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A wind turbine that is free from intermittent fluctuations due to changing wind speeds while still extracting maximum power.


Description

Summary

Storing wind energy as compressed air and then using it "on demand" is not a new idea. Researchers have been working on it for decades.The economic and ecological viability of the concept has been proven. Wind+compressed air storage has a levelized cost of electricity comparable to coal but GHG emissions 1/10th of coal[2]. It also raises the capacity factor from a wind turbine from 40% to 80%[1].

The machine that I propose hopes to tackle the redundancy of first converting wind energy into electricity and then into compressed air for storage.

I hope for a charitable ear regarding the following

The main goal of the machine that I propose is to compress air. All this machine intends to do is to take kinetic energy of fast moving air (wind) and convert it into potential energy in the form of pressurized air. Ideally by the principle of conservation of mass and energy we could convert all the fast moving air into compressed air.  It could be compared to a large centrifugal/axial compressor where the air is already accelerated. Axial compressors can achieve an efficiency as high as 80-95%[3], hence so should the machine that I propose (fig 1,2,3,4).

I am not certain if this contradicts the Betz limit of 59.3% [4] (assumes wind as incompressible). The machine I propose is slightly different because the compressed air that we require as our end product is extracted out of the “wind” itself.

But if you are not convinced by my abstraction:

An economic study concerning “wind-electricity-compressed air” versus “wind-compressed air” has also been done by Madlener(2013)[5] .This paper theorizes a wind turbine connected mechanically to a wind turbine, but does not consider my hypothesis. Even so the paper states that the cost of energy generation of “wind-compressed air”  would be lower than both just "wind-electricity" and “wind-electricity-compressed air”. Above all the efficiency gained by omitting the generator could be anywhere between 3%-9%(ref table) depending on the design.

 

 


Category of the action

Reducing emissions from electric power sector.


What actions do you propose?

The Actions I propose:

  1. Detailed simulations and analysis and prove the concept theoretically.
  2. I may do a master thesis on the topic so that would be a first step towards contributing to the intelligence pool.
  3. Pilot phase: To test the idea, an old wind turbine could be retrofitted with an a compressor and storage pipes.
  4. I believe that the technological advances in aerodynamics, thermal storage, compressed air storage are already made, they all need to be funneled into producing this machine.
  5. Promote compressed air storage by educating people about its benefits
  6. Identify locations and markets where compressed air could be directly used to satisfy cooling loads
  7. Identify locations that require off grid solution where grids are weak or non existent.
  8. Give operators economic incentives for reducing the load on existing grids. There should be an incentive for providing "smoothening loads". According to Madlener/Latz 2013[5] one of the drawbacks of wind turbine +compressors is that current laws do not proved incentives for smoothening loads.
  9. Promote a decentralized approach rather than the conventional centralized approach. According to Succar an integrated de-centralised approach to wind power generation and storage results in higher capacity ratios,reduced storage capital, reduced green house emissions and a lower leveliized cost of electricity. The paper also states that cost reduction of up to 10% could be realized with joint wind and storage.

10. Give operators incentives for ensuring their power generators match demand.

11. Reduce the amount of transmission lines. Growing economies around the world are facing situations that the electricity demands are outpacing the growth of the transmission lines. Making new transmission lines needs a lot of initial investment that is just not available. We need to use our resources wisely. But storing power and consuming it at source we reduce the need of the large "all encompassing" energy grid.

Research and development:

To realize an idea like this we would need to collect data regarding all the different components of the machine which include

1) Wind turbine blade geometry

2) Drive train options

3) Compressor technologies and configurations

4) Different compressed air storage technologies

5) Thermal storage, especially adiabatic and solid thermal storages

6) Electric generators and their interface with the expander

7) Expander technologies

Process steps:

1) Theoretical calculations covering aerodynamics, solid and fluid mechanics, static mechanics and electrical engineering.

2 A blade element model (BEM) of the turbine should be made.

3) A CAD model of the machine should be made

4) FEM and CFD analysis should be performed

5) A detailed cost assessment needs to be made based on the bill of materials.

6) A final economic analysis can then be made

 

 

 

 

 

 


Who will take these actions?

