Wind turbine and photovoltaic generating efficiency in Africa

As the technology of climate-dependent energy sources is improving - both cheaper and more efficient - the energy sources are becoming more accessible for many of the nations in Africa. However, little is known about the underlying climate that would therefore be harvested by renewable technologies - namely, wind and solar - because these have not been well measured in this region in the past. Here, we present a study that uses publicly available data and methods to develop hourly onshore wind and solar photovoltaic (PV) electricity generation for the years 1979-2010. To do this, we use reanalysis climate data and well-trusted wind farm and solar PV simulation models as well as publicly available geospatial data. The primary purpose of this dataset is to be used in an energy-expansion-planning model of the African continent in a forthcoming study. We find that wind resources vary more over time and space than solar across Africa. Due mostly to these variations in wind resources, we find that the East African Power Pool shows the most potential for wind and solar and the Central African Power Pool shows the least potential. Using an aggregation of areas with the highest potential during the peak demand hours, we develop 'representative sites', one for each country. With these sites, we identify pairs of countries that have potential to participate in mutually beneficial power trade because these resources exhibit negative correlation in reference to each other. Most notably, we find that wind in Kenya and wind in Uganda, which are neighbouring countries, exhibit particularly beneficial characteristics in relation to each other

Planning for large-scale wind and solar power in South Africa: Identifying cost-effective deployment strategies through spatiotemporal modelling

South Africa hopes to expand wind and solar power. Success depends on how and where to deploy the technologies. This study develops a 10-year database of expected power generation for these technologies across South Africa. A power system model simulates the performance of different spatial deployment strategies in 2040. The results suggest that optimization of the location and quantities of the technologies could significantly reduce the cost of greenhouse gas abatement compared to conventional approaches. The data and techniques utilize open-source satellite data and software to minimize the cost of analysis, an approach that could be translated to other contexts

Is current irrigation sustainable in the United States? An integrated assessment of climate change impact on water resources and irrigated crop yields.

While climate change impacts on crop yields has been extensively studied, estimating the impact of water shortages on irrigated crop yields is challenging because the water resources management system is complex. To investigate this issue, we integrate a crop yield reduction module and a water resources model into the MIT Integrated Global System Modeling framework, an integrated assessment model linking a global economic model to an Earth system model. We assess the effects of climate and socioeconomic changes on water availability for irrigation in the U.S. as well as subsequent impacts on crop yields by 2050, while accounting for climate change projection uncertainty. We find that climate and socioeconomic changes will increase water shortages and strongly reduce irrigated yields for specific crops (i.e., cotton and forage), or in specific regions (i.e., the Southwest) where irrigation is not sustainable. Crop modeling studies that do not represent changes in irrigation availability can thus be misleading. Yet, since the most water-stressed basins represent a relatively small share of U.S. irrigated areas, the overall reduction in U.S. crop yields is small. The response of crop yields to climate change and water stress also suggests that some level of adaptation will be feasible, like relocating croplands to regions with sustainable irrigation or switching to less irrigation intensive crops. Finally, additional simulations show that greenhouse gas (GHG) mitigation can alleviate the effect of water stress on irrigated crop yields, enough to offset the reduced CO2 fertilization effect compared to an unconstrained GHG emission scenario

Characterizing wind power resource reliability in southern Africa

Producing electricity from wind is attractive because it provides a clean, low-maintenance power supply. However, wind resource is intermittent on various time scales, thus introducing variability in power output that is difficult for electric grid planning. In the following study, wind resource is characterized using metrics that highlight these intermittency issues, therefore identifying areas of high and low wind power reliability in southern Africa at different time scales. After developing a wind speed profile, these metrics are applied at various heights in order to assess the added benefit of raising the wind turbine hub. Furthermore, since the interconnection of wind farms can aid in reducing the overall intermittency, the value of interconnecting near-by sites is mapped using three distinct methods. Of the countries in this region, the Republic of South Africa has shown the most interest in wind power investment. For this reason, we focus parts of the study on wind resource in the country. The study finds that, although wind power density is high in South Africa compared to its neighboring countries, wind power resource tends to be less reliable than in other parts of southern Africa - namely, central Tanzania and parts of Kenya. We also find that South Africa's potential varies over different time scales, with higher potential in the summer than winter, and higher potential during the day than at night. This study is concluded by introducing a variety of methods and measures to characterize the value of interconnection, including the use of principal component analysis to single out areas with a common signal

Alcune considerazioni su polemica antiebraica e polemica anticlericale alla fine dell'Ottocento

Tra la polemica antiebraica e la polemica anticlericale che si sviluppano negli ultimi decenni dell'Ottocento, è possibile delineare un confronto che consente di contestualizzare meglio ciascuna di esse, evidenziando le analogie esistenti, ma anche gli specifici tratti distintivi. È questo un campo di ricerca ancora poco esplorato, soprattutto per quanto concerne l'Italia, e in questo breve saggio ci si limiterà ad abbozzare la questione, cogliendo qualche spunto dall'esperienza italiana e da quella francese, che alla fine del XIX secolo appaiono per molti versi largamente "comunicanti"

Optimized reservoir operation model of regional wind and hydro power integration. Case study: Zambezi Basin and South Africa

The present study develops a reliability assessment method of wind resource using optimum reservoir target power operations that maximizes the firm generation of integrated wind and hydro power. A combined water resources model for a system of reservoirs that implements a priority based linear programing algorithm and a single node power grid system model is implemented on an hourly time step. This model was then accompanied by a genetic algorithm solver to determine optimum operation targets for each storage reservoir aiming at maximizing the 90th percentile power generation produced by the integration of wind and hydro over the entire simulation period. This model is applied on the reservoir storages and hydro power system in the Zambezi River basin to demonstrate how storage reservoirs could be used to offset wind power intermittence in South Africa subjected to different physical and policy constraints. Based on the optimized target operation and hourly data for the year 2010, the water resources system and power interconnection system were simulated together to assess the maximum firm generation of power as a result of the new wind and hydro combination target for storage hydro power plants. The result obtained indicates that high regulation of wind and hydro can be achieved as a result of combined operation and showed an increased level of wind penetration in South Africa's power system over the reference scenario. The results also indicated a reduced level of coal power utilization and less cycling requirement. This will have a positive outcome in terms of contributing to South Africa's goal towards reducing greenhouse gas emissions and the efforts to build green energy supply and resilience to the impacts of climate change