Clean Energy wind power rainbow

Published on September 14th, 2015 | by Bruce McF


Can Renewable and Nuclear Energy Be Friends?

By BruceMcF

There is an ongoing general discussion about variable renewable energy – which is how to balance sustainable energy like solar and wind that don’t carry the risk of total destruction of our society, and riskier forms such as nuclear energy.

wind power rainbow

Renewable energy includes a range of low or no carbon sources of energy – but not all renewable energy is sustainable, and not all is low or no carbon. And not all low or no carbon energy sources are from renewable energy resources.

Among the sustainable, no/low carbon renewable energy resources, the most abundant involve the harvest of variable renewable energy, with windpower and solar PV being the most notable. So one obvious strategy for a no-carbon-emitting energy system is to base it on collecting as much of these affordable variable renewables as practicable, and then use other no/low carbon sources to fill in the gaps.

However, in some quarters, this elicits a counter-argument. The most “successfully de-carbonized” economies of the world today are either those with a very high reliance on reservoir hydropower … which while very useful in the United States offers nowhere near a large enough economic resource to meet any large fraction of our current consumption … or those with a very high reliance on nuclear power.

Indeed, near the beginning of this month, Stephen Lacy briefly reported on a report from the Breakthrough Institute that raised an alarm that the new Clean Power Plan may in fact oversee a net increase in GHG emissions. The final plan does not include measures to avoid the decommissioning of substantial numbers of nuclear power plants. And the numbers are stark:

  • The 30 nuclear plants at risk by 2030 avoid over 100 MMT of CO2 emissions
  • New non-hydropower renewables are expected to avoid 60 MMT of CO2 emissions by 2030
  • New nuclear plants under construction are expected to avoid under 30 MMT of CO2 by 2030

So where retention of those 30 nuclear power plants would find us over 80 MMT of avoided CO2 ahead, and in a position to accelerate that in the following decade … their closure could leave us over 10 MMT below where we are now.

Why I say “No/Low Carbon”

Independent of what is normally called Carbon Capture and Sequestration, the industrial scale process of trying to capture CO2 from large fixed sources and finding a way to push it under ground, there are also