Large-scale hydroelectricity has a bad reputation amongst environmentalists despite the fact that there are no obvious greenhouse emissions from it. A primary reason for this is, of course, the flooding of often pristine environments, the massive ecological damage resulting from disturbed river flow, and the disruption of communities that results. But, beyond that, there is the release of methane gas from rotting vegetation that was either submerged by the dam, or washes in with the water inflow and accumulates on the dam bottom. Methane is a highly potent greenhouse gas, roughly 20 times more powerful than CO2. But methane is also the primary component of natural gas – a perfectly fuel for generating electricity, industrial use, or home heating. That’s why rubbish tips around the world are sprouting small power generators using the methane released from the decomposition of rubbish. But methane dissolved in water at the bottom of a lake isn’t quite as easy to get at.
Brazil’s space agency INPE is working on a project to extract this methane, and burn it for electricity. Essentially, the plan is to ensure that the dam’s hydroelectric turbines get water from the top of the dam, not the bottom, ensuring that the hydroeletric generation process doesn’t encourage methane release. Then, they intend to pump bottom water to the surface, and use a rotor to turn it into droplets. The water will then release its methane. They believe that some dams with especially high methane content have enough methane available to increase total power output by 50%. However, the idea is likely to be pretty controversial in Brazil, because tapping methane in hydro dams forces Brazil to admit that the methane exists, and is gradually being released into the atmosphere.
The idea of extracting methane from lakes isn’t unique to Brazil, by the way – it’s also being done in a natural lake in Rwanda. It might have the side benefit there of reducing the buildup of methane in that lake. Every 1,000 years or so, the Rwandan lake apparently “turns over”, releasing a lethal blanket of methane throughout the countryside killing everything in its path…
In any case, this technology appears to be a win-win one – more power, at what should be a reasonable cost (gas turbines are cheap, and extracting the gas shouldn’t be too expensive), and reducing net greenhouse emissions into the bargain. While Australia doesn’t have the enormous dam systems of Brazil, we do have dams, and rotting biomass does accumulate at the bottom of some of them. Wonder whether there’s be enough to exploit in any Australian reservoirs?
AFAIK, and it’s been a little while since I last read up on this, this is particularly an issue for tropical dams, and is not relevant (doesn’t really occur) for temperate dams. Also the effect only lasts for 50 years or so. So the only reservoirs you’d be looking at are recent ones in the north.
While a bit off the thread, methane gas extraction is becoming competitive and controversial closer to home for other reasons. In the Hunter Valley coalfields, mining companies are starting to see the advantages of using methane from coal seams for energy. At the same time, AGL is drilling for the same resource for the metropolitan market. While the mining leases are off limits to them, they are chasing private land holders for drill rights. This has particularly upset primary producers such as vineyards who say the drilling can have devastating consequences on groundwater.
Wait, you mean there’s water in some Australian reservoirs? Show me the way to these bountiful oases, I’ll hitch my swag and a few empty primus bottles and beat a path to the promised land!