Zeyad Al-Suhaibani

Estimating and Comparing the Exergetic Solar Radiation Values of Various Climate Regions for Solar Energy Utilization

Energy resources and their utilization intimately relate to sustainable development. In attaining sustainable development, increasing the energy efficiencies of processes utilizing sustainable energy resources plays an important role. The utilization of renewable energy offers a wide range of exceptional benefits. There is also a link between exergy and sustainable development. Exergy analysis has been widely used in the design, simulation, and performance evaluation of various energy systems as well as renewable energy sources. In this regard, determination of exergy of solar radiation is very crucial for various solar energy-related applications and is based on the relative potential of the maximum energy available from radiation. The efficiency factor limiting the gain of the maximum useful energy from the solar radiation is significantly similar to that of the Carnot efficiency for the heat engines. The main objectives of this study are two-fold, namely, (i) to comprehensively review various solar exergy models used in solar energy-related applications, and (ii) to determine the solar exergetic values for some regions of Saudi Arabia and Turkey, which are taken as two illustrative examples to which various models have been applied and compared. In this regard, the ratios of solar radiation exergy to solar radiation energy (exergy-to-energy ratio) for northeastern Saudi Arabia are calculated to be on average 0.933 for both approaches of Petela and Spanner and 0.950 for Jefers approach at outside air temperatures between 16.18 and 33.01°C. These ratios for Izmir, Turkey are obtained to be on average 0.935 and 0.951 for the same approaches at a temperature range of 15–22°C, respectively. The values found using Jefers approach appear to be 2% larger than the approaches of Petela and Spanner, while those are very close to the value of 0.95 proposed by Nobusawa.

Exergetic and sustainability performance assessment of geothermal (ground source) ejector heat pumps

Although ejectors have been used in cooling/refrigeration and Heat Pumps (HP) applications for a long time, utilisation of Geothermal Ejector Heat Pump (GEHP) with Ground–Heat Exchanger (GHE) is a new idea, which has recently appeared in the literature. In this study, we model a GEHP system with a GHE in terms of exergetic aspects and apply our model to this system in the heating mode. The system consists of mainly three parts, namely a GEHP unit, a GHE, and a heat distribution system. We determine the exergy transports between the components and the consumptions in each of the components of the whole system and we also calculate exergy efficiency and Sustainability Index (SI) values for the system components to evaluate its performance. In this regard, exergy efficiency values for the GEHP unit and whole system are calculated to be 85.3% and 84.6% on the product/fuel basis at dead (reference) state values for 19°C and 101.325 kPa, respectively. An improvement of about 16.17% in the energetic and exergetic coefficient of performance value of the GEHP unit is obtained by adding an ejector to the HP system. SI values for some system components such as ejector, compressor, condenser and evaporator are also obtained to be 1.82, 2.79, 3.22 and 3.94, respectively.

Modeling of Transient Energy Loss From a Cylindrical-Shaped Solid Particle Thermal Energy Storage Tank for Central Receiver Applications

The use of solid particles as a heat transfer and thermal energy storage (TES) medium in central receiver systems has received renewed attention in recent years due to the ability of achieving high temperatures and the potential reduction in receiver and TES costs. Performance of TES systems is primarily characterized by the percentage of heat loss they allow over a prescribed period of time. Accurate estimation of this parameter requires special attention to the transient nature of the process of charging the TES bin during solar field operation and discharging during nighttime or at periods where solar field operation is interrupted. In this study, a numerical model is built to simulate the charge-discharge cycle of a small cylindrical-shaped TES bin that is currently under construction. This bin is integrated into the tower of an experimental 300-kW (thermal) central receiver field being built in Riyadh, Saudi Arabia, for solid particle receiver research, most notably on-sun testing of the falling particle receiver concept within the context of a SunShot project. The model utilizes a type of wall construction that had been previously identified as showing favorable structural characteristics and being able to withstand high temperatures. The model takes into account the anticipated charge-discharge particle flow rates, and includes an insulating layer at the ceiling of the bin to minimize heat loss by convection and radiation to the receiver cavity located immediately over the TES bin. Results show that energy loss during the full charge-discharge cycle is 4.9% and 5.9% for a 5-hour and 17-hour discharge period, respectively. While large, these energy loss values are primarily due to the high surface-to-volume ratio of the small TES bin being investigated. Preliminary analysis shows that a utility-scale TES bin using the same concept will have an energy loss of less than 1%.Copyright

