Energy Innovation: Massive Solar Downdraft Tower Proposed in Arizona

Arizona
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 turbine] thermocycle.
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 efficiency.
Triangular thermocycles intrinsically have low Carnot efficiencies.
Bret Cahill

Arizona Arizona As long as there is a breeze new dry air will be available. But does moist air have more mass?

Arizona Arizona Probably a rhetorical question.
Answering anyway: No.
At constant temperature, the density of air decreases as the relative humidity increases.
Molecular weight of air: 29 Molecular weight of water: 18
Larger mole-fraction of water vapor decreases density.

tp://theenergycollective.com/sbattaglia/203741/energy-innovation-so... tp://theenergycollective.com/sbattaglia/203741/energy-innovation-so... Except in August.
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.
Bret Cahill

Arizona Arizona Thanks, that is a much better post than most of your liberal ramblings. :-)

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 shaped tower.
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 plant.
Bret Cahill
p://theenergycollective.com/sbattaglia/203741/energy-innovation-so... p://theenergycollective.com/sbattaglia/203741/energy-innovation-so...

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?
Arizona Arizona

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.
Bret Cahill

p://theenergycollective.com/sbattaglia/203741/energy-innovation-so... p://theenergycollective.com/sbattaglia/203741/energy-innovation-so...
Mark L. Fergerson

Why isn't this an issue with ducted fans?
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.

Dear Mark Fergerson:
... 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 chosen.
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 elevator?
Could a few of these carefully placed actually destroy a heat bubble, or even prevent it from forming?
David A. Smith

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.
Assume:
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?
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 very scarce.

Give an example of where this is an issue with _any_ turbulent flow in channels?
Well know laws like the mechanical energy balance and the equation of motion for fluid flow in conduits.
Computer modeling is only necessary here for tweaking.
It must be large because it will not scale down nicely.
They need to play around with something big.
A cooling tower from the Palo Verde plant would be enough to demo the effect..
Zero size as all that's really necessary is a good analysis.
Last month Shell Oil said most energy would be coming from PV by 2060.
Shell got out of solar 4 years ago.
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.
Understatement?
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 else.
The more money thrown at things that don't work, the less money that will be available.

nnovation-so... Give an example of where this is an issue with _any_ turbulent flow in channels?
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 trillion.
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.
Bret Cahill