by: Michael Hoexter
In the first part of this mini-series for policymakers, I addressed the marquee issue in energy currently, finding a replacement for limited, expensive and polluting petroleum; I concluded that a three-pronged approach based on electric traction in transportation would go the furthest in reducing our dependence on petroleum.
But that electricity would need to be generated in a timely manner… or energy would need to be stored or accessible in a ready form. In this next installment I am going “upstream” to look at what our choices are in a post-oil, post-carbon world to generate electricity in a clean, useful and timely manner.
Why is Electricity the Energy Carrier of Choice?
There are sound physical reasons why, in the first installment of this series, the three main contenders for the energy supply for transport turn out to be the three electron economies, the Renewable, the Nuclear and the Coal CCS. We have determined there that electric drive vehicles either attached to the grid or powered by some version of a battery can do most of the on-land transport tasks that are now dependent on oil supplies. There are other reasons why electricity is valuable for driving stationary machinery as well which we will go into in the final installment of this series.
Why then is electricity preferable to biofuels, hydrogen and coal to liquids? In addition to zero emissions at end use, electricity has benefits in efficiency and availability in almost all stages of its production, transmission, and consumption. Electric generators can be built to use a wide variety of types of energy (heat, light, mechanical energy) to create the highly usable and flexible energy carrier, electric current. In other words, electricity is the ultimate in “flex-fuel”. All renewable energies (wind, sun, geothermal heat, wave, tidal, biomass, natural chemical and thermal gradients) can be converted into electricity with existing technologies. In addition, while we must shift the way we generate electricity in most instances, this is not a full-scale rebuilding of our energy system but a modification of existing infrastructure, so in the end, less expensive.
Existing electrical generation technologies convert a fairly large amount of the primary energy that they receive into electric energy. Current solar panels, for instance, can convert anywhere from 10 to 40% of the energy of the sun into electricity depending on the technology; by contrast plants convert at most 1% of the energy of the sun into biomass, an energy harvest that is further reduced if that biomass is converted into a liquid biofuel rather than burned in a biomass electric generation facility.
Additionally, electric motors, because of the physics of the electromagnetic force, are incredibly efficient at generating torque, the useful product of engines and motors. An electric motor of medium or larger size (90-95% efficient) requires somewhere between one third and one-quarter the amount of energy to do the same work as an internal combustion engine(20-30% efficient): they therefore generate 3 to 4 times more torque per unit energy put into them, than all but the largest and most efficient house-sized diesel ship engines (50% efficient).
Electricity also can be used for a huge variety of functions for the end user: generating mechanical movement, heat, light and sound. So electricity is both flex-fuel and flex-use. It is no wonder that, even with no consideration for the current energy and climate concerns, more and more devices have been designed with more electronic components to increase their functionality, including petroleum powered automobiles (electronic fuel injection, stability control, drive by wire, etc.).
Electricity’s weakness has been that electrical energy storage is bulky and heavy in comparison to the portable liquid fuels to which it is often compared. Batteries and ultracapacitors are still relatively large and expensive compared to a liquid fuel tank and the hydrocarbons that are pumped into it. As the drawbacks of fossil fuels are starting to be more widely recognized, the positive attributes of alternatives are once again being recognized. Also, substantial investment is once again flowing into resolving this one final hitch in electricity’s otherwise near-ideal attributes and the technological development curve promises rapid advances.
In the distant future, we may have other energy carriers with more favorable characteristics but for the foreseeable future it makes the most sense to build on the advantages of electricity.
A Choice of Primary Energies: What is the Clean Energy of Tomorrow?
Usable electricity just doesn’t appear but is generated from a pre-existing or primary energy; one of the great decisions of the 21st Century will be how we choose to generate electricity. We have established that there are under consideration three main carbon-reduced or carbon neutral “clean” primary energies for electricity: renewable energy, nuclear energy, and coal with carbon sequestration. While electricity itself is “flex-fuel” meaning that any and all of these methods can be used to generate electricity, we will need to arrive at a differentiation of, if not a prioritization of, which methods are going to be the most sustainable and ultimately the main driver of the new electron economy, post-coal and post-oil. To guide policy and investment, we can create a “loading order” for these resources, though a multi-track approach is also probable if not desirable.
Third Place: the Coal CCS Electron Economy
Is coal with carbon capture and storage (CCS) the primary energy source for the Electron Economy? Of the three alternatives, coal generation with CCS is the least promising as it has some major strikes against. However it does have some advantages as well.
