Integrated solar-hydrogen combined heat and power / solar-thermal systems for power and hot water supply in standalone applications
Creators: name: Assaf, Jihane
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 380107
subject: Financial economics
classificationCode: 400803
subject: Electrical energy generation (incl. renewables, excl. photovoltaics)
classificationCode: 401703
subject: Energy generation, conversion and storage (excl. chemical and electrical)

description: Solar energy can currently be transformed into electricity and heat through photovoltaics (PVs) and solar thermal collectors respectively, particularly in household and residential applications. However, the intermittent supply of solar energy - e.g. during the night-time or cloudy periods - as well as its seasonal variability, offer some challenges to maintain a continuous supply in systems relying on the solar source. This suggests the need for employing reliable energy storage in systems relying on the solar source. Hydrogen has been seen to be a promising energy carrier suitable to store energy, especially for long term, in contrast to batteries that have been used for short term energy storage only. A hydrogen storage system comprises mainly an electrolyser, hydrogen storage (i.e. hydrogen storage tank), and a fuel cell. In a solar-hydrogen system, the electrolyser is powered by the excess electricity generated by the PV (i.e. after that the PV meets the power demand), and thus, the electrolyser can produce hydrogen through the electrolysis of water, by using this excess electricity. The hydrogen produced is stored in a storage tank for example. When the solar radiation is not sufficient or unavailable for the PV to meet the power demand, the fuel cell is fed by the stored hydrogen to generate the required electricity and fill up the power deficit from the PV. This is done cleanly with no emissions through the chemical reactions between hydrogen and oxygen (i.e. usually taken from air). While the fuel cell is in operation and is producing electricity, it also produces heat. Instead of being lost, this heat was used in previous research to heat water for an onsite application (i.e. hot water demand of a household). However, it was found that this solar-hydrogen (SH) combined heat and power (CHP) system, while it meets 100% of the power demand of a Victorian Australian household, it could meet only around 50% of its annual hot water demand (from the fuel cell heat). On the other side, solar-thermal collectors can provide heat from solar energy. However, a solar- thermal (ST) system (collectors with hot water storage tank), in its best design, cannot meet the full hot water demand of a household and falls deeply short in meeting this demand in winter. Hence, another source of heat is needed for this purpose. So, the novel idea of the project is to study a solar-hydrogen CHP system integrated with a solar thermal system for power and hot water supply from solar energy to a household. In fact, when the solar radiation is low or unavailable, there is a shortage of heat supply from the collectors, which coincides with the absence of adequate electricity supplied by the PVs. This is the time that the fuel cell of the SH system operates to provide power and hence the heat generated by the fuel cell can be harvested and utilised. As originality of this integration, a complementary operational aspect of the two heat sources (SH CHP and ST) is foreseen. Due to the possibility of the matching opportunity offered by the complementary operation of the two heat sources (SH CHP and ST), the hybrid integrated SH CHP-ST system proposed provides opportunities for making the entire heat and power supply system more cost effective, reliable, and independent. A model that simulates theoretically the behaviour of the system is developed together with an experimental validation of the heat integration. The possible configurations of such system are investigated with the selection of the best configuration. The characteristic performance of this integration is drawn out and a techno-economic analysis carried. A multi-objective sizing optimisation is developed which considers simultaneously maximising the electric and thermal reliability of such system, minimising its cost, and minimisation the percentage of energy wasted by the PV. Taken a conservative remote household in Victoria, Australia, this system was proved to be able to meet annually 100% of its power demand and 95% of its hot water (with meeting more than 90% of the hot water demand in winter). Other possible sizing options and results obtained from the multi-objective sizing optimisation are also provided. The system is proved to be competitive economically against conventional energy systems used in remote areas (i.e. diesel generator for power supply and gas water heat for hot water supply).