For the first time, Lawrence Livermore National Laboratory (LLNL) has published state-by-state energy and water Sankey diagrams in one location so that analysts and policymakers can find all the information they need in one place. These diagrams depict energy use and water flow during the year 2010, the latest year for which comprehensive data is available.
LLNL worked with the US Department of Energy (DOE) and the National Energy Technology Laboratory (NETL) to produce the atlas of hybrid energy/water Sankey diagrams for each of the states, such as the California estimated energy and water flow chart for 2010 (below).
Sankey diagrams can be used to frame important discussions around energy and material resources, use and disposition. These new diagrams provide federal, state and local planners, governmental agencies, educators and nongovernmental organizations with detailed information to support decision-making about public investment in innovation and energy-water policy.
General location of energy and water categories. Energy and water generally “flows” from left to right. Some water resources also flow up to energy resources (petroleum, biomass, natural gas, and coal). LLNL.
Policy intended to advance the security, affordability and sustainability of energy and water can occur at the federal, regional, state and local level. States often are responsible for instituting responsive and impactful energy and water policy. Much of the data necessary to visualize energy and water flows, and thus to inform policymakers, are collected at the state level.
There are a number of major interactions between energy and water supplies, infrastructures and disposition across the economy. The major uses of water in energy applications include:
Thermoelectric Cooling: Water is used as a heat sink for energy rejected during the process of turning thermal fuels (eg. coal, natural gas, geothermal and nuclear) into electricity. Most power plant cooling systems can be classified as either once-through or recirculating. In most once-through systems, water is withdrawn from a body of surface water. The temperature of the water is elevated by 5 - 15K, usually via heat transfer in the power plant’s condenser, before the water is discharged back to the surface. In contrast, most recirculating systems depend on the large latent heat of vaporization of water to dissipate the energy load. In these systems, far smaller quantities of water are withdrawn from surface and/or groundwater sources, but a much larger share of the withdrawn water is consumed via evaporation in cooling towers.
Hydropower: The gravitational potential energy of water which fell as precipitation on elevated land is converted to electricity in hydroelectric turbines. Water withdrawal is not estimated for this application because impoundment of water and subsequent release downstream of dams and turbines is not consistently considered a “withdrawal”.
Oil and Natural Gas Extraction: Oil and natural gas operations can both produce and consume water. When oil and natural gas are extracted from the subsurface, water is often extracted along with them. This produced water may contain organic compounds and salts which can potentially be treated before being discharged into subsurface water. Produced water must be treated and/or re-injected into the subsurface. Water is also injected into some oil and natural gas wells, either for secondary flooding and enhanced recovery or at high pressure for hydraulic fracturing.
Coal Production: Water is used extensively in the mining industry, and in the case of coal mining (extraction of an energy resource), water is used for washing and dust control in ongoing operations. Water used in coal mining may be consumed or discharged to surface water supplies. Coal-associated water can also seep out of the mine and must be pumped, treated and injected or discharged. Disposal of coal-mining wastewater through subsurface injection is not included in this analysis.
Biomass Production: In regions of the country where there is inadequate rainfall during the growing season, irrigation is used to support the growth of biomass feedstocks (chiefly corn) for biofuels production. This upstream use of water to produce an energy feedstock can be the dominant water input into some biofuel production pathways.
Fuel Refining: Water is an input into the industrial processes that produce both petroleum-based fuels and biofuels. Gasoline, diesel and kerosene (jet fuel) are produced in oil refineries, which withdraw and consume water as a process input and for cooling purposes. Similarly, ethanol is produced in dry mills, which also use water as a process input and as a cooling medium.
The major uses of energy in water management include:
Water Treatment and Distribution: Withdrawal and treatment of water for potable use by municipal water suppliers requires energy input. Many water treatment processes are pressure (or gravity) driven (i.e. water flowing through filter beds or impurities settling out of water), so most of the energy consumed in water treatment is in the form of electricity used to drive pumps. Similarly, the energy used to withdraw water from surface and subsurface sources, and the energy used to by distribution systems, is consumed in pumping.
Wastewater Treatment: The major energy-consuming processes used to remediate municipal wastewater (sewage) for release back into the environment are also primarily pressure- or gravity- driven. These processes include aeration, sedimentation, decanting and dewatering. The wastewater treatment industry is also a major consumer of electricity. Processes such as anaerobic digestion can recover some of the energy in the organic component of sewage as methane which can be burned for heat, exported to for sale or converted to electricity for internal use or grid export. This analysis considers only the net consumption of electricity in wastewater treatment.
Agricultural Water Supply: Because waters for irrigation, livestock and aquaculture do not require the same level of treatment as potable water, the energy intensity of agricultural water use (per unit water) is lower than that of municipal water supply. Nonetheless, pumping for withdrawal and pressurization of water in the agriculture sector (the largest sector in terms of water consumption) requires significant quantities of electricity.
Conveyance: In some regions, particularly in the arid Western United States, water is conveyed over long distances from surface supplies to agricultural, industrial and municipal users. The energy required to drive the pumps that power these conveyance systems is almost exclusively electric. In this analysis, conveyance energy is apportioned to the end user (largely municipal and agricultural users) and lumped in with the energy of withdrawal and treatment.
The analysis includes a combination of diverse sources of background data and builds upon the methodology used by DOE to create a national energy/water diagram.
The methodology and assumptions used to create these charts is described in an accompanying report, and the data depicted in the charts is publicly available for download. The diagrams, data and report are a toolbox for technologists, policymakers and educators to explore the structure of energy-water systems at the state level.