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A review of the technology for reducing GHGs. Updated Jan 2010 |
Please note: this page is still under development; the statements made are an honest impression from various information on the web, but no guarantee is made for their accuracy. On this page:
Other
Technologies for Stationary Energy (i.e. electricity generation)
In this section: In comparing ways of generating electricity, there are several considerations:
I.e., can it guarantee to meet a predicted demand? At one extreme, wind is very unpredictable; at the other, hydro can be used to store energy from other sources (by pumping water back up). In between, an energy source may be reliable but inflexible, i.e. it's most efficient if you run it at constant output, or reliable and flexible but with no ability to absorb and store energy from other sources. This issue would be solved by large, cheap, efficient batteries, but there is no prospect of that any time soon.
I.e., how quickly can capacity be expanded? Given the urgency of climate change, we cannot wait 30 years for the ideal solution.
References: http://www.theglobaleducationproject.org/earth/energy-supply.php
In this section
Electricity from wind has been around for 120 years, with commercial generation since 1941. Current costs go as low as 6 to 7 cents/kWh for the most suitable sites, making it about the same as new coal-fired, and can be expected to fall a little as the technology evolves. Its main disadvantage is unpredictability, but mixed with other technologies could provide 20% of Australia's needs. References: http://en.wikipedia.org/wiki/Wind_energy http://en.wikipedia.org/wiki/History_of_wind_power http://www.res-australia.com/resources/about-wind-power.aspx http://beyondzeroemissions.org/category/keywords/renewable-energy/wind-energy/large-scale-wind-power http://www.evwind.es/noticias.php?id_not=3172
This concentrates the sun's rays to heat molten salts to 500oC. As needed, this is then used to generate steam to drive a turbine. Adequate salt storage and diverse sites in the grid make it suitable not just as baseload but as a flexible source to be mixed with unpredictable sources such as wind. There are two main versions: parabolic trough and power tower. Current generation cost is around 15 cents/kWh, but is expected to fall to the same or less than coal. References: http://en.wikipedia.org/wiki/Concentrated_Solar_Power http://www.beyondzeroemissions.org/media/newswire/molten-salt-magic-ingredient-091110 http://www1.eere.energy.gov/solar/pdfs/csp_prospectus_112807.pdf
This turns light directly into electricity, avoiding the inefficiencies of a heat stage and the need for water as a coolant. That also makes it viable for domestic scale generation. However, current PV materials are still rather inefficient and can overheat, and the most efficient are very expensive. Current cost is around 20 cents/kWh, but technological advances could make this much more attractive one day. References: http://en.wikipedia.org/wiki/Photovoltaics http://www.renewableenergyworld.com/rea/news/article/2007/08/what-solar-power-needs-now-49617
This involves injecting water into hot rocks deep underground. The water is recycled, but other water may be used as coolant. The key cost with this is the initial drilling; the hot rocks are deeper than most mines. Cost from most suitable sites is around 7 cents/kWh. There is a worry that the injection of water may trigger earthquakes. In principle, this may only be bringing on earthquakes that would have happened one day in any event, but it remains at least a legal issue. This may rule out some sites. There may be some amount of GHGs and other undesirable gases released from underground in the process. References: http://en.wikipedia.org/wiki/Geothermal_energy http://www.rnp.org/RenewTech/tech_geo.html
Biomass may be existing crop waste or purpose grown. If crop waste, the energy density is low, and the main cost is gathering it from a broad area. This tends to lead to small scale combustion, which in turn results in incomplete burning and smogs (which have a powerful greenhouse effect). If purpose grown, collection is still something of an issue, plus it may displace food crops. Either way, it is unlikely to provide more than about 10% of world demand ever. References: http://en.wikipedia.org/wiki/Biomass http://www.bmu.de/english/press_releases/archive/16th_legislative_period/pm/pdf/42805.pdf
The designs for collecting wave power are more varied than for any other energy source. Several years of experiments are needed to select the best. Current installations are achieving 15-20 cents/kWh, but this is expected to fall to 5-7 cents. Some estimates claim as low as 2-3 cents! In Australia, there may be limited sites producing reliable energy and close to urban centres. Even so, it has been claimed that it could supply 35% of Australia's current demand. References: http://en.wikipedia.org/wiki/Wave_energy http://www.rnp.org/RenewTech/tech_wave.html http://www.abc.net.au/rn/scienceshow/stories/2008/2378304.htm
