Sustainable Hydropower: A New Flow of Ideas
Posted by Daniel Kammen of World Bank October 25, 2011
What can be done to diversify our clean energy technology options? In
recent years we have seen a number of seemingly �old� technologies
undergo a reassessment, and a reinvention. Geothermal power, once
assessed as �an excellent source of baseload energy, but likely
limited in commercially exploitable capacity� has undergone a
renaissance.
Here�s the new view in the latest IPCC Special Report on Renewable
Energy Sources:
In 2008, global geothermal energy use represented only about 0.1
percent of the global primary energy supply. However, by 2050,
geothermal could meet roughly 3 percent of the global electricity
demand and 5 percent of the global demand for heating and cooling.
That dramatic expansion of scope � a factor of 15 on a global scale �
is a function of new technology options and forecasts for higher
fossil fuel prices. But it is only one example.
Another technology undergoing a dramatic expansion of options is that
of hydropower. Conventional dams, large and small, use either a
natural, or more commonly, an artificial �head� or drop to harness
energy.
Thus, the energy available is increased with higher dam, and thus a
larger flooded reservoir for conventional dams. Therein lies the
problem of big dams that inundate ecosystems, displacing people and
wildlife, and in some cases � ironically � generating large amounts of
greenhouse gas emissions from the decomposition of flooded, submerged,
biomass.
(Related: �Two Rivers: The Chance to Export Power Divides Southeast
Asia� and map: �Exploiting a Land of Plenty�)
Some dams have even caused earthquakes.
Enter so called �hydrokinetic� energy technologies. Conventional dams
alter the river, creating artificial lakes. In hydrokinetic power
plants, the energy does not come from falling water, but by extracting
the kinetic (movement) energy from the water.
This is very exciting because new turbines, nozzles and indeed
innovations in everything from jet engines to ocean craft to the
design of pipes can come into play to extract energy from flowing
water. Hydrokinetic systems are applicable in both river and ocean
currents, and can reduce the need for reservoirs and disruption of
waterways dramatically, because no- or minimal- storage of water is
needed. The array of hydrokinetic options is dizzying, and is a
wonderful and promising field of innovation. A recent survey
published in Applied Energy noted no fewer than ten promising options:
Turbine Systems:
- Axial (Horizontal): Rotational axis of rotor is parallel to the
incoming water stream (employing lift or drag type blades)
- Vertical: Rotational axis of rotor is vertical to the water surface
and also orthogonal to the incoming water stream (employing lift or
drag type blades)
- Cross-flow: Rotational axis of rotor is parallel to the water
surface but orthogonal to the incoming water stream (employing lift or
drag type blades)
- Venturi: Accelerated water resulting from a choke system (that
creates pressure gradient) is used to run an in-built or on-shore
turbine
- Gravitational vortex: Artificially induced vortex (via funnels)
effect is used in driving a vertical turbine
Non-turbine Systems:
- Flutter Vane: Systems that are based on the principle of power
generation from hydroelastic resonance (�flutter�) in free-flowing water
- Piezoelectric: Piezo-property (charge accumulation or current
generation in response to mechanical force in some specific materials)
of polymers is utilized for electricity generation when a sheet of
such material is placed in the water stream
- Vortex induced vibration: Employs vibrations resulting from vortices
forming and shedding on the downstream side of a bluff body in a current
- Oscillating hydrofoil: Vertical oscillation of hydrofoils can be
utilized in generating pressurized fluids and subsequent turbine
operation.
- Sails: Employs drag motion of linearly/circularly moving sheets of
foils placed in a water stream
There is a still a great deal to do in terms of technological
reliability, cost, and how to scale these to be megawatt, or tens of
megawatts, or more. Large conventional dams can be anything up to
many giga-watts in scale. In an earlier blog (�Building a New Nation
and New Energy in South Sudan�) I described the Fula Rapids on the
White Nile, a location as powerful as it is beautiful, where energy
production and river conservation may be a great candidate for this
technology.
It is nice to see evolving technology, particularly one thought of by
many as mature and unchanging, up for a wave of innovation.
(Related: �New Dam a Go and a Blow to Megafishes?� and �Will Dam
Removal in the West Restore Salmon?�)
Daniel Kammen is the World Bank�s chief technical specialist for
renewable energy and energy efficiency. He is an adviser to National
Geographic�s Great Energy Challenge initiative.
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