Renewable Energy最新文献

Cooling of data centers requires a significant amount of energy, comparable to the energy consumption of the servers themselves. The current design of the centralized cooling systems for data centers is based on ideal IT loading conditions (i.e., 100 % loading). However, such conventional design often results in significant oversized cooling systems and leads to substantial energy waste, since most data centers operate at part load in their lifespan. To address this issue, this study proposes an optimal design for centralized cooling systems with multiple chillers under progressive loading. The optimization problem, aimed at minimizing life-cycle cost, is formulated adopting SLSQP (Sequential Least Squares Programming) algorithm. A cooling system model is developed using the manufacturer's performance data of cooling equipment. The optimal designs in different climate zones are identified according to energy performance under full-range loads and ambient temperatures. Furthermore, this study comprehensively analyzes and compares free cooling hours, cooling energy, and life-cycle cost of the optimized designs with conventional designs. The results show that the optimized cooling systems could operate more energy-efficiently, despite decreased free cooling hours (13–860). Significant cooling energy savings over the lifespan could be achieved, i.e., 4–22 %, corresponding to the PUE reductions of 0.02–0.11, depending on climate conditions and control strategies.

Photovoltaic-battery water pumping systems (PVBWPSs) can provide fresh water and irrigation in off-grid areas. Previous research has focused on direct current (DC) voltage versus frequency to control the speed of a pump. However, the use of photovoltaic (PV) modules with batteries to create a high-performance hybrid system with fixed and variable frequencies of supply power remains challenging, particularly in an off-grid water pumping system with limited power and water supplies. Based on a conventional frequency conversion mode and power balance, this work addresses fixed and variable frequencies under changing solar irradiance conditions for a PV system and a PV system combined with a battery (PVB) mode to improve energy utilisation. According to DC power balance and centrifugal pump theories, a mathematical model of the power supply frequency in the PVBWPS is presented, as well as the loss of load probability (LLP) and pumping coefficient (C_p), through which the performance metrics are obtained. The formulated models are validated through the experimental PVBWPS, which includes 2.19 kWp PV modules, a 9.6 kWh battery bank, and a 0.75 kW centrifugal pump. The experimental results show that the root mean square error (RMSE) and maximum relevant error (RE) of the frequency are 0.14 Hz and 0.74 %, respectively. Consequently, the output performances are revealed via software simulation. The calculated results indicate that the maximum pumping volume for fixed-power-frequency operation is 48 Hz, which is 27.56 m³ on a sunny day and 17.63 m³ on a cloudy day. On a rainy day, the maximum pumping volume is 3.27 m³ at 41 Hz. Similarly, the C_p values reach maxima of 2.51 m³/kWh and 2.11 m³/kWh at 48 Hz in both sunny weather and cloudy weather, respectively, while on rainy days, the C_p peaks at 0.77 m³/kWh at 41 Hz. Moreover, every 1 Hz increase in the fixed frequency mode leads to a rise in the LLP, while the minimum change is at 46–48 Hz for cloudy and rainy days. Furthermore, the simulations revealed that for variable frequency control, the volume of water pumped in the PVB mode reached 40.19 m³, 29.36 m³, and 15.11 m³, which are increased by 4.91 %, 21.83 % and 103.09 % compared with the variable frequency PV mode, and 45.83 %, 66.53 % and 362.08 % higher than in PV fixed frequency mode, respectively. Compared with the PV mode, the system weighted efficiency of the variable-frequency PVB mode is increased by 2.06 %, 4.98 %, and 8.36 % under three weather conditions. This work provides critical theoretical guidelines for the design and operation of high-performance PVBWPs.

In this paper, we study optimal market operations and grid effects of office building from an energy community perspective. Commercial buildings such as offices can include many stakeholders and new flexible assets that can offer suitable use cases to form energy communities or enter energy and reserve markets. The office building we focus in this study has a real-world counterpart with historical measurement data and involves three stakeholders and their assets. The stakeholders are the owner, the tenant, and the operator of flexible assets. These assets are the battery energy storage system (BESS) and the electric vehicles (EV) charging system (EVCS) that both can operate in response to energy price fluctuations and in a reserve market. Different cases are studied where either the owner or the tenant is paying the EV charging, and where the flexibility of the EV charging is either active or not. We show that, when the owner pays for the energy of the EVCS and the tenant is using it, there is a beneficial case to form a coalition between them and share the benefits. Operative cost-benefit calculations are conducted where the community benefits are shared according to the Shapley value and the power flows at the building’s connection point are simulated based on the market operations. The sensitivity of the flexibility and the maximum power of EVCS to the results are studied. Harnessing benefits from the markets shows significant effects on the power flows at the connection point.

