Water: A limited resource
Every day, Duke Energy relies on a significant amount of water to generate reliable electricity. We harness the power of flowing water through our 48 conventional hydroelectric power plants and two pumped-storage hydroelectric facilities. Water is heated into steam to turn turbines in our fossil-fueled and nuclear plants, and is then cooled so we can recycle and use it again. We also use water in equipment that controls air emissions at our power plants.
When talking about water used for energy production, it’s important to differentiate between water withdrawn and water consumed.
Water withdrawn is the total volume brought into the plant from a water source, such as a lake or river. Often a large portion of this water is returned to the source and available to be used again. Water consumed is the amount of water removed for use and not returned to its source.
Where does the water go?
Cooling accounts for most of our water consumption. All electric plants that use steam turbines, including coal, natural gas, oil and nuclear, require cooling to condense the steam when it exits the turbine.
The type and design of power plants affect the volume of water withdrawn and consumed. Two primary types of water-based cooling systems are used in electric power plants:
- Closed-loop systems recirculate cooling water and remove excess heat through a cooling tower or pond. Although closed-loop systems withdraw less water than once-through systems, they consume 30 to 40 percent more, through higher evaporation rates.
- Once-through cooling systems withdraw large quantities of water, but return most of it to the source. The primary concern with this design is potential harm to aquatic life near the plant, from the mechanisms used to withdraw the water and the higher temperature of the water returned.
Due to environmental concerns linked to once-through cooling, regulations for new steam-generation power plants require closed-loop systems. This in turn has greatly reduced water withdrawals at our newer power plants, but increases our consumption. We continuously look for ways to more effectively use our water resources.
Unlike issues such as climate change that require global solutions, water use must be addressed regionally and locally. Duke Energy continues to work with government, community and private sector partners to help manage this critical resource.
Protecting and conserving
- Duke Energy and its subsidiaries, including Duke Energy Progress and Duke Energy Florida, have joined a dozen other companies and the Electric Power Research Institute in supporting the new Water Research Center at Georgia Power’s Plant Bowen in Cartersville, Ga. The center is testing a thermal siphon cooler that could significantly reduce the water needed for power-plant cooling towers.
- We are partnering with the City of Crystal River, Fla., and the Southwest Florida Water Management District to build a system to receive reclaimed water from the city’s wastewater treatment plant. This will help reduce the use of groundwater by our Crystal River Energy Complex.
- We are the first company in Florida to build and operate more than 2,000 megawatts of generation using primarily alternative water supplies. The Hines Energy Complex uses treated domestic wastewater from the City of Bartow, Fla., as makeup supply to the plant’s cooling pond. A water-cropping system across the 8,000-acre plant site captures, stores and manages stormwater for additional supply. The plant is also developing the ability to reuse treated industrial wastewater from nearby industries.
- The University of Florida Water Institute was created through a partnership with Progress Energy to develop sound, science-based solutions to global water problems. The institute hosted its third symposium in February 2012, bringing together more than 450 experts to discuss challenges to sustainable water resources in Florida and beyond.
- Jocassee and Bad Creek are pumped-storage hydroelectric stations that use the same water over and over again, for more efficient use of water resources. Each plant uses two reservoirs to generate electricity. Water stored in the upper reservoir is released to spin turbines at the base of the dam to generate electricity. The water then flows into the lower reservoir. During off-peak hours, power is used to reverse the turbines and pump water from the lower reservoir to the upper reservoir for storage until later use.
- The Drought Management Advisory Group — comprising Duke Energy, other large water users and several state environmental, geological and natural resource agencies — spearheads efforts to reduce water consumption during periods of drought in the Catawba-Wateree River system.
- We also continue to collaborate with the Catawba-Wateree Water Management Group, a first-of-its-kind nonprofit corporation formed by Duke Energy and 18 public water system owners along the Catawba River. Members are working on a variety of projects as part of the group’s strategic plan to address long-term supply and demand issues. For example, a “smart” irrigation pilot program explored the use of new technology to better manage lawn watering systems of customers who live on company-operated reservoirs. The group is also developing a Water Supply Master Plan to identify collaborative actions the group will take to ensure the region’s water supply can meet its needs for at least the next 50 years.
- Duke Energy Brazil is partnering with São Paulo’s Agricultural State Institute to recover water springs on small farms near the reservoir of our Chavantes hydroelectric plant. Making this water available to the farmers for irrigation conserves water in the reservoir, and helps protect local ecosystems and water quality.