• Energy Research
• Closed Access close
• Restricted close
• 7. Clean energy close
• 6. Clean water close
• DK close

Abstract District heating (DH) enables the utilisation and distribution of heating from sources unfeasible for stand-alone applications and combined with cogeneration of heat and power (CHP), has been the cornerstone of Denmark’s realisation of a steady national primary energy supply over the last four decades. However, progressively more energy-efficient houses and a steadily improving heat pump (HP) performance for individual dwellings is straining the competitive advantage of the CHP–DH combination as DH grid losses are growing in relative terms due to decreasing heating demands of buildings and relatively high DH supply temperatures. A main driver for the DH water temperature is the requirements for domestic hot water (DHW) production. This article investigates two alternatives for DHW supply: (a) DH based on central HPs combined with a heat exchanger, and (b) a combination of DH based on central HPs and a small booster HP using DH water as low-temperature source for DHW production. The analyses are conducted using the energyPRO simulation model and are conducted with hourly varying factors; heating demands, DH grid losses, HP coefficient of performance (COP) and spot market prices in order to be able to analyse the relative performance of the two options and their performance over the year. Results are also compared to individual boilers and individual HPs. The results indicate that applying booster HPs enables the DH system to operate at substantially lower temperature levels, improving the COP of central DH HPs while simultaneously lowering DH grid losses significantly. Thus, DH performance is increased significantly. Additionally, performance for the DH HP with booster combination is considerably better than individual boiler or HP solutions.

Abstract The use of photovoltaic solar power generation is rising as worldwide energy demand increases. Therefore, reliability, safety, life cycle, and improved efficiency of photovoltaic plants have all become a major concern in research nowadays. In this context, monitoring systems are necessary to guarantee the required operating productivity and to avoid overpriced maintenance costs. This paper studies the non-ideal operating conditions for grid-connected photovoltaic plants and proposes an anomaly detection methodology that combines the advantages of the 2-sigma, short-window simple-moving average control charts with shading strength and irradiance transition parameters to detect early deviation in photovoltaic plant operational data. The key aspect of proposed methodology is that it requires neither historical data for model training procedure nor parameters from previous simulation. Only instantaneous meteorological and electrical parameters are required. The efficiency of the condition monitoring methodology has been validated through experimental results conducted in actual operating conditions. Results demonstrated that the proposed methodology is effective to identify non-ideal operating conditions for grid-connected photovoltaic plants, i.e., (i) normal operating condition, (ii) natural dynamic shading, (iii) artificial dynamic shading, and (iv) artificial static shading. Moreover, a low-cost and non-invasive internet-of-things-based embedded architecture is proposed to monitor photovoltaic plant operation in real-time.

Abstract For Solid Oxide Fuel Cells (SOFCs) to become an economically attractive energy conversion technology, suitable materials and structures which enable operation at lower temperatures, while retaining high cell performance, must be developed. Recently, the perovskite-type La 0.6 Ca 0.4 Fe 0.8 Ni 0.2 O 3 oxide has shown potential as an intermediate temperature SOFC cathode. An equivalent circuit describing the cathode polarization resistances was constructed from analyzing impedance spectra recorded at different temperatures in oxygen. A competitive electrode polarization resistance is reported for this oxygen electrode using a Ce 0.8 Gd 0.2 O 1.9 electrolyte, determined by impedance spectroscopy studies of symmetrical cells sintered at 800 °C and 1000 °C. Scanning electron microscopy (SEM) studies of the symmetrical cells revealed the absence of any reaction layer between cathode and electrolyte, and a porous electrode microstructure even when sintered at a temperature of only 800 °C. The performance of this cathode shows favorable oxygen reduction reaction (ORR) properties potentially making it an excellent choice for IT-SOFC application.

Abstract This paper presents a novel load frequency control (LFC) model for an interconnected thermal two-area power system in the presence of wind turbine generation and redox flow battery (RFB). The study model includes frequency and voltage excitation loops with needed interactions between them along with the power system stabilizer. A two-degree of freedom (2DOF)-based controller called 2DOF-Hybrid controller is developed as secondary controller in automatic generation control (AGC) to adjust the power outputs of generator and RFB. Also, the dynamic performance of the proposed controller in the RFB loop is evaluated. The Hybrid controller comprises a fractional-order proportional-integral-derivative (FOPID) controller and a tilt-integral-derivative (TID) controller. In order to obtain accurate and realistic results, the outputs of thermal power plants are restricted by considering the limitations of the governor dead-band and generation rate constraint. Since the controller performance depends on its parameters, these parameters are optimized using a modified sine–cosine algorithm (MSCA). The dynamic performance of the proposed 2DOF-Hybrid controller as secondary controller of the AGC loop is compared with integral-double-derivative (IDD), integral-tilt-derivative, proportion-integral–derivative (PID)-DD, 2DOF-PID, 2DOF-TID, and 2DOF-FOPID ones under different scenarios. In addition, the superiority of the MSCA is compared with benchmark metaheuristic methods including an SCA, a genetic algorithm, a particle swarm optimization, and a differential evolution. The sensitivity analysis is also carried out to show the robustness of the proposed controller versus the changes of the parameters. The simulation studies on two-area and New England 39-bus power systems are carried out to examine the advantage of the presented LFC scheme. A range of power system signals such as frequencies of areas, terminal voltages, and tie-line power flow is demonstrated to compare the controllers. The results disclose that the proposed LFC scheme provides better dynamic performance compared to other ones. Moreover, RFB modeling based on the proposed controller is superior to conventional RFB modeling in reducing the amplitude of the oscillations.

