Taking the high road to large scale solar power

In principle there’s more than enough sunlight falling on the earth to meet all our energy needs in a sustainable way, but the prospects for large scale solar energy are dimmed by a dilemma. We have very efficient solar cells made from conventional semiconductors, but they are too expensive and difficult to manufacture in very large areas to make a big dent in our energy needs. On the other hand, there are prospects for unconventional solar cells – Graetzel cells or polymer photovoltaics – which can perhaps be made cheaply in large areas, but whose efficiencies and lifetimes are too low. In an article in this month’s Nature Materials (abstract, subscription required for full article, see also this press release), Imperial College’s Keith Barnham suggests a way out of the dilemma.

The efficiencies of the best solar cells available today exceed 30%, and there is every reason to suppose that this figure can be substantially increased with more research. These solar cells are based, not on crystalline silicon, like standard solar cell modules, but on carefully nanostructured compound semiconductors like gallium arsenide (III-V semiconductors, in the jargon). By building up complex layered structures it is possible efficiently to harvest the energy of light of all wavelengths. The problem is that these solar cells are expensive to make, relying on sophisticated techniques for building up different semiconductor layers, like molecular beam epitaxy, and currently are generally only used for applications where cost doesn’t matter, such as on satellites. Barnham argues that the cost disadvantage can be overcome by combining these efficient solar cells with low-cost systems for concentrating sunlight – in his words “our answer to this particular problem is ‘Smart Windows’, which use small, transparent plastic lenses that track the sun and act as effective blinds for the direct sunlight, when combined with innovative light collectors and small 3rd-generation cells,” and he adds “Even in London a system like this would enable a typical office behind a south-facing wall to be electrically self-sufficient.”

Even with conventional technologies, Barnham calculates that if all roofs and south-facing walls were covered in solar cells this would represent three times the total generating capacity of the UK’s current nuclear program – that is, 36 GW. This represents a really substantial dent in the energy needs of the UK, and if we believe Barnham’s calculation that his system would deliver about three times as much energy as conventional solar cells, this represents pretty much a complete solution to our energy problems. What is absent from the article, though, is an estimate of the total production capacity that’s likely to be achievable, merely observing that the UK semiconductor industry has substantial spare capacity after the telecoms downturn. This is the missing calculation that needs to be done before we can accept Barnham’s optimism.

22 Responses to “Taking the high road to large scale solar power”

  1. Phillip Huggan says:

    I’m putting my money on printable polymer solar cells made more durably. I hope their durability can be improved.

  2. Richard Jones says:

    My instinct is to agree with you, Phillip. I think there’s a huge amount of scope for work to be done improving the performance of printable solar polymer solar cells, particularly in understanding the relationship between the processing conditions, the nanoscale structure that self-assembles during the processing, and the resulting device performance. I’m just in the process of writing a grant proposal to do just this sort of study, in fact, having had some useful conversations with Christof Brabec from Konarka.

  3. Zelah says:

    I understand our Nano enthusiasm for Solar, but…

    What happens at night?

    If climate change is for real (Iran instability is for real), then Nuclear is the only option until the Hydrogen/Solar economy starts which is 50 years away…

    An amateur mathematician

  4. Richard Jones says:

    One of the interesting points the Barnham article made was that in typical commercial buildings (he showed the data for Imperial College) demand for electricity is heavily peaked in the day-time, in part due to the high electricity demands of air-conditioning and refrigeration. Of course, demand for the two latter purposes is pretty strongly correlated with the amount of sunlight there is.

    I am an enthusiast for solar but I’m also realistic about the time its going to take to build up capacity, so I wouldn’t be as opposed to nuclear as an interim stop-gap as Barnham is.

  5. Phillip Huggan says:

    I think the solar economy is less than 5 years from beginning. It is the type of thing that can be implemented in bits and pieces as opposed to hydrogen needing new infrastructures built. 2005 advances in hydrogen storage were encouraging. I think a 6% room temperature hydrogen storage material is doable (what a US authority says is needed for vehicles). Right now a team is at 7.5% under cold temperature conditions.

    Iran looks stable to me…perhaps the “n” is a typo?

  6. Zelah says:

    Hi Philip

    When I was talking about Iranian instability, I was talking about the strong possibility of sanctions (How effective I do not know).

    Now regarding the Hydrogen economy, when will it be self sustaining economy without subsidies? My guess is competitive hydrogen production is 20 years off. That guess requires massive solar power deployment in North Africa!

