Higher Residual Load Research Articles

Geospatial optimisation of wind and solar energy generation: A framework for optimised resource allocation

Wind and solar power generation profiles exhibit a high degree of power output variability and uncertainty compared to conventional fossil fuel generation plants. However, it is generally accepted that this variability and uncertainty can be mitigated by geographic siting and dispersion of the renewable energy plants, particularly with the view to leverage aggregation effects. In this context, this paper proposes a framework for the geospatial optimisation of wind and solar PV generation for scenarios with a high penetration of wind and solar renewable energy. The proposed optimisation framework represents a probabilistic risk-based approach that seeks to minimise the number of events where high residual load values require ancillary service interventions to maintain power balance. In this approach, the wind and solar resources are categorised in terms of the statistical properties of the associated spatiotemporal wind and solar power profiles for a given set of daily and seasonal Time of Use periods. It is thereby recognised that the resource characteristics and grid impact of wind and solar generation profiles can be interpreted with reference to the daily and seasonal cycles exhibited by the demand profiles, wherein some Time of Use periods are more important than others. The proposed framework is implemented for a number of baseline case studies and optimisation case studies, using wind and solar resource data sets covering South Africa. Overall, it is concluded that this approach can leverage geospatial site optimisation to substantially reduce the risks associated with high residual load events. Furthermore, the proposed framework is highly flexible in that the formulation of the minimum and maximum allocation constraints allows application for real-world scenarios whereby stringent capacity allocation constraints can be applied.

Enhanced copper cyanide complex precipitation using polymer-surfactant aggregates

Precipitation of metal cyanide complexes using quaternary ammonium salts has been used in cyanidation solutions after gold leaching. Due to the high residual load of metal cyanide complexes and ammonium salts, this method does not apply to effluents containing moderate or low cyanide concentrations. To overcome these limitations, in this study, we introduce poly(sodium 4-styrenesulfonate) (PSS) into a solution containing cetyltrimethylammonium bromide Sinpharm (CTAB), to form polymer-surfactant aggregates (PSAs) and enhance the removal efficiency of Cu and TCN. 93.8% and 97.0% of Cu and TCN, respectively, were removed from the synthetic solution (Cu 0.5 mM and CN 1.5 mM) under optimum dosage of 150 ppm PSS and 0.8 mM CTAB, resulting in 92.2% of substrate usage. The addition of 3.0 mM CTAB without PSS resulted in only 46.3% of substrate usage, even though the removals of Cu and TCN were 92.2 and 93.6%, respectively. The presence of thiocyanate ions significantly reduced the removal efficiency due to the competitive interaction with PSAs, whereas the pH of the solution and the temperature did not have any noticeable impact. Tests performed with an industrial effluent corroborated the results obtained with synthetic solutions: PSAs react with copper cyanide to form a precipitate that can be separated from the solution.

Effects of meteorological and climatological factors on extremely high residual load and possible future changes

Under high variable renewable energy (VRE) penetration, the occurrence of low VRE production, such as dark doldrums (Dunkelflaute) and wind-solar drought, can threaten a secure and continuous energy supply owing to an imbalance between electricity demand and supply. In this study, historically reconstructed long-term VRE generation and electricity demand were used to investigate the relationship between extremely high residual load (demand minus VRE output) and weather/climate in Japan. The impact of changes in the VRE's installed capacity on this relationship was also investigated using three simple future target scenarios. The results showed that the increase in installed VRE capacity causes greater daily and weekly residual load variabilities and affects the seasonality of its peaks. To study the weather patterns associated with high residual load events, self-organizing maps were applied to atmospheric circulation fields derived from atmospheric reanalysis data. The high residual load was associated with enhanced cold surge-type weather patterns during winter at the current low VRE installation level. However, under future increased VRE penetration, the weather patterns leading to high residual load will change to cloudy-windless types typically caused by a southern coastal extratropical cyclone. There is also considerable interannual variability in the frequency of high residual load events, which changed significantly with increasing VRE capacity. It is crucial to incorporate the dependence of climatic conditions into designing power systems to maintain the stability of a power system under future conditions.

Introducing a new wind speed complementarity model

Minimizing the residual load is essential in countries with a high share of variable renewable energies (VRE). Optimally, new wind turbine sites provide high resource availability and the potential for smoothing the temporal course of the residual load. Current high spatial resolution wind atlases are limited to the ability to find high capacity factor (CF) sites but do not provide CF during periods of high residual load. Thus, we derive a new high-spatiotemporal resolution wind speed model for adjusting wind turbine site selection to residual load. The model (WiCoMo) is developed at six-hourly temporal resolution and 25 m × 25 spatial resolution up to 200 m height from 1991 to 2018 in the study area of Germany. Residual load-weighted and adjusted CF in 2015–2018 is mapped using the new model and considering the national residual load. Besides, complementarity between CF and VRE is evaluated. According to the standard CF, there is a northwest-southeast CF gradient. Relying on the residual load adjusted CF site suitability in southern Germany increases compared to the rest of the country. The introduced model may be a valuable tool for adapting wind resource assessment in Germany on the increasing role of VRE in the electricity mix.

