IV. Conventional Fossil-Fuel Electricity Generation
(originally published May 14, 2007)
In the last 3 posts, I have brought in Ulf Bossel’s electron economy concept to highlight the efficiency and environmentally friendly potential of an economy that relies to the highest degree possible on energy delivery through electricity. Building an electron economy means replacing where feasible and desirable combustion of fossil fuels with electric-driven transport and heating applications. In the second post, I’ve discussed how electricity can be distributed efficiently through the world’s electric grids and how these might be improved. The last post was a quick overview of some developments in the area of mobile electricity storage, one of the key areas of innovation and improvement that will decisively influence future demand for electric energy in the transport sector. Not yet in the picture though is how, in the first place, the grid or for that matter storage devices are supplied with electric current or electric potential.
Electricity is generated through physical or chemical processes whereby electrons are impelled to flow or have the potential to flow with a certain force through a conductor. With the exception of photovoltaic cells, most electricity is generated by dynamos: assemblies of conducting wires rotated through a magnetic field that in turn induces a current in those rotating wires. We are thus indebted to the intuitively difficult to understand relationship between electricity and magnetism for much of the electric energy we use. In dynamos, the energy required to make electricity is largely the energy needed to rotate these often rather massive wire assemblies through the magnetic field. In most cases, the rotational energy is created by heated gases/water vapor that push a turbine to rotate around its axis that in turn is attached to the dynamo. In windmills, wind energy pushes the vanes of the windmill (the turbine) that transmit their rotational energy to the dynamo contained within the head of the windmill. Alternatively, in a photovoltaic cell, the energy of photons from light displaces electrons in a specially designed semi-conductor that in turns produces a current in an attached conducting wire.
Currently (no pun intended), the energy required to heat the gases that turn most dynamos comes from the burning of fossil fuels, mostly coal and natural gas. One of the main challenges of creating a sustainable economy is finding ways to generate electricity (and energize transport) without putting fossil carbon into the atmosphere. In my first in a series on electric generation, I will deal with the most problematic sources of rotational energy for dynamos, the fossil fuels.
One of the major challenges for powering the electron economy in the next couple decades is dealing with coal. Coal is, from the point of view of climate change as well as more localized forms of pollution, the dirtiest way to generate electricity. Coal has a high carbon content with mixtures of various impurities that are sent into the air when coal is burnt. Per unit energy released, burning coal creates more carbon dioxide than natural gas and most petroleum derivatives as well as other chemicals such as oxides of nitrogen and sulfur. It is also the most plentiful fossil fuel on earth and coal deposits are widely dispersed around the world, including an approximate 400-year supply in North America as well as substantial deposits in China. Continuing and expanding the use of coal is a massive temptation for policy makers, investors, and system operators as it is cheap and plentiful.
Currently coal-fired plants generate 50% of the electricity in the United States and China is rapidly building coal-fired plants to fuel its rapid economic growth. Furthermore there are various initiatives to prolong the use of coal by designing ways to capture and store carbon dioxide gas after burning coal. How we as a species deal with coal and whether we use coal or desist from using it, will determine in large part how we deal with climate change.
“Clean Coal”: An Oxymoron?
President Bush and others have hailed “clean coal” as a source of energy independence and climate security. The phrase “clean coal” has been around for a number of years and can refer to a wide variety of processes that clean the emissions that come from burning coal. In most advanced industrial nations with environmental regulations, gases from coal fired electric generation plants are already scrubbed for sulfur and nitrogen oxides which produce among other health hazards, acid rain. The introduction of scrubbing technologies raises the cost of coal-fired electricity and the higher the degree of emission controls the higher the cost.
When solid coal is made into a gas prior to combustion, a process called Integrated Coal Gasification Combined Cycle (IGCC), more pollutants and impurities can be sequestered, though energy and financial costs go up with these currently rare, high-technology plants.
