The Energy Tower - Cheap Renewable Energy ?

[a_unique_person]

http://www.energytower.org/index.html#calculations

The idea is to leverage an available heat source to transfer much larger amounts of heat between the ambient air and the ground using a heat pump system. This heat source could be solar thermal, geothermal, coal or other waste heat sources. A convection tower (bi-directional chimney) allows the large quantities of air to move across the heat exchangers without expending energy as in a forced air system. A large subterranean heat storage system (water, sand, stone or earth, either natural or man-made) is used to store both the heat from the air and the heat collected from the solar/geothermal source until the air is cooler (either day/night cycle or seasonal). This stored heat is relatively close to the system (as compared to deep geothermal) and the energy to pump the heat is relatively low.
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The system uses both a low boiling point fluid steam turbine and wind turbines in the tower to generate electricity.
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This is an amalgamation of the SEGS, OTEC, Solar Tower, Water Spray Down Draft Tower, Low Temperature Geothermal and Shallow Thermal Storage ideas and has several fundamental improvements in efficiency, location independence and reliability over these systems when deployed separately. See the background page for more information on existing systems.
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1. A tower is built to allow large quantities of air to move across heat exchangers by natural convection without expending energy.
2. Solar thermal or deep geothermal heat is used to power a heat pump which moves a much larger amount of heat from the air.
3. Both the heat from the air and the heat powering the heat pump are stored in shallow heat storage and this is used to exploit the difference in temperature changes due to day time heating between the air and shallow underground, either day/night or seasonally. In effect this creates a local geothermal source and the low media transfer energy allows for an efficient geothermal power generation system. This source is reliable and may be used for base load electrical generation and structure heating.

Looks quite complex. Can it work?

 

[autumn1971]

No. Lot's of scientific words in there, but it all comes down to the impossibility of a perfect transfer of energy. On the website the telling phrase is in the "Benefits" section, to wit, "the energy stored or removed from the earth is used in the opposing cycle."
This will always be less than the energy put into tapping the potential of the heat sink.
I'm sure it can be expressed very elegantly in mathematical terms, but that is a job I advisedly leave to those more comfortable with the language of physics.

 

[a_unique_person]

Is that where the word 'leverage' comes in? I think in this context it means getting something for nothing.

 

[autumn1971]

I believe that the authors intend to distract the reader with the word, which is much used (usually incorrectly) by those with MBAs. I also believe that those with MBAs are the audience that the authors(porducers? financiers? How does one refer to the folks who pay to have a site with their message put up if someone else does the designing but the folks supply the words?) wish to reach. The term leverage implies power to these people, who simply don't understand the science of the description.

 

[burrahobbit]

Improbable.

I couldnt get the site to open but have seen fairly detailed info on the other tower ideas. This seems like an attempt to get on to all the bandwagons at once- Solar, geothermal, energy storage...

Another steorn..

 

[Paul C. Anagnostopoulos]

Does anyone else have misgivings about energy generation systems that move heat around with abandon? Large arrays of photoelectrics that absorb sunlight rather than it hitting the ground? Geothermal ground systems? Geothermal ocean systems?

I don't know. I just have this feeling ...

~~ Paul

 

[pvt1863]

It sounds like a lot of gibberish.

First of all, if the heat storage system is subterranean, then it is almost certainly below the heat exchangers in the chimney. While natural circulation can be used to move the air in the chimney, the coolant that transfers the heat from the chimney to the storage system will have to be forced since their positioning makes natural circulation in that loop impossible. It is a little misleading for them to say that the first loop in their system (the chimney) doesn't require forcing while only mentioning in passing that a heat pump will be needed to move the heat to storage.

It should also be mentioned that natural circulation makes for poor heat transfer. Natural circulation convective heat transfer coefficients are typically orders of magnitude lower than forced convection ones. To make up for this, large temperature differentials would have to be used to get good heat transfer rates (which is all but impossible given the heat source), or the mass flow of air will have to be astronomical.

Second, the thermodynamic efficiency of the plant will be very low. The efficiency is a function of the temperature differential across the power generation portion of the plant. Using low boiling point steam turbines means that this delta T is going to be very low, not to mention the fact that Tmax is going to be limited by the source -- solar and shallow geothermal aren't going to give very high maximum temperatures. Very low efficiencies in a turbine system mean bad economics.

Third, where is the condenser? All steam cycle plants need a condenser unless you want to destroy your turbines. Is this design going to use a cooling tower, or will it be built near a body of water for the ejection of waste heat?

The whole idea is fairly silly because it centers around using a heat pump to raise the temperature of a storage medium and then using that hot storage medium to drive a steam cycle. This process -- which is similar to trying to cool your house by opening your refrigerator -- is bad thermodynamics.

 

[Randi]

I dunno...

