Since the international community began taking climate change seriously, wind, sea and solar power have been trumpeted as the answer to the world's eco-prayers. Now the great white hopes are carbon capture and storage (CCS) and biomass.
Both are said to be capable of contributing to a worldwide cut in CO2 emissions and both, unlike their feted predecessors, have the potential to work on an industrial scale. But which works the best?
Carbon capture to reduce emissions
Carbon capture and storage is exactly what the name suggests it is. CO2 produced during the burning of fossil fuels is captured and stored in natural containers such as old oil and gas fields. Supporters point out that as an abundant energy supply, fossil fuels are here to stay and therefore CCS is the only viable way to achieve the 80% reduction in CO2 demanded by G8 leaders before 2050. They say that a power plant using CSS can reduce CO2 emissions by 80%-90%, although critics point out that some of the stored gases may leak back into the atmosphere.
Creating energy from biomass sources like waste is supposed to be a carbon-neutral process, as the CO2 released when the energy is generated is balanced by that absorbed during production. However, even supporters agree that CO2 emissions can still be significant, depending on the growth cycle and type of the biomass used.
"At plant level, conversion to CCS and biomass can both reduce CO2 emissions by over 90%," says Emerging Energy Research's research director Alex Klein. "However, if you're looking for something to help reduce emissions globally it has to be CCS. Transporting the biomass required to work on such a huge scale would be too big a challenge."
In the UK, biomass is ahead of CCS in some respects. E.ON and Scottish Power are still competing for government backing to build the first CCS coal-fired power station.
CCS is, however, in commercial use at several plants in the US and supporters say it would be quicker and easier to implement than biomass on an industrial scale as it can be done using existing infrastructure.
"It isn't necessarily quicker to introduce CCS than biomass," says Klein. "It all depends on the specifics of the site. Identifying where to store the CO2 removed by CCS can be a long process. Biomass plants can be held up by access to long-term sources of fuel. If they have to invest in processing and collection it can take a long time to organise."
The cost of CCS
The environmental benefits of CCS and biomass may be huge but so are the costs of implementing them. Biomass is expensive to harvest, store and extract and adding CSS features to existing power stations is not cheap. However, both methods have financial upsides that their supporters claim make them cost effective.
CCS not only allows the continued use of low-cost fossil fuels, it also means that CO2 can be injected into aging oil fields and unminable coal seams to boost recovery of crude oil and coal bed methane.
According to figures published by Advanced Resources International (ARI), using CO2 in this way could by 2012 annually reduce emissions by 200 millions tons, add 260 million barrels of oil and increase natural gas production by 1.1 trillion cubic feet. ARI calculates that CCS would therefore generate $170bn worth of enhanced resource recovery by 2012 and a staggering $4tn by 2050.
In theory, biomass is cost effective because the feedstocks are relatively cheap and can be sourced locally, cutting down the need for expensive and environmentally damaging transport.
The energy can also be supplied locally, which reduces the need for large pipelines. However, in reality some biomass producers are known to import material, which negates many of the benefits.
"It's impossible to compare CCS and biomass on costs unless you know the specifics of the sites," says Klein. "It's certainly fair to say that the CO2 captured from CCS can be used to help enhanced oil recovery. It depends on where you're located, but there's some short-term prospects for this in the US and I think longer term we might see it in the North Sea and China.
"Biomass production depends on the region. The majority of projects source fuel locally and are therefore constrained by what is available. Some large-scale operators in northern Europe import their fuel sources, which has implications for cost and overall emissions."
Biomass energy has several other environmental issues to contend with. Turning waste into energy means less rubbish being left in potentially harmful landfill sites. This can help reduce costs and prevent landfill gas, which is 21 times more potent than CO2, being released into the atmosphere. Burning biomass also releases fewer atmospheric pollutants like sulphur dioxide than burning fossil fuels.
On the flip side, critics point out that an increase in biomass energy would lead to large-scale crop production in order to keep up with demand for feedstocks. This would mean large numbers of trees being cut down, which would damage the natural carbon balance and potentially damage wildlife.
BECCS and the future outlook
The world clearly needs to do something about the amount of CO2 being released into the atmosphere. The question is: do you capture and store it or do you produce energy using methods that don't produce so much of it? The answer, quite possibly, lies in a combination of the two.
Bio-energy carbon capture and storage (BECCS) is an emerging idea that seeks to combine biomass production with CSS techniques to generate energy with negative CO2 emissions.
The International Panel on Climate Change believes BECCS will be vital in achieving emissions reduction targets as, if successful, it can actually help remove CO2 from the atmosphere.
"The success of BECCS is probably going to be commensurate with the scaling of CCS," says Klein. "If that industry develops there will almost certainly be a role for biomass within that. CCS has significant potential to address the risk of CO2 on a global scale but in reality both CCS and biomass will have a part to play in the future."