Current installations are achieving 10-12 cents/kWh, but this is expected to fall to 4-6 cents. Given the high capital cost, it may surprise that the unit cost is expected to drop so. This may be because the land used is not considered of commercial value. The necessary landscaping impacts wildlife and may cause GHG emissions as with hydro. In Australia, there are few suitable sites. References: http://en.wikipedia.org/wiki/Tidal_power http://www.rnp.org/RenewTech/tech_wave.html http://www.sustainabilitycentre.com.au/TidalPowerWA.pdf
There may be significant GHG emissions from the reservoir. According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 W/m2 of surface area) and no clearing of the forests in the area was undertaken, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant. The best sites produce very cheap electricity (about half the price of coal), but Australia already exploits most viable sites. References: http://en.wikipedia.org/wiki/Hydroelectricity
CCGT stands for Combined Cycle Gas Turbine. This is the most efficient gas-based power generation to date. While it has only 60% of the CO2 emissions per unit of energy as coal, it is a more expensive fuel and the known reserves would only power humanity for 50 years at current demand. References: http://en.wikipedia.org/wiki/CCGT
Carbon Capture and Storage (CCS, or "Clean coal")
In addition to the CO2 produced in combustion, some CO2 and other undesirable gases are released during mining. Capture reduces the carbon footprint 80-90%. Despite the billions invested in trials, it shows no sign of being competitive with the best renewables, whether applied to new coal plant or retrofitted to existing plant. Even if the storage is safe for a thousand years, we would be leaving posterity a legacy they'd prefer to be without. References: http://en.wikipedia.org/wiki/Carbon_capture_and_storage#Australia
It is essential that we stop using this ASAP. Coal has been storing excess carbon safely for millions of years. Once we release it into circulation it will be hard to take it back out. References: http://en.wikipedia.org/wiki/Coal
While no GHGs are emitted during operation of the generator, there is a large footprint from the vast quantities of concrete needed for construction of the plant, plus the ongoing impact of mining and transporting the ore. Current nuclear power station production technology generates large quantities of radioactive waste that must be stored for centuries, some for millennia. At the same time, known reserves would only meet the world's energy demand for 200 years. Fast breeder reactors, still only experimental, could reuse existing waste, produce much less waste in future, employ sources other than uranium, and so extend the resource to thousands of years. The dream has for decades been fusion, the power source of the sun. This 'burns' water and promises almost limitless power for little radioactive waste. Despite decades of international effort, it is still unclear whether it can ever become reality. References: http://en.wikipedia.org/wiki/Nuclear_power_plant http://en.wikipedia.org/wiki/Environmental_effects_of_nuclear_power#Carbon_dioxide http://en.wikipedia.org/wiki/Breeder_reactor http://en.wikipedia.org/wiki/Nuclear_fusion
As well as technologies for generating electricity, it is important to look at how we could distribute it across the grid more efficiently. The present system uses alternating current (AC), even though direct current (DC) is more efficient. For long-distance transmission, very high voltage levels are needed for efficiency. These must be stepped down to much lower voltages for domestic use. To transform voltage so, the current needs to be AC. When the grid was built, converting from DC to AC was inefficient. Nowadays there better ways to convert DC to AC, so a DC distribution network would save energy. And given a more efficient distribution network, there are more options for siting the power generation. References: http://en.wikipedia.org/wiki/Electrical_power_industry#History The special consideration for transport is portability. Glossing over walking and cycling, clearly to be encouraged for their health benefits as well as being carbon-neutral and cheap, we have:
Electric Vehicles Even if the electricity is produced from fossil fuels, electric vehicles have a lower carbon footprint than petrol and diesel vehicles. This is because power stations convert fuel to electricity with an efficiency of up to 40%, whereas a car engine only achieves about 20%. Some is lost in the transmission of the electricity, but it still comes out ahead. A key problem has been the batteries, both their weight and their life expectancies. Lithium ion batteries and their derivatives have been a great advance, but still expensive.
