrically independent from the compression gas subsystem (sub-system 2). However, the sub-system 2 capacities depend to the size of the electrolyser.
Case studies
The main objective of the proposed PV/H2Fuel system sizing method is to optimise the system components sizing for achieving high energy efficiency with rational system costs. To verify the relevance of this method, Algiers (36.8 °N) is chosen as the location test for setting up two service stations with the HCNG fuel dispensers. In the simulation, the PV array efficiency is ηpv1 = ηpv2 = 15%, the MPPT converter efficiency is ηmp1 = ηmp2 ≈ 95%, the DC/AC converter efficiency is ηac1 = ηac2
Conclusions
For a clean photovoltaic hydrogen production used in the preparation of the HCNG fuel, a new system sizing method based on a simple PV/H2Fuel system design is proposed in this paper. The presented PV/H2Fuel system consists of two sub-systems electrically independent. The fact that the hydrogen compressor works only when the electrolyser is in operation during daylight hours, the required power for running the gas compressor is also provided by a second PV array. The advantage of this sizing
Acknowledgements
This work was supported by the “ Ministère de l'Enseignement Supérieur et de la Recherche scientifique” of the Algerian Government under PNR Project ‘‘Carburant solaire’’. I thank all the member of the project and especially Mr. Mahmah and Mr. Becherif for their help.
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