Hydrogen has been getting lots of coverage lately, but the other "H", hydroelectric power, quietly supplies about 4% of this country's total energy consumption and about 7% of our electricity. In fact, the primary publicity hydropower gets these days tends to be bad, relating to the environmental impact of dams, impediments to fish spawning, and some of the same age-related problems as much of our other infrastructure. And as with most other forms of renewable energy, it turns out that when deployed on a sufficiently large scale, it creates as many adversaries as supporters. Perhaps the answer lies in smaller scales: mini- and micro-hydropower.
The idea of mini-hydro, or "run-of-the-river" hydro, as it is sometimes called, is that the energy of the current is tapped without having to build a dam to pen in water and force it through large turbines. A mini-hydro turbine functions more like an underwater windmill. It may also be a better fit than conventional hydroelectric power in developing countries, requiring as it does less upfront investment and less infrastructure, such as construction roads that can permanently alter settlement and land-use patterns.
The whole subject of hydropower merits more discussion in the future, since it still represents the largest fraction--by far--of renewable power in this country and elsewhere. With the world looking for more power but lower greenhouse gas emissions, hydropower is an obvious part of the solution, and mini- and micro-hydropower may be the forms that will be most broadly acceptable, given today's concerns about dams.