I've been asked for an opinion on this "energy" concept. I'm just not able to do so, due to my ignorance of the subject. If this is just a method of tapping geothermal or other such energy sources, it's not at all new...

 

[rohar1]

Performance Enhancement to CSP/SEGS systems

Hi,
I have been the main contributor to the energytower.org design, with a lot of help from a lot of great people in various areas.

The energytower.org system isn't that complicated, it is just a performance enhancement to CSP/SEGS systems. The largest solar power plant in the world is the CSP plant at Kramer Junction, California (~385MW).

The main performance enhancement is to use the trough solar thermal collectors to transfer ~ 1:1 heat from the air, doubling the output. The rest of the system is design allowing the CSP plants to be feasible in non arid locations and to lower the supplemental natural gas usage.

Some good documents on Solar Chillers were recently published by the European Solar Thermal Industry Foundation. Absorption chillers have been around for many years, but the solar absorption/adsorption chillers are fairly new.

There are links on the energytower.org site to these documents and more information, I am new to this forum and cannot post URLs.

 

[Horatius]

The whole idea is fairly silly because it centers around using a heat pump to raise the temperature of a storage medium and then using that hot storage medium to drive a steam cycle. This process -- which is similar to trying to cool your house by opening your refrigerator -- is bad thermodynamics.

This was my take on it. Nothing actually impossible, like PM, but a lot of things that might sort-of work, but just aren't very efficient, or well-thought out. Not impossible, just impractical.

 

[burrahobbit]

Just managed to look at the site.

I am dubious of the thermodynamic feasibility of the design. Most of the issues were covered well by pvt1863.

The basic solar tower concept was interesting but did not seem to have any significant advantage over the solar concentrator based plants. Also a number of engineering and economic issues.

This concept has the additional problem of storing the heat, ammonia refrigeration, ammonia absorbtion in water and stripping (not a trivial problem that)

I wouldnt put my money in that

 

[Dr. Imago]

My initial thought is that this would be hopelessly impractical. Even if such a system were able to produce energy, the cost of it would far outweigh the value of the actual energy output. Sounds like an issue of scalability.

Just an initial reaction. Like Mr. Randi, I don't have enough practical understanding to foresee what kind of energy outputs such a system would generate. My hunch is "not much" at least on the scale that would be required for it to be meaningful.

-Dr. Imago

 

[rohar1]

My initial thought is that this would be hopelessly impractical. Even if such a system were able to produce energy, the cost of it would far outweigh the value of the actual energy output. Sounds like an issue of scalability.

Again, sorry for the non-linked links.

The calculations for various implementations are here:
energytower.org/index.html#calculations

You have to look at solar absorption chillers to understand some of the concepts.
estif.org/281.0.html
is a good start.

It is very difficult to implement CSP/SEGS systems outside of arid locations. The traditional CSP plant uses evaporative cooling towers to complete the Rankine cycle. In a tropical location, this is impractical due to the high humidity. The solar isolation in Florida is high, but the traditional solar steam plant will not function well in high humidity. There is a large amount of energy in warm humid air that can be extracted and the ammonia absorption system essentially creates a heat upgrade when the ammonia is absorbed into water (exothermic). Once the ammonia is absorbed into water the aqueous ammonia carries the heat from the anhydrous ammonia and the rest of the system functions the same as a SEGS Rankine cycle.

fplenergy.com/portfolio/solar/solar_plant.shtml

As far as costs, the main evaluation criteria is Energy Returned Over Energy Invested (EROEI), but when comparing renewable clean systems to fossil fuels you have to fairly evaluate the hidded costs in fossil fuels (environmental damage, war, etc).

There is an essay on evaluating energy systems here:
energytower.org/bushel_and_rod.html

 

[RenaissanceBiker]

Interesting site, Robert. I would be pleasantly surprised if you managed to get a velocity of 20 m/s inside the tower by convection alone. I think you need to enlist the aid someone familiar with computational fluid dynamics. I would be concerned about the effects of a cross wind on the movement of air inside the tower. It seems that all your calculations and illustrations assume there is no wind blowing across the top and/or bottom of the tower. Also, what is the initial capital cost of building one? I live in the southeatern US so I took a brief look at the tropical one. You need 866,000 sq. m of solar collectors? That's about 214 acres! It seems to me that you could put a lot of wind powered generators on a site like that.

 

[monoman]

Funnily enough i was asked to help translate a patent document for such a system in Bulgaria a couple of months ago. When i say translate, i mean from patent English into normal English!

I recognised it because i'd seen it somewhere a couple of weeks before.

No idea how it works though.

 

[rohar1]

answers

Thanks for the interest.

Interesting site, Robert. I would be pleasantly surprised if you managed to get a velocity of 20 m/s inside the tower by convection alone. I think you need to enlist the aid someone familiar with computational fluid dynamics.

