By Daniel Kammen for National Geographic Society
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.
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:
– 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
– 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.