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Biomass and organic solid waste are considered as very potential alternative energy sources in the future, leading to the realization of a clean and CO2-free energy system. Therefore, the effective conversion of biomass and organic solid waste to a secondary energy source is urgently demanded. In addition, hydrogen is considered very promising among the secondary energy sources due to its advantages of cleanliness, wide range of conversion and utilization technologies, high energy efficiency, and high gravimetric energy density. This paper reviews several possible routes and key conversion technologies of biomass and organic solid waste to hydrogen. Recent progress related to biological and thermochemical conversion technologies is described. Thermochemical route includes gasification, pyrolysis, steam reforming, partial oxidation, and thermochemical cycle; while biological route covers fermentation (dark and photo), biophotolysis (direct and indirect), enzymatic, and microbial electrolysis. In addition, several challenges regarding the conversion and utilization of biomass and organic solid waste to hydrogen are also discussed in order to clarify the feasibility of biomass and the organic solid waste-based hydrogen economy.

Hydrogen (H2) is a secondary energy source (energy carrier) which has advantages of high cleanliness and efficiency, leading to its potential utilization in the future energy system. However, H2 suffers a great challenge in its storage because of low volumetric energy density. Among the available technologies and media for H2 storage, ammonia (NH3) is considered very promising due to its characteristics of high hydrogen density, excellent storage, high stability, and matured technology and infrastructure. Currently, NH3 is massively produced through Haber-Bosch process conducted at high pressure and temperature. Therefore, large energy is consumed to synthesize NH3. There are several other alternative technologies for NH3 synthesis, including thermochemical, electrochemical, photochemical, and plasma-assisted processes. This paper reviews mainly both thermochemical and electrochemical NH3 production technologies, including their updates and challenges, and also by considering both technological feasibility and applicability. In addition, several projects and efforts carried out by several countries to utilize NH3 as potential fuel in the energy system are also overviewed. Furthermore, technological analysis, challenges, and recommendations are also provided with the objective of evaluating the potential adoption of NH3 in the future energy system.

For Indonesia's renewable energy mix target in the electricity generation sector, biomass co-firing in existing Coal Fired Power Plant (CFPP) is one of the applicable methods in the context of Indonesia's electricity generation industry. Among the various applicable power plant, Circulating Fluidized Bed (CFB) boiler-type CFPP is one of the power plant types applicable for co-firing. As various CFB manufacturers claim, CFB boilers can consume substantial biomass fraction, up to 30% of the original fuel mass flow rate. However, biomass co-firing will increase the load factor of the boiler equipment, such as coal feeders and combustion air supply draft fans. This paper shows that up to 30% of biomass co-firing can increase coal feeder working-level until 100.68% with typical coal and 108.76% with design coal. Primary Air (PA) and Secondary Air (SA) fan load also increased to 100.86% compared to typical coal and 100.99% compared to design coal. As for Induced Draft (ID) fan loading can reach up to 101.10% with typical coal and 102.25% with design coal. Also, 30% biomass co-firing results in higher auxiliary power consumption. Draft fan power consumption increases by 31.43 kW with typical coal and 43.29 kW with design coal. This study recommends that power plant engineers conduct such analysis to compare the baseline power profile and equipment capacity to the off-design basis of high fraction biomass co-firing. The purpose of the analysis is to identify the various limiting factors that may arise from high fraction co-firing, such as limitation of draft fan capacity and/or reduction of efficiency that arise due to the increase in auxiliary power consumption.

Ammonia (NH3) is one of the most valuable chemicals due to its multipurpose utilization in many applications. Beside major application as fertilizer in agriculture, NH3 is a promising hydrogen (H2) carrier because it has a high content of H2 and technically available storage and transportation systems. At present, most of NH3 is synthesized from a series of steam reforming process to the feedstock of H2 and nitrogen (N2) production, followed with the catalytic Haber-Bosch reaction. In this study, an integrated system of N2 production system, NH3 synthesis system and a power generation process is proposed to produce NH3 efficiently. Thermochemical cyclic process of an endothermic reaction of Al2O3 reduction by carbon in N2 atmosphere, is coupled with oxidation/steam-hydrolysis of aluminum nitride (AlN) back to Al2O3, producing NH3 without catalyst and the need of H2 production system. The thermal energy required for reduction reaction is covered by the heat generated during exothermic reaction and combustion process, and the remaining heat is utilized in power generation. Heat circulation optimization is carried out by applying the enhanced process integration, resulting in a highly efficient system. The proposed system is analyzed through an adjustment of the main parameters: oxidation temperature, steam turbine inlet pressure, and temperature, to observe their effect on system performance and efficiency. The proposed system can reach a very high system efficiency of 69.3%. The oxidation reaction temperature is observed to play major role in determining the system performance due to temperature dependent NH3 yield.

A dry steam power plant utilizes geofluid, which is the saturated or superheated vapor generated in the Earth’s interior as the working fluid. Compared to the other cycles of a geothermal power plant, the dry steam cycle has an advantage of lower capital costs due to a simpler configuration and higher enthalpy, which results in a higher output capacity. However, in order to achieve a vapor state, higher temperatures and specific pressure are basically required. In this chapter, the system configuration of the dry steam cycle is initially explained, especially in terms of thermodynamics analysis. In addition, recent developments related to the dry steam cycle in order to enhance the system as well as improve the total energy efficiency are also discussed. Several case studies are also provided in order to give a more detailed description related to the dry steam cycle.

