On 22/12/23 06:17, Timothy Collinson - timothy.collinson at port.ac.uk
(via tml list) wrote:
> As a penance for absence or slow responses as a small contribution
> hereabouts, here's another in my occasional series of flicking through
> the New Scientists at work:
>
> tc
>
>
>
> *New Scientist 11th November 2023*
> Ocean heat could supply limitless clean energy to tropical islands,
> James Dinneen, p.13
> 140--year-old idea to exploit the temp diff between layers of ocean
> useful in tropical islands
> barrier to past projects was cost of installing kilometres of large
> pipes to reach deep water
> Global OTEC to avoid that (in 1.5 mW floating system for Sao Tome and
> Principe) by using platform 10km offshore and then transmitting
> electricity back via cable
>
> ObTrav: more on OTEC (ocean thermal energy conversion which might be
> useful on lower tech water (or near water) worlds, or anything with a
> hydrosphere really.  But haven't we been here before in _The
> Millennial Project_ by Marshall T. Savage?
>
Collision,

How about combining this with vortex engines (www.vortexengine.ca)?  In
short, small, artificial, controlled cyclones that let whatever heat
source they're cooling (such as unaltered land or sea surface) reject
heat to the stratosphere, constraining heat loss with spinning air
rather than structure. If the vortex separates from the base structure
(eg due to a bit of a draft), it quickly dissipates as it's now off its
heat source.

IIRC, another of classical OTEC's problems was its pants thermal
efficiency - Carnot limit ~7%.  The vortex engine mob seem to reckon
they can pull out 20% or so of the waste heat of the primary process -
18% or so of the original heat input to the OTEC system, more than
tripling overall electrical output.  That's neglecting any direct power
extraction from the surrounding sea surface.

I'm not sure if classical OTEC could hammertime the piping concerns by
having all the heavy gubbins on a floating or moored platform (oil rig
style), then have high voltage submarine power cables to carry the juice
to shore.

A comparatively low tech brute-force-over-underpants option (at least
for most TU) for the actual platform gubbins would be a pneumatically
stabilised platform - basic idea is an orthogonal, modular grid of
concrete pipes, capped at the top by the platform and open to the soggy
bit underneath.

Adjacent concrete pipes have piping and valves to let air flow between
them as needed as the waves travel by (default air pressure in-pipe
being something like 3-4 atmo), putting the whole platform on shockies. 
If you're really enthused, you could bung bidirectional wind turbines in
the connecting air piping to extract some of the waves' kinetic energy
as it gets shoved around, shrinking the waves a bit as a nice side
effect. Something like a compounded 30% wave height reduction per 50 m
of platform length.

The interstitial spaces between the pipes would be filled with enough
gubbins for the platform to maintain bouyancy in the event of complete
air loss.  It's claim to fame is the modularity mentioned above and no
inherent limit to platform size.

ObTrav: Consider a balkanised oceanworld, one with comparatively sod-all
land to start with and none available for an external party (such as
Terran Confederation, Zhodani Consulate, Ziru Sirka, etc) to bung a
downport on.  So space has to be built, in the form of (depending on
traffic) a roughly square PSP, 2 km on a side, moored to a seamount or
two.  With the leading corner of the platform oriented into the
prevailing wind/waves, that gives at least 3.5 linear km of sheltered
anchorage (since the platform is not only physically blocking most of
the wind at sea level, it's actively sucking power out of of the waves)
to hook wharves, jetties, etc up to, to support the downport's
inherently multimodal operations.

OTEC comes in to generate a bit of power and more importantly, nutrient
upwellings to support fisheries.  The vortex engines are cooling towers
(for all the waste heat generated) and power plants, backing up the
integral power generation.  The implicit intervention threat by the
external party helps keep a lid on platform-affecting shenanigans.

Alex