Cooling loads are a substantial part of the total electricity demands of countries in the Middle East and North Africa (MENA). Fortunately, because of its warm and sunny climate, the MENA region is naturally suited to solar cooling technologies. This article summarizes the most recent research and developments in solar thermal cooling technologies. The working principles and a general literature survey of solar thermal cooling technologies including absorption, adsorption, and desiccant is presented. This is followed by a summary of the literature specific to the MENA region, along with a survey of the prototypes and commercial installation of solar cooling across the MENA region. Based on this review, pilot solar cooling projects in the region are around 1180 kWc, which are split between space conditioning and industrial refrigeration applications. Most of the pilot projects are of absorption cooling type using an ammonia–water binary cycle and parabolic trough solar collectors. However, a few adsorption cooling systems are employed with a water–silica working pair and flat plate collectors. Finally, desiccant cooling systems are still in their infancy, as research and experimental systems in educational institutes.
This paper presents a mathematical model for estimating the optimal sizing and assessing a standalone hybrid power system's performance entirely based on variable renewable energy sources and coupled with a hybrid energy storage system. This study evaluates how different levels of the main components' capital cost and the loss of power supply probability would affect the cost of energy and the power system's optimal sizing. The case study selected for this study was Ometepe Island in Nicaragua, where the crater lake of an extinct volcano was considered a feasible upper reservoir of a pumped storage hydropower plant, reducing the investments associated with this component. The mathematical formulation considers energy storage losses and gains, and the Pareto efficient solutions of the multi-objective optimization model simultaneously increase reliability, reduce the cost of energy, and minimize curtailment energy. By employing time-series with an hourly resolution, the model allows assessing the impact of the interannual variability of renewable energy sources on the system's performance. As for the case study, the cost of energy obtained from the model results ranges between (sic)0.047/kWh and (sic)0.095/kWh, based on international reference values, and these values match the information available in the literature and other databases.
Uncertainty is a common and critical problem for planning the capacity and operation of integrated energy systems (IESs). This study evaluates the effects of uncertainties on the capacity and operation of an IES. To this aim, system planning and operation with uncertainties are optimized by a two-stage stochastic programming model and compared with a referencing deterministic case. Specifically, the uncertainties of photovoltaic (PV) generation and energy demand are investigated. Regarding system capacity, a larger energy storage capacity is needed to accommodate a higher uncertainty. The superimposed uncertainties have a higher effect on system capacity than the sum of the effect of each uncertainty. The uncertainty of energy demand has a higher impact than the uncertainty of PV generation. Regarding system operation, the increase in operation cost is smaller than the increase in investment cost and total cost. In addition, the average flexibility provided by the energy storage increases with uncertainty and uncertainties affect the change rate for power charging/discharging of the electric energy storage. Regarding the effect on the grid, the uncertainties increase not only the magnitude of ramping-rate, but also the frequency of power-dispatch.
This paper intends to numerically analyse the performance of liquid desiccant systems on the supply air conditions for closed poultry barns. A commercially available evaporative cooler for poultry barns was modified into a desiccant dehumidifier by circulating desiccant solutions of LiCl-H2O and CaCl2-H2O instead of water. Ambient air conditions for one of humid and subtropical climates were simulated based on an ∊-NTU effectiveness model for an externally cooled liquid desiccant dehumidifier. Also, a distinctive temperature-humidity index (THI) was implemented to study the environmental thermal conditions that the poultry were subjected to. Concerning the thermal comfort for broilers, the results show that conventional direct evaporative cooling systems are not feasible when the ambient air is near saturation. The THI values for ambient and direct evaporative cooler were positioned mainly in the severe heat stress region, with THI value in the range of 80 to 82, and most air outlet conditions were near saturation. The numerical results for the liquid desiccant systems show a consistent reduction in humidity ratio and air dry-bulb temperature. The assessment of air outlet temperature and humidity in terms of THI values was shifted out of the emergency and danger zone with a preference for LiCl solution.