- Taps into a still vast energy store (coal deposits) so can be called upon when needed independent of weather conditions and in response to electric demand.
- Provides jobs and revenue for existing industries and communities (coal mining and coal transport)
- Uses an unsustainable fuel – coal will run out
- Coal mining is often very destructive to the landscape and to coal miners.
- Mass carbon dioxide release from underground is considered unlikely but potentially lethal for people and wildlife as well as defeating the purpose of CCS.
- CCS may not reduce or eliminate the other pollutants associated with coal combustion including mercury emissions, SOx and NOx.
- There are still no functioning plants/it is an experimental technology
- CCS plants will be much more expensive than existing coal plants, removing one of the prime selling points of coal, i.e. that it is cheap
- CCS or “clean coal” has been used as a public relations “cover” to justify the building of new coal generating plants without adding the “optional” CCS facilities.
Coal with CCS may have a role in a transition to a more sustainable energy system but it is by design a stop-gap solution.
Second Place: the Nuclear Electron Economy
In the light of concerns about climate change, some environmentalists as well as those with the nuclear industry, have emphasized nuclear's energy's carbon neutrality, advocating it as the solution to climate change
In light of concerns about climate change, the role of nuclear power in a future or transitional energy system has been re-evaluated. Worries about nuclear plant safety, nuclear weapons proliferation, and nuclear waste are being balanced against the fact that nuclear plants during their operation do not emit carbon dioxide into the atmosphere. Unlike coal-fired generation, nuclear power technologies, especially if we consider prototype reactors, vary greatly and massive government investment has gone into researching a wide variety of reactor designs; however one type, the pressurized light water reactor, still predominates in commercial nuclear plants. I will treat nuclear as two concepts then, existing nuclear and potential nuclear designs. I am considering potential future nuclear designs at all because the physics and history shows at least the potential for a high energy yield, though at a price worth assessing.
A. Existing Nuclear (Pressurized Light Water Reactors)
Most existing nuclear reactors use regular (light) water as both a coolant and what’s called a neutron moderator. They depend on an enrichment process by which fuel pellets are formed with a higher concentration of the fissionable isotope Uranium 235 rather than the much more common and stable U238 isotope. These reactors pros and cons are as follows:
- Carbon neutral under operation
- Established technology with track record of producing electricity with few safety incidents
- Produce power in the same profile as most coal generation plants (a constant baseload); can be used as a coal substitute
- Remaining Uranium 235 supply functions as an energy store that can be tapped into at will
- Nuclear power enables power production in areas with poor natural and renewable resources
- Nuclear fuel is compact and highly energy dense
- Produces large amounts of highly radioactive nuclear waste that will need to be stored for millenia in isolation from the biosphere.
- The uranium enrichment process can also produce higher concentrations of U235 suitable for nuclear weapons.
- The Chernobyl reactors were pressurized light water reactors; accidents and assaults on these plants have a chance of resulting in catastrophic releases of radioactive materials
- Naturally occurring, economically extractable U235 will run out sometime in the latter half of the 21st century, especially if new nuclear plants are built out aggressively.
- Constructing nuclear power stations takes over 5 years making them ineffective in a crucial period of climate change
- Inclusive of insurance costs, which are so high that they must be assumed by governments and therefore taxpayers, nuclear power stations are very expensive
Pressurized light water reactors then are not a particularly promising solution to our energy crisis, especially in the longer term.
B. A Future Fuel-Reprocessing or Thorium-based Nuclear Power System
Some nuclear power advocates believe that most or all of the drawbacks of the current nuclear power system can be remedied through technological development of a combination of new reactor designs, new ways to process fuel, and the extraction of fissionable fuels (uranium and thorium) from new sources. In sum or as piecemeal solutions these changes are supposed to reduce the toxicity and amount of nuclear waste, increase the amount of fissionable fuel up to several thousand-fold, and reduce the risk of nuclear proliferation. These technologies however do not represent a unified plan but rather a series of technology proposals that build upon past or existing prototype reactor designs and fueling systems that have either been built or speculatively might be built.
