What a concept.Every day there are new innovations and more
opportunities to cash in on alternate power generation. This looks
like one in the works if they can get through the regulators. It is
real and it is a billion dollar enterprise.
Energy Innovation: Massive Solar Downdraft Tower Proposed in Arizona
The specific volume and possibly the pressure drop with the initial
misting but what's the rest of the thermocycle?
Because of the higher density the pressure at the bottom of the tower
is greater than outside the tower, maybe 6% at most. So the next step
is an adiabatic expansion step, same expansion as in a Brayton [gas
Unless you wanted to "send the air over a mountain" to dry it out
again the addition of heat would then be the third and last step to
complete the cycle.
Not that Carnot efficiencies have any effect on the operational costs
of renewable energy but the developer claims 70 - 80% Carnot
Triangular thermocycles intrinsically have low Carnot efficiencies.
On Sat, 30 Mar 2013 11:42:38 -0400, emoneyjoe wrote:
Probably a rhetorical question.
Answering anyway: No.
At constant temperature, the density of air decreases as the relative
Molecular weight of air: 29
Molecular weight of water: 18
Larger mole-fraction of water vapor decreases density.
You can make a lighter than air balloon in the desert work with water
vapor if the fabric is filmy enough.
100% r.h. air has maybe 1 - 2% lower density at the same pressure and
same 40 C temp. In the downdraft tower the absolute temperature of
the misted air, however, is 7% lower so the density might be 6% higher
than outside the tower.
delta p = rho g h = 0.06 X g X 600 meters.
That's significant but at $2/watt, the downdraft idea is at least 5X
the price of PV.
The real solution involves energy storage.
The adiabatic compression step was left out.
The thermocycle is:
1. isobaric cooling
2. adiabatic compression
3. adiabatic expansion
4. isobaric heating
From Bernoulli's eqn., delta gravity head + delta velocity head +
delta pressure head = 0
Since the gravity delta is only about 1 kPa the venturi effect must be
responsible for most of step 2. That would explain the diffuser
Otherwise, if they are just using the velocity head with wind
turbines, then the best they can do is a little over 40% of Carnot
efficiency -- 10% at best -- and the overall efficiency would be
considerably less than 4%.
Efficiency plays a role in the capital cost of a renewable power
On Sun, 31 Mar 2013 07:55:11 -0700 (PDT), Bret Cahill
I don't see any application of venturi unless
something can be inducted at the throat.
If it could produce multi-hundred megawatt
power 24/7, then it should be done at least once.
But I see saturating all the incoming air
to be a big problem, lots of filter media, and
I am not sure how to get the process started,
run the alternators by grid power to start?
They probably have their calculations correct but first run some tests
with an idle cooling tower from the Palo Verde or other nuke plant.
They'll just string thousands of misters across the top. No Aspen pad
is necessary as everything can be monitored and tweaked so that all
the mist evaporates in the first 20 m or so.
Just misting the air at the top will cause a powerful downdraft
because the abs temp drops by 10% and the density increases by 10%.
If the turbines really are expanding the air then the exhaust will be
even cooler than ordinary swamp cooled air. A pleasant outdoor
summer retreat, now impossible in Yuma, could be designed around the
base of the tower.
With an additional heat exchanger -- this would be many acres of
tubing -- this could be done near a binary geo thermal plant to
precool the dry air going into the cooling tower. Getting the cold
side down a degree is more valuable than getting the hot side up a
degree, Carnot = 1 - Tc/Th. Ormat will definitely be interested as
the high voltage power lines are already in place.
Dear Mark Fergerson:
On Sunday, March 31, 2013 9:20:38 PM UTC-7, email@example.com wrote:
I worry about spawning tornadoes from such a structure. Statistically and long
term of course.
Wonder how they will get the mandatory red lights on top, to warn off aircraft?
The top will drift easily 20% downwind, so locations will have to be carefully
I wonder when they spray herbicides or insecticides in adjacent fields, what
venting those so high they end up in adjacent states will do?
Could such a structure reduce the weight of initial sections of a space
Could a few of these carefully placed actually destroy a heat bubble, or even
prevent it from forming?
David A. Smith
On Sun, 31 Mar 2013 21:37:49 -0700 (PDT), Bret Cahill
Good question, some times it is,
but at higher RPM air is projected far
enough the effect can't get started.
It was an anticipated problem
with the F-35C, the lift fan has some
special features to deal with it.
Usually there is a little breeze,
so maybe it won't be a problem
most of the time, only one way
to find out.
Where is this an issue with _any_ turbulent flow in channels?
Before you get all worried about smoke rings you need to look at the
power from the adiabatic expansion first.
300 m dia.
600 m height
22 m/sec flow rate
10% increase in density.
Vol flow rate = 1,600,000 m^3 / sec
Pressure difference at the bottom of the tower = 1 kPA
Why aren't they claiming 1.6 GW?
On Mon, 1 Apr 2013 08:14:39 -0700 (PDT), Bret Cahill
Good design of any movement of air or
water has to assure the intake doesn't
start pulling in the exhaust.
For most systems the volume of the
flow is a small part of the local region,
with things like this tower, the volume
of the flow is a big part f the region.
And the situation is worse than
other types of systems because the
flow is great and the only difference
between the exhaust and the needed
inflow is moisture saturation of the air.
As long as the exhaust does not
become a substantial part of the in flow,
everything is fine.
The proof of the pudding is .........
Frankly I think the size for the working
prototype is too large, and the fact
that they are asking for investors is
a problem with me, they should be
just establishing that it will work,
and develop a solid business plan
and get bank loans to build a working
prototype, why are they so anxious
to give away a big part of the pie
to get the thing started?
What do you think the smallest
possible positive proof working
prototype could be?
I am more interested in systems
for the individual home or business,
the market is bigger, the need is
greater because grid power isn't
available everywhere, and why
create things that make the
public dependent on big money
projects if user-owned, smaller
ones would work.
I am perfectly willing to go along
with AGW prevention technology
if the results are such that it costs
less than fossil fuel within the next
ten years and which can replace
fossil fuel when oil and coal become
On Mon, 1 Apr 2013 16:53:56 -0700 (PDT), Bret Cahill
In calm winds, how long would it take
for the atmosphere for 20 miles in all
directions to be solid fog, isn't that
what saturated air is?
And why does it take the largest
volume structure in the world to show
the thing works?
The largest structure to date,
472 Million cubic feet, Boeing 747 factory.
The energy tower;
2200 x r x r x pi = 2200 x 750 x 750 x 3.1416
= 2200 x 1767000 = 3+ Billion!
Please check my numbers.
Keep talking, it looks worse and worse.
Without a lot better storage, PV is not
going to be that great.
I think shallow geothermal using high
volatility working fluids will beat everything
The more money thrown at things
that don't work, the less money that
will be available.
Give an example of where this is an issue with _any_ turbulent flow in
The deniers who sneer at "playstation modeling" simply haven't done
much design work.
They can extrapolate off a Palo Verde cooling tower.
They don't need turbines. The wind alone will be enough.
Then high density energy storage is where we need to spend a few
The 800 lb gorilla is transportation. Either slot car the freeways or
go with some kind of metal air reaction, i.e., H2 fuel cell, sodium
air battery, H2 ICE.
Obama's $200 million on motor vehicles is a joke.
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