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Hi Big Gav,
question: does a thermal difference exist between the lake surface and the 600m depth? If so then since you are pumping water up anyway and if it is large enough you might be able to run a unit like an OTEC (Ocean Thermal Energy Convertor) from it. In addition cool lake water could be used for air conditioning in the hot summer months.
A few links;
www.otecnews.org
www.xenesys.com
Regards, Nick.
Hi Nick,
Presumably the depths of the lake are cold and there is a significant temperature difference - but I didn't see this discussed anywhere.
I did a little reading about OTEC a few years ago - there were some experiments in Hawaii and perhaps Japan being done - opinions were varied - as always :-) - as to whther or not this could produce useful amounts of power.
I see some places using cold water from lakes directly for cooling buildings (in Toronto, for example), but this probably isn't a great concern at Rwanda right now.
Thanks for the links - I'll check them out - I'll be doing a post on the potential for ocean power at some point and this was one area I was going to look into...
In a tropical climate there is unlikely to be any cold weather to create cold bottom water. So unless a cold mountain stream brings in water from a much higher elevation you wouldn't expect much thermal stratification. OTEC was much discussed thirty years ago, but it seems to have been largely abandoned. I did see one mention of someone looking at it recently, so the idea is not completely dead.
Believe it or not the mountains to the north of the lake have snow on them :-)
Well - they do for the moment - the glaciers are shrinking very rapidly - one more victim of global warming it seems...
http://en.wikipedia.org/wiki/Ruwenzori_Range
http://www.skimountaineer.com/ROF/ROF.php?name=Karisimbi
I don't think a high temperature at depth is needed to run an engine off this resource (or a low temperature at depth, either). In its current form, it is blowing a stream of water 50m above the surface of the lake. That is already mechanical power. To capture that power requires water turbines as are used in a small scale hydropower facility and some ingenuity with plumbing to separate the mixed flow of gas and liquid. It does not require the high efficiency heat exchangers that are needed for OTEC. This would be a nifty local power resource. But keep in mind, this is one energy resource that definitely should be depleted, and not developed in a sustainable way.
I've heard proposals to run engines off a salinity gradient between fresh water and salt water. This would be an engine that runs off the gradient in CO2 concentration. OTEC is a heat engine. Heat engines run off a gradient in temperature. With the development of coal resource in Europe, a lot of effort went into the study of thermodynamics. A big branch of physics was created and, as a side effect, all sorts of other engines were invented theoretically. The resource needed to run any of them never had the availability of coal-derived high temperature, so they were never really turned into practical inventions.
OK, great. I'm one of the contributing editors to the otecnews site so if you need any input let me know. The Xenesys site has some useful stuff. This company has a process that greatly increases the efficiency of energy extraction.
I got quite excited over the potential of OTEC a few years back as it is a 24/7/365 deliverer of energy unlike the other renewables -coupled with perhaps the creation of Ammonia as a carrier and bulk transport from the tropics... Well, not done any costings and its currently a 'fantasy-tech' so won't help much for the next couple of decades...
...and 'enemy of state', you don't need cold water coming in, any water below a certain depth is in the dark and a lot colder than the sunlit surface water hence the thermal difference. Works like a ground source heat pump.
Nick.
noutram, eos,
try this link for the thermocline and stratification profile of the lakes.
http://pagesperso-orange.fr/mhalb/kivu/eg/eg_1c_structure.htm
http://pagesperso-orange.fr/mhalb/nyos/2006/index2006.htm
Temperature variation is small, but traces a step "C" to actually increase at the bottom. Here, stratification maintained by high density gradients. Fascinating.
Thanks - I might ask you some questions in a few weeks time...