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Hydrogen is seen as a promising and inevitable energy carrier in the transition towards a carbon-free energy era. This study reviews the potential for carbon-free hydrogen production, utilisation and exportation from the State of Qatar. The study aims to introduce a roadmap for current and future exploration of carbon-free hydrogen production and exportation from Qatar, for which an assessment of several available alternatives for the production of hydrogen in Qatar is performed. These alternatives include the use of natural gas as a feedstock for hydrogen production through steam methane reforming (SMR), solar integrated steam methane reforming with carbon capture, as well as the possibilities for hydrogen production from electrolysis using renewables and ammonia as another intermediate. The potential of each alternative is reviewed based on selected technical, economic and environmental criteria. The findings of this review study indicate that the production and exportation of blue ammonia currently present the best pathway for Qatar, while green hydrogen is expected to become as competitive as blue ammonia in the mid-future. It is widely accepted that as the technologies associated with clean hydrogen production improve, and the cost of renewable energy falls, green hydrogen will become quite competitive in the region. • A review of sustainable pathways for hydrogen exploration in Qatar is presented. • Development of a decision-making framework is presented for hydrogen production and exportation. • All production alternatives are reviewed based on technical, economic and environmental criteria. • The production and exportation of blue ammonia currently present the best pathway for Qatar. • Green hydrogen is expected to become as competitive as blue ammonia by the near/mid future. [ABSTRACT FROM AUTHOR]

Transporting energy in liquefied forms results in reduction in volume, which enables energy to be transported economically over long overseas distances. In this study, liquefied natural gas, liquid ammonia and methanol are proposed to transport the energy of natural gas in different forms to overseas. Due to temperature difference between the energy storage medium and the ambient, a portion of liquefied energy carriers mass is lost as boil-off gas (BOG). Therefore, a technical assessment based on energy and exergy analyses is conducted in this work to assess the total required energy and losses due to BOG for each energy carrier. To make a fair comparison among the energy carriers, the ship volume capacity is the fixed factor. The results show that the total daily energetic BOGs for LNG, ammonia, and methanol are calculated as 0.610%, 0.098%, 0.034% while the exergetic BOGs are 0.491%, 0.068%, 0.032%, respectively. Ammonia and methanol generate significantly less daily BOG, respectively, compared to LNG during the full supply chain, which make them alternative for efficient energy carrier transport. Image 1 • Boil-off gas determination of potential energy carriers for overseas transportation. • Energy required for production of LNG: 6.73 MJ/kg and ammonia: 6.73 MJ/kg. • Daily sea shipping BOG rates are LNG: 0.12%, ammonia: 0.024%, methanol: 0.005%. • Comparison of LNG, ammonia, and methanol using energy losses within supply chain. [ABSTRACT FROM AUTHOR]

• The energy consumption to produce LRCH 4 is found to be about 31.4 kWh e /kg. • BOG recovery can reduce fuel consumption and emissions for LNG and LH 2. • Blue LNG and LRCH4 are more favorable than conventional LNG in terms of regulations. • LH 2 infrastructure is not yet ready, whereas LRCH 4 infrastructure is available. • Further comparative economic and environmental studies are needed for feasibility assessment. This study aims to assess the energy consumption characteristics of various fuels, namely liquified natural gas, liquefied renewable methane, and liquefied hydrogen from production to overseas transportation, by covering broad color spectra of grey, blue, and green. A quantitative assessment is implemented to calculate how much energy is consumed to produce, store, and transport fuels. Carbon capture scenarios are also considered, along with boil-off gas recovery and utilization options for increased value chain effectiveness. Thereafter, a qualitative assessment is performed to compare the use of fuels from four perspectives: (i) technology, (ii) infrastructure, (iii) scalability, and (iv) regulations. The obtained quantitative results indicate that the energy consumption to produce liquified natural gas, liquefied renewable methane, and liquefied green hydrogen is about 0.49, 31.4, and 62.3 kWh e /kg of fuel, respectively. The energy consumption to store liquified hydrogen in a 2,000 m3 on-land storage tank for one day while recovering 100% of the generated boil-off gas is about 4,840 kWh. Moreover, the qualitative results indicate that the infrastructure is ready, and regulations are available to use liquefied renewable methane as fuel, whereas the infrastructure of liquified hydrogen still needs to be ready, and the associated regulations require amendments. [ABSTRACT FROM AUTHOR]