This study introduces a comprehensive framework aimed at enhancing power system optimality through a two-stage optimization process and the development of a deep-based model for optimal scheduling prediction (OSP). Initially, a Bidirectional Long Short-term Memory (Bi-LSTM) architecture is employed to accurately forecast wind power in the first stage. Subsequently, a convolutional Generative Adversarial Network (GAN) model utilizes these predicted wind power values to generate synthetic scenarios. These scenarios, based on the preceding 10 days’ wind power predictions, serve as inputs for the subsequent power system optimization stage. To streamline computational efficiency, the power system optimization is conducted via a two-stage model. The outputs from this process, alongside other pertinent parameters, are utilized to train the proposed deep-based OSP model. The efficacy of the proposed model in rapidly and reliably predicting optimal scheduling is evaluated using the 118-bus power system. Results indicate that the innovative approach demonstrates exceptional speed and precision in determining optimal scheduling for the power system. Specifically, the proposed OSP model accurately forecasts optimal dispatch for ten days ahead in a mere 0.38 s, with an error rate below 0.001. Furthermore, the model exhibits a 92 % correlation in predicting optimal dispatched wind power. Sensitivity analysis highlights that optimizing the arrangement of the proposed deep-based model using an automatic hyperparameter optimization software framework (OPTUNA) can significantly enhance performance accuracy, potentially by up to 24 %.

Analyzing low-renewable-output events, termed “energy droughts” is crucial for renewable energy systems. However, due to the challenges in hydropower regulation and complex spatiotemporal correlations among resources, the assessment and contributions of various resources to energy droughts in hydro-wind-photovoltaic (PV) energy systems (HWPSs) remain unexplored. To address these issues, this study evaluated energy droughts and compound resource droughts rather than single-resource in HWPSs, exploring the propagation. Assessments of frequency, duration, and severity relied on weather-to-resource conversion models and total power obtained through complementary operation. Estimating propagation probability from resource to energy droughts was achieved via the C-vine copula, quantifying resource contributions to drought propagation. Results of a case study in the Yalong River Basin indicated that (1) short-lived compound resource droughts have been increasingly frequent recently, peaking during winter or summer. After incorporating hydro energy resources, the severity and annual average occurrence of compound droughts decreased (from 18.56 to 5.24 events/year). (2) Complementary operation effectively reduced the probability of drought propagation. (3) Hydro and PV energy resources were pivotal contributors to drought propagation, contributing 49.1 % and 40.1 % when representing 53.4 % and 22.5 % of the total system capacity, respectively. Therefore, the study offers valuable insights into energy drought warnings and risk mitigation.

The selective catalytic conversion of bio-ethanol into valuable chemical compounds, particularly 1-butanol (i.e., Guerbet reaction), has gained significant attention due to its potential to replace fossil sources in the future. This work continues the search for a catalyst with high ethanol conversion and selectivity toward desired products. The novelty of the study lies in its use of copper-lithium-aluminum mixed metal oxides as heterogeneous catalysts. Li–Al oxides were prepared via urea precipitation, and copper was introduced in two ways: (i) during co-precipitation and (ii) post-synthetic impregnation. Gas-phase reaction in a fixed-bed reactor was realized at varying temperatures and pressures. The properties of the mixed metal oxides proved to be crucial, as a wide range of products was observed. Catalysts that shifted from acidic to basic properties, and those with different redox properties, significantly affected ethanol conversion and selectivity toward the desired higher alcohols. Compared to previously used magnesium-aluminum mixed metal oxides, a lower amount of copper was required to achieve similar or higher ethanol conversion (71 %) and butanol selectivity (30 %) at 300–350 °C and 10 MPa. Thus, lithium-aluminum mixed metal oxides showed the potential to surpass magnesium-aluminum mixed metal oxides with further study and adjustment of their properties.

Ground Source Heat Pumps, in the framework of Shallow Geothermal Energy Systems, outperform conventional Heating Ventilation and Air Conditioning systems, even the high efficiency Air Source Heat Pumps. At the same time, though, they require considerably higher installation costs. The utilization of dwellings' foundations as ground heat exchanger components has recently demonstrated the potential to generate significant cost reductions primarily attributed to the reduction in expenses associated with drilling and backfill material (grout). These elements are referred to in the literature as Thermo-Active Structures or Energy Geo-structures (EGs). The current study employs a ‘mixed studies’ review (i.e., literature review, critical review and state-of-the-art review) methodology to comprehensively examine and assess the compatibility and integration of different renewable energy sources and environmentally friendly technologies with foundation elements deployed as EGs. These mainly include heat pumps, district heating and cooling networks, solar-thermal systems, waste heat, biomass and other types such as urban structures. Emphasis has been given on the advancement on this area, with the current study identifying and addressing two primary categories. The first category involves the integration of EG elements with sources that are able to supply green electricity, referring to renewable energy electricity obtained from on-grid or off-grid integration. The second category, involves a direct or indirect integration with sources that provide heat, or vice versa. The technical and non-technical barriers of such integrations have been discussed in detail, with the technical challenges generally involving engineering design, and system optimization, whereas non-technical challenges encompassing the economic, social, and policy domains.

