Contribution to frequency control through wind turbine inertial energy storage

An innovative way for wind energy to participate in some sort of frequency control using kinetic energy stored in the rotor for a fast power reserve that could be delivered in a short period (from several seconds up to a few tens of seconds) is presented. This kinetic-energy-based fast reserve is ensured despite wind speed variations - a disoptimisation of the power coefficient through the modification of the rotor speed set point or through the pitch control. In case of a frequency drop, the power coefficient could then be increased to produce more energy. This approach could help to reduce the dynamics and the depth of the frequency drops and therefore allow wind farms to participate in frequency control. Basic economic aspects of the provision of fast power reserve by wind turbines as a function of the amount of reserve considered are also discussed.     

Caring for pregnant teens and their mothers, too

STUDY OBJECTIVE: To describe the sexual behavior and contraception use among a sample of high school and vocational school adolescents in Barcelona, Spain. DESIGN: Cross-sectional study. METHODS: A random sample of 3139 students, aged 14 to 19 years, living in the city of Barcelona, were surveyed by means of an anonymous, self-administered questionnaire. SPSS/PC+ was used for statistical analysis. Significance criterion was set at 0.01. MAIN RESULTS: 13% of the students had previously participated in sexual intercourse; percentages between the sexes was equal. Frequency increased with age. Boys had their first experience at a significantly earlier age, but girls participated in sexual intercourse more often. The majority of adolescents used condoms as their primary contraceptive method; seven (3.3%) of the sexually active girls had been pregnant, and two (1%) boys had caused their partners to become pregnant. CONCLUSIONS: The rate of sexual activity among adolescents in Barcelona is low compared with those in both European and American studies. However, a higher rate of condom use is observed.