On a sidenote from http://www.warmdebate.com/forum/storing-solar-energy, the idea of storing energy ultimately bound for electrical production via a non-electrical means was sparked by an idea I had several months earlier. The idea was to mechanically compress air using wind turbines, and then passing this compressed air to a storage device for later conversion to electricity, effectively storing it for extended periods of time in a highly efficient manner (as opposed to generating electricity, and storing that electricity by some other means and requiring more conversion steps). After realizing that this technology was patented in 2007, 2 years earlier, by a company called General Compression, I came upon a similar idea of using wind turbines to pump water into high altitude water reservoirs. While I didn't go ahead with this (instead opting for another topic: http://www.warmdebate.com/forum/storing-solar-energy), here is an excerpt from my thesis proposal of this unpatented tech that I submitted to the Technische Universität München in 2009:
Design of a Mechanical Wind Energy Storage System
1. Topic Description
This project will involve feasibility assessments, overall design, as well as extensive commentary on possible applications for a system of wind turbines and pumps powered by wind turbines, directly transferring mechanical energy from the wind to hydraulic power. This will eliminate the need for electrical generation (and associated losses) as a middle step when storing energy in high altitude water dams.
2. Key Questions and Problems
With the prospect of rising energy costs, renewables will play an increasing role in the future of our energy supply. However, the problem inherent in many of the available renewable technologies is that they cannot easily be stored and released on demand. Wind is a prime example of this. The harness-able power available in the form of wind is effectively infinite and inexhaustible, but the difficulty in storing energy from wind is making it difficult for wind to become an effective solution (Gravity Power, LLC, 2010).
In Germany, a large and growing fraction of electricity is generated from wind, of which a growing fraction will need to be stored if renewable are to play a serious role in our energy supply. To date, wind energy is harvested exclusively through the conversion to electricity. This makes sense if the electricity is to be consumes immediately (which has been the case in the past, since renewable have not played a significant role and are simply “absorbed” by the grid), but is an unnecessary waste if the energy is to be stored in the form of potential energy in reservoirs.
The following questions will need to be answered during this phase:
- Will the thesis focus on a system operating on a single turbine, or will it require the use of an entire wind farm?
- Will more expensive, high altitude turbines be used, or simply smaller scale models?
- Will the water pressure be generated at the turbine shaft, or will the mechanical energy be transferred to ground level first? (a supporting pump might be needed in this case, to pump the water to the primary pump)
3. Schematic comparison of conventional wind energy storage systems with the solution proposed in this study
Figures 1 below represents the current technological standard in regards to energy from wind power using high altitude dams. Figure 2 represents the technology proposed in this report. The essential difference between the two systems is that the technology proposed here simply skips the electrical energy generation step inherent in the old system. Since every conversion of energy necessitates a certain degree of loss, this new system is necessarily more efficient by design.
4. Prior Knowledge
Although the technologies involved in the individual components of this system are well documented (the turbine, pump technologies, etc), there somewhat little research into the particular topic of using wind power to directly store energy without generating electricity. Wind turbine technology has been a focal point of renewable energy research since the early 20th century, with turbine technology more or less perfected today (White, 2003). Pump technology, required to transport the water to high altitudes, is also a well-documented field that has been perfected since the late 1800s (Juvinall & Marshek, 2000). Essentially, it will be the task of this project to optimize already documented technologies to the task of generating and retrieving energy from wind, with water as a medium.
There are several available technologies for storing wind energy, none of which are very efficient. The most vastly applied mechanism involves pumping water to reservoirs or hydro dams at higher altitudes, then generating electricity from generators as the water is allowed to pass down to ground level (Bueno & Carta, 2006).
4. References
Bueno, C., & Carta, J. A. (2006). Wind powered pumped hyrdo storage systems, a means of increasing the penetration of renewable energy in the Canary Islands. Renewable and Ustainable Energy Reviews, 312.340.
Gere, J. M. (2002). Mechanics of Materials, 5th SI Edition (pp 212-214). Cheltenham: Nelson Thornes.
Incropera, F. P., & DeWitt, D. P. (2002). Fundamentals of Heat and Mass Transfer (pp 143-149). Brisbane: John Wiley & Sons.
Juvinall, R. C., & Marshek, K. M. (2000). Fundamentals of Machine Component Design (pp 28-41). Brisbane: John Wiley & Sons.
Perlman, H. (2009, October 19). Hydroelectric power water use. Retrieved January 10, 2010, from Website of the U.S. Geological Survey: http://ga.water.usgs.gov/edu/wuhy.html
U.S. Department of the Interior Bureau of Reclamation Power Resources Office. (2010, January 1). Hydroelectric Power.
White, F. M. (2003). Fluid Mechanics, 5th Edition (pp391-392). Sydney: McGraw Hill.