The two variables that will affect wind speed are tower height and negative buoyancy, both are variable. If you look at the output calculations, the majority of the power generation is in the steam turbine not the wind turbine. The other convection tower generation ideas are depending strictly on the air convection for power generation and require extremely high towers for any serious output.

The energytower.org design requires a high enough tower to move sufficient air by negative buoyancy across the heat exchangers, but the air turbine output is only 10% of the steam turbine output in the 100m tower sample calculations, so it wouldn't make a lot of sense to go to engineering extremes on tower height. On the other hand, gravitational acceleration is 9.8 m/s/s, so any increase in tower height is an exponential increase in power output.

I would be concerned about the effects of a cross wind on the movement of air inside the tower. It seems that all your calculations and illustrations assume there is no wind blowing across the top and/or bottom of the tower.

It's buried in the energytower.org/index.html#benefits section, but "A rotating or finned air intake/output leveraging prevailing winds would increase performance and it should also improve system startup."

It's not in the drawings for simplification.

Also, what is the initial capital cost of building one? I live in the southeatern US so I took a brief look at the tropical one.

A barrel of oil costs $60 (plus $800 billion in the middle east wars, a lot of dead kids and the pain of having to watch to Al Gore get an Oscar).

What did putting a man on the moon cost?

Sorry if thay if that is a little snarky sounding, but that's the one question I get tired of. If a kid dies in Afganistan, what did that cost? Oil and Natural Gas are not cheap and it isn't going to get magically better.

You need 866,000 sq. m of solar collectors? That's about 214 acres!

The Kramer Junction Solar plant covers 2.5 million square meters.
flagsol.com/SEGS_tech.htm

They are out in the desert on low-value land, but the solar trough collectors could be on roofs or attached to the tower. I would imagine the roof of your local shopping mall would be a good location.

Rather than trough reflective collectors, a fresnel lens collection system could be incorporated into underground collectors. The fresnel idea would have the glass lenses flush with the ground and much less ugly than fields of trough collectors.

It seems to me that you could put a lot of wind powered generators on a site like that.

You can do both with the land, no one wants to live under a 60' propeller.
In locations with consistent winds, wind turbines are a more economical choice. The wind doesn't blow everywhere and is generally not reliable enough for base load power generation, but it is relatively cheap supplimental clean power and the fastest growing clean power solution.

energytower.org/bushel_and_rod.html tries to put forward some tools for evaluating energy systems.

 

[pvt1863]

Thanks for the interest.

The two variables that will affect wind speed are tower height and negative buoyancy, both are variable. If you look at the output calculations, the majority of the power generation is in the steam turbine not the wind turbine. The other convection tower generation ideas are depending strictly on the air convection for power generation and require extremely high towers for any serious output.

The energytower.org design requires a high enough tower to move sufficient air by negative buoyancy across the heat exchangers, but the air turbine output is only 10% of the steam turbine output in the 100m tower sample calculations, so it wouldn't make a lot of sense to go to engineering extremes on tower height.

If so little is gained, then why incorporate it at all?

On the other hand, gravitational acceleration is 9.8 m/s/s, so any increase in tower height is an exponential increase in power output.

Not true. The movement of fluids displacing one another due to density differences is going to have little to do with freefall acceleration. The speeds involved are much slower and terminal velocity is reached very quickly. Adding additional height may not increase the velocity at all.

Another thing needs to be pointed out. All these tower designs run on the assumption that the air up in the atmosphere is more dense because it is colder. The designers/endorsers often neglect the fact that the air at higher altitudes has a different composition than air at lower altitudes. The heavier molecules in air don't reach that high in the same concentrations they are at near sea level -- we are all familiar with the fact that air "thins" and Oxygen levels are low at high altitude. It is possible that the density difference between warm surface air and cold high altitude air is smaller than hypothesized because the warm surface air has to carry heavier molecules up with it.

Along those lines, water vapor would be a serious concern in a system like this. As the warm surface air rises, it will cool. As it cools, water vapor can condense. This can cause serious trouble for any turbine system in its path.

A barrel of oil costs $60 (plus $800 billion in the middle east wars, a lot of dead kids and the pain of having to watch to Al Gore get an Oscar).

What did putting a man on the moon cost?

Sorry if thay if that is a little snarky sounding, but that's the one question I get tired of. If a kid dies in Afganistan, what did that cost? Oil and Natural Gas are not cheap and it isn't going to get magically better.

First of all, dragging politics into this is not going to help your cause. Saying "reducing dependency on unstable regions" is fine, but slinging mud and making controversial emotional pleas is begging for this to turn into a thread about politics.

Secondly, oil is not your competition. This tower is producing electricity. America and the rest of the industrialized world generates very little electricity from oil. Oil must be refined, can be problematic when burning on a scale large enough to drive a power plant, and makes the plant owner vulnerable to volatile fuel prices. Your competition is coal, natural gas, and nuclear power.