A copula-based assessment of renewable energy droughts across Europe

Meeting carbon-reduction targets will require thorough consideration of climate variability and climate change due to the increasing share of climate-sensitive renewable energy sources (RES). One of the main concerns arises from situations of low renewable production and high demand, which can hinder the power system. We analysed energy droughts, defined as periods of low energy production (wind plus solar generation) or high residual load (demand minus production), in terms of two main properties: duration and severity. We estimated the joint return periods associated with energy droughts of residual load and power production. We showed that moderate winter energy droughts of both low renewable production and high residual load occur every half a year, while summer events occur every 3.6 and 2.4 years (on average). As expected, the occurrence of energy droughts tends to decrease with the degree of the severity of the energy drought, and moderate and extreme energy droughts showed longer return periods for most countries. In general, we found a large variability across Europe in summer, with some countries (e.g. Italy) being more sensitive to energy droughts. Our results highlight the relevance of sharing RES during prolonged periods of low production and high demand.

Importance of renewable resource variability for electricity mix transformation: A case study from Germany based on electricity market data

The success of the German electricity mix transformation depends on the variable renewable energies solar photovoltaics and wind. Their extensive exploitation until 2030 and beyond is a cornerstone on the road to climate neutrality, which Germany aims for in 2045. We use actual electricity generation and consumption data from 2015 to 2021 to analyze the development and potential of renewable energy shares in the German electricity mix and discuss future challenges for implementing the transformation until 2030. Current electricity consumption mostly exceeded renewable electricity generation, leading to consumption-supply mismatch and large residual loads. Renewable electricity generation met the net electricity consumption in 0.16% of all hours analyzed. No day renewables met net electricity consumption; substantial residual loads always occurred. The natural variability of the territorial availability of solar and wind was identified as the main reason for the high residual load shares. Results of a high-resolution wavelet analysis illustrate in detail the extend of the temporal, territorial variability of wind and solar along the studied timeline. Together with the annual gross electricity consumption values discussed for 2030 of 650–800 TWh these findings were used for projecting the future consumption-supply mismatch. The most optimistic scenarios show that only strict compliance with the targeted expansion and moderate increase in electricity consumption enables the achievement of set energy goals. Missing expansion targets and increasing electricity consumption challenge the 2030 renewable generation targets in 47% of the most optimistic scenarios. It is concluded that the natural variability of solar and wind will continue to be a major challenge for meeting Germany's electricity consumption in the near future.

Effects of Meteorological and Climatological Factors on Extremely High Residual Load and the Possible Future Changes

Effects of Meteorological and Climatological Factors on Extremely High Residual Load and the Possible Future Changes

Biomass in the electricity system: A complement to variable renewables or a source of negative emissions?

Biomass is often assigned a central role in future energy system scenarios as a carbon sink, making negative greenhouse gas emissions possible through carbon capture and storage of biogenic carbon dioxide from biomass-fuelled power plants. However, biomass could also serve as a strategic complement to variable renewables by supplying electricity during hours of high residual load. In this work, we investigate the role of biomass in electricity systems with net zero or negative emissions of carbon dioxide and with different levels of biomass availability. We show that access to biomass corresponding to ca. 20% of the electricity demand in primary energy terms, is of high value to the electricity system. Biomass for flexibility purposes can be a cost-efficient support to reach a carbon neutral electricity system with the main share of electricity from wind and solar power. Biomass-fired power plants equipped with carbon capture and storage in combination with natural gas combined cycle turbines are identified as being the cost-effective choice to supply the electricity system with flexibility if the availability of biomass within the electricity system is low. In contrast, in the case of excess biomass, flexibility is supplied by biomethane-fired combined cycle turbines or by biomass-fired power plants.

Additional Comparisons of Interlocked Fabric and Laminated Fabric Kevlar 49/Epoxy Composites

Compression, gas gun planar impact, and post-impact short beam shear test results are presented for a novel interlocked fabric reinforced Kevlar 49/epoxy composite. This material has roughly 4% fiber volume fraction in the through-the-thickness direction. For the purpose of comparison, similar results are also presented for a laminated Kevlar 49/epoxy composite. Both materials have a compressive stress-strain curve that can be approximated as bilinear with a secondary modulus of on the order of 10% of the initial modulus. Although the materials have comparable yield strengths (∼ 10% difference), their respective initial and secondary moduli are not in as close agreement (up to 50% difference). Gas gun planar impact spall test data indicate that relatively low levels of impact stress (∼1 kbar, ∼100 MPa) generate matrix cracking in both materials. The interlocked fabric's binder yarns, however, show no visible sign of damage even at an impact stress level of 5.1 kbar (510 MPa). Post-impact short beam shear test data for both materials show that once a threshold impact level is exceeded (∼1 kbar, ∼100MPa), specimen stiffness and load carrying capacity decrease as the impact level is increased. This is presumably because of mid-plane matrix cracks of increasing size and density. Even though the properties of the interlocked fabric reinforced composite are substantially reduced by impact at the 5.1-kbar (510-MPa) level, the binder yarns give the material a degree of integrity that would not otherwise exist. The interlocked fabric reinforced Kevlar 49/epoxy composite has a higher residual load carrying capacity than the laminated Kevlar 49/epoxy at all impact levels.