There are proposals for pairing coal or other fossil fuel fired facilities with algae ponds that would capture emitted carbon dioxide into a useful bio-oil that could be used as biodiesel. If such schemes can work, the carbon intensity of coal electricity would be reduced by 40%-45% as approximately twice the energy would be produced per carbon emission, which would ultimately be emitted from the combustion of the biodiesel.
The ultimate in “clean coal” are proposals for carbon capture and storage (CCS), where carbon dioxide is stored in underground spaces like old oil fields and mines that have fallen into disuse. Estimates are that these schemes would capture 90% of the carbon dioxide emitted and store it in a well-sited facility for millennia. An international consortium of energy companies, co-sponsored by the US DOE, has initiated the building of a prototype facility called Futuregen but carbon capture is still at least a decade off and its applicability to most sites where coal is used to generate electricity has not yet been established.
The Electron Economy and Coal Generation
The electron economy concept as outlined in my previous posts implies that there is a double (or greater than double) payoff for using electricity as an energy carrier. If we allow the inertia of governments and the fossil fuel economy to continue in the area of electricity generation, coal will continue to increase as a means of generating electricity. Are we doing ourselves and the planet any favors by replacing the use of petroleum transport fuels with additional coal fired electricity generation?
Firstly, coal generation at its dirtiest, without minimal scrubbing, will not be continued on a mass scale within the context of advanced industrial or densely populated developing nations like China: there are too many direct health costs that will never be returned to, especially in an era where sustainability and climate change is starting to be the new common sense. The Chinese government, as focused as it is on economic growth has come to realize that cleaner than “raw” coal energy solutions need to be found. Plus brown air and sick competitors at the 2008 Beijing Games are going to defeat many of the PR gains that the PRC is targeting for that massive sporting event. So our thought experiment here assumes that coal emissions around the world will be scrubbed of large portions of particulate matter, nitrogen and sulfur oxides. But we are assuming that coal’s full complement of invisible, odorless carbon dioxide will be sent into the atmosphere for the next decade or so.
The United Nations Environment Program estimates that coal emits 25% more carbon dioxide per unit energy than oil. Simplifying our analysis we will say that burning coal emits 1.25 units of CO2 for the 1 unit that petroleum emits when it is combusted. Let’s compare a lithium ion battery electric vehicle charged from a purely coal fired grid. Now if a coal plant is 38% efficient in generating electricity and an electric motor is 90% efficient and assuming 10% transmission losses and 10% charge/recharge losses for the lithium battery we arrive at .22 units of work per unit of C02. An internal combustion engine is just 20% efficient and petroleum emits 1 unit of CO2, so it is also doing .20 units of work per unit of CO2. So in this comparison, per unit of CO2, on a 100% coal-fired grid, the battery electric car does just a bit more work than the internal combustion gasoline car. If the power plant used the same gasoline to drive its turbines, the battery car would do .27 units of work as compared to the .20 for direct combustion in the engine.
Coal, as it currently stands, then is not good at all in environmental or climate terms but if you are substituting a moderately efficient coal facility and a battery-powered vehicle for fossil fuel powered transport, you come out slightly ahead. Furthermore, preparing the energy demand side for cleaner alternatives means that a relatively dirty coal fired grid can be more easily switched over to cleaner and renewable energy sources than our liquid petroleum infrastructure.
If coal is for the next decades, the grim Dickensian alternative in fossil fuel power generation, natural gas is the bright(er) star though by no means an environmental “free lunch”. Currently used to generate 19% of the power in the US, natural gas is a combination of hydrocarbon gases, primarily methane, with some ethane, propane and butane thrown in and when burnt, produces about half the carbon dioxide per unit energy that coal does and about 30% less than petroleum products. Natural gas is usually found in underground pockets near other fossil fuels like petroleum and coal. Components of natural gas, methane primarily, are produced as “biogas” from the anaerobic activities of microbes from landfills, sewage, peat bogs and any organic decay or digestive process including that of animals.
