Hong Kong has a limited land area, and researchers have checked how much of the city could be powered if most of its water reservoirs were fully or partially covered with floating PV systems. In the best case, full coverage could cover more than 15% of the city’s total demand and more than 60% of housing demand.
Researchers from the University of Exeter in the United Kingdom have evaluated the deployment of floating PV (FPV) on Hong Kong’s water reservoirs.
The team simulated two different cases. Firstly, FPV meets household demand and produces and stores hydrogen, which is converted back into electricity at night when solar energy is not available. In the second case, hydrogen production via electrolysis is used exclusively to fuel the city’s transportation system.
“This work sets a clear path for Hong Kong, where land availability is limited and rooftop construction remains the main option for photovoltaic deployment,” said corresponding author Aritra Ghosh. pv magazine. “In this context, utilizing 18 existing reservoirs for floating PV systems has the potential to generate a substantial portion of electricity, which could significantly contribute to residential electrification across Hong Kong.”
Ghosh said that according to the team’s findings, “at 60% coverage, the FPV systems generate approximately 4.8 TWh of electricity annually, while 100% coverage generates approximately 7.72 TWh per year. When combined with hydrogen storage, the full-coverage FPV system could provide electricity to approximately 490,000 households.”
Image: University of Exeter, International Journal of Hydrogen Energy, CC BY 4.0
To achieve these results, Ghosh’s team began by identifying reservoirs in Hong Kong. To this end, they used files downloaded from the Planning Department for spatial analysis. They excluded most irrigation reservoirs from the study because they were too small for an FPV installation. Only the Ho Pui Irrigation Reservoir was considered, given its larger size, along with 17 impounding reservoirs. Seven reservoirs are located on Hong Kong Island, one on Lantau Island, and the remaining ten are located in Kowloon and the New Territories.
Using PVsyst and HOMER Pro, the group considered crystalline silicon PV modules with a power of 350 W and an efficiency of 19.2%. Each measures 1775mm x 1038mm x 30mm, with an area of 1.82m2. Each module had an open-circuit voltage of 40.1 V, a short-circuit current of 11.15 A, and a bifaciality of approximately 70%. The operating temperature ranged from –40 C to 85 C.
With a theoretical coverage of 100%, the total annual energy production from all 18 reservoirs is 7.72 TWh, of which the Plover Cove Reservoir accounts for 49.5%. Capping all these reservoirs was found to meet 17.2% of the city’s annual electricity demand in 2022, and 61% of residential sector demand. At 60% coverage, the total effective annual energy generated by the PV arrays is 4.8 TWh, with Plover Cove Reservoir producing almost half of this, at 2.37 GWh per year. With a coverage of 60%, 36.5% of electricity consumption in homes could be covered.
The group has further focused on the potential implementation of 60% FPV coverage as this has been shown to optimize energy production, reduce algae growth and water evaporation and minimize negative impacts on the aquatic ecosystem. Two cases were tested, namely household electricity and hydrogen refueling for the transport sector.
Image: University of Exeter, International Journal of Hydrogen Energy, CC BY 4.0
In the first case, the FPV directly stimulates household demand. At the same time, part is fed to the electrolyser for hydrogen production, which is then stored as compressed gas in the hydrogen tank. At night and during periods of low solar production, fuel cells use hydrogen to generate electricity, which is then supplied to households. The efficiency used is 75.8% for the electrolyser and 60% for the fuel cell. To fuel the transport sector, different hydrogen demand profiles have been tested, ranging from 500 kg to 100,000 kg per day at the largest reservoir.
“The results show that annual hydrogen production ranges from 180,502 kg to 36,310,221 kg depending on reservoir size, with associated levelized costs of hydrogen (LCOH) between $10.2/kg and $19.4/kg,” the scientists said. “The hydrogen produced could support ongoing hydrogen bus projects and future expansion to other vehicle types as Hong Kong moves towards a hydrogen-based transportation system. After coupling FPV systems with hydrogen generation units, the new levelized electricity cost (LCOE) ranges from $0.029 to 4.01/kWh. Thus, suggesting the feasibility of a hydrogen-integrated FPV system in Hong Kong.”
According to the research team, the FPV systems alone produced an LCOE of $0.037/kWh and all sites achieved a high performance ratio (PR) of approximately 88%. To meet Hong Kong’s 2035 target of 1-2% solar in the fuel mix, the results revealed, only 6-12% of reservoir surfaces would need to be covered.
The research work appeared in “Analysis of the potential of floating photovoltaic solar energy in Hong Kong: green hydrogen production and energy application”, published in the International Journal of Hydrogen Energy.
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