Tag Archives: Solar Energy

Graphene: Big promise for new solar technologies

A big step in improving the efficiency of photovoltaic cells in on the horizon. A paper published over the weekend in Nature Physics describes the ability of a substance called Graphene to convert a high percentage of the energy from sunlight into electricity. Graphene uses more of each photon’s energy, and a wider range of photons of different energy levels (using a broad spectrum of the Sun’s energy), compared to existing solar cells. From the abstract of the paper:

The conversion of light into free electron–hole pairs constitutes the key process in the fields of photodetection and photovoltaics. The efficiency of this process depends on the competition of different relaxation pathways and can be greatly enhanced when photoexcited carriers do not lose energy as heat, but instead transfer their excess energy into the production of additional electron–hole pairs through carrier–carrier scattering processes. Here we use optical pump–terahertz probe measurements to probe different pathways contributing to the ultrafast energy relaxation of photoexcited carriers. Our results indicate that carrier–carrier scattering is highly efficient, prevailing over optical-phonon emission in a wide range of photon wavelengths and leading to the production of secondary hot electrons originating from the conduction band. As hot electrons in graphene can drive currents, multiple hot-carrier generation makes graphene a promising material for highly efficient broadband extraction of light energy into electronic degrees of freedom, enabling high-efficiency optoelectronic applications.

Peter Sinclair has summarized the info on Graphene and has links to various sources here.

K. J. Tielrooij,J. C. W. Song, S. A. Jensen, A. Centeno, A. Pesquera, A. Zurutuza Elorza, M. Bonn, L. S. Levitov & F. H. L. Koppens. Photoexcitation cascade and multiple hot-carrier generation in graphene. Nature Physics (2013) doi:10.1038/nphys2564. Source

Photo of solar cells credit: bkusler via Compfight cc

Is Solar Energy Totally Bogus or Something that Gives Hope?

I recently posted a simple Internet meme suggesting that if we subsidized solar energy like we subsidized fossil fuels that this could be good. I posted that on Google Plus an it engendered way over 300 comments, many of which attempted to explain, often rather impolitely, that solar energy was inefficient or in some other way bad. I’m pretty sure most of those comments come to us courtesy of the bought and paid for climate change denialist campaign, funded by Big Oil to the tune of many tens of millions of dollars to date. Most of the commenters were saying similar things, most of which were either incorrect or irrelevant, and far too many of them showed up on this comment at once to be explained by normal internet behavior, at least on my Google Plus page. This was a move made by the denialists, and rest assured … they are doing this more and more often as time goes by.

What I found interesting about this is the fact that the main complaints were about how inefficient, expensive, or otherwise technologically poor those cheap Chinese photovoltaic cells are. I’m not going to argue about that here. I’ve got some friends who have put those photovoltaic cells on their homes and they are glad they did it. I take their word above random anti-Planet internet trolls. I also know that simple photovoltaic fuel cells are used in a lot of highly specialized applications where running a wire to some light or comm device or something is impractical, but a battery charged up by a solar cell will do. The detractors of solar energy are so vehement in their position on this that they would probably insist that building a miniature coal plant next to the remote airport up by the cabin, or next to the highway by some DOT electrical device would be preferable.

Here’s the thing. When I say “solar” I mean energy produced by accessing radiation coming form the sun more or less directly. Wind energy is a form of “solar” because the wind moves around because of the sun. Fossil fuels are solar because it was photosynthesis that converted the Sun’s energy to carbohydrates. But of course I’m not talking about that. I am talking about the hand full of different ways in which solar energy can be harnessed pretty directly including but not limited to cheap Chines solar panels.

The most obvious use of solar energy is passive heating. Back in the 1970s, we (in the US anyway) discovered that there was an energy crisis. We then promptly forgot about it, as various suficial patches were applied and energy seemed to not be an issue any more. But if we were not acting like total morons (which we tend to do) we would have gone ahead and added attention to passive solar to zoning regulations and to best practices in architecture. Of course, that did happen to some extent, but not in any comprehensive or meaningful way. Imagine if most buildings–residential, commercial, built over the last 40 years were built with attention to passive solar design. That would probably have resulted in a decrease in fossil fuel use for those buildings in the two digit percentage range. A lot of buildings have been built over the last four decades. We’d be using several percent less fossil fuel for our buildings today had we done that.

The professional and avocational naysayers of solar energy helped cause us to miss that boat, and they want us to keep missing that boat. They should be ashamed of themselves.

Then there’s direct solar heating. This is another way to use solar energy in which you pass liquids through devices that are set out in the sun (i.e., on your roof). This may be used directly or indirectly to heat the water we use in our buildings. In areas where there is never a significant freeze, such devices can directly heat the water. Otherwise, a non-freezing liquid is used to capture and store the heat, which in turn is transferred to heat water or air inside a home or other building. This may be one of the best ways to use solar energy since it is relatively low tech and can be made of easily obtainable parts. Cheap devices can create essentially free energy. Imagine if most homes, commercial buildings, and other structures built over the last 40 years had a direct solar system to contribute to the heating of water and air in the building. Again, there’d be a few percent off our current annual carbon contribution to the atmosphere.

Then there’s the rather esoteric and very experimental but very cool looking use of solar in which fluids stocked with organisms are passed under the sunlight up on the roof. In one such system, the CO2 rich exhaust from a gas or oil heating plant is passed through a liquid full off algae. The algae live off the CO2 and sunlight, and are strained out to produce … I don’t know, soilent green or something. You can probably burn the algae. This serves as a carbon sink. This is probably not a technology that will make a major contribution to anything until we have genetically modified algae working in concert with solar collectors to do something really interesting.

Then there are the high performance solar systems, of which there are two types. Both involved concentration of solar energy using mirrors or lenses. In CSP, of Concentrated Solar Power, piles of mirrors are used to focus the sunlight on a thing that gets heated way up and runs a turbine. There are many systems like this running around the world, and the general consensus globally is that wherever you have a lot of sun (arid regions, generally) this method of producing electricity is cheaper per watt than some other methods, and on par with the average fossil fuel plant. The other type of high tech system concentrates the sunlight on a device that converts sunlight to electricity.

And, then there are the grand schemes of solar power. Such as…

… TREC, which is a grand vision for connecting solar power in North Africa, wind power from the Eastern Mediterranean to the North Sea, bio-mass, and hydropower with a high-voltage direct current (HVDC) system of power lines to provide assured renewable electricity for the Mediterranean basin and Europe.

… written up here.

So those are several ways in which solar energy can be exploited. Photovoltaic panels is only one way. So when someone suggests that we should consider using more solar energy, maybe subsidize it to get the industry moving along, or simply to make it more common in recognition of the very high external costs of fossil fuels (which are not counted in the actual cost of running coal power plants or driving trucks with diesel, etc.) don’t bring up cheap Chinese photovolatics first.

Every flat roof on a school, parking garage, shopping mall, or other commercial or industrial building that is not grabbing sun in some way and using it for something is an affront against the planet and an insult to our grandchildren.

Solar Furnace Photo Credit: pluvialis via Compfight cc