If solar power is to ever displace fossil-based power, then cost-effective ways of storing that captured solar energy -- must be developed.
For all those times "when the sun don't shine."
Well according to this little noticed news from University of Arkansas researchers -- such low cost means of storing the concentrated rays of the sun, may not be a far distant, future dream. They developed a Thermocline Heat Storage reservoir system with a extremely low cost kWh footprint, and without the common problems usually associated with other such energy cycling systems.
At least that is among their claims ...
by Nicholas Brown, cleantechnica.com -- November 12, 2012
[...]$0.78 per kWh, efficiencies of up to 93.9%, with up to 600 C thermal storage ...
The New Method
The new method from the University of Arkansas researchers is a structured thermocline system in which there are parallel plates of concrete with steel pipes running through them. The steel pipes transfer heat absorbed by solar panels into the concrete, which stores it until it is needed to boil water and produce steam (which is usually the case), or supply heat to other heat-powered generators such as Stirling engines or thermoelectric modules.
This thermocline concept survived temperatures up to 600 degrees Celsius (1,112 degrees Fahrenheit) and absorbed heat at an efficiency of 93.9%.
It has an impressively low cost of $0.78 per kWh, far less than the U.S Department of Energy’s goal of $15 per kWh.
To give you a better idea of how this compares to batteries: Lead-acid batteries cost upwards of $25 per kWh, lithium-ion batteries cost $50 to $100 per kWh. Lithium-ion batteries can last 4 times longer than lead-acid batteries depending on the type and usage.
OK, so what's the catch? Or it is that Americans truly love their fossil fuels ... and that never-ending, inevitable pain-at-the-pump?
Needless to say, I was intrigued. So did a little more digging, and eventually found their presentation papers. (I hope their professors gave them an A.)
Here are some of the significant snippets from each those little-noticed papers:
DEVELOPMENT OF A STRUCTURED THERMOCLINE THERMAL ENERGY STORAGE SYSTEM
Brad M. Brown
Matt N. Strasser
R. Paneer Selvam
University of Arkansas
Department of Civil Engineering
4190 Bell Engineering Center
Fayetteville, Arkansas, USA
The main problem encountered in thermocline, TES systems is thermal ratcheting. Thermal ratcheting occurs during thermal cycling of the TES system. Increased tank temperature during the charge cycle results in thermal expansion of the tank; expansion of the tank allows smaller material from the packed aggregate bed to settle towards its base. When the tank cools and contracts during the discharge cycle, residual stresses are introduced to the tank’s walls due to the material settlement. Repeated thermal cycles can result in catastrophic rupture of the tank.
This paper focuses on the development of a structured thermocline TES system with concrete replacing the typical, packed-bed filler material. Replacing the packed bed with structured concrete avoids the issue of thermal ratcheting. Solar salt is incorporated as the heat transfer fluid (HTF).
Concentrating solar power plants focus the sun’s emission to heat a HTF fluid that is run into a power plant’s power block to drive the generation of electricity. A problem with CSP plants is that they cannot produce electricity when there is cloud cover or during the night. TES systems are being developed to continue to supply heat to the power plants during times when direct sunlight is not available.
Three forms of energy storage for TES system concepts exist: sensible heat, latent heat, and chemical storage. Of the three, sensible heat storage has been suggested as the most practical option to store thermal energy (Herrmann and Kearny 2002).
Concrete, which has an approximate media cost of $1 per kilowatt-hour thermal (Hermann and Kearny 2002), has been researched as a sensible heat storage medium.
Concrete and molten solar salt were incorporated in a TES system and proved to be a promising combination. The molten solar salt incorporated in such TES is capable of
operating at temperatures exceeding 500 C (Coastal Chemical Company 2011).
Depictions of the cross sections of thermocline tanks populated with each of these two arrangements are provided in Fig. 1.
Fig. 1: Axisymmetric (Left, 1A) and Parallel-Plate (Right, 1B) Concrete Arrangement in Thermocline Tank
Concrete can store heat? Who knew?
University of ArkansasI guess the concrete just needed someplace for the expanding thermal pipes to go ...
R. Paneer Selvam (PI)
Matt Strasser (GRA)
Paper # 0074
Goal: Develop a Thermal Energy Storage (TES) System to Increase Economic Viability of Concentrating Solar Power Plants (CSPs)
• A Structured Thermocline TES is a Viable Option to Decrease TES Cost Compared to the Cost of a Two Tank System
• The Structured Filler Material’s Geometry Should be Optimized to Maximize Heat Transfer Between the HTF and Filler Material
• A Parallel Plate Filler Material Model Provided Higher Discharge Efficiency and Energy Storage Capacity than a Axisymmetric Model
• Axisymmetric Model: 62.68 % and 12.22 kWh (Per Unit Cross Section)
• Parallel Plate Model: 65.59 % and 16.41 kWh (Per Unit Cross Section)
This research work was supported by a grant from the U.S. Department of Energy (Grant # DE-FG36-o8G018147) through the University of Arkansas.
So the Government (us) funded their work -- so does that mean that the Government (we the People) will ever let us, the tradition-bound American energy-consumer, ever benefit from it?
Even though the sun don't shine all the time -- it does appear that there are cost effective ways of saving a big chunk of that Solar Energy, for the inevitable rainy day.
And hey we, us, the Government of by and for the people, happen to own the patents. No middle-man oil barons about it.
Just Free, Clean, Concentrated Energy from the Sun -- waiting for someone smart enough to "bottle it" ... someday.
Shoot, it might even be us ... we the people, that make it happen someday ... (like last week).