The Intertubes have been buzzing over a new “metallic grass” created from a common tobacco virus, which scientists have been deploying to make water boil more efficiently. That means creating more steam with less energy, and that could be a really huge deal for power plants that run on steam-driven turbines, so naturally our thoughts turned to concentrating solar power.
Concentrating solar power (CSP) has taken its share of lumps from critics, the basic complaint being that it is not as cost-effective as other forms of solar energy harvesting. Stepping up the efficiency of the CSP process could be a game-changer, so let’s take a look at how that tobacco virus fits in.
Concentrating Solar Power Today
For those of you new to the topic, our friends over at Argonne National Laboratory have a good rundown on the basics of CSP. The general idea is to use mirrors to corral a wide swath of solar energy onto a narrow field, which enables you to heat molten salt, oil, or some other special fluid.
The fluid then goes to a more or less standard electrical generating system, where it boils water for steam to run a turbine.
If that sounds relatively inefficient compared to your typical photoelectric solar system, which generates a current at the solar cell itself, you have company. Here in the US, our friends over at Engineering.com recently summed up the state of CSP technology and concluded that “from a dollars-per-watt standpoint, these CSP plants do not provide the most bang for the buck.”
Nevertheless, the Energy Department has staked its reputation on a recently completed series of five utility-scale, high-profile CSP projects in the US. Along with the aptly named Agua Caliente in Arizona, that includes the Google solar showcase Ivanpah in California.
Those efforts have actually been paying off, and the cost of CSP has been sinking rapidly over the past few years. The Energy Department is continuing to sink funds into efficiency R&D to help bring costs down even further, partly with the help of next-generation, integrated energy storage systems.
Although CSP may still be less efficient than your typical photovoltaic system in terms of the raw numbers, when it comes to planning out the power supply on a regional basis, utility-scale CSP could compete against natural gas, at least in some areas.
A Better Tomorrow For Concentrating Solar Power
As far as efficiency improvements go, the new tobacco virus discovery could be huge. While the Energy Department has been focusing mainly on advancing the solar end of the technology, CSP steam turbines are typically standard, tried and true pieces of equipment. In other words, low-hanging fruit, ripe for the picking.
The new research comes to us from Drexel University. It involves the field of phase-change heat transfer, which has to do with how fluids boil, evaporate, and condense.
When you’re looking at ways to make the conversion of fluid to steam as efficient as possible, the key factor is to balance the introduction of liquid with the rate at which vapor is being produced.
They have a name for when that balance fails — critical heat flux — and it is definitely a thing to be avoided according to lead researcher Matthew McCarthy:
Critical heat flux is essentially the failure of a surface during boiling, where the production of vapor cannot be balanced by replenishing liquid. The result is an uncontrollable and often dangerous increase in surface temperature.
What happens is that a layer of vapor forms over the surface, preventing heat from dissipating into the liquid.
The Tobacco Virus Cure
The solution would be some kind of surface treatment that can either delay the formation of the vapor layer or eliminate it entirely. That would involve some kind of “wicking” mechanism that enables the surface of the liquid to stay wet instead of trapping a layer of vapor.
That’s where tobacco comes in.
The Drexel team has found that the tobacco mosaic virus has a structure ideal for wicking. It is relatively simple as far as viruses go. It’s a rod-shaped structure with thousands of protein strands surrounding one strand of RNA.
The team introduced a mutation that acts like a molecular-scale “hook,” enabling the virus to attach itself to metal surfaces as well as silicon and polymers. From that platform, it forms a layer of nanoscale bristles.
The next step is a metal shell over the bristles, which puts the viruses out of action. What you’re left with is the aforementioned “metallic grass.” Like super-tiny sponges, the bristles wick liquids in and keep them in contact with the surface.
Here’s an image of the bristles coated with nickel, on a silicon platform:
The icing on the cake, in terms of cost-effectiveness, is that it’s relatively inexpensive to create metallic grass. Here’s McCarthy again:
It requires no electricity, power, heat, or special equipment—just a series of solutions at room temperature. After the coating process is complete, the now-inert viruses are fully encased, resulting in a conformal coating of high surface area metallic nanostructures.
So far, the team has found that it can achieve a significant (“greater than three-times”) increase in critical heat flux, which means that you can get your system to keep operating under a higher rate of heat transfer. They’ve also found that the coating triples the efficiency of the boiling process.
In addition to using the new coating in new systems, McCarthy also foresees using it to retrofit existing systems, so you could see those five showcase CSP systems in the US stepping up their game.
Image Credits: (top, via Wikimedia Commons) “TMV structure simple” by Thomas Splettstoesser (www.scistyle.com); (bottom) courtesy of Drexel University.
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