Although recent studies have shown that electricity systems with shares of wind and solar above 80% can be affordable, economists have raised concerns about market integration. Correlated generation ...from variable renewable sources depresses market prices, which can cause wind and solar to cannibalise their own revenues and prevent them from covering their costs from the market. This cannibalisation appears to set limits on the integration of wind and solar, and thus to contradict studies that show that high shares are cost effective. Here we show from theory and with simulation examples how market incentives interact with prices, revenue and costs for renewable electricity systems. The decline in average revenue seen in some recent literature is due to an implicit policy assumption that technologies are forced into the system, whether it be with subsidies or quotas. This decline is mathematically guaranteed regardless of whether the subsidised technology is variable or not. If instead the driving policy is a carbon dioxide cap or tax, wind and solar shares can rise without cannibalising their own market revenue, even at penetrations of wind and solar above 80%. The strong dependence of market value on the policy regime means that market value needs to be used with caution as a measure of market integration. Declining market value is not necessarily a sign of integration problems, but rather a result of policy choices.
Display omitted
•Decreasing market value (MV) with wind and solar share can be avoided by CO2 pricing.•In long-term equilibria, wind and solar subsidies reduce MV, but CO2 prices do not.•Models with rising CO2 prices draw in wind and solar (VRE) with no reduction in MV.•Falling MV in models with VRE subsidy does not necessarily indicate integration problems.•These results are confirmed using theory and in a power system model.
There are two competing concepts in the literature for the integration of high shares of renewable energy: the coupling of electricity to other energy sectors, such as transport and heating, and the ...reinforcement of continent-wide transmission networks. In this paper both cross-sector and cross-border integration are considered in the model PyPSA-Eur-Sec-30, the first open, spatially-resolved, temporally-resolved and sector-coupled energy model of Europe. Using a simplified network with one node per country, the cost-optimal system is calculated for a 95% reduction in carbon dioxide emissions compared to 1990, incorporating electricity, transport and heat demand. Flexibility from battery electric vehicles (BEV), power-to-gas units (P2G) and long-term thermal energy storage (LTES) make a significant contribution to the smoothing of variability from wind and solar and to the reduction of total system costs. The cost-minimising integration of BEV pairs well with the daily variations of solar power, while P2G and LTES balance the synoptic and seasonal variations of demand and renewables. In all scenarios, an expansion of cross-border transmission reduces system costs, but the more tightly the energy sectors are coupled, the weaker the benefit of transmission reinforcement becomes.
•Cross-sector and cross-border integration of renewables in Europe are compared•The first open, spatially- and temporally-resolved energy model of Europe is presented•Flexibility from battery electric vehicles balances daily variations of solar power•Power-to-gas and thermal storage balance longer-term variations of demand and supply•High benefit of grid expansion becomes weaker with tighter sector coupling
To determine the effectiveness of school-based interventions that focus on changing dietary intake and physical activity levels to prevent childhood obesity. MEDLINE and EMBASE were searched (January ...2006 to September 2007) for controlled trials of school-based lifestyle interventions, minimum duration of 12 weeks, reporting weight outcome. Thirty-eight studies were included; 15 new studies and 23 studies included within the National Institute for Health and Clinical Excellence obesity guidance. One of three diet studies, five of 15 physical activity studies and nine of 20 combined diet and physical activity studies demonstrated significant and positive differences between intervention and control for body mass index. There is insufficient evidence to assess the effectiveness of dietary interventions or diet vs. physical activity interventions. School-based physical activity interventions may help children maintain a healthy weight but the results are inconsistent and short-term. Physical activity interventions may be more successful in younger children and in girls. Studies were heterogeneous, making it difficult to generalize about what interventions are effective. The findings are inconsistent, but overall suggest that combined diet and physical activity school-based interventions may help prevent children becoming overweight in the long term. Physical activity interventions, particularly in girls in primary schools, may help to prevent these children from becoming overweight in the short term.
Cost optimal scenarios derived from models of a highly renewable electricity system depend on the specific input data, cost assumptions and system constraints. Here this influence is studied using a ...techno-economic optimisation model for a networked system of 30 European countries, taking into account the capacity investment and operation of wind, solar, hydroelectricity, natural gas power generation, transmission, and different storage options. A considerable robustness of total system costs to the input weather data and to moderate changes in the cost assumptions is observed. Flat directions in the optimisation landscape around cost-optimal configurations often allow system planners to choose between different technology options without a significant increase in total costs, for instance by replacing onshore with offshore wind power capacity in case of public acceptance issues. Exploring a range of carbon dioxide emission limits shows that for scenarios with moderate transmission expansion, a reduction of around 57% compared to 1990 levels is already cost optimal. For stricter carbon dioxide limits, power generated from gas turbines is at first replaced by generation from increasing renewable capacities. Non-hydro storage capacities are only built for low-emission scenarios, in order to provide the necessary flexibility to meet peaks in the residual load.
•Influence of input data and assumptions for a highly-renewable scenario are studied.•System costs are robust to input weather data and moderate cost assumption changes.•Onshore wind can be replaced by offshore at low cost if there is enough national transmission.•As carbon dioxide limits are tightened, costs rise only slowly if there is grid capacity.•Storage is economic above 80% renewables; without storage 99.9% is possible, but costs double.
