Thermal energy storage has been attracting more and more attentions due mainly to its distinctive features on peak-load shifting capability for systems with renewable energy involved. To further improve the overall thermal efficiency for charging/discharging processes, heat transfer techniques to enhance phase change heat transfer are typically employed. This paper introduced a novel concept of partially-filling ratio of metal foam into PCM. The melting heat transfer can be expected to be further enhanced with partially filled metal foams. To this aim, an axisymmetric twodimensional computational model was established. A series of numerical simulations were carried out to study the effect of filling ratio of metal foam on the melting performance of a TES tube. Good agreement was achieved through the comparison of temperatures obtained from simulation and experimental measurements. Based on the results, it can be concluded as follows: if the goal was to enhance heat transfer simultaneously to save material cost, the suggested filling ratio was 0.90; if saving material cost was the aim, the filling ratio can be further reduced to 0.85. The proposed novel TES unit with partially-filled metal foam outperformed other competing heat transfer techniques, favoring a progressive potential in thermal energy storage applications.
This paper presents a method for spatially representing the total temporal energetic complementarity between three different variable renewable sources, by means of an index created from correlation coefficients and compromise programming. The method is employed to study the complementarity of wind speed, solar radiation and surface runoff on a monthly scale using continental Colombia as case study, during the year of 2015. Results show that the combination of solar radiation and surface runoff presented the highest energetic complementarity during this year, heavily influenced by El Niño phenomenon.
The frictional pressure drop characteristics in gas channels of Polymer Electrolyte Fuel Cells (PEFCs) are modelled in this work. The two-phase flow in gas channels of PEFCs has its special features: (1) combination of reactant gas, water vapor and liquid water, (2) flow in micro/mini channels, (3) reactant consumption, (4) condensation from water vapor, (5) continuous water introduction from reaction and (6) flow pattern transitions. Therefore, previous two-phase pressure drop correlations, primarily for adiabatic gas liquid flow, might not be able to capture the pressure drop in the gas channel with a porous wall. The new flow pattern based pressure drop method covers three major flow regimes in gas channels, i.e., the single-phase gas flow zone, and droplet/mist flow and slug/film flow in the two-phase flow zone. In the droplet/mist flow regime, a homogeneous flow modelling was adopted, while in the slug/film flow regime, a modified Chisholm value of 8.5 was used. The new predictive tool presents improved accuracy in pressure drop estimation for different current densities and stoichiometric ratios of operating PEFCs.
Committed to green and low-carbon development, many countries like China is increasing its efforts to promote the development of its service economy such as tourism industries. Considering that tourism is an increasingly important contributor of energy consumption and pollutants emission, its green/low carbon development will play a significant role for China. Given the characteristics of renewable/green energy resources and tourism, a possible path is promoting the co-development of tourism and distributed energy which can create new economic growth points in addition to reduce the emission of greenhouse gases (GHGs) and critical air pollutants (CAPs) compared to transitional development pattern. This study attempts to develop an evaluation framework to investigate the effects of the codevelopment of tourism and distributed energy. A typical tourism and distributed energy co-development project in Shenzhen which is a typical low-carbon development city is took as an example to demonstrate the application of the framework and related methods proposed to assess the benefit. The results indicate that the emission reduction effect is 0.5 thousand tonnes (Tt) of CAPs and 7.8 Tt of GHG in 2017. The proposed framework can effectively help China identify the effects of the co-development of tourism and distributed energy, which is helpful to formulate policy and implement actions for next step action aiming at promoting green/low-carbon development and ecological civilization construction.
Although integration of higher shares of renewable energy sources in the energy mix improves sustainability, it has profound consequences for the electricity markets. The uncertainty and variability of renewables escalates the need for cost-effective ways to balance supply and demand in real-time. Energy storage systems are considered a viable solution to hedge against the intermittency of supply. However, most prior studies suggest marginal or even negative profitability of batteries when participating in one stage of the electricity market. Given the physical characteristics of batteries which make it suitable for in multiple market stages, we investigate the profitability of batteries when simultaneously participating in the day-ahead and balancing markets. We formulate a stochastic programming framework to choose optimal market position, optimal bidding strategy, and optimal capacity split between the two markets. Our results show that participation of batteries in multiple stages of the electricity markets generates additional profit for the battery. The optimal strategy is to participate in the dayahead market with full capacity as a seller and with fullcapacity in the down-regulation secondary balancing power market as a buyer.
Cities evolved to be major energy consumption centers. However, their potential to generate electricity from renewables is in most cases constrained to photovoltaics. Therefore, transforming them into sustainable and self-sufficient urban areas is a challenging task. In this preliminary study, we have investigated the match between photovoltaics (PV) generation and electrical load of five commercial buildings located in Sweden. First, the rooftop PV potential was assessed. Secondly, the optimization was performed aiming at reducing the energy flow between building/buildings and local electrical network. Results indicate that from the perspective of minimal power flow (for single buildings) optimal are PV system oriented to the southeast and southwest with a relatively small tilt angle of 15°.