Photovoltaic systems supported by energy storage are commonly applied solutions for supplying power in off-grid locations. Properly designed systems can ensure reliability at a level comparable to conventional diesel generators. In addition, renewables-based systems not only have lower cost of maintenance (its operation is not fuel supply dependent) but also a significantly smaller environmental footprint. In this paper, a PV-battery system is designed to supply four different loads in a remote location. The cost of reliability as well as related emissions are estimated and compared with a diesel generator. In contrast to the previous approach, PV-battery system reliability of is determined in a long-term horizon. The performance of the PV-battery is influenced not only by the variability of irradiation and temperature but also the degradation of PV system efficiency and a drop in battery capacity. In the available literature these three aspects are frequently neglected but even if considered, then never simultaneously. Based on the conducted analysis the following conclusions are drawn: PV-battery system has a significantly lower environmental impact than a diesel generator but it is not close to zero as the system tends to be oversized and the utilization of PV generation is relatively low; the solar energy system supplies variable loads at a cost comparable to a diesel generator (0.68 (sic)/kWh) but for constant loads it is more expensive by over 0.3 (Sic).
The claim of a green data centre is generally made based on a net-zero CO2 emission through a ‘balance-sheet’ approach, which considers renewable electricity through on-site installation or purchase agreement as abatement measures against the use of fossil electricity from the electric grid on an annual basis. However, when the hourly dynamic fuel mix is accounted for in the assessment, the annual net-zero energy approach does not lead to a true carbon neutral data centre. In response, two approaches based on net-zero energy and net-zero CO2 emission respectively are proposed and investigated regarding the goal of net-zero CO2 emission. A data centre in Singapore with typical load profiles is used as a case study, different scenarios considering climate change and projected future energy are defined to examine the impacts of dynamic energy mix on the net CO2 emission of the data centre. The net-zero energy approach is found to result in significant amount of annual CO2 emissions. In comparison, the net-zero CO2 emission approach can assure a true net-zero CO2 emission, but this approach will require an increase of PV capacity by 20% and 60% as compared to the net-zero energy approach based on assessment for the year 2030 and 2050, respectively.
The backup power system (BPS) is essential to data centers (DCs) in case of grid outage. Currently, the diesel generator (DG) is the most commonly used solution. However, due to the need of decarbonization, fuel cells (FCs) are emerging as a promising alternative. This paper conducts a holistic economic analysis to investigate the benefit from using FCs to replace DGs, which takes into account more key impact factors. Different requirements by different Tiers of DCs, such as on the BPS runtime and the BPS test time, are considered. Under the benchmark condition, i.e. 800 USD/kW for the FC capital cost, 4.8 USD/kg, 1.25 USD/L and 90 USD/ton for hydrogen, diesel, and CO2 prices, the payback period is 13.4 years and 13.1 years when using FCs to replace DGs for Tier 1–2 DCs and Tier 3 DCs. Since Tier 4 DCs require more units, FCs can be economically feasible if the FC capital cost reduces by 20.3 %, the diesel price increases by 19.7 %, or the green hydrogen price decreases by 35.5 %, compared to the benchmark conditions. Among the factors, the FC capital cost, the diesel price, and the hydrogen price are found to affect the payback period mostly.
Economic and environmental benefits are the most important in the operation of community integrated energy systems (CIES), modeled as a bi-objective optimization problem. In the case of the uncertainties from loads and renewable energy generators, the effectiveness of the operation strategies may be degraded in the practical applications of CIES. In this paper, an improved triangle splitting based bi-objective optimization method is proposed to search for the Pareto optimal solution of the CIES operation. The general preference of decision-makers in practical applications is utilized in the search process to reduce the detailed search interval and consequently improve the optimization efficiency. In addition, a bi-objective uncertain optimization framework is established for the economic-environmental operation of the CIES under uncertainties. The correlation between uncertainties is considered to generate the operation scenarios, in which the solution probability function is employed to determine the final operation strategy with robustness. A comprehensive case study is conducted based on a practical CIES in China, proving the feasibility and effectiveness of the proposed methods.