    Nuclear is different.

    1. If oil is at 60 dollar a barrel, nuclear is ALREADY COMPETITIVE EVEN INCLUDING WASTE STORAGE!

    2. One could CLEANLY (except for nuclear waste) produce Hydrogen from salt water kick starting the process.

    3. Unless politics change, we will still need a nuclear deterent. Therefore we will need a nuclear industry no matter what the enviromentalists say.

    However, I could change my mind if something could be done via nanotech about CO2! Is there any really cool Nanotech (artificial chlorophyll CO2 conversion?).

    An amateur mathematician

  7. Phillip Huggan says:

    I see Iran as the most stable nation in the middle east, at the moment. If the sanctions are endorsed by Russia and China, they might be effective. But energy hungry China will surely not cut off one of her chief oil suppliers of the future. I think Russian management of fuel processing with IAEA supervision is the best that can be hoped for.

    I agree nuclear is competitive at $60 a barrel, but it is very difficult to forecast where oil prices will be in a few years time, and once a reactor has been slated for construction it is fixed and unalterable generating capital. There are many ways oil prices could plunge (or rise) in the years ahead. Nuclear is cheaper than oil, but not by too much.

    Sorry, the idea I meant to state in my previous post was that wind and solar power sources generate electricity during off peak loads. So if you oversaturate the landscape with these sources, they can be used to store hydrogen using a regenerative hydrogen fuel cell (wherever water is available). Hydrogen fuel cells can be made to operate in reverse (regenerate) very easily. There are still issues with safety in transporting hydrogen, but strong carbon composites should save the day.

  8. Richard Jones says:

    One additional point about nuclear is that while it probably is competitive now, this to some extent relies on the fact that the price of uranium is currently very low. If worldwide nuclear capacity increases a lot the price of uranium will rise considerably because there isn’t that much high grade ore in the world.

    In relation to hydrogen, one of the selling points of the generation IV reactors currently being designed is that they can be run hot enough to use the process heat to split water into hydrogen and oxygen thermochemically, which is a lot more efficient than first generating electricity and then splitting the water electrolytically.

    I’m not sure whether the desire to maintain nuclear weapons is a big factor in those states that already have them; the UK currently has a civilian stockpile of plutonium which amounts to 70 tonnes. The size of the military stockpile isn’t public but it’s probably a similar order of magnitude; this is a vast quantity compared to any forseeable military demand.

  9. Zelah says:

    Regarding Nuclear costs.

    It depends if you include Carbon emissions! If the government was to put into effect a Carbon Tax, to deal with global warming, no matter what happens in the marketplace, Nuclear is cheaper! Infact, due to the Fuel Taxes in the UK, Nuclear made Hydrogen would be cheaper than petrol even though hydrogen i believe is 3 times less efficient by weight! So, if you want a hydrogen economy, build new nuclear powerplants and Voila!

    Also here is a link outlining a realistic low price future for nuclear given the right research:

    http://www.wired.com/wired/archive/13.02/nuclear.html

    Finally, there are the costs of building Nuclear power plants. Basically, this boils down to the ‘Not in my backyard’ syndrome. Even though nuclear radiation from coal / gas powerplants are HIGHER than that from nuclear one, the public are unjustifiably scared. Well if we do the right thing and go nuclear, the government will just have to have some backbone! The truth is that we already subsidise alternative fuels which has not stopped the rise of carbon electrical production!

    There is not cost effective alternative in the short term!

  10. Philosophicles says:

    Carbon nanotube films are looking good for storing hydrogen in a battery form, that will replace current rechargable batteries, and could benefit the free energy movement. They are slated for possible production in 3 years from a new nanotech company at Nanergy.com. These batteries can currently hold about 1.5% of their weight in hydrogen, and they need to be at 2.5% to be competative. With these batteries we could use solar panels to regenerate our own private supply of hydrogen and store it safely, and use it efficiently!

  11. Zelah says:

    The problem Philosophicles is producing enough Hydrogen that it would be commercial. Yet again, this could only be done in enough volume in the North Africa desert with all of the political problems it provides!

    To reiterate, Nuclear is the only option in the SHORT TERM which can deliver these 3 fundemental design characteristics.

    1. It is competitive with Carbon based hydrogen production TODAY.

    2. There are NO POLITICS in terms of supplies (Major producers are Australia , Canada and USA).

    3. Medium/Long term cost predictability. Even if high grade uranium started to run short, then move to Fast Breeders and use plutonium / thorium / Low grade uranium . Finally move to Fusion post 2050 (Kick started or course by Fission)!