One of the objectives of these scenarios is to widen the potential base of nuclear fuels by creating reactors that can turn much more plentiful Uranium 238 or Thorium 232 into a fissionable fuel (Uranium 233 or 235 or Plutonium 239). Others suggest extracting fuel from sea water, which has a small but nevertheless plentiful fraction of uranium isotopes in it. The net effect of these new fuel processing and sourcing proposals is to extend the supply of fissionable fuels to hundreds if not thousands of years into the future. Still others suggest reactor designs that will not allow weapons-grade uranium and plutonium to be isolated. Some tactics involve using discarded nuclear wastes as fuels as well as producing a much smaller radioactive waste product with a half-life in the hundreds of years rather than in the tens of thousands of years.
Out of concern for the urgency of the climate crisis, I depart from the orthodoxy of some advocates of renewable energy by agreeing that it is desirable to do research into reactor designs that at least reduce the toxicity of current nuclear waste and create a safer nuclear fuel cycle. While it is difficult to pin down what the pros and cons of this ideal future nuclear energy system might be, the following are some advantages and disadvantages of foreseeable nuclear power systems:
- Carbon neutral or negative (in certain conditions) under operation
- A future nuclear system might be able to reduce our current nuclear waste problem
- Fuel is compact and easily transportable
- Nuclear energy that can make U238 or thorium fissionable can tap into a very large store of fuel, and can therefore be used at will for many years to come; according to advocates for thousands of years.
- Like conventional nuclear power, could produce baseload power, substituting for coal generation
- Removing proliferation risks could make cleaner power available to more countries
- Safer reactors are desirable if nuclear energy is to continue to be part of our energy mix
- Nuclear power enables power production in areas with poor natural and renewable resources
Risks and Disadvantages
- The described future nuclear system is more than a decade and perhaps decades away. Climate change is upon us now.
- All nuclear power irreversibly transforms its fuel into less energetic fuels; even after thousands of years it will run out
- The promised benefits may not materialize.
- The complexity of these proposed systems is very high, making oversight difficult and increasing the potential for unforeseen difficulties and consequences
- As yet uncharted safety issues will emerge with new radioactive fuels or coolants like liquid fluorine.
- Developing these systems would be a major expense drawing on government research funds diverted from less elaborate technological systems like renewable energy and energy storage.
- Existing fuel reprocessing systems have proliferation risks attached; they isolate plutonium.
- The compact power of fissionable elements may have more appropriate uses in some future technology (spaceships?) other than power generation for daily use.
The Nuclear Electron Economy, be it in its conventional form or a potentially improved future form, is a runner-up to the Renewable Electron Economy largely because it is not ultimately sustainable, carries with it large technological and safety risks, and its deployment as a substitute for fossil generation is many years away.
First Place: the Renewable Electron Economy
As you might expect from an analyst who has written about the Renewable Electron Economy, I believe that the mainstay of our future energy system will be electric generators powered by renewable energy. However, I hope to show here that this choice has a basis largely in economic, scientific and technological reality rather than my personal prejudice or some of the social utopian ideals to which renewable energy has been attached.
Though I am for a comprehensive push to develop and deploy all types of renewable electric generators, constructing a Renewable Electron Economy, where renewable energy does the heavy lifting, will require a focus on specific strengths and weaknesses of renewable energy. Advocates for renewable energy have tended to either cluster into an “anything goes” ecumenical approach or focus on renewable energy as a self-generation option for households and business. Some have championed renewable energy as a means to even dismantle a widely interconnected grid through each power user autonomously producing their own power. Why one would want to dismantle the grid seems to be a matter of personal preference or fixed ideas about how society should function rather than a reflection on the electric grid’s usefulness.
The approach to renewable energy I favor emphasizes the power of widely cross-linked generators to tap into the strengths of renewable energy and address its weaknesses in an energy economy where residential, commercial and governmental users are actually depending on renewable electricity to provide them with the energy they need. Solar panels on rooftops or small windmills alone will not, with current generation and storage technology, be sufficient to substitute for the day and night, always-on power of our current grid. Combining large and small generators including solar thermal with storage, hydroelectric, pumped storage, biomass power plants, as well as more familiar wind and photovoltaic generators can reproduce under most conditions, the reliable power of the grid.
The most promising technology in this area is not simply horizontally networked generators but a well-orchestrated mini-grid regulation system that can be called a “renewable combination power plant”. The renewable combination power plant joins discrete renewable generators together to deliver power exactly as it is needed by grid users, just as is done today with conventional power plants. In contrast, isolated renewable generators without storage produce power according to the availability of their primary renewable energy. The combination power plant operators respond to signals from the power grid operators about when and how much power is needed. A renewable combination power plant requires, as at least some components, clean storage technologies or dispatchable renewable resources like biomass power plants, hydroelectric, pumped storage, and solar thermal with storage. These controllable resources are then extended by wind, wave, tidal, geothermal or photovoltaic solar power which produce power whenever they have incoming renewable energy.
