WC Archive

Although we at WorldChanging tend to trumpet the proliferation of distributed renewable energy systems, we do recognize that the big centralized systems can be green, too. Two different big green power projects showed up in my inbox this week, and they're both worth taking a look at.

The first is the new "tidal lagoon" power system under construction at the mouth of the Yalu River in China. British company Tidal Electric is the lead engineering group on the project. At 300 MW, it will be the largest tidal power project in the world. Tidal lagoon power systems use large-scale enclosures which generate power as they are filled or emptied by the change in tides. Lagoon systems present less of a disruption to the local ecosystem than the "barrage" generators more often used in tidal power systems (such as the current largest tidal power generator, the Rance River project in Brittany, France). Although tidal power is not available at a constant rate, it is predictable, making it easy to integrate into existing power grids. Despite the size of this project, it looks like a winner.

As ambitious as tidal lagoons may be, they pale in comparison to the Solar Thermal Tower scheduled for construction in Australia. At a kilometer in height, with a base collector five kilometers across, the tower would be potentially the largest construction project ever. The principle is simple: air beneath the collection area is heated by the sun, much as in a greenhouse, and rises up the tower, where the differential in pressure between the top and the bottom keeps the air moving fast enough to drive turbines -- in essence, it's a heat-pumped super-windmill system. The tower is supposed generate 200 MW, and should be able to do so fairly constantly, even at night. A test tower built in Spain in the late 80s demonstrated that the technology works, albeit on a much smaller scale. The Solar Tower has been approved by the Australian government, and construction is intended to begin next year (a 2002 New Scientist article about the idea suggested that work was supposed to begin in 2003, so this may be one of those perpetually-a-year-away endeavors).

There are still many questions about the feasibility of the Solar Tower, ranging from keeping it stable in the winds at 1 km to whether a heat-trapping project of that size would alter the regional environment. There's also the question of cost -- can it be built inexpensively enough to make the power generated competitive with more conventional approaches? I'm skeptical, but I do think that it's a worthwhile project. It's hard to tell whether something so audacious can also be practical -- it's easy to be caught up in the spectacle of the kilometer-high tower and the roughly twenty square kilometers of greenhouse glass.