Countries are under increasing pressure to reduce greenhouse gas emissions as an act upon the Paris Agreement. The essential emission reductions can be achieved by environmentally friendly solutions, in particular, the introduction of low carbon or carbon-free fuels. This study presents a comparative life cycle assessment of various energy carriers namely; liquefied natural gas, methanol, dimethyl ether, liquid hydrogen and liquid ammonia that are produced from natural gas or renewables to investigate greenhouse gas emissions generated from the complete life cycle of energy carriers accounting for the leaks as well as boil-off gas occurring during storage and transportation. The entire fuel life cycle is considered consisting of production, storage, transportation via an ocean tanker to different distances, and finally utilization in an internal combustion engine of a road vehicle. The results show that using natural gas as a feedstock, total greenhouse gas emissions during production, ocean transportation (over 20,000 nmi) by a heavy fuel oil-fueled ocean tanker, and utilization in an internal combustion engine are 73.96, 95.73, 93.76, 50.83, and 100.54 g CO 2 eq. MJ−1 for liquified natural gas, methanol, dimethyl ether, liquid hydrogen, and liquid ammonia, respectively. Liquid hydrogen produced from solar electrolysis is the cleanest energy carrier (42.50 g CO 2 eq. MJ−1 fuel). Moreover, when liquid ammonia is produced via photovoltaic-based electrolysis (60.76 g CO 2 eq. MJ−1 fuel), it becomes cleaner than liquified natural gas. Although producing methanol and dimethyl ether from biomass results in a large reduction in total greenhouse gas emissions compared to conventional methanol and dimethyl ether production, with a value of 73.96 g CO 2 eq. per MJ, liquified natural gas still represents a cleaner option than methanol and dimethyl ether considering the full life cycle. Image 1 • Environmental assessment of LNG, ammonia, methanol, DME, and hydrogen. • GHG emissions during complete life cycle of natural gas and renewable fuels. • Methanol, DME, and ammonia from natural gas emit 88.7, 88.9, 90.9 g of CO 2 /MJ, respectively. • Liquid H 2 (solar electrolysis) full life cycle emits 41.29 g of CO 2 /MJ as the cleanest fuel. [ABSTRACT FROM AUTHOR]

• Daily BOG rates of LNG, DME, methanol, ammonia, and hydrogen are calculated. • BOG rates during land storage, loading, ocean transportation, unloading are assessed. • The effects of pumping time and heel percentage during loading and unloading are shown. • Energy carriers' capability of carrying the most amount of natural gas energy is assessed. The technological barriers against energy transport includes low energy density, intermittent supply and immobility of the energy sources. A potential and sustainable solution to overcome these barriers is to use an effective and efficient energy carrier which can store, transport and distribute energy in a technically feasible manner. Therefore, this study presents five potential energy carriers for overseas energy transport; liquifed natural gas (LNG), dimethyl ether (DME), liquid ammonia, methanol and liquid hydrogen which are used to carry the energy of natural gas in liquefied form from a supplied region to a demanded region. During the supply chain of the energy carriers, the amount of boil-off gas (BOG) for each energy carrier is calculated. A sensitivity analysis affecting BOG rates is implemented under variety of parameters, namely; ambient temperature, storage pressure, land storage time, ocean transportation time, heel percentage and pumping time. This study shows that the daily BOG rates for LNG, DME, ammonia, methanol, and hydrogen are calculated as 0.471%, 0.159%, 0.129%, 0.049%, and 3.438%, respectively. Methanol delivers the greatest mass, DME delivers the greatest energy and hydrogen loses the greatest mass as BOG during the supply chain. The highest BOG generation mainly occurs during ocean transportation phase, implying that ocean transportation time is the most critical parameter among the studied parameters. [ABSTRACT FROM AUTHOR]