While natural gas is cleaner than coal in its natural and most commonly processed states, reserves of natural gas are less than coal though considered to be somewhat greater than for liquid petroleum and more widely dispersed. Estimates for the peak in natural gas production is thought to be somewhere between 2010 and 2020 which contrasts with the expected Hubbard Peak for oil production before 2010. Natural gas has the relative disadvantage of being easier to extract therefore more easily exhaustible. In a simple natural gas fired power plant, natural gas is burnt and the expanding resultant gases drive a turbine which in turn drives a dynamo.
In electricity generation, the current state of the art in natural gas is in a combined cycle power plant. Combined cycle refers to the use of a secondary generator that uses the waste heat from the gas turbine to create steam and drive a secondary steam turbine that turns another dynamo generating more electricity. Combined cycle natural gas plants achieve efficiencies of around 60% with electricity alone. A combined heat and power plant which uses the steam in the second cycle for a heating application (if a need for the heat is close at hand) has an efficiency of 80-90%. As mentioned above, coal or liquid hydrocarbons can be put through an Integrated Gasification Combined Cycle plant which first creates a “syngas” fuel and then puts it through two cycles to extract maximum energy from the fuel.
If we plug a combined cycle natural gas plant into the thought experiment we did earlier, the battery electric vehicle charged from the grid would do about three times the work per unit CO2 emitted that the petroleum powered vehicle would do, if electricity were generated purely via combined cycle natural gas.
Petroleum of various grades is used to fire some power plants, though this is increasingly rare. As of 2005, oil represents 3% of the US power generation mix. As noted above, among the fossil fuels petroleum emits a mid level of carbon dioxide per unit energy, less than coal but more than natural gas. As with coal and more than with natural gas, emissions from oil fired plants include various particulate and toxic compounds that should be scrubbed from emissions.
“Greenfield” vs. “Brownfield” Energy Development: Exemplars and Heroes
A discussion of fossil fuels as backward looking as that may be, brings up another factor regarding how advisable, how sustainable one electric generation alternative is as compared to another. Policy makers, concerned consumers/citizens, investors, and system operators need to ask themselves whether a specific power generation or other energy project is substituting for an existing carbon-emitting energy source or is slated to meet new demand for electricity or energy in general. This issue is particularly relevant to the electrification of the developing and underdeveloped world, which represents mostly new demand.
A relevant metaphor may come from the building industry where “greenfield” development refers to building that occupies previously undeveloped or agricultural land, while “brownfield” development redevelops land that has already been built upon or paved. With the greening of the building industry, greenfield development is considered much less desirable than brownfield development as it expands the ecological footprint of human development. The same contrast can be extended to energy development. A “greenfield” energy development is intended to address new demand while a brownfield energy development is intended to replace existing generating capacity. The impact of cleaner energy alternatives is greater in a brownfield energy development than a greenfield development as there is in addition to the lower relative emissions of the new development, the retirement of a higher polluting facility. A dirty new facility has greater impact as a greenfield development as the future development lower carbon and carbon-neutral alternatives is set back.
New cleaner or zero-carbon technologies stand out as shining examples of what might be if they simply add capacity to an already “dirty” grid or meet new demand in the developing world. If cleaner or zero-carbon technologies can actually retire dirtier parts of the grid, this is evidence of true heroism in addition to being a shining example for those who are involved in the energy business.
Thus there will be a combination of heroic and exemplary efforts on the part of political, consumer, and business leaders to overcome the temptations of using up the store of fossil fuels to power our civilizations. I am using the word “heroic” advisedly to suggest that risk is involved, even risk that overlooks short-term self-interest in the interest of longer term self-interest and goals. There need to be heroic acts along with rational calculative ones for leaders to take what ultimately are the best choices for long-term sustainability.
I have attempted here to show that the electron economy can be powered by our current mix of fossil and non-fossil fuels and some benefit can be derived from converting energy demand from fossil fuel combustion to grid-fueled electric transport. A white paper on the Tesla Motors website comes to a similar conclusion though perhaps in a more elegant manner. The fossil-fuel focused scenario in my posting here though does not in the remotest way convey the potential of an electron economy which will be broached more completely in the upcoming postings on renewable power generation and the controversial nuclear question.