    Of course the major drawback is Nuclear Proliferation. I.e what do we tell the Iranians?

    This drawback is quite simple in my humble opinion (IMHO). Do not buy Iran oil! Rightly, the American see this as European weakness, who have ALREADY moved toward NUCLEAR (France, Germany, Belgium, UK etc) and could lead the way!

    What is really needed is a Nanotech solution to CO2 production! if not then Nuclear is the way forward!

    An amateur mathematician

  12. Zelah says:

    Another Note.

    Recycling CO2 gas.

    Has anyone got any recent info on Nakamichi Yamasaki Iron catalyst CO2 conversion to Butane / Propane utilising waste heat from power plants?

  13. David Wright says:

    I am amazed that this is being promoted as a new invention. I saw it first on an Australian Broadcasting Corporation programme called The New Inventors some time early last year. It was not a new invention then but an adaption of an earlier one seen first in the 1970′s

  14. Richard Jones says:

    David, I’m not sure whether you are talking about III-V quantum well solar cells, sunlight concentrators or the combination of the two, but in any case you’re of course right that they’re not new inventions. But the article I was talking about (and maybe I didn’t make this clear) wasn’t reporting them as such, it was arguing for an early large scale roll-out of the technology; it was about economics as much as science.

  15. Hugh Knowles says:

    With regards to the costs of nuclear and the potential of mcrogeneration it is worth reading Amory Lovins work at http://www.rmi.org/sitepages/pid171.php#NucFreeMil

    Nuclear is not economically viable and there are a number of other myths surrounding it which are analysed by Lovins. E.g. Nuclear stations are not as reliable as the industry would have you believe – even the new designs.
    Will leave RMI to do the rest of the deconstruction…..

  16. Steven says:

    Gentlemen, it is evident that you have pondered the energy situation, giving consideration to the future. I rather feel that Plasma and Fusion technologies will surpass the continued development of Solar. What is your perception of these technologies?

  17. Shawn says:

    Gentlemen,

    We all realize that high level radioactive waste takes 100′s of years to decompose. Solar and Wind Energies are the way to go for the benefit of our existing natural resources. I foresee building from the atom up will greatly decrease solar cell production costs and enable us to research and develop an alternative energy source that will be cost effective and good for our environment. My money goes to nanotechnology.

  18. Richard Jones says:

    Steven, I’ve not followed the fusion story in great detail, though I’m certainly aware of an increasing emphasis on this direction in the UK. There was a recent article in Science, though, which had a very sceptical view on its feasibility as a large scale power source on engineering and economic grounds.

  19. Steven says:

    I agree that thier is a need for environmental consideration. Plasma technology converts gas (Helium and Argon are commonly used) to plasma, a super heated state of matter. At this time I do not percieve an environmental concern over plasma. The temperatures that are attainable with plasma are almost surreal. This equates to megawatts of power with virtually no fuel consumption, barring the use of gasses. I insert this quote from Foresight Nanotechnology Inc. It’s a great site.

    “OrionSolar believes its dye cell photovoltaic technology can decrease the cost of solar energy to about $0.70 per peak watt, compared to the about $6 to $9 per peak watt of energy generated by traditional silicon-based photovoltaic cells.”

    Maybe your money will pay off in Solar.

  20. Richard Jones says:

    I agree that unconventional photovoltaics like dye sensitised nanoparticle cells hold a lot of promise – I wrote about these here a while ago.

  21. Zelah says:

    I am very disturbed by what Hugh Knowles believes.

    I am not disputing that there are cheaper alternatives to Nuclear. I am disputing that it is possible to save the planet from CO2 overheating cost effectively without Nuclear! Low CO2 emmissions like say 20% reductions are ineffectual against China / India combo!

    Unless you do not believe in CO2 Global Warming (which is fair enough!) http://www.rmi.org pose more questions than answers!

  22. David Lidzey says:

    Zelah – you said

    “I understand our Nano enthusiasm for Solar, but…

    What happens at night?”

    Provided excess electrical energy is recovered from PVs during the day, it is perfectly possible to store such energy using a bank of batteries or capacitors!

    It seems to me that solar energy provides a much longer term and safer alternative to nuclear power – particular when the costs of decommisioning (which often seem to become more and more expensive when they are practically implemented) – are taken into account.

    The large cost of building nuclear power plants will also inevitably reduce the amount of funding available to develop truly sustaininble energy sources.