Educational Institutions could also use their vast resources such as wind tunnels, labs and other facilities to aid in the development of the idea.

Governments need to promote energy storage and make laws that subsidize crucial technologies. They must also incentivize energy storage. 

Industrial player should have a stake and I believe they would be actively involved in the development process.

Investors: Without money from investors and other private equity I think achieving this machine would not be possible.


Where will these actions be taken?

These machines could be deployed anywhere with good wind speeds, but it would be especially suitable for countries that have weak grids. 

In developing countries current wind turbines are threatening the stability of the grid and in some cases do more harm than good. I could really see these machines being implemented in regions like this.

Probably due to the initial development costs involved I could see Europe and the US taking the initiative. But I'm quite certain they will pass on their know-how for the rest of the world to follow.


How much will emissions be reduced or sequestered vs. business as usual levels?

As previously mentioned, wind along with diabatic compressed air storage produces 1/10th the GHG emissions of a comparable coal fired power plant and roughly 1/4th of a combined cycle gas power plant[1][2]. With the onset of adiabatic CAES technology these figures are bound to reduce further.

As these machines could replace peak loading power plants  they will also offset the high GHG emissions that arise from spinning reserve plants.

Decentralized as opposed to centralized storage is proven to be more economical and ecological[3].This will also improve the emission of this machine as there would be no longer the need to make large grid infrastructure.

 

 


What are other key benefits?

  1. Reduce GHG emissions by producing and storing renewable energy
  2. Making wind power reliable and less intermittent.
  3. Reducing the cost of wind energy
  4. Reducing the use a rare earth metal that go into some of the electric generators
  5. Improving the overall efficiency and capacity factor of wind generated power
  6. With the recent discovery of cheap gas reserves, some governments may be unwilling to invest in expensive renewable technologies. A wind turbine like this could be perfect to meet them half way. Wind energy and gas could be used together if a combustion chamber is used to heat up the compressed air (diabatic storage). I believe change cannot always be instant and drastic, it needs to be eased into and I think this kind of a machine is perfect for that.


What are the proposal’s costs?

The cost of making a 100-300 KW prototype could cost 2-3 million US Dollars.

This cost would heavily depend on how intuitive our approach is. I am quite certain all the technology already exists, only the individual components would need a little tweaking.


Time line

 

Year 1-2- Detailed scientific analysis to prove the viability of the idea

Year 3-4- Make engineering calulations. Establish contacts with interested industrial players.

Year 4.- Manufacture and test the prototype

Year  5 onwards- Mass role out of the machines


Related proposals


References

[1] Baseload wind energy: modeling the competition between gas turbines and compressed air energy storage for supplemental generation.Jeffery B. Greenblatt,, Samir Succar, David C. Denkenberger,Robert H. Williams, Robert H. Socolow

[2] Alfred Cavallo, Controllable and affordable utility-scale electricity from intermittent
wind resources and compressed air energy storage (CAES)

[3] Axial flow compressors, Meherwan, P.Boyce

[4] Betz, A. (1966) Introduction to the Theory of Flow Machines.

[5] Economics of centralized and decentralized compressed air energy storage for enhanced grid integration of wind power, Madlener/Latz

[6] Wind Coupled To Compressed Air Energy Storage (CAES) For Baseload Power Generation, Succar

2011 Cost of Wind Energy ReviewS. Tegen, E. Lantz, M. Hand, B. Maples, A. Smith, and P. SchwabeNational Renewable Energy Laboratory (http://www.nrel.gov/docs/fy13osti/56266.pdf)

The cost of wind power variability, Warren Katzenstein and Jay Apt (http://www.sciencedirect.com/science/article/pii/S0301421512006246)

DG ENER Working Paper The future role and challenges of Energy Storage (http://ec.europa.eu/energy/infrastructure/doc/energy-storage/2013/energy_storage.pdf)

Energy and exergy analysis of a micro-compressed air energy storage and air cycleheating and cooling system Y.M. Kim a, D. Favrat    (http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1949&context=iracc)

Renewable energy technologies: Cost analysis series (http://www.irena.org/DocumentDownloads/Publications/RE_Technologies_Cost_Analysis-WIND_POWER.pdf )