- Published on March 30, 2016
Head of Department at Deltares Software Centre
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Reservoirs are evaporating tremendous amounts of water to the atmosphere. The hydrological cycle of the earth is altered significantly by increased evaporation, due to man-made reservoirs and irrigation schemes.
UNEP estimates that the evaporation from reservoirs surpasses domestic and industrial water consumption.
Mighty rivers, tamed by dams
Worldwide, the number of reservoirs is still growing. Reservoirs are constructed for multiple purposes: (1) to attenuate high discharges in rivers, (2) to generate electricity from hydro-power, and (3) to save water for agriculture, industry and households. Mighty rivers, such as the Nile and the Yangtze, have been tamed by large dams.
Satellite images tell the story
Satellite images reveal the ongoing construction of reservoirs. The shape of the reservoirs reminds of the former river valleys that were turned into expanded and deep lakes.
A trend analysis at the
Google Earth Engine platform with images from Landsat missions, measured during 2000 to 2015, shows that new reservoirs were constructed in South-East Asia. On the other hand, the reservoirs in the South-West of the United States were shrinking, due to drought.
New reservoirs in Myanmar. The bright blue colour indicates the increase in water acreage. On the basis of Google Earth Engine, 2000-2015.
Shrinking reservoir near Las Vegas, United States. The bright green colour indicates the decrease in water acreage. On the basis of Google Earth Engine, 2000-2015.
Floating solar power plants
Recently, a new function of lakes and reservoirs was discovered by the solar industry: surface waters can host floating solar power plants. Space is often scarce near urban areas, and landscape regulations can be strict. By building on water, a crowded city can still expand.
In Great-Britain, a 6.3 MW floating solar power plant was constructed on the Queen Elisabeth II reservoir near London. The plant provides 6,800 households with sustainable energy.
In Japan, a 13.7 MW floating solar power plant is constructed on a reservoir in the
Chiba prefecture. The plant will provide 5,000 households with sustainable energy, when finished in 2018.
Also
India is planning a 50 MW floating solar power plant near Kerala, following the construction of several floating power plants on canals.
How to reduce evaporation
Reservoirs are losing large quantities of water to the atmosphere. The evaporation rate depends on solar radiation, temperature and wind speed. A recent
study by
Stockholm University showed that evaporation from irrigation schemes has increased and raised the human
water footprint.
Evaporation can be reduced by covering the surface of the reservoir. For instance in California, the reservoirs of Los Angeles were covered by millions of plastic balls to reduce evaporation and to protect water quality from excessive algae growth.
Floating solar panels
A floating solar power plant will also reduce the evaporation, because the panels cover the water surface. Water conservation and energy production will go hand in hand: a winning combination.
Floating solar power plants are a challenge for engineers, because water levels in reservoirs are fluctuating, and electricity must be transported to the shore via power lines. The electricity infrastructure of the hydro-power plant in the dam is already there.
Smart reservoir operation adapts the production of hydro-power to variations in the production of solar electricity and energy demand during the day.
Environmental considerations
Covering the surface of a reservoir has consequences for the quality and ecology of the water. A positive side effect is that algae growth decreases when the sunlight is blocked. As the solar panels intercept the incoming radiation, this energy is no longer available to warm the water of the reservoir. A point of attention is the transfer of oxygen from the atmosphere to the water. Oxygen is necessary for the natural decay of organic matter and pollutants.
The impact of floating solar power plants on the chemistry and ecology of water systems can be investigated with
simulation models. Also
underwater drones can be used to monitor the ecosystem below floating constructions.
Conclusion
Reservoirs play multiple roles in the water management of river catchments. Evaporation of water from the reservoir can cause a significant water loss. By covering reservoirs with floating solar panels, two benefits are combined: the sustainable production of electricity and water conservation.
