The quantity-quality transition in the value of expanding wind and solar power generation.

Wind and solar photovoltaic generators are projected to play important roles in achieving a net-zero-carbon electricity system that meets current and future energy needs. Here, we show potential advantages of long-term site planning of wind and solar power plants in deeply decarbonized electricity systems using a macro-scale energy model. With weak carbon emission constraints and substantial amounts of flexible electricity sources on the grid (e.g., dispatchable power), relatively high value is placed on sites with high capacity factors because the added wind or solar capacity can efficiently substitute for running natural gas power plants. With strict carbon emission constraints, relatively high value is placed on sites with high correlation with residual demand because resource complementarity can efficiently compensate for lower system flexibility. Our results suggest that decisions regarding long-term wind and solar farm siting may benefit from consideration of the spatial and temporal evolution of mismatches in electricity demand and generation capacity.

Spatial constraints in large-scale expansion of wind power plants.

When wind turbines are arranged in clusters, their performance is mutually affected, and their energy generation is reduced relative to what it would be if they were widely separated. Land-area power densities of small wind farms can exceed 10 W/m2, and wakes are several rotor diameters in length. In contrast, large-scale wind farms have an upper-limit power density in the order of 1 W/m2 and wakes that can extend several tens of kilometers. Here, we address two important questions: 1) How large can a wind farm be before its generation reaches energy replenishment limits and 2) How far apart must large wind farms be spaced to avoid inter-wind-farm interference? We characterize controls on these spatial and temporal scales by running a set of idealized atmospheric simulations using the Weather and Research Forecasting model. Power generation and wind speed within and over the wind farm show that a timescale inversely proportional to the Coriolis parameter governs such transition, and the corresponding length scale is obtained by multiplying the timescale by the geostrophic wind speed. A geostrophic wind of 8 m/s and a Coriolis parameter of 1.05 × 10-4 rad/s (latitude of ∼46°) would give a transitional scale of about 30 km. Wind farms smaller than this result in greater power densities and shorter wakes. Larger wind farms result instead in power densities that asymptotically reach their minimum and wakes that reach their maximum extent.

The diagnosis of heart failure in the community. Comparative validation of four sets of criteria in unselected older adults: the ICARe Dicomano Study.

OBJECTIVES: We sought to compare construct and predictive validity of four sets of heart failure (HF) diagnostic criteria in an epidemiologic setting. BACKGROUND: The prevalence estimates of HF vary broadly depending on the diagnostic criteria. METHODS: Data were collected in a survey of community dwellers who were > or =65 years of age living in Dicomano, Italy. At baseline, HF was diagnosed with the criteria of the Framingham, Boston, and Gothenburg studies and of the European Society of Cardiology (ESC). Left ventricular mass index and ejection fraction, left atrium systolic dimension, lower extremity mobility disability, summary physical performance score, and 6-min walk test were compared between HF and non-HF participants to test for construct validity of each set of criteria. Predictive validity was evaluated with follow-up assessment of cardiovascular mortality, incident disability, and HF-related hospitalizations. Comparisons were adjusted for demographics, comorbidity, and psychoaffective status. RESULTS: Of 553 participants, 11.9%, 10.7%, 20.8%, and 9.0% had HF, according to Framingham, Boston, Gothenburg, and ESC criteria, respectively. In terms of construct validity, Framingham and Boston criteria discriminated HF from non-HF participants better than Gothenburg and ESC criteria across the measures of cardiac function and global performance. The Boston criteria showed a superior predictive validity because they indicated a significantly greater adjusted risk of cardiovascular death (hazard ratio3.9, 95% confidence interval 1.2 to 13.2), incident disability, and hospitalizations in participants with HF. CONCLUSIONS: The Boston criteria are preferable to Framingham, Gothenburg, and ESC criteria for the diagnosis of HF in older community dwellers because they have good construct validity and more accurately predict cardiovascular death, incident disability, and hospitalizations.

Sex-related differences in the length of disability prior to death in older persons.

BACKGROUND AND AIMS: It is acknowledged that, in spite of their generally worse health, women live longer than men. However, whether women also enjoy longer disability-free lives is still unclear. Using data from a representative, Italian cohort followed for 6 years, this study aimed at estimating differences between men and women in the age of disability onset and in total survival. METHODS: In 1989, 651 persons aged > or = 65 years were interviewed and their medical status was assessed by a geriatrician. In 1995, the time of onset of disability was reconstructed by re-interviewing 392 survivors and collecting proxy information for 201 subjects who had died. No information was available for 58 subjects who refused to be re-interviewed or were lost to follow-up. Data on changes in functional status were also collected by proxy interview for 34 additional persons who had died during the follow-up period, although they had not been originally interviewed at baseline. RESULTS: Of the 235 deaths, 113 were men and 122 were women. On average, the age at death was 3.5 years higher among women than among men. However, the age at onset of disability was similar in the two sexes. In survival analysis in which age was the time variable, women were as likely as men to develop disability, but significantly less likely to die over the follow-up period. CONCLUSIONS: Compared with men, women experience longer disability before death. This may be due to sex-related differences in the lifetime prevalence of lethal vs. disabling diseases.