Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site dciem.UUCP Path: utzoo!dciem!mmt From: mmt@dciem.UUCP (Martin Taylor) Newsgroups: net.misc Subject: Re: renewable energy Message-ID: <1513@dciem.UUCP> Date: Thu, 4-Apr-85 17:14:35 EST Article-I.D.: dciem.1513 Posted: Thu Apr 4 17:14:35 1985 Date-Received: Thu, 4-Apr-85 19:17:22 EST References: <608@vortex.UUCP> <491@spp2.UUCP> <706@mhuxt.UUCP> <2085@sun.uucp> Reply-To: mmt@dciem.UUCP (Martin Taylor) Organization: D.C.I.E.M., Toronto, Canada Lines: 33 Summary: >> There is only ONE renewable energy resource on this planet: Solar Energy. > >Not quite. I'll grant that direct solar and indirect solar (oceanic >temperature differences, nuclear fusion, wind, etc.) are the largest >energy sources in which the entropy is beyond our control. But there >are others. One which comes to mind is gravitational, available >indirectly in tides. Another is from the rotation of the earth. Some >of the wind power could be considered indirect rotational energy. >-- >Doug Pardee -- Terak Corp. -- !{hao,ihnp4,decvax}!noao!terak!doug Still not quite! Tidal energy is misleading in two ways: (i) it subtracts from the rotational energy of the earth and of the earth-moon system, slowing the earth and driving the moon away, so it isn't "renewable". Once the Earth stops, it stops. (ii) The height of a tide depends on resonance between the 13-ish hour forcing function and the bays in the coastline. If their surge resonance is around 13 hours (or a subharmonic?) the tides will be high. Lowering the Q of the resonance by taking work from the tide will to some extent lower to tide in question, (usually -- I expect you could find situations where the resonant frequency was such that a tidal power station might actually raise the tide height, but that's speculation). Both of these effects are very small, so the "not quite" is really "almost". Wind power is really direct solar power, just as is power derived from burning biomass. -- Martin Taylor {allegra,linus,ihnp4,floyd,ubc-vision}!utzoo!dciem!mmt {uw-beaver,qucis,watmath}!utcsri!dciem!mmt