Hybrid Vehicles
Hybrid vehicle can mean any of a variety of technologies: TBA
Biofuels Biofuels can be produced from
These can only provide a small proportion of total demand, but are being used, mostly by the companies that generate the waste.
Hydrogen The hydrogen is produced from electricity, but this can be from intermittent sources, such as wind power. To replace a given quantity of petrol you only need a third of the hydrogen by weight, but that is vastly more by volume at atmospheric pressure. So storage is a problem. It can be pressurised, as with LPG, or stored in a tank containing materials which absorb the hydrogen. In the vehicle, the hydrogen can be burnt to drive a combustion engine much like that used with petrol, or it can be converted back to electricity in a fuel cell. The latter is much more efficient but there are major technical challenges still to be overcome.
LPG Already widely used, but emits 80% as much CO2 as petrol and global reserves are limited.
Mass Transit
TBA http://en.wikipedia.org/wiki/Green_transport Since there is already more CO2 in the atmosphere than is safe (380+ ppm compared with 350), there is a need to draw CO2 back out. This can be done by natural means such as increased forest, natural with intervention (biochar), or by engineering (artificial trees).
Biochar is another name for charcoal; a fuel that will burn at the higher temperatures needed for some processes than would the biomass from which it was made. But calling it biochar puts the accent on an alternative use, namely, to sequester carbon. Some energy is still derived from the charring process, but much less than by burning the biomass completely. The resulting char is used to remediate soils, greatly improving their retention of water and nutrients, while also removing the carbon from circulation for hundreds of years. It has been calculated that carried out on a world scale, largely by peasant farmers, this could draw down enough carbon. Organising it would be a major challenge.
Artificial trees and scrubbing towers These are methods for extracting CO2 from the atmosphere, but still as CO2. It then has to be sequestered in the same way as with CCS. This may be cheaper than retrofitting CCS to existing plant because the scrubbers would be sited close to the repository.
Ocean fertilisation Phytoplankton are the main photosynthesising organisms in the oceans. Their abundance is often limited by lack of iron, so the idea is to fertilise the oceans with iron and generate phytoplankton blooms to absorb CO2. Numerous experiments have been conducted, with varying results; in some cases the sequestration is only temporary. If it works, it is relatively cheap. The main concern is the inherent uncertainty in monkeying with ecology. Experiments continue. References: http://en.wikipedia.org/wiki/Biochar http://physicsworld.com/cws/article/news/40254 http://en.wikipedia.org/wiki/Carbon_dioxide_air_capture http://en.wikipedia.org/wiki/Iron_fertilization The term geo-engineering has been used to cover rather a wide range of proposals.
Low-tech:
Most proposals relate to rooves. In some places, this can pay for itself in reduced air-conditioning costs. However, the same savings might be made more cheaply with insulation, so an incentive is needed to encourage the whitening of rooves.
High-tech:
References: http://en.wikipedia.org/wiki/Cool_roof http://2020science.org/2009/05/27/steve-chus-white-revolution/ http://en.wikipedia.org/wiki/Geoengineering http://www.climateandfuel.com/pages/exotic.htm http://www.mindfully.org/Air/2002/Decreased-Pan-Evaporation1nov02.htm Other Agricultural methane TBA Renewable Energy Policy Network for 21st Century
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