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Research Papers

J. Sol. Energy Eng. 2017;140(1):011001-011001-15. doi:10.1115/1.4038047.

The global trend of energy consumption shows that buildings consume around 48% of the total energy, of which, over 50% is for heating and cooling applications. This study elucidates on cooling load reduction with phase change material (PCM) incorporation in a building envelope. PCM provides thermal shielding due to isothermal heat storage during phase change. PCM selection depends upon its phase change temperature, thermal capacity, and thermal conductivity, as they play a vital role in assessing their impact on energy conservation in buildings. The uniqueness of this study underlies in the fact that it focuses on the utilization of PCM for New Delhi (28.54°N, 77.19°E) climatic conditions and adjudges the suitability of three commercially available PCMs, based on the overall heat load reduction and their characteristic charging/discharging. The study aims at finding an optimum melting and solidification temperature of the PCM such that it may be discharged during the night by releasing the heat gained during the day and mark its suitability. The results of mathematical modeling indicate that as per the design conditions, the melting/solidification temperature of 34 °C is suitable for New Delhi to absorb the peak intensity of solar irradiation during summer. Based on the thermophysical properties in literature (Pluss Advanced Technologies Pvt. Ltd., 2015, “Technical Data Sheet of savE® HS29, PLUSS-TDS-DOC-304 Version R0,” Pluss Advanced Technologies Pvt. Ltd., Gurgaon, India. Pluss Advanced Technologies Pvt. Ltd., 2015, “Technical Data Sheet of savE® OM32, PLUSS-TDS-DOC-394 Version R0,” Pluss Advanced Technologies Pvt. Ltd., Gurgaon, India. Pluss Advanced Technologies Pvt. Ltd., 2012, “Technical Data Sheet - savEVR HS34, Doc:305,” Pluss Advanced Technologies Pvt. Ltd., Gurgaon, India), mathematical modeling showed HS34 to be suitable for New Delhi among the three PCMs. To ratify this, characteristic charging and discharging of HS34 is tested experimentally, using differential scanning calorimeter (DSC). The results showed that HS34 is a heterogeneous mixture of hydrated salts having super-cooling of 6 °C, reducing its peak solidification temperature to 30.52 °C during the cooling cycle also making it unsuitable for peak summers in New Delhi.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2017;140(1):011002-011002-12. doi:10.1115/1.4038048.

The integration between renewable energy systems (RESs) and oil shale system ensures reliable power generation source with a competitive energy generation cost when compared to costs of conventional systems. In addition, this integration will prevent considerable amount of CO2 emissions. This study aims to determine the size of a grid-tied hybrid system in Al-Tafilah, Jordan that maximizes the yearly overall fraction of demand met with levelized cost of electricity (LCOE) equal to or lower than the local cost of electricity generation. In addition, the effect of the integration of lithium-ion batteries as short-term energy storage systems (ESSs) will be investigated in addition to the effect of carbon social cost on the economics of the system. The maximum FH by the hybrid system in Al-Tafilah is 97.2% with ESS and 96.9% without ESS where 70.4% of the demand is met by the 12 MW oil shale system; however, to achieve these fractions, enormous installed capacity of photovoltaic (PV) and wind is required where 99% of the energy production is excess and LCOE is larger than COEcon. The maximum FH with LCOE equals to COEcon can be achieved by 12 MW oil shale, 3.5 MW PV, and 6 MW wind turbines without ESS. Such size will have FH of 87.23%, capacity factor of 46.1%, RES fraction of 16.9%, net present value (NPV) of 34.8 million USD, and a payback period of 4.8 years.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2017;140(1):011003-011003-13. doi:10.1115/1.4038050.

In this paper, a genetic algorithm-based multi-objective optimization of a building-integrated photovoltaic/thermal (BIPV/T) system is carried out to find the best system configurations which lead to maximum energetic and exergetic performances for Kermanshah, Iran climatic condition. In the proposed BIPV/T system, the cooling potential of ventilation and exhaust airs are used in buildings for cooling the PV panels and also heating the ventilation air by heat rejection of PV panels. Four scenarios with various criteria in the form of system efficiencies and useful outputs are considered to reflect all possible useful outputs in the optimization procedure. This study models a glazed BIPV/T system with various collector areas (Apv=10,15,25,and30m2) and different length to width ratio (L/W=0.5,1,1.5,and2) to determine the optimum air mass flow rate, bottom heat loss coefficient, depth of the channel as well as the optimum depth of the air gap between PV panel and glass cover that maximize two defined objective functions in different scenarios. Results showed that using fourth scenario (with the annual total useful thermal and electrical outputs as objective functions) and first scenario (with the annual average first- and second-law efficiencies as objective functions) for optimizing the proposed BIPV/T system leads to the highest amount of useful thermal and overall outputs, respectively. Moreover, it was concluded that, if the electrical output of the system is more important than the thermal output, the first scenario gives better results.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2017;140(1):011004-011004-11. doi:10.1115/1.4038051.

