Work can only be extracted from a gradient of energy, not merely energy
itself. Solar energy is the input of new energy into an existing system;
if you didn't capture it to do work, it would heat the surface it hit,
or bounce around until it did. It's the gradient between the energy of
the photon and the energy of the substrate that allow you to capture
energy into a workable form.
Tidal, too, is not "ambient". Tides are pulled up and down by the
momentum and gravity of the moon, which makes me whimsically wonder
whether the harvesting the ultimate source of the energy (the momentum
of the Moon) means that Tidal would actually gradually slow down the
moon into a decaying orbit.
To offer a simple example; you can extract work from a heat source by
boiling water into steam, and extracting energy from the difference in
pressure between the heated chamber and the outside, or between the
heated chamber and a cooled chamber (where the steam condenses, creating
a pressure-gradient).
If you were to just put the turbine into the heated chamber, without a
gradient, it wouldn't matter how much energy you poured into the system,
you'd get no work done.
To offer another example; "ambient" energy can be analogised to water
content. A vessel may be half full, or entirely full, but that doesn't
affect how much energy it provides. Only when you start to pour the
liquid does its embodied energy become useful; you capture the momentum
of the falling liquid to generate energy. Sure, more water means more
energy can be generated, but unless there's a gradient (somewhere for
the water to fall), you can't generate any energy from it.
So, venus may be a lot hotter than Earth, but that on its own does not
make it any more useful for generating energy, unless you can either A)
Discover a potent gradient of energy within venus or B) Find a way to
let energy escape venus, and then convert that energy gradient into a
potential difference (voltage) for electrical generation.
So, the question: Is venus known for having greater gradients of energy
than Earth, or merely higher ambient energy?
On 01/02/12 15:56, mad_casual wrote:
> On Jan 31, 11:32 am, Cathal Garvey <cathalgar...@gmail.com> wrote:
>> Surely for a heat-pump to work, you need to have a gradient, not just
>> lots of heat.
>>
>> To ask that another way: Are there larger heat *gradients* on Venus with
>> which to generate useful energy, or is there just more ambient energy,
>> which is of no use?
>
> 1. Ambient energy isn't 'of no use'. Many of the 'eco' options being
> looked at on Earth make use of nothing but ambient energy (tidal,
> wind, gravity and flow,...). The only trick is on Venus they have to
> work at or avoid 500ish degrees C.
>
> 2. Between Earth and Venus, there is a fantastic thermal gradient.
> Using existing technology, we float manned oil rigs on oceans to drill
> miles into the Earth to actively pump out our dominant energy source
> and for almost half a century we've had the technology to float
> massive structures in an atmosphere 90 times less dense than Venus'. I
> don't mean to imply quid pro quo, but 'drilling' into Venus for energy
> and or materials seems a lot more obvious and abundant than doing
> anything on Mars.
>
> Turn the question around. You're a colonist on Mars and you need to
> build something or power something you've built. Where do you get the
> materials and energy? Earth? The Sun?
>
>>
>> Venus is scary precisely because it used to be almost identical to
>> Earth, except that Earth developed life and Venus succumbed to runaway
>> global warming. There but for the grace of an ecosphere go we.
>>
>
> Correct me if I'm wrong, but there's no evidence that a runaway
> greenhouse effect similar to Venus' could occur on Earth and the
> planet's history would suggest the opposite. Ignoring gross celestial
> differences (Earth's faster rotation, the creation and existence of
> the Moon, etc), immediately preceding the Oxygen Catastrophe was the
> Huronic Glaciation and 'Snowball Earth' has been hypothesize in
> several time periods since. In all likelihood, if we discovered a
> parallel universe where life never existed on Earth, Venus and Earth
> would have similar albedo except Venus' surface is 500 degrees and
> Earth's is -20.
>
> Venus is scary the same way an autoclave or submarine is scary.
> Personally, the trip to either planet is going to be about 100X as
> "scary" as actually being at the destination.
>
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