Analysis of Water Consumption Associated with Hydroelectric Power Generation in the United States

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1 Analysis of Water Consumption Associated with Hydroelectric Power Generation in the United States Dave Lampert, Assistant Professor Civil & Environmental Engineering Oklahoma State University American Water Resources Association 2016 Annual Conference November 17, 2016

2 Acknowledgements CJ Mitchell, Oklahoma State University Hao Cai and Uisung Lee, Argonne National Laboratory

3 Sustainability in the face of Global Environmental Changes Coupled fluxes Energy, H 2 O, C, N, P, etc. Acceleration of Carbon and H 2 O cycles Irrigation Energy production Urbanization The Earth System Energy Water Ecology Food Atmosphere C, N, P, H2O, and Energy cycles Competition for Freshwater Resources Other Land Urban Development Agriculture Oceans/Seas

4 Quantifying Water Consumption for Energy In the face of competition, it is critical to assess the water demands for all sectors Water accounting is complex due to inconsistent system boundaries (withdrawal vs. consumption, rain-fed agriculture, etc.) and significance of local issues Need for standard definitions (blue water, green water, etc.) Brief overview of water for energy

5 What is Water Consumption? Water withdrawn from a resource and not returned at a similar level of quality Conversion of water from a useful form to a less useful form (analogous to energy consumption)

6 Water Consumption in Agriculture Irrigation Withdrawal Evapotranspiration (Water Consumption) System Boundary Irrigation Withdrawal Precipitation Farm Irrigation Runoff Precipitation Runoff Water Resource Precipitation Evapotranspiration Anthropogenic Flows Natural Flows Agriculture

7 Water Consumption for Petroleum Recovery and Mining Make-up water (water consumption) Petroleum Injection Well Disposal/discharge Production Well Recycled water Treatment (optional) Produced water Soil System Boundary Petroleum Reservoir

8 Water Consumption in Energy Conversion Processes Evaporation, blow down, and processing (water consumption) System Boundary Power plants, chemical manufacturing facilities, refineries, biofuel conversion facilities Withdrawal Return flow Water resource

9 Water Consumption in Thermal Power Plants energy conversion process useful energy energy conversion process useful energy waste energy waste cool water warm water warm water energy waste cool water energ Cooling Water y tower make-up a Resource Water Resource Once-through cooling Cooling Tower a Sensible heat Latent heat Sensible heat Latent heat Waste heat from energy conversion dissipated by evaporation (latent heat) and temperature differences (sensible heat); three primary cooling technologies energy conversion process useful energy waste cooling water Energy energy Conversion Process Dry Cooling closed loop conductor Sensible heat

10 Water Consumption for Hydropower Reservoir construction is needed to match supply and demand, but the storage increases evaporation and decreases water availability downstream

11 Does Hydropower Demand Increase Storage? Needed for water supply Built for hydropower? Increasing the dam height increases the hydropower production, but at the cost of excess evaporation. Have we built excess storage for electricity at the expense of water?

12 Comparison of Electric Power Generation Life Cycle Water Consumption Water Consumption in gal per kwh Hydropower reservoir Evaporation dominates Thermoelectric Pathways Similar Driven by energy efficiency and cooling technologies Fuel cycle relatively small Geothermal varies by technology

13 Regional Electricity Mixes Water Consumption in gal per kwh Hydropower dominates Regional mixes vary by order of magnitude FL, TX have limited hydro/water consumption

14 Approaches for Allocating Water Consumption for Hydropower No allocation Primary purpose Economic valuation Withdrawals Comparison of reservoir volume that would be needed with and without hydropower demands

15 Hydropower Allocation 1. Estimated gross reservoir evaporation 2. Subtracted background land surface evapotranspiration 3. Grouped generation facilities 1. no reservoir 2. multipurpose reservoir 3. dedicated reservoir 4. Allocated 55% of the multipurpose reservoir burden to electricity (Pasqualetti and Kelly, 2008) 5. US Average: gal/kwh ( gal per kwh depending on allocation

16 County-level analysis of Hydropower Storage

17 Approach Compile PRISM Climate Normals from a grid to the county level Estimate water surface evaporation and background evapotranspiration in each county from climate data Compile total storage, total surface area and total hydropower production in each county Develop a predictive model for surface area as a function of water withdrawals, precipitation, and hydropower using machine learning algorithms Use models to forecast county-level surface area with and without hydropower

18 Evapotranspiration by county (in/year) from correlation with annual mean daily temperature, annual mean min and max temperature, and annual precipitation Stanford and Selnick, Estimation of Evapotranspiration Across the Conterminous United States Using a Regression With Climate and Land Cover Data, JAWRA, 2013

19 County-level evaporation (in/yr) from a simplified version of the penman equation from elevation, mean temperature, latitude, and mean dew-point. Linacre, E.T. A simple formula for estimating evaporation rates in various climates, using temperature data alone, Agricultural Meteorology, 1977

20 Water consumption intensity and hydropower facilities

21 The Southwest dominates (in particular Lake Mead) The reservoirs are essential for multiple purposes So the question becomes: how much storage is for hydropower?

22 Water Withdrawals and Hydropower Locations County-level withdrawals from 2010 USGS Water Census hypothesized to act as a predictor for storage

23 County-level water storage (acre-feet) calculated from National Inventory of Dams

24 Machine Learning Algorithm Machine learning algorithms were used to develop a relationship between water storage and surface area as functions of surface water withdrawals and hydropower Python programming including the Python Data Analysis Software (Pandas) and Scikit-learn modules A random forest algorithm was used 80% of the data were used to train the model and 20% were used to test it Water Storage as function of withdrawals and hydropower produced an R 2 =.52 (explains majority of variability even if not great)

25 Preliminary Results The model was then used to predict storage with and without hydropower for each county, with the difference in water consumption allocated to hydropower Total storage loss with excess hydropower: 295 million acre-ft to produce 78 MW of electricity 14 gallons per kwh on average in the US

26 Potential Significance Lake Mead (Hoover Dam) ~2 Million acre-ft of evaporation per yr ~1 MW capacity ~73 gallons per kwh Desalination ~$0.005 per gallon Power generation ~$0.10 per kwh 73 gallons of water is ~$0.36 versus $0.10 for the electricity Is this a wise trade-off- of water for energy?

27 Conclusions and Future Ideas Hydropower is the most water consumption intensive way to produce electricity The creation of excess storage in a constrained system decreases total water supplies Early planning centered around power generation and created excess storage and evaporative water consumption Differentiating storage for purposes is challenging Need to incorporate additional explanatory variables for recreation and other benefits Analysis of variance in the model The value of the water should be compared with the electricity production regionally