Future Aspects of Geothermal Energy in Saudi Arabia

Geothermal energy seems to be a clean, proven, and reliable resource for supplying the needs of a sustainable society and helping to improve the global environment. Although the studies on geothermal resources exploration in Saudi Arabia were started in 1980, since then any serious geothermal projects have not been undertaken, excepting to the availability of some potentially resources-rich geothermal locations. The first in situ determination of the thermal properties of the underground soil required for the design of borehole heat exchangers was reported in 2009 for the first time. In this study, future aspects of geothermal energy were treated first. The exergetic aspects of some geothermal resources available were then explained using a specific exergy index. Finally, the results obtained were given and discussed. It is expected that some barriers hindering the utilization of geothermal resources in Saudi Arabia will be overcome and geothermal energy utilization will become a viable option in the near future.

Experimental measurements of thermal properties of high-temperature refractory materials used for thermal energy storage

This paper builds on studies conducted on thermal energy storage (TES) systems that were built as a part of the work performed for a DOE-funded SunShot project titled “High Temperature Falling Particle Receiver”. In previous studies, two small-scale TES systems were constructed for measuring heat loss at high temperatures that are compatible with the falling particle receiver concept, both of which had shown very limited heat loss. Through the course of those studies, it became evident that there was a lack of information about the thermal performance of some of the insulating refractory materials used in the experiments at high temperatures, especially insulating firebrick and perlite concrete. This work focuses on determining the thermal conductivities of those materials at high temperatures. The apparatus consists of a prototype cylindrical TES bin built with the same wall construction used in previous studies. An electric heater is placed along the centerline of the bin, and thermocouples are used to ...

Experimental study of compatibility of reduced metal oxides with thermal energy storage lining materials

Solid particles have been shown to be able to operate at temperatures higher than 1000 °C in concentrated solar power (CSP) systems with thermal energy storage (TES). Thermochemical energy storage (TCES) using metal oxides have also found to be advantageous over sensible and latent heat storage concepts. This paper investigates the compatibility of the inner lining material of a TES tank with the reduced metal oxide. Two candidate metal oxides are investigated against six candidate lining materials. XRD results for both the materials are investigated and compared before and after the reduction of metal oxide at 1000°C in the presence of lining material. It is found that the lining material rich in zirconia is suitable for such application. Silicon Carbide is also found non-reacting with one of the metal oxides so it needs to be further investigated with other candidate metal oxides.

Comparing the Energetic and Exergetic Performances of a Building Heated by Solar Energy and Ground-Source (Geothermal) Heat Pump

In this study, we considered a building, which had a volume of 336 m3 and a floor area of 120 m2, with indoor and outdoor air temperatures of 20 oC and 0 oC, respectively. For heating this building, we selected two options, namely (i) a ground-source (geothermal) heat pump system (Case 1), and (ii) a solar collector heating system (Case 2). We employed both energy and exergy analysis methods to assess their performances and compare them through energy and exergy efficiencies and sustainability index. We also investigated energy and exergy flows for this building and illustrated from the primary energy transformation through the heat production system and a distribution system to a heating system, and from there, via the indoor air, across the building envelope to the surrounding air. We calculated that the total exergy efficiencies for Cases 1 and 2 were 4.7%, and 26.1% while sustainability index values for both cases were 1.049 and 1.353 at a reference (dead) state temperature of 0 oC, respectively.