The Solar Two demonstration power plant, built by the US Department of Energy, generated power for seven days and nights continuously using only solar power, which was stored for night time use as heat.
Even with current technology, however, there is one renewable technology that can do a majority of the work of current fossil generators, solar thermal electric with thermal storage also called CSP (concentrating solar power) with storage. Sited in desert or semi-arid areas, solar thermal electric uses mirrors to focus direct sunlight on a thermal fluid, like water, oil or molten salt that is used to make steam to generate electric or stored as heat in heat storage for later, similar use. The relative efficiency and low cost of thermal energy storage, the relative vastness of the world’s major deserts, and the consistency of the desert sun are the strengths of CSP with storage. Solar thermal with 16 + hours storage or solar baseload can substitute for coal generation during much of the year and about 1% of the area of the world’s deserts could generate all the power that the world currently uses.
The use of CSP to serve a majority of the world’s power customers requires the building of long distance power lines mostly likely using high voltage DC technology that can theoretically transmit power for 4000 miles with about 20-25% losses. There are a number of concepts now being discussed including DESERTEC which links Europe with North Africa and the Middle East, as well as a concept I promote, the Solar Southwest Initiative, that foresees linking the Southwestern and Sonoran desert with power demand centers across North America. In the end, local resources and distant renewable resources will combine to produce a complex but more robust and reliable clean power grid.
Added to the options of the combination power plant and solar thermal with storage are several other technologies that will significantly contribute to the Renewable Electron Economy: small and medium hydroelectric, deep geothermal, as well as better publicized wind and solar photovoltaic. Developing these renewable power resources in some of the more favorable areas will involve the building of some new electric transmission, which advocates of small-scale renewable energy have often opposed (or opponents of transmission have often advocated small-scale renewables as if they substituted for large-scale renewables). The balancing of renewable energy flows across space and time to meet current demand for power requires transmission that links supply and demand.
Currently wind energy is one of the least expensive renewable energy sources and in the future solar photovoltaic (the flat panel technology seen on roofs and emergency call boxes) will probably be as inexpensive as wind. While both of these technologies are currently the “marquee” renewable technologies, alone they will not be able to shut down fossil power plants. Until electric energy storage will be plentiful and cheap these technologies will function best in the context of combination power plants
As described here, the Renewable Electron Economy has the following advantages and disadvantages:
- Carbon neutral or negative (in certain conditions) under operation
- Primary energy (fuel) is free
- Generators can be scaled from very small to very large; investment amounts can range from a few hundred dollars to several billion dollars.
- Primary energy is virtually endless
- With the exception of biomass and certain geothermal wells, have no non carbon emissions
- Mature or rapidly maturing technologies in most categories of renewable generator.
- Deployable within a few months to a few years for most technologies (within critical period to reverse emissions trends)
- Dependent upon a diversity of primary energies
- Many renewable energies are periodic or intermittent
- Renewable energies occur naturally as energy flows rather than energy stores or stocks (with the exception of biomass); an all-renewable grid needs to build up and carefully manage stored energy.
- Overreliance on biomass, the primary natural energy storage medium, may tax soil and the biosphere.
- The reduction in solar energy around the winter solstice may present challenges for a solar-dominant all-renewable grid especially during times of low wind.
- Catastrophic reductions of solar radiation (i.e. volcanic eruptions) can reduce the main energy in-flows; solar radiation is important to both solar and wind generators
The Renewable Electron Economy organized around combination renewable power plants and solar thermal power with thermal storage will minimize or eliminate most of the drawbacks of renewable energy. The emergence of scalable deep geothermal power or EGS, will address the latter two, more difficult but lower-frequency challenges facing an all-renewable grid.
Al Gore’s Call: 100% Renewables in 10 years
Al Gore has inspired many of us with his call for a 100% renewable grid to be built in 10 years and, in the area of energy policy, we are in dire need of inspiration. On the other hand, considerations of reality, scientific and financial, need to work together with vision and inspiration to construct a functioning clean energy system in the real world. In my next installment I will take a look at the policy and economic drivers for creating a Renewable Electron Economy that will serve our energy needs and make the survival of a human-friendly biosphere more likely.
Original Post: http://terraverde.wordpress.com/2008/08/20/policy2/