About 50% of the solar energy absorbed at the Earth’s surface is used to drive evaporation, a powerful form of energy dissipation due to water’s large latent heat of vaporization. Evaporation powers the water cycle that affects global water resources and climate. Critically, the evaporation driven water cycle impacts various renewable energy resources, such as wind and hydropower. While recent advances in water responsive materials and devices demonstrate the possibility of converting energy from evaporation into work, we have little understanding to-date about the potential of directly harvesting energy from evaporation. Here, we develop a theory of the energy available from natural evaporation to predict the potential of this ubiquitous resource. We use meteorological data from locations across the USA to estimate the power available from natural evaporation, its intermittency on varying timescales, and the changes in evaporation rates imposed by the energy conversion process. We find that harvesting energy from natural evaporation could provide power densities up to 10 W m-2 (triple that of present US wind power) along with evaporative losses reduced by 50%. When restricted to existing lakes and reservoirs larger than 0.1 km2 in the contiguous United States (excluding the Great Lakes), we estimate the total power available to be 325 GW. Strikingly, we also find that the large heat capacity of water bodies is sufficient to control power output by storing excess energy when demand is low. Taken together, our results show how this energy resource could provide nearly continuous renewable energy at power densities comparable to current wind and solar technologies – while saving water by cutting evaporative losses. Consequently, this work provides added motivation for exploring materials and devices that harness energy from evaporation.

Made available in DSpace on 2017-07-10T17:37:37Z (GMT). No. of bitstreams: 1 Jose_Carlos_Santana.pdf: 1639183 bytes, checksum: 140fa728ba20e8e4fff9a83d0aa21ea5 (MD5) Previous issue date: 2009-08-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The reflective screen is an option to promote the shading, to reduce the air temperature in greenhouse, and to allow a better growth and developments of the plants. This way, the present work had as objective evaluates the effect of the air temperature, evaporation and the air s evaporative power on the acting of four cultivate of curly lettuce (Itapuã, Paola, Vera and Veronica) under greenhouse with and without reflective screen, in the conditions of summer at west of Paraná. The experiment was carried at Assis Chateaubriand/PR, in a private property in a greenhouse with organic cultivation system. The greenhouse had the following dimensions 4.5m height, 3m pier, 60m length, and 5m wide. The greenhouse was divided into two equal parts, forming two atmospheres with 30m length each. One of the rooms was covered with polyethylene with low density, 100 micras of denseness and the other room, under this covering, it was installed to the height of the foot-righ, the reflective screen 50%. Inside each room three small evaporimeter were established to 0.4m height, and a meteorological protection at 1.5m height, containing Piche evaporimeter, maximum and minimum thermometer and Dattalogger. In order to evaluate the productive characteristics of the cultivate, treatments distributions followed the randomized design (DCA), with 6 replications. The evaluations were done at 0, 7, 14, 21 and 28 days after the transplantation (DAT). The, minimum, medium and maximum air temperatures observed in the room without term reflective screen were respectively 16,3; 25,1 and 38,4 °C; and 16,7; 24,6 and 36,2 °C in the room with reflective screen. The reflective screen reduced significantly the air temperature and it was influenced by the weather conditions, mainly on cloudy or rainy days. The amount of evaporated water in the atmosphere without reflective screen was 26% upper than the other one. The air s evaporative power was 4,16mm in the atmosphere without reflective screen and 3,82mm in the atmosphere with it. However it was not observed a significant statistical difference between those numbers. The cultivates of Itapuã, Vera and Verônica lettuce demonstrated better results in productivity in relation to Paola in both evaluated atmosphere. However, when it compares the atmospheres, the one without reflective screen presented productivity of 14.97 t ha against 12.61 t ha to the atmosphere with reflective screen / A tela termorrefletora é uma opção para promover o sombreamento e reduzir a temperatura do ar em ambiente protegido, e permitir um melhor crescimento e desenvolvimentos das plantas. Neste sentido, o presente trabalho teve como objetivo avaliar o efeito da temperatura do ar, evaporação e poder evaporativo do ar sobre o desempenho de quatro cultivares de alface crespa (Itapuã, Paola, Vera e Verônica) sob ambiente protegido com e sem a utilização de tela termorrefletora, nas condições de verão da região oeste do Paraná. O experimento foi instalado no município de Assis Chateaubriand, PR, em propriedade particular em ambiente protegido com sistema de cultivo orgânico. O ambiente protegido cujas dimensões eram 4,5 m de altura, 3 m de pé-direito, 60 m de comprimento e 5 m de largura. Foi dividido em duas partes iguais, formando dois ambientes com 30 m de comprimento. Um ambiente coberto de polietileno de baixa densidade, 100 micras de espessura, e o outro, abaixo da referida cobertura, foi instalado à altura do pé-direito, a tela termorrefletora 50%. No interior de cada ambiente foram instalados três tanques de evaporação a 0,4 m de altura e abrigo meteorológico à 1,5 m de altura, contendo evaporímetro de Piche, termômetro de máxima e mínima, e Dattalogger. Para avaliar as características produtivas das cultivares, utilizou utilizou-se o delineamento em blocos casualizados (DBC), com 6 repetições. As avaliações foram realizadas aos 0 7 14 21 e 28 dias após transplante (DAT). As temperaturas do ar mínima, média e máxima observadas foram de 16,3; 25,1 e 38,4 ºC; para ambiente sem tela termorrefletora e de 16,7; 24,6 e 36,2 ºC para ambiente com tela termorrefletora, respectivamente. A tela termorrefletora reduziu significativamente a temperatura do ar e foi influenciada pelas condições do tempo, principalmente dias nublados ou chuvosos. A lâmina de água evaporada no ambiente sem tela termorrefletora foi 26% superior ao outro ambiente. O poder evaporativo do ar foi de 4,16 mm em ambiente sem tela termorrefletora e de 3,82 mm no ambiente com tela. Contudo não se observou diferença estatística significativa entre estes valores. As cultivares de alface Itapuã, Vera e Verônica demonstraram resultados superiores de produtividade em relação a cultivar Paola nos dois ambientes avaliados. Porém, quando compara os ambientes, aquele sem tela termorrefletora apresentou produtividade de 14,97 t ha-1 contra 12,61 t ha-1 do ambiente com tela termorrefletora