Abstract Building materials with high thermal and hygric inertia can moderate the fluctuation of indoor temperature and relative humidity, and thus can improve the indoor thermal comfort and reduce the building energy consumption passively. In this study, a novel hygrothermal control material was prepared based on Metal-Organic Frameworks (MOFs) and microencapsulated phase change material (MicroPCM). The new MOF/MicroPCM composite has a dual functionality of adsorption and desorption of both heat and moisture, can offer an accurate passive control of the indoor hygrothermal environment. N-octadecane was encapsulated by polymethylmetracrylate (PMMA) as MicroPCM for the thermal buffering. MIL-100(Fe) was prepared by the hydrothermal reaction method as the humidity buffering material. A series of hygrothermal control composite materials were obtained by grinding MicroPCM and MIL-100(Fe). Physicochemical properties of the synthesized materials were characterized by SEM, TEM, XRD, FTIR, N2 physisorption, Water vapor sorption isotherm, DSC and TGA techniques. Hygrothermal properties of the composites were analyzed in comparison to pure MicroPCM and MIL-100(Fe). The thermal and humidity buffering behavior of the composites containing 50% MicroPCM was analyzed by numerical simulations. The results show that the composites possess an excellent thermal and humidity buffer capacity, which can be used for building energy-saving and improving thermal comfort.

Abstract Numerous efforts have been done for achieving the maximum penetration of renewable energy sources (RESs) in the autonomous grids of Greek islands, which never exceeded 10%, despite the exceptional wind and solar potential. Large fluctuations on demand during summer, winter, and 24-h period in combination with the technical restrictions of diesel generators of the existing conventional power stations are a major concern of power supply system. Reversing the roles of diesel generators and wind farms (WFs), to use WF as the basic energy source and diesel generators as stand-by system changed in fact the whole philosophy of energy supply systems in islands and created perspectives for the fundamental reformation of the conventional energy supply systems in autonomous grids. In fact, methods of contemporary interim medium term energy storage are investigated for hybrid systems in order to adjust the stochastic behavior of wind energy to the demand, to provide the system with guaranteed power. This Wind–Hydro Plants in combination with the most adequate RES forming an Renewable Energy Supply System (RESS), increase further the economical penetration of RES into autonomous grids up to 90% or even 100% and simultaneously reduce drastically the fuel costs. Furthermore, a supergrid is examined and compared with RESS as another efficient way for achieving higher penetration of RES.

Abstract This paper presents the basic idea, design considerations and field test results for a novel concept of an energy storage system. The system is of the underground pumped hydro storage (UPHS) type where energy is stored by lifting a mass of soil through the pumping of water into an underground cavity. The cavity is formed by two impermeable membranes welded along the edges. A simple model captures the dynamics of the system revealing the importance of both visco-elastic and plastic effects for the cyclic loading of the soil. The results indicate that the efficiency of this new concept will be very close to that of the traditional pumped hydro storage (PHS) technology and the energy lost by deformation of the soil will be between 0.04 and 0.12% for a full scale system of 30 MW power and 200 MWh capacity. A key feature of the concept is the relatively price efficient design where the main cost is movement of soil. A cost analysis indicates that a full scale system will be economically viable when connected to the European power grid where the main revenue will come from selling ancillary services. The storage cost for a full scale 30 MW/200 MWh system is estimated to be approximately 5.3 EUR cent/kWh. The estimated cost of installed power is 1111 EUR/kW and the related cost of installed storage capacity is 208 EUR/kWh.

Abstract Anaerobic digestion of animal by-products was investigated in batch and semi-continuously fed, reactor experiments at 55 °C and for some experiments also at 37 °C. Separate or mixed by-products from pigs were tested. The methane potential measured by batch assays for meat- and bone flour, fat, blood, hair, meat, ribs, raw waste were: 225, 497, 487, 561, 582, 575, 359, 619 dm 3 kg −1 respectively, corresponding to 50–100% of the calculated theoretical methane potential. Dilution of the by-products had a positive effect on the specific methane yield with the highest dilutions giving the best results. High concentrations of long-chain fatty acids and ammonia in the by-products were found to inhibit the biogas process at concentrations higher than 5 g lipids dm −3 and 7 g N dm −3 respectively. Pretreatment (pasteurization: 70 °C, sterilization: 133 °C, and alkali hydrolysis (NaOH) had no effect on achieved methane yields. Mesophilic digestion was more stable than thermophilic digestion, and higher methane yield was noticed at high waste concentrations. The lower yield at thermophilic temperature and high waste concentration was due to ammonia inhibition. Co-digestion of 5% pork by-products mixed with pig manure at 37 °C showed 40% higher methane production compared to digestion of manure alone.