Hydropower has played an important role in Europe in recent decades, offering a unique combination of safe, low-cost, and clean power generation. Today, it is still one of the largest renewable energy sources (RES), accounting for about 35 % of RES electricity generation. However, grid stability is threatened by the increasing amount of undispatchable RES. Flexibility and dynamics such as energy storage and rapid response are urgently needed to achieve EU policy goals. In such a context, hydropower can play a key role, not only as a provider of regulated renewable energy but also due to its ability to balance a renewable energy system in the short term and the medium/long term by pumped storage technology. All these aspects underline the new role of hydropower, which aims to strengthen grid stability and power supply resilience and to enable higher penetration of volatile RES. In this context, the aim of this paper is to demonstrate the role of hydropower at the European level as well as the needs and opportunities of modernization to fully exploit its potential. In particular, this study provides, the assessment of the today flexibility offered by hydropower to the power system at the European level by leveraging a database of information collected through the participants to the working groups of the COST Action Pen@Hydropower which includes stakeholders in the hydropower sector of 34 European countries. The study confirms the key role of hydropower in future energy scenarios with 30 % of the flexibility demand at all time scales met by hydropower. Furthermore, the paper presents a review of the digitalization solutions and innovative technologies that support the growth of a new generation of sustainable hydropower together with the modernization opportunities for existing hydropower plants. The results of this work have practical implications for stakeholders in the hydropower sector and policymakers as it provides evidence at the European scale of the role of hydropower technology in balancing the power system and the need to have supportive frameworks and adequate markets to fully exploit the European hydropower potential to achieve the energy transition goals.

Fossil fuel depletion and environmental toxins have made photocatalytic H₂ production of paramount significance. A novel and unique technique for producing sustainable H₂ and valorizing biomass using infinite solar energy is biomass photoreformation. Nevertheless, this environmentally friendly method is usually linked to severe reaction circumstances, insufficient selectivity, and restricted biomass conversion. Here, we present a novel one-pot photoreformation technique over porous g-C₃N₄ nanosheets surface-modified with Pd nanoparticles to convert d-glucose to H₂. By stacking the g-C₃N₄ photocatalyst into a 2D nanosheet structure, some of its inherent drawbacks can be mitigated. Furthermore, the inclusion of noble metal nanoparticles in these g-C₃N₄ nanosheet structures could significantly boost existing photocatalytic activity. The majority of solar radiation is composed of visible light, which makes up 45% of it, and ultraviolet light, which makes up 5%. Therefore, our focus has been on utilizing abundant visible light to facilitate biomass reformation. After 4 h of continuous irradiation, our composite photocatalyst exhibited exceptional visible light activity; its H₂ evolution was 1839.84 μmolg⁻¹h⁻¹, or about 27 times higher than that of undoped g-C₃N₄ nanosheets. The effectiveness of three different Pd loadings on g-C₃N₄ nanosheets for glucose reforming was examined. In the quest for an improved H₂ evolution visible light active photocatalyst, g-C₃N₄ nanosheets made at various pyrolysis temperatures loaded with optimized Pd weight percentage were also examined.

The aim of this work was to investigate the effects of biochars derived from different feedstocks and pyrolysis temperatures on the anaerobic digestion (AD) of kitchen waste (KW). Nine biomass feedstocks (corn straw (CS), Dicranopteris dichotoma (DD), bamboo (B), KW, tea residues (TR), mushroom cultivation waste (MW), cassava lees (CL), Chlorella (C), and sargassum (S)) were pyrolyzed at different temperatures (300 °C, 500 °C, and 800 °C). Biochar varied in physicochemical properties (e.g., specific surface area, total pore volume, and organic functional group) depending on both feedstock type and pyrolysis temperature. This further impacted the enrichment of functional microbial consortia and development of methanogenic pathways, resulting in a varied AD performance. The addition of biochars generated respectively from CS, MW, and S at 800 °C, 300 °C, and 500 °C significantly improved the maximum methane production rate (Rm) and methane yield, while other biochars enhanced either Rm or methane yield. Therefore, the efficacy of biochar on methanogenesis associated with both the feedstock type and pyrolysis temperature. The findings offer a beneficial reference for the selection and application of biochar to improve the AD performance.