• Energy Research
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Abstract Compared with other traditional energy sources, renewable energy, which results the less pollution and has numerous resources, is a significant factor in addressing the current issues of the serious environmental pollution and the resource depletion. Large-scale renewable energy integrated to the grid could bring change in both morphological structure and operation modes of energy transmission. Therefore, it is necessary to research the evolution mechanism of the future transmission network with a high proportion of the renewable energy. In this paper, an evolution framework of power system with high proportion of renewable energy is proposed. Firstly, a network equivalence and simplification based on power transfer distribution factors (PTDFs) is proposed, which can effectively simplify the decision-making process of evolution of large-scale power system. Then, an annual production simulation (8760 h) which takes into account renewable energy and load fluctuations is used to find out the bottleneck of the power grid. Based on the above methods, evolution strategy of power system with high proportion of renewable energy is studied for finding out optimal expansion strategy. A real power system of Zhejiang province is used as a test system. Test results demonstrate the feasibility of the proposed evolution framework.

Six corrosion protection systems for offshore wind power constructions have been subjected to offshore conditions on a test site in the North Sea in three different exposure zones, namely splash zone, intermediate zone, and underwater zone. The systems included single- and multiple-layered organic coatings, metal-spray coatings, and duplex coatings. Special testing specimens were designed and manufactured and exposed to an offshore environment for three years in order to characterize particular constructive details for different corrosivity zones. The following target parameters were investigated: intensity of fouling, anti-corrosive effect, coating adhesion, coating integrity, flange corrosion, coating performance over welds, and condition of screw connections. Fouling was an issue in the underwater zone and in the intermediate zone, but it did not affect the coating corrosion protection capacity. It was found that duplex systems, consisting of Zn/Al spray metallization, intermediate particle-reinforced epoxy coating, and polyurethane top layer, provided the highest anti-corrosive effect. Mechanical damage to the coatings initiated coating delamination and substrate corrosion. Effective coating systems should be either very resistant to impact or able to compensate for corrosion of the steel. Flange connections were found to be critical structural parts in the splash zone in terms of corrosion. Notable crevice corrosion was observed at places. Except for one coating system, welds have been protected well. Welds, however, affected the corrosion of the steel inside the uncoated internal sections in the underwater samples. Coating integrity on difficult-to-coat structural parts was satisfactory for all systems.

Abstract For the first time the electrical conductivity of bamboo biographite-based material reported a ground-breaking milestone of 4.4 × 104 (S/m). This reported conductivity by far exceeded all previous reported conductivity measurements obtained from renewable carbon. Controlled high-temperature thermal carbonization of biomass, notably Asian bamboo, at extended residence times elicited surprising growth of nano-layered biographitic structures with a layer-to-layer distance of less than 0.3440 nm. Moreover, thermodynamically dispersed bamboo and pine biographitic nano-layered carbon-based lightweight composites in a polyamide matrix were found to be intrinsically conductive both thermally and electrically. Electromagnetic interference (EMI) shielding device made from bamboo renewable carbon/cellulose nanofiber (CNF) composites possesses EMI shielding effectiveness (SE) of ∼23 dB. These results constitute a new advancement in the materials science of nano-layered graphites from renewables and their applications as EMI filtering devices and as electrode materials in air cathodes, electronics, supercapacitors in energy storage devices, and thermal management of batteries and sensors.

Abstract To ensure techno-economically suitable installation of ground source heat pump (GSHP) systems, thermal and hydrogeological properties of the subsoil need to be investigated. In this paper, the geothermal potential for three types of GSHP installations in the urban area of Wuhan city is assessed based on preliminary geological investigations. The potential for shallow geothermal energy is evaluated for surface water heat pump systems (SWHP), groundwater heat pump systems (GWHP) and ground coupled heat exchanger heat pump systems (GCHP). The mapped shallow geothermal potentials provide essential information for the installation of GSHPs and for the management of geothermal resources of Wuhan city. Furthermore, the heat transfer rates for some typical configured borehole heat exchanger (BHE) are tested by field Thermal Response Tests (TRT). In order to understand the techno-economic feasibility of the GSHPs, different types of the installed systems are measured and analyzed.

