A thermo-economic model and a simulation analysis of a solar hydrogen system using IPSEpro

Abstract

The high growth of world population and modern lifestyle are increasing the world’s energy consumption and fossil fuel depletion, as well as increasing environmental and economic adverse impacts. This concern is encouraging scientists and governments to create more reliable, long-lasting and environmentally benign energy sources. Renewable energy sources, particularly solar energy, are nowadays suggested as being one of the main alternative and future sources of energy to traditional fossil fuel sources. Nevertheless, the main challenge in utilizing solar energy is its high utilization cost and variability, when a storage or backup system is required. To overcome this problem, many researchers have introduced hydrogen because it is the cleanest, most abundant and safest fuel that can be used as an energy carrier or a backup system in place of batteries and fossil fuel generators. Solar hydrogen system (SHS) technologies are still immature and a few experimental projects have been installed around the world, inspiring more studies to improve these technologies towards a hydrogen-economy objective. Very little software is commercially available to use for simulation and optimization of a solar hydrogen system and no effective software has been developed for thermo-economic analysis. However, in this study a thermo-economic model library component for solar hydrogen system units such as photovoltaic (PV), photovoltaic thermal (PV/T), fuel cell and electrolyzer have been developed and validated using the commercially available software package IPSEpro. The developed models, along with the existing IPSEpro model libraries have been used to; design, optimize and simulate the entire system to meet the energy demands of a small community in three different sites. The sites considered were Sabha and Misurata in Libya, a hot region as well as Newcastle in United Kingdom in a cold region, using yearly average and a typical summer and winter actual weather data for each site. A parametric study was carried out to investigate the effects of the environmental, main operation and economic parameters on the performance and outputs of each component and the entire system. A thermo-economic analysis of the SHS showed that the PV unit has the highest factors for; (exergy destruction (exdf), destruction cost (CD), investment and destruction summation (ZTCD), and the lowest exergoeconomic (fk), followed by the fuel cell and the electrolyzer. However, the low (fk) factor of the PV and the fuel cell units indicated that a high level of attention has to be focused on increasing the unit’s exergy efficiency. Moreover, the high (fk) factor of the electrolyzer indicates that the reduction of the unit investment cost (ZT) has the priority for unit performance improvement and production cost reduction. It has also been established that, for a SHS at base condition, A. A. El-sharif iii Newcastle University the system’s exergy efficiency was 5.07% with a daily average output electricity cost of 0.23$/kWh. However, for Sabha and Newcastle, the yearly average electricity cost was 0.40$/kWh and 0.77 $/kWh respectively. This is still uncompetitive compared with (+- 0.15 $/kWh) typical current electricity market prices. In addition, the study clarified that SHS will be economically reasonable if the costs of the CO2 emission and fossil fuels consumed are considered in the analysis, particularly in Sabha and Misurata regions. Nevertheless, in these regions the photovoltaic electricity is competitive to the traditional power plant current prices. The analysis also shows that the variation in the environmental, economic and operation parameters have a significant effect on the system and its units’ performance and output costs. The parametric study mainly considered the variation of; ambient temperature (Ta), solar intensity (Sirr), module surface temperature (PV/Tc), interest rate (ir), capacity factor (CF), capital cost (CFC), lifetime (ny), price of output hot water (cwh), cell voltage (Vc), stoichiometric ratio (StH2), hot water temperature and mass flow rate. The parametric study results revealed that the optimum SHS operation conditions will achieve at the smallest ambient temperature and the highest solar intensity. It is also found that recycling the output streams, particularly the hydrogen and utilizing the output hot water of the unit’s cooling system will significantly enhance its performance and reduce the production costs. The study proves that increasing the output hot water of the PV/T system to utilize it in a low thermal energy system using an electric heater is unfeasible. More investigation is recommended to build an integrated IPSEpro thermo-economic model to utilize the SHS output hot water in a low thermal energy system using a solar collector.