Epithelial organoids are stem cell–derived tissues that approximate aspects of real organs, and thus they have potential as powerful tools in basic and translational research. By definition, they ...self-organize, but the structures formed are often heterogeneous and irreproducible, which limits their use in the lab and clinic. We describe methodologies for spatially and temporally controlling organoid formation, thereby rendering a stochastic process more deterministic. Bioengineered stem cell microenvironments are used to specify the initial geometry of intestinal organoids, which in turn controls their patterning and crypt formation. We leveraged the reproducibility and predictability of the culture to identify the underlying mechanisms of epithelial patterning, which may contribute to reinforcing intestinal regionalization in vivo. By controlling organoid culture, we demonstrate how these structures can be used to answer questions not readily addressable with the standard, more variable, organoid models.
Prevalence estimates of osteopenia and osteoporosis (reduced bone mineral density; BMD) in HIV-infected patients and the role of antiretroviral therapy (ART) varies in the literature.
We conducted a ...meta-analytical review of cross-sectional studies published in English to determine the pooled odds ratios (OR) of reduced BMD and osteoporosis in the following groups: HIV-positive versus HIV-negative; ART-treated versus ART-naive; protease inhibitor (PI)-treated versus PI-untreated. We searched the MEDLINE, PubMed, and EMBASE databases for eligible references between January 1966 and November 2005. Random effects models were used to generate pooled OR estimates and confidence intervals.
Of 37 articles identified, 20 met the inclusion criteria. Of the 884 HIV-infected patients, 67% had reduced BMD, of whom 15% had osteoporosis, yielding a pooled OR of 6.4 and 3.7, respectively, compared with HIV-uninfected controls (n = 654) using 11 studies with available data. Compared with ART-naive patients (n = 202, 10 studies), ART-treated individuals (n = 824) had a 2.5-fold increased odds of prevalent reduced BMD. The risk of prevalent osteoporosis (seven studies) was similarly elevated in ART-treated individuals. Compared with non-PI-treated HIV patients (n = 410, 14 studies), PI-treated patients (n = 791) had increased odds of reduced BMD and osteoporosis (12 studies). Few studies adjusted for important covariates such as HIV disease severity or treatment duration.
The prevalence of osteoporosis in HIV-infected individuals is more than three times greater compared with HIV-uninfected controls. ART-exposed and PI-exposed individuals had a higher prevalence of reduced BMD and osteoporosis compared with their respective controls. The influence of other disease and treatment variables on these estimates could not be determined.
Culture-independent microbiome studies have increased our understanding of the complexity and metabolic potential of microbial communities. However, to understand the contribution of individual ...microbiome members to community functions, it is important to determine which bacteria are actively replicating. We developed an algorithm, iRep, that uses draft-quality genome sequences and single time-point metagenome sequencing to infer microbial population replication rates. The algorithm calculates an index of replication (iRep) based on the sequencing coverage trend that results from bi-directional genome replication from a single origin of replication. We apply this method to show that microbial replication rates increase after antibiotic administration in human infants. We also show that uncultivated, groundwater-associated, Candidate Phyla Radiation bacteria only rarely replicate quickly in subsurface communities undergoing substantial changes in geochemistry. Our method can be applied to any genome-resolved microbiome study to track organism responses to varying conditions, identify actively growing populations and measure replication rates for use in modeling studies.
Despite heightened awareness of the clinical significance of social phobia, information is still lacking about putative subtypes, functional impairment, and treatment-seeking. New epidemiologic data ...on these topics are presented from the National Comorbidity Survey Replication (NCS-R).
The NCS-R is a nationally representative household survey fielded in 2001-2003. The World Health Organization (WHO) Composite International Diagnostic Interview Version 3.0 (CIDI 3.0) was used to assess 14 performance and interactional fears and DSM-IV social phobia.
The estimated lifetime and 12-month prevalence of social phobia are 12.1% and 7.1% respectively. Performance and interactional fears load onto a single latent factor, and there is little evidence for distinct subtypes based either on the content or the number of fears. Social phobia is associated with significant psychiatric co-morbidity, role impairment, and treatment-seeking, all of which have a dose-response relationship with number of social fears. However, social phobia is the focus of clinical attention in only about half of cases where treatment is obtained. Among non-co-morbid cases, those with the most fears were least likely to receive social phobia treatment.
Social phobia is a common, under-treated disorder that leads to significant functional impairment. Increasing numbers of social fears are associated with increasingly severe manifestations of the disorder.
To reach ambitious European CO2 emission reduction targets, most scenarios of future European electricity systems rely on large shares of wind and solar photovoltaic power generation. We interpolate ...between two concepts for balancing the variability of these renewable sources: balancing at continental scales using the transmission grid and balancing locally with storage. This interpolation is done by systematically restricting transmission capacities from the optimum level to zero. We run techno-economic cost optimizations for the capacity investment and dispatch of wind, solar, hydroelectricity, natural gas power generation and transmission, as well as storage options such as pumped-hydro, battery, and hydrogen storage. The simulations assume a 95% CO2 emission reduction compared to 1990, and are run over a full historical year of weather and electricity demand for 30 European countries. In the cost-optimal system with high levels of transmission expansion, energy generation is dominated by wind (65%) and hydro (15%), with average system costs comparable to today's system. Restricting transmission shifts the balance in favour of solar and storage, driving up costs by a third. As the restriction is relaxed, 85% of the cost benefits of the optimal grid expansion can be captured already with only 44% of the transmission volume.
•Optimal transmission expansion allows highly renewable systems at current cost levels.•Restricting transmission expansion leads to a non-linear cost increase by up to 30%.•A relatively moderate amount of transmission already locks in most of the benefits.•Wind generation is mostly smoothed by transmission, solar PV by shortterm storage.
PDF