Floating solar still is a suitable technology for remote or rural coastal area applications. The device should be made of low-cost materials available locally to provide more access to the broader community. However, the low-cost materials usually do not have the best physical properties, decreasing the overall solar still performance. This work demonstrated a low-cost floating solar still prototype entirely made of locally available materials. To further understand the influence of different parameters on the solar still performance and guide the prototyping process, we also performed the system's heat and mass transfer analysis. Our experimental results indicate a high absorber temperature (59.5 °C), even on a cloudy day. Our model also fits the temperature measurement reasonably. However, the recorded overall efficiency still suffers mainly due to the collection system, which decreases the overall performance; an example of a practical challenge, which is often overlooked but plays a crucial role in increasing the readiness level of the prototype.

Silicon nanocrystals (SiNCs) featuring size-dependent novel optical and electrical properties have been widely employed for various functional devices. We have demonstrated SiNC-based hybrid photovoltaics (SiNC-HPVs) and proposed several approaches for performance promotion. Recently, owing to the superiorities such as low power operation, high portability, and designability, organic photovoltaics (OPVs) have been extensively studied for their potential indoor applications as power sources. SiNCs exhibit strong light absorption below 450 nm, which is capable of sufficient photocurrent generation under UV irradiation. Therefore, SiNC-HPVs are expected to be preferably used for energy harvesting systems in indoor applications because an indoor light source consists of a shorter wavelength component below 500 nm than solar light. We successfully demonstrated SiNC-HPVs with a PCE as high as 9.7%, corresponding to the output power density of 34.0 μW cm−2 under standard indoor light irradiation (1000 lx). In addition, we have found that SiNC defects working as electron traps influence the electrical properties of SiNCs substantially, a thermal annealing process was conducted towards the suppression of defects and the improvement of the SiNC-HPVs performance.

Most of the highly efficient luminescent silicon nanocrystals (SiNCs) reported to date consists of organically capped silicon cores. Here, we report a method of obtaining Si/SiO2 core/shell nanoparticles emitting at a peak energy of 1.5 eV with very high quantum yields (53-61%). The same method led to quantum yields of ~ 30% for porous silicon powder emitting at 1.9 eV. The SiNCs were very stable under continuous excitation for several hours. The lifetime at 1.5 eV was over 232 μs, the longest ever reported for SiNCs, consistent with the very high luminescence efficiency. The SiNCs were first fabricated by non-thermal plasma synthesis or anodization in the case of porous silicon. Then, a thin oxide shell (~ 1 nm) was grown using high-pressure water vapor annealing. This oxidation process allows for the growth of very good quality oxide with low defect concentration and low stress, resulting in very good surface passivation, which explains the very high quantum yields obtained.

A novel type silicon nanocrystal-based hybrid solar cell is demonstrated here, where two individual junctions are designed carefully and arranged in parallel with each other. It is found that complementary absorption can be realized by double parallel junctions, and more photons in a wide energy range can be absorbed. As a result, device efficiency has been enhanced more than twice compared to single junction reference device. In addition, its working principles are also studied extensively.

Despite the potential of hydrogen (H2) as an energy carrier, its storage and transportation are challenging and become two of the keys in the successful adoption of H2. Among various methods of H2 storage, ammonia (NH3) shows very promising characteristics of high gravimetric and volumetric H2 densities, possibility for direct utilization, and established infrastructure. This work proposes an integrated system consisting of NH3 decomposition through a thermo-catalytic process and H2-based power generation. The thermal energy demanded for the endothermic reaction of thermo-catalytic NH3 decomposition is supplied from the combustion reaction of H2. The remaining heat is used to generate the electricity using a combined cycle, and the overall heat circulation is optimized based on enhanced process integration (EPI) to achieve a highly efficient system. Four types of catalyst (ruthenium, molybdenum nitride, nickel oxide, and lithium nitrohydride), having different reaction temperature and conversion rate, are employed in the system and their performance are then evaluated. The results show that both parameters have an influence in determining the system efficiency and power generation efficiency with different behavior. The conversion rate has a strong effect on the system efficiency as it determines the amount of H2 produced from the NH3 decomposition process. Meanwhile, the reaction temperature has a major effect on the power generation efficiency. The proposed system with lithium nitrohydride shows the highest power generation efficiency of 43.7%, while the highest overall system efficiency of 48.3% can be achieved when ruthenium catalyst is employed.

Current researches on silicon nanoparticles (Si NPs) are mainly focusing on the crystallized one, while some basic optical and electrical properties of particles with different crystallinities are still unclear. Hence, in this work, Si NPs with different crystallinities were easily fabricated with non-thermal plasma by changing the input power, and the crystallinity effects on the optical, electrical, and photovoltaic properties of particles were extensively studied. It is found that amorphous particles have strong light absorption, especially in short wavelength region; however, the carrier mobility is relatively poor. This is mainly because of numerous dangling bonds and defects that exist in Si NPs with poor crystallinity, which work as carrier trapping centers. As a result, the efficiency of Si NPs-based hybrid solar cells increases monotonously with particle crystallinity. This indicates that highly crystallized Si nanocrystals with less defects are desirable for high efficiency solar cells.