Abstract Ever-growing energy demands and unacceptable emissions from fossil fuel combustion are major driving forces for expanding alternative, green energy sources. Hydro-power is one promising ecological alternative to meet these energy requirements. Such systems do not require any weir or dam and, thus, can be employed with minimum ecological impact. However, available designs are not yet suitable as efficient water energy converters, in particular for conditions corresponding to low water speeds (as mostly found in practice), due to low power output. Savonius turbines are particularly robust and cost-efficient, but show a poor efficiency. This article aims at maximizing the output power of a hydraulic Savonius turbine by modifying the blade profile. The main difference in this work compared to previous studies is that the blade shape of the concave and convex sides evolve independently from each other (no constant blade thickness). Twelve geometrical parameters are involved during shape optimization. To obtain optimal conditions, many transient computational fluid dynamics (CFD) simulations are performed using the industrial flow simulation code Star-CCM+, driven by the in-house optimization library OPAL++ relying on evolutionary algorithms. The optimization process takes into account the output power coefficient ( C p ) as a target function. Compared to the traditional Savonius turbine, a relative increase of C p by almost 12% is obtained at a tip speed ratio of 1.1. The performance of the optimal geometry was compared to the standard design over the whole range of operation. This comparison revealed additionally that the performance was improved by almost 15% at a tip speed ratio of 1.2. The performance of the optimal design is superior for the whole range of operation, particularly at a tip speed ratio exceeding 0.8. Finally, it was checked that the optimal design is still self-starting.

Abstract For the future energy system it becomes increasingly important that biogas plants produce electricity in a demand-oriented way to compensate electricity production from fluctuating sources like wind power and photovoltaics. Flexibilisation concepts provide a coordinated feeding management, which consider different gas production kinetics of used substrates to adjust the biogas production. To enable the generation of a prospective timetable, suitable forecast models for power demand were evaluated. The resulting 48-h forecasts of power demand of a “real-world laboratory” demonstrated that the four selected models achieve comparably good results with a mean absolute percentage error (MAPE) between 13 and 16%. Further evaluation showed that forecasts over longer periods of up to 14 days are advantageous as they are possible without compromising forecast quality.

Abstract Standardization of biogas technology is immensely important for the promotion of the biogas industry worldwide. China has built a complete biogas standard system, which is divided into common, household biogas, biogas engineering, biogas digester for domestic sewage treatment, output utilization, and service system standards. The problems and potential barriers for biogas standardization in China are analyzed and come down to sluggish standard, overlapped standard, government-dominated standard, and lagging international standard. Accordingly, all potential biogas standards should be evaluated and placed under the same department. China Biogas Society and China Association of Rural Energy Industry play leading roles in developing enterprise or group/association biogas standards and ISO biogas standards. The bio-natural gas standard system and experimental standardization should be developed as well to replenish biogas standard system. A paradigm shift in biogas standardization should be from government-dominated to market-oriented model. The lessons learned for other developing countries includes expanding standardization to multi-aspects to realize full lifecycle control and management, building rapid responding mechanism of standardization to adopt industry transformation, integrating outdated standards into new versions, and establishing market-based standard system.

Abstract In Germany renewable energies in the heat market are promoted by the Renewable Energies Heat Act (EEWarmeG) and by government grants. Ultimately, these two instruments are not only about short-term market success, but rather about the perspectives of climate protection and resource conservation. The focus of this report is therefore on the long-term significance of the current design of government grants and EEWarmeG. We will introduce and discuss the quantitative goals and structural changes strived for as well as – on a slightly shorter time horizon – the quality assurance regulations which must accompany the steady and stable growth of renewable energies. In the process, we will elaborate in particular on heat pumps, which have recently been added to the government support programme, along with solar collectors. Some explanations regarding the structural relationships between EEWarmeG and government grants round off this contribution.

Accurate estimation of extreme wave conditions is critical for offshore renewable energy activities and applications. Wave power is the transport of energy by wind waves, and the capture of that energy to do useful work. Wave energy converter (WEC) devices are designed to sustain the wave-induced loads that they experience during both operational and survival sea states. The extreme values of these forces are often a key cost driver for WEC designs. These extreme loads often occur during severe storms; therefore careful examination of harsh wave conditions during the device design process is needed. Consequently the development of a specific extreme condition modeling method is essential. This paper presents a novel method for estimating extreme wave statistics, based on the hourly measured wave height maxima at the location of interest. Wave measurements, analyzed in this paper, were collected at SEM-REV offshore sea station located near the coast of France, during years 2001–2010. Note that applied statistical methodology is general and can be well applied to a measured WEC response, and its technology risk assessment. Accurate estimation of extreme wave conditions is critical for offshore renewable energy activities and applications. SEM-REV is known French wave energy test site. The method, referred to as ACER method, is presented in brief detail. ACER method provides an accurate extreme value prediction, utilizing available data efficiently. In this study the estimated return level values, obtained by ACER method, are compared to the corresponding return level values obtained by Gumbel method. Based on the overall performance of the proposed method, it is concluded that the ACER method can provide a robust and accurate prediction of extreme wave height at a given location.