This paper presents a comparison of air conditioners using the conventional heating, ventilation, and air conditioning heat pumps and the one using solar heat stored underground, also known as shallow geothermal air conditioning. The proposed air conditioner with solar heat stored underground reunites practical data from an implementation of the heuristic perturb-and-observe (P&O) control and a heat management technique. The aim is to find out the best possible heat exchange between the room ambient and the underground soil heat to reduce its overall consumption without any heat pump. Comparative tests were conducted in two similar rooms, each one equipped with one of the two types of air conditioning. The room temperature with the conventional air conditioning was maintained as close as possible to the temperature of the test room with shallow geothermal conditioning to allow an acceptable data validation. The experiments made both in the winter of 2014 and in the summer of 2015 in Santa Maria, South Brazil, demonstrated that the conventional air conditioner consumed 19.08 kWh and the shallow geothermal conditioner (SGC) consumed only 4.65 kWh, therefore, representing a reduction of energy consumption of approximately 75%.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Sol. Energy Eng. 2017;140(1):014501-014501-9. doi:10.1115/1.4038046.

Small horizontal axis wind turbines (HAWTs) are increasingly used as source of energy production. Based on this observation, the blade element momentum theory (BEMT) is applied all along the blade span to calculate the optimal turbine aerodynamic performances. The main objective is to optimize the HAWT blade profile for specific initial conditions. The effects of three geometric parameters (the blade tip radius, the number of blades, and curvature) and one dynamic parameter (the tip speed ratio (TSR)) are determined for an upstream air speed of 7 m/s. A new empirical relation for the chord distribution over the blade span is presented here; c(r)/R=c0+A[1+r/R]exp(Br/R), where c0 = 0.04 is the chord offset, A = 1/Z is an amplitude, and B = [(Z/5) + 2] is the decay constant. It takes into account both the effect of blade tip radius and the number of the blades.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2017;140(1):014502-014502-9. doi:10.1115/1.4038052.

The solar photovoltaic thermal system (PVT) facilitates conversion of incoming solar radiations into heat and electricity simultaneously. The beam split photovoltaic thermal system (BSPVT) is one of the PVT systems. In this system, the incoming solar beam is splitted and used separately for PV and thermal system. The feasibility of water, silicone oil, and coconut oil as spectrum filter for C–Si solar photovoltaic system is reported in the literature recently. However, the changes in the optical behavior of the liquids due to extended exposure to sunlight (aging effect) had not been considered in most of the previous studies. The current study includes the methodology for the selection of liquids for BSPVT systems, estimation of external quantum efficiency (EQE) of a solar cell using liquids, and the aging effect on the liquid spectrum filters. The spectral response of the solar cell is analyzed using BENTHAM, (PVE 300) for 300–1100 nm. In this study, it has been observed that the aging of silicone oil reduces the electrical performance of the solar cell. On the other hand, the aged coconut oil improves the electrical performance of the solar cell as compared to the fresh coconut oil spectrum filter.

Commentary by Dr. Valentin Fuster
J. Sol. Energy Eng. 2017;140(1):014503-014503-6. doi:10.1115/1.4038314.

Three grid-connected monocrystalline silicon arrays on the National Institute of Standards and Technology (NIST) campus in Gaithersburg, MD have been instrumented and monitored for 1 yr, with only minimal gaps in the data sets. These arrays range from 73 kW to 271 kW, and all use the same module, but have different tilts, orientations, and configurations. One array is installed facing east and west over a parking lot, one in an open field, and one on a flat roof. Various measured relationships and calculated standard metrics have been used to compare the relative performance of these arrays in their different configurations. Comprehensive performance models have also been created in the modeling software pvsyst for each array, and its predictions using measured on-site weather data are compared to the arrays' measured outputs. The comparisons show that all three arrays typically have monthly performance ratios (PRs) above 0.75, but differ significantly in their relative output, strongly correlating to their operating temperature and to a lesser extent their orientation. The model predictions are within 5% of the monthly delivered energy values except during the winter months, when there was intermittent snow on the arrays, and during maintenance and other outages.

Commentary by Dr. Valentin Fuster

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