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Microalgae offer a great potential to contribute significantly as renewable fuels and documented as a promising platform for algae-based bio refineries. They provide solutions to mitigate the environmental concerns posed by conventional fuel sources; however, the production of microalgal biofuels in large scale production system encounters few technical challenges. High quantity of nutrients requirements and water cost constrain the scaling up microalgal biomass to large scale commercial production. Crop protection against biomass losses due to grazers or pathogens is another stumbling block in microalgal field cultivation. With our existing technologies, unless coupled with high-value or mid-value products, algal biofuel cannot reach the economic target. Many microalgal industries that started targeting biofuel in the last decade had now adopted parallel business plans focusing on algae by-products application as cosmetic supplements, nutraceuticals, oils, natural color, and animal feed. This review provides the current status and proposes a framework for key supply demand, challenges for cost-effective and sustainable use of water and nutrient. Emphasis is placed on the future industrial market status of value added by products of microalgal biomass. The cost factor for biorefinery process development needs to be addressed before its potential to be exploited for various value-added products with algal biofuel.

HITEC molten salt (7% NaNO3, 53% KNO3, 40% NaNO2) has been identified as a suitable heat transfer fluid for concentrated solar power (CSP) systems, such as parabolic trough collectors (PTC) and evacuated tube solar collectors (ETSC). In order to optimize the flow and heat transfer performance of HITEC in ETSC, a molten salt heat transfer test rig was built to conduct an experimental study, varying inlet and outlet temperatures and mass flow rates of HITEC. Results show that the heat loss of HITEC in ETSC is lower than the other tubes. The convective heat transfer coefficient of HITEC is much lower than that of HITEC in round tube. Because the experimental data of HITEC in ETSC largely differed from the classical correlation equations, a new empirical heat transfer correlation equation was set for HITEC in ETSC, and the deviation between the experiment data and new correlation was within ±19.2%. Finally, by comparing the inlet and outlet temperatures of ETSC under different irradiation intensities, it is concluded that the ETSC can work stably when the temperature exceeds 700 W/m2.

Occupancy-based strategies for the control of ventilation systems in buildings are effective for achieving energy savings and user comfort. Savings in energy consumption of more than 50% can be achieved by controlling heat, ventilation, and air conditioning (HVAC) systems with accurate sensory and occupancy information. In this study, the flow through the damper of the variable area valve (VAV) system and the speed of the blower’s variable frequency drive (VFD) are controlled in the HVAC system, on the basis of human occupancy and indoor parameters, namely, temperature and humidity, segment-wise in the building. In the proposed model, the flapper angle of the VAV is estimated using the indoor temperature, external temperature, and number of occupants. The occupancy data are fed to the controller proposed to regulate the flow through the ducts of the system, which is based on the flapper angle of the VAV, in order to maintain human comfort. The proposed scheme makes it possible to detect abnormalities in energy utilization and to trace maximum utilization in the building based on occupancy, with the control parameters of the HVAC adjusted for a comfortable indoor environment. Performance evaluation of the VAV system with its proposed control strategy, temperature, and flow distribution is simulated using Fluent software. A laboratory grade prototype incorporating the proposed control strategy is then developed, tested under three different conditions, and the results are reported. The experimental results show that an energy saving of 18% can be achieved.

The facades of buildings provide significant potential for photovoltaic panels integration, allowing renewable energy deployment within the built environment. In literature, various options, such as building-integrated photovoltaics, building-integrated photovoltaics-thermal collectors, building-attached photovoltaics, and rooftop photovoltaics, have already been explored. However, this study aimed to develop a new solar photovoltaic collectors’ integration with vertical-green balconies in old high-rise buildings considering the façade reconstruction concepts mainly focusing on the water heating application. The objective of this study is to conduct a preliminary research study investigating such integration possibilities with old buildings considering the façade reconstruction concepts, followed by exploring various benefits. For this, an old high-rise building was rebuilt scientifically and rationally. PHOENICS tool was used to gauge and assess the building’s wind environment first, followed by the solar photovoltaic collector-based facade installation and preliminary assessment. The results include the system design, economic analysis of the solar photovoltaic collector’s application for water heating, calculation of the energy-saving rate, and functional analysis of the solar photovoltaic collectors combined with a vertical green balcony. The outcome of this study suggested that the process-specific rationalization plan can be applied in future urban architecture renovation.

Two-stage synthesis problems simultaneously consider here-and-now decisions (e.g., optimal investment) and wait-and-see decisions (e.g., optimal operation). The optimal synthesis of energy systems reveals such a two-stage character. The synthesis of energy systems involves multiple large time series such as energy demands and energy prices. Since problem size increases with the size of the time series, synthesis of energy systems leads to complex optimization problems. To reduce the problem size without loosing solution quality, we propose a method for time-series aggregation to identify typical periods. Typical periods retain the chronology of time steps, which enables modeling of energy systems, e.g., with storage units or start-up cost. The aim of the proposed method is to obtain few typical periods with few time steps per period, while accurately representing the objective function of the full time series, e.g., cost. Thus, we determine the error of time-series aggregation as the cost difference between operating the optimal design for the aggregated time series and for the full time series. Thereby, we rigorously bound the maximum performance loss of the optimal energy system design. In an initial step, the proposed method identifies the best length of typical periods by autocorrelation analysis. Subsequently, an adaptive procedure determines aggregated typical periods employing the clustering algorithm k-medoids, which groups similar periods into clusters and selects one representative period per cluster. Moreover, the number of time steps per period is aggregated by a novel clustering algorithm maintaining chronology of the time steps in the periods. The method is iteratively repeated until the error falls below a threshold value. A case study based on a real-world synthesis problem of an energy system shows that time-series aggregation from 8,760 time steps to 2 typical periods with each 2 time steps results in an error smaller than the optimality gap of the synthesis problem (2%). This corresponds to a reduction of the number time steps and thus a reduction of the size of the synthesis problem by a factor of 1,000 with excellent accuracy in cost estimation. Thus, the proposed method enables an efficient and accurate synthesis of energy systems. Frontiers in Energy Research, 5 ISSN:2296-598X

This paper presents the integration of renewable energy sources such as photovoltaics, wind, and batteries to the grid. The hybrid shunt active power filter (HSHAPF) is optimized with the Gray wolf optimization (GWO) and fractional order proportional integral controller (FOPI) for harmonic reduction under nonlinear and unbalanced load conditions. With the use of GWO, the parameters of FOPI are tuned, which effectively minimizes the harmonics. The proposed model has effectively compensated the total harmonic distortions when compared with without the filter and with the passive filter, the active power filter with a PI controller, and the GWO-FOPI-based controller. The performance of the proposed controller is tested under nonlinear and unbalanced conditions. The parameters of the FOPI controller are better tuned with the GWO technique. The comparative results reflect the best results of GWO-FOPI-based HSHAPF. The suggested controller is built in the MATLAB/Simulink Platform.