Water is indeed everywhere but I wonder if we haven’t reached the limits of the impact water will have on the electric power fuel mix of the United States. The Energy Information Administration estimates that conventional hydro has a 6.6% share of power generation in the U.S.
While many consider conventional hydro to be environmentally friendly there are significant environmental impacts when dams are built and water flow is interrupted. In the case of pumped storage hydro electricity is used to pump water uphill at night so air emissions are incurred when those facilities are powering up. As a result meaningful large hydro projects are hard to come by right now. The focus has shifted to uprates of existing hydro facilities and the development of smaller, non-conventional hydro projects.
The FERC recently announced a special section of their website for small/low impact hydropower as a portal to assist with licensing of, projects that involve little change to water flow and use and are unlikely to affect threatened and endangered species. This past week the Department of Energy announced new funding for marine and hydrokinetic energy.
The DOE says that, The nations ocean waves, tides, currents, thermal gradients, and free-flowing rivers represent a promising energy source located close to centers of electricity demand. What they’re talking about are very small generators that are able to extract power from the up and down movement in the ocean or the current deep beneath a river. Trials of such technology have been underway for a while. A new tidal generator was installed in New Yorks East River in September of 2008.
While these are promising developments there’s the issue of how much energy is really available from these technologies. Small hydropower can be anything from a few kilowatts (kW) to 10 megawatts (MW). The tidal projects can go up to a megawatt at full utilization.
What you actually get out of hydro depends on many different factors. Small hydropower can be greatly affected by the amount of rainfall which is very variable. Tides are predictable but I read one study that put the capacity factor (actual output / total possible output) at below 40%. Im sure that improvements in the generating technology could increase the capacity factor of tidal significantly. How long those improvements will take remains to be seen.
Over the next few year thousands of megawatts of older, inefficient coal plants will be retiring. How much of that coal capacity will be replaced by small hydro and tidal power? Very little if any. The small size of low impact hydro and tidal projects combined with uncertain performance will limit them to pilot projects and niche applications.
I could certainly visualize oil and gas platforms that are far offshore eschewing diesel generators in favor of tidal turbines for some of their electricity needs. Likewise I could see small industrial facilities purchasing the output of a low-impact hydro project to offset some of their electricity consumption. But the amount of electric power needed to replace older technologies and meet growing electricity demands can only be provided by other newer power plants that rely on efficient gas turbines, or wind and solar power.