The air conditioning in hot and arid climates remains one of the grand challenges for food production in greenhouses. Therefore, significant efforts are given to determine the suitable techniques for effective cooling of greenhouses. Usually, greenhouses are used in colder climates to gather sunlight for heating purposes. However, hot climates with elevated solar irradiation characteristics suffer from high temperatures within the greenhouse. In this study, we propose a unique method solving the extensive cooling requirement of greenhouses in hot arid climates by employing an optimal spectra management strategy. The novel sun-tracking roof design of the greenhouse incorporates hot dielectric mirrors and solar panels, which help to reduce the cooling load and provide electricity to the vapor compression cooling unit. The spectrum above 750 nm is reflected to vertically aligned InGaAs solar cells for additional power generation, whereas the c-Si solar cells are able to provide effective shadowing at noontime without significant comprimise on photosynthetically active radiation (PAR) while producing power. The results showed an average reduction of 28.9% and 25.4% in the cooling load of the proposed greenhouse compared to the conventional greenhouse during the summer and winter seasons for sun tracking hours (10:00 a.m. to 1:00 p.m.), respectively, at a set greenhouse temperature of 28 °C. The proposed greenhouse produced an average of 22.18 kWh/day of electrical energy throughout the year. The novel roof significantly lowers the cooling load and partially meets the energy demand of greenhouses without compromising on photosynthetically active radiations to enter the greenhouse. • Proposed a novel greenhouse roof integrating hot mirrors and solar PVs for optimal spectra management. • The infrared spectrum is not allowed to enter the greenhouse and utilized by InGaAs PVs. • Proposed greenhouse has significant lower cooling load than conventional greenhouse. • Proposed greenhouse is optimally designed for self-sufficient greenhouses in hot arid climates. [ABSTRACT FROM AUTHOR]

Ammonia is one of the most abundantly used chemicals in the world, and it is a potential hydrogen carrier for possible solutions of hydrogen storage and transportation. The conventional method of ammonia production is energy-intensive that requires high pressure and it is dominantly dependent on fossil fuels for hydrogen and nitrogen production. With the electrochemical synthesis option, ammonia can be produced at atmospheric pressures and lower temperature levels. Hydrogen production via water electrolysis using renewable energy can further reduce carbon emissions. In this work, ammonia production via an electrochemical process in a molten salt medium is modelled through electrochemical impedance spectroscopy using several equivalent circuit models. Then, afterwards, for a case study in Qatar to produce renewable ammonia, wind data are used to predict the annual ammonia production rates where the wind turbine rated power is 6 MW. The electrochemical modelling results show that two main parameters emerged as the most influential on the modelling of the low frequencies region; the capacitance of the electrolyte, and the capacitance of the electrode. Furthermore, it is found that the Warburg diffusion limit showed little to negligible effect on the shape in the low-frequency region. The best performing model in terms of the goodness of fit is model 11 with a value of 4.75 × 10−7, which was modelled by 9 circuit elements (resistors, inductor, capacitors and Gerischer elements) and 12 adjustable parameters. Moreover, Models 11 and 12 reached a goodness of fit in the order of 10−7. Some models included a larger number of variables but offered poorer fit or insignificant improvement, which does not provide justification for the additional elements. Image 1 • Ammonia production is studied via an electrochemical process in molten salt medium. • Electrochemical modeling is conducted via electrochemical impedance spectroscopy. • A case study in Qatar is proposed for renewable ammonia production from wind energy. • Renewable-based ammonia can play an important role for hydrogen and energy storage. [ABSTRACT FROM AUTHOR]