 

[autumn1971]

Isn't this analogous to claiming to have found a way to use the energy produced by falling water to transport more water to the top of the generator?

 

[rohar1]

If so little is gained, then why incorporate it at all?

If you look through the Calculations documents, the convection turbine is still ~ 10 MWh/day base load electrical generation.

Not true. The movement of fluids displacing one another due to density differences is going to have little to do with freefall acceleration. The speeds involved are much slower and terminal velocity is reached very quickly. Adding additional height may not increase the velocity at all.

Freefall acceleration has everything to do with buoyancy. You are right in the original posting, that an experienced fluid dynamics engineer could add a lot of value to designing air flow through the convection tower, but in the example calculations on a 100m tower, the peak velocity is 44m/s of a falling body, expecting a velocity of 20m/s doesn't appear to be a poor estimate to me, but I am not a fluid dynamics engineer.

Another thing needs to be pointed out. All these tower designs run on the assumption that the air up in the atmosphere is more dense because it is colder. The designers/endorsers often neglect the fact that the air at higher altitudes has a different composition than air at lower altitudes. The heavier molecules in air don't reach that high in the same concentrations they are at near sea level -- we are all familiar with the fact that air "thins" and Oxygen levels are low at high altitude. It is possible that the density difference between warm surface air and cold high altitude air is smaller than hypothesized because the warm surface air has to carry heavier molecules up with it.

You could be right, it needs to be prototyped to understand all the factors. A pilot updraft solar tower was built in spain in the 1980's and ran for several years. Enviromission is trying to build updraft solar towers in Australia and U.S. The energytower.org design is a different system and again is more of a performance enhancement to SEGS systems and a way of making SEGS systems feasible in moderate climates.

The solar isolation at Regina, SK Canada in the summer is ~5kWh/m2/day, which is about the same as the Mojave desert, but that is only during the summer months. In the winter we have short days and -20C temperatures. The energytower.org idea is to make SEGS systems feasible in this type of climate by storing thermal energy through the summer and then generating power with that heat through the winter. The convection tower is a part of that system, but not the whole system.

Along those lines, water vapor would be a serious concern in a system like this. As the warm surface air rises, it will cool. As it cools, water vapor can condense. This can cause serious trouble for any turbine system in its path.

Condensation is a normal consideration in any chiller design. The condensation in the system is very useful and there is a large amount of distilled water condensed at a height that can be used for many purposes.

First of all, dragging politics into this is not going to help your cause. Saying "reducing dependency on unstable regions" is fine, but slinging mud and making controversial emotional pleas is begging for this to turn into a thread about politics.

You were the one that mentioned cost. I assumed you meant that the current energy supply was fine and cost efficient. I was pointing out the hidden costs of fossil fuels. I wasn't slinging mud, I think Al Gore has done a lot of good for public awareness, but again you were the one that mentioned cost. If you read through The Bushel and Rod it goes through some of the considerations in evaluating energy systems.

I find that the general public thinks that in modern society using millions of years of solar energy stored in fossil fuels is "cheap" and going to last forever. The entire developed world should submit this notion for Mr. Randi's Challenge, but I think that we will get proved wrong.

In designing a system that can capture solar energy "real-time" well enough that it can compete with solar energy condensed over millions of years in fossil fuels isn't an easy task and it isn't going to be solved with snake oil and permanent magnet tricks like Steorn and many others are slinging.

I am attempting to design a system that a good blacksmith and stonemason could build with common materials. I own 2 sections of farm land, and arc welder, a backhoe, a cement mixer and an internet connection and I know how to use all of them. I would rather put effort into solving a real problem than run around attempting to debunk conspiracy theories. If you don't believe that I can build a scalable renewable power system with common sense and common materials, watch me.

Secondly, oil is not your competition. This tower is producing electricity. America and the rest of the industrialized world generates very little electricity from oil. Oil must be refined, can be problematic when burning on a scale large enough to drive a power plant, and makes the plant owner vulnerable to volatile fuel prices. Your competition is coal, natural gas, and nuclear power.

Yes, oil is generally not used directly for power generation except for locations like Hawaii and remote and backup power generation. If you read through Background and Prior Art there is a detailed explanation of moving agriculture and rail transport towards electricity.

With clean renewable electricity many transportable clean energy products can be manufactured that can replace fossil fuel products and electric consumer vehicles aren't a new idea.

 

[rohar1]

Isn't this analogous to claiming to have found a way to use the energy produced by falling water to transport more water to the top of the generator?

no

It's claiming that rather than building a solar steam plant, building a solar absorption chiller and utilizing/storing the heat is a more cost efficient and location independent system.

www.energytower.org
European Solar Thermal Industry Foundation Solar Chiller Document