Access
This article is part of Nature's premium content.
Published online 13 August 2008 | Nature | doi:10.1038/454816a
Energy alternatives: Electricity without carbon
To read this story in full you will need to login or make a payment (see right).
Comments
Reader comments are usually moderated after posting. If you find something offensive or inappropriate, you can speed this process by clicking 'Report this comment' (or, if that doesn't work for you, email webadmin@nature.com). For more controversial topics, we reserve the right to moderate before comments are published.
Thanks for much needed information on energy alternatives. Did the authors consider the possibility of harvesting some of the 50,000 billion metric tons of Hydrogen that the Sun discards each year in the solar wind? Until there is better evidence that CO2 causes global warming, it may be premature to report, "So a global response to climate change must involve a move to carbon-free sources of electricity." http://myprofile.cos.com/manuelo09
Excellent review of energy generation alternatives. Two quick comments. First, the article says that hydropower is "second only to fossil fuels". It says this same thing about biomass. Which is it? Second, in the disadvantages for hydropower, the release of methane and CO2 from decomposing biomass is sited. I have heard this quoted from anti-dam people before and it strikes me as a little deceptive. Are you saying that without the dam, the biomass would *not* decompose? That's a bit like saying that the reason leaves fall off trees is because of nearby dams. Also, it is important to note the CO2 generated by rotting vegetation was only recently pulled from the atmosphere. This is a net zero carbon emission and is part of the normal seasonal cycle of the earth as seen in the Keeling curve. One might even argue that a dam facilitates the removal of carbon from the atmosphere because some of the biomass is captured as sediment which is not released from the bottom of the catchment basin. But that's probably miniscule.
Thanks for a great summary of energy generation pros and cons! However, I think the debate on energy technologies misses one critical element: our behaviour as energy users. Clearly, sustainable and carbon-free energy generation is a great goal and some very innovative solutions are appearing. It would be equally impressive to see some of the same enthusiasm directed toward 'energy education', or seeking ways to simply use less. Ultimately, we will need to question the assumption that energy generation capacity must always increase. Better to do it sooner than later. regards
David: hydropower is second in terms of electricity generation capacity, while biomass is second overall: most biomass is burned in fires and stoves, though, not used to generate electricity Oliver Morton
This is an excellent review but, further to Adam's comment, we tend to concentrate on the supply side and neglect improving energy efficiency which, particularly in the case of housing, can have considerable health and wellbeing impacts. I live in Christchurch, NZ, and at the current price of electricity here (ca. 8p a unit)it is estimated that some 54 000 households out of the 386 000 in the city are affected by 'fuel poverty'(>10% of income is required to achieve adequate warmth). Improvements in insulation etc. would give substantial social and health benefits that increasing power generation would not deliver
For David Myer's question: http://www.google.com/search?q=biomass+reservoir+decomposition+anoxic+methane
Not to belabor the point made in other postings on increasing efficiency as a carbon-free strategy for meeting electricity demand, but there is much hard data available on the costs and potential of this approach. Setting higher efficiency standards for appliances, establishing building codes requiring high efficiency lighting, better insulation so that air conditioning costs are lower and use of natural light are all examples of how we can use electricity more efficiently. Harvesting these "negawatts" may be the fastest and cheapest way to cut carbon emissions. Amory Lovins and his Rocky Mountain Institute have spent decades studying this approach.
I was very disapointed that algea farming was not mentioned under bio mass anergy. Algea can produce 20000 gallons of suel oil per acre per year. One tenth the state of New Mexico could provide all of the oil we need. No imported oil and the oil supplied would be carbon neutrol. If you don't believe it look up algea farming on the internet.
The capacity factor of solar cited is of course quite location sensitive, so it inappropriate to quote a single capacity factor as you do when you write, "Of all renewables, solar currently has the lowest capacity factor, at about 14%." As a counter-example, the capacity factor of the Stirling Energy Systems plant being built in Victorville, CA for Southern California Edison is estimated as 23.9%. The company Ausra claims to have a cost-effective Thermal Energy Storage for their Concentrated Solar Power system. They claim in their whitepaper that they could power the U.S. 24x365. They write, "The 2005/6 U.S. national grid had a generating capacity of 1067 GW and non-coincident peak load of 789 GW. Based on the current technology, a CLFR with SM3 and storage would require 1.5 square miles for 177 MW, translating a national land requirement equal to 23,418 km^2 or a square with 153 km sides."
"Algea", nothing. The energy problems of the world will be solved by a website I went to that reduced my computer's electricity consumption to -2 kW. I know I wrote down the URL somewhere. There was frost on the cooling air outlet. I think energy carriers are important (http://www.eagle.ca/~gcowan/235_248.pdf ).
The biomass portion of this article neglects the large possibilities from bioengineering of algae and plants to produce easily extracted liquid fuels and biochemical products using tailored biosynthetic pathways. Current genetic engineering techniques now make readily feasible the ideas put forth by Melvin Calvin over 40 years ago. He was just a bit ahead of his time. For example one can readily imagine large expanses of poor quality land being used to produce fuel from algae using sewage as a source of nutrients and salt water as the water source. This would avoid the use of farmland for biofuels with the concommitant effect on food prices we already see happening.
You appear to have neglected solar power satellites - perhaps not feasible immediately, but the obstacles are engineering ones, not theoretical breakthroughs. One of the above technologies (probably nuclear) could provide enough capacity until a workable solar power satellite system could be developed. We don't have to limit ourselves to the sunlight that hits the earth...
A wellcome overview! Just to mention that a summary of this review has appeared en français at http://www.sauvonsleclimat.typepad.fr/ It contains a couple of critical comments on some of the proposed figures for the future.
One thing is for sure. Liquid fuels, biofuels or otherwise, are going to become a precious commodity worth their weight in gold. We need to prioritize finding ways to use as little as possible. I'm skeptical we will find ways to produce liquid biofuels without destroying carbon sinks and biodiversity or driving up the cost of food, especially in the short term. And if we ever do, you can bet that producing them will be incredibly expensive compared to simply pumping an energy dense liquid out of a hole in the ground.