By ASHLEY E. ORGAN, Assistant Editor On Dec. 1, 2010, Ken Salazar announced that the Obama administration has officially banned drilling in the eastern Gulf of Mexico for at least seven years. Energy Secretary Steven Chu appeared on CNBC on Dec. 2, providing his approval of the ban and stressing the need to viable alternative energy sources. Although renewable energy sources appear to be simple solutions, “Nine Challenges of Alternative Energy,” an essay by David Fridley, staff scientist at the Lawrence Berkeley National Laboratory, as part of the Post Carbon Reader series, addresses the challenges that could influence the development of alternative energy. In my blogs, Is alternative energy that easy? (on Oct. 6) and Alternative energy presents additional challenges (on Oct. 26), I provided Fridley’s first six issues. Here are the final three: 7. Water A number of alternative energy sources, especially biomass-based energy, are large water consumers critically dependent on a secure water supply, Fridley said. Key ethanol and biodiesel feedstocks can require hundreds or many thousand times more “full-cycle” water than the supply required for gasoline refining. Dry climates could limit the amount of water available for development of alternative energy. According to Fridley, approximately 2.5 gallons of water are required to produce one gallon of gasoline. In the processing stage alone, biomass and unconventional fossil-fuel energy require greater water usage: • Coal-to-liquids production consumes 8 to 11 gallons of water per gallon of output; • Corn ethanol requires 4 to 6 gallons; and • Cellulosic ethanol requires 11 gallons. 8. The Law of Receding Horizons Due to price linkages in the energy and biomass markets, rising oil prices tend to push up the price of natural gas and coal. For processes that are heavily dependent on these fuels, higher oil prices bring higher production costs. For example, the corn ethanol industry has two major input costs: the processing of fuel (usually natural gas) and the corn feedstock. Rising oil prices after 2004 pushed the natural gas price up, increasing the processing energy costs for ethanol, Fridley said. The “law of receding horizons” reflects a general orientation toward financial and economic accounting to gauge project viability and prospects. 9. Energy Return on Investment According to Fridley, consuming energy to produce energy is unavoidable. The concept of energy return on investment (EROI) can be very high (e.g., 100 units of energy produced for every 1 unit used to produce it) or low (only 0.8 unit of energy produced for every 1 unit used in production). The challenge in transitioning to alternative energy, Fridley said, is whether energy surpluses can be sustained and whether the current type of social and economic specialization can be maintained. Biofuels, for example, produce very little or no energy surplus due to its low EROI values. Conversely, wind energy has a high EROI, but is subject to problems of intermittency and citing issues. It is important to look beyond simple financial payback from alternative energy sources, Fridley said.