By Gary Matteson
Marvin Goldman has once again been thinking outside the box in his commentary, published Feb. 27 in The Davis Enterprise. Professor Goldman proposes to address California’s water needs for future generations by pumping bay seawater south to a massive desalination plant.
Pumping water and running desalination plants require energy. The professor proposes that concentrated solar be the source, at least for the desalination part of the plan.
The problem with Goldman’s thesis is that there is only a defined amount of concentrated solar energy that can be produced in a technically feasible manner for California. In a recently published chapter titled “Energy Planning for Regional and National Needs: A Case Study — The California Forecast (2005-2050),” I have examined the energy needs of California and possible sources of energy to meet those needs.
In this analysis, I have determined the amount of energy that can be produced from concentrated solar power and I have defined the industrial, transportation and residential needs that will consume that energy. Running desalination plants at the size and scale envisioned by Goldman is not one of them. In fact, by 2050, the amount of the technically feasible renewable energy generation will not be enough to meet California’s energy needs.
In 2005, California consumed 6.7 quads of energy and I have forecasted that the amount required in 2050 is 11.7 quads (one quad equals 1,015 BTUs or 1,018 joules). In making this forecast, it was determined that concentrated solar power would require 5,900 square miles of land to meet the projected demands, demands that did not include desalination and pumps for transporting water to the south at the level envisioned by Goldman’s plan.
My estimate of solar power generation will meet only about 45 percent of the state’s energy needs in 2050 or 5.39 quads.
Given global warming and legislative initiatives from elected officials, the deployment of renewable energy is desirable, but certainly not the total solution to meeting California’s energy requirements in 2050. The population and its desire for additional energy consumption, on a per capita level, starts to push the energy consumption past the available sustainable-energy mix after 2050. While Californians of the 2050 era certainly would not want to return to the days of dependence on unsustainable-energy sources, the issue of falling back into that trap or conserving more (on a per capita basis) will be clearly before the state’s taxpayers.
Goldman’s commentary did not mention cost. Currently, there is little data on the cost for large-scale commercial desalinated water when the energy is provided from a concentrated solar system. What is known is that plants that desalinate seawater produce that water at a cost, on average, of 80 cents per cubic meter of water. The additional cost of pumping seawater 100 plus miles to south is not included in these cost data.
If we take the present water volume consumed in the city of Davis, which is just over 36,000 cubic meters per day, this works out to be about $29,000 per day to supply desalinized seawater (from a local plant that has received seawater from the bay area) to the 68,000 residents and business of the city. Again, the cost of pumping the seawater 40 miles to Davis is not included. The present average cost for water deliveries by the city is about $17,000 per day with significant seasonal variation in the volumes delivered.
The costs are important for two reasons. First, the citizens of California, in my energy forecast, are going to have come up with $1.9 trillion, in the 2005-to-2050 timeframe, to finance all of the capital investment for the technically feasible renewable energy production. Second, the addition of desalinization plants and seawater pumping could be well beyond the financial capability of the state.
Of course, there are plans to pump significant flows of fresh water to the south. If this pumping scheme were relocated to pump seawater, then the big tunnel project may not be necessary. I am reminded that desalinization plants are currently able to make only about 40 percent desalinated water out of seawater. The pumping requirement for seawater would be at least 2 1/2 times greater in volume to make up for this “pure water recovery factor.”
Finally, there is the problem of disposal of the waste water from the desalination plant. The present practice is to put this reverse osmosis concentrate back into the ocean. This would be an added pumping cost for a plant sited in the Central Valley of California.
— Gary Matteson, a Davis resident, is past associate director of utilities and energy services for the University of California Office of the President. Citations for this opinion piece are available at www.davisenterprise.com/?p=432655
The following sources were used in writing this response:
* W.W. Clark II (ed.), 2013, The Next Economics: Global Cases in Energy, Environment, and Climate Change, Chapter 5 Energy Planning for Regional and National Needs: A Case Study – The California Forecast (2005-2050), DO1 10.1007/978-1-4614-49720-_5, Springer Science+Business Media New York 2013.
* Saha and Bhattacharya, 2010, Membrane desalination: Methods, Costs and Technology, Irena A Urboniene, Editor, Desalination: Methods, Costs, and Technology, Chapter 5, pp:206, ISBN 978-1-61668-909-4.
* Eftihia Tzen, 2010, Renewable Energy Sources for Seawater Desalination- Present Status and Future Prospects, Irena A Urboniene, Editor, Desalination: Methods, Costs, and Technology, Chapter 10, pp:332-332, ISBN 978-1-61668-909-4.
* Paul Selsky, 2011, City of Davis Water Distribution System Optimization Plan, Brown and Caldwell, Chapter 3 Water Demands, CIP No 8217. May. 10540 White Rock Road Suite 180, Rancho Cordova, CA.
* Robert Beggs, 2013, Integrated Water Resource Study, presented to City of Davis Water Advisory Committee on July, 25, 2013, Brown and Caldwell. Website: http://city-council.cityofdavis.org/Media/Default/Documents/PDF/CityCouncil/Water-Advisory-Committee/Agendas/20130725/Item-5-Staff-Report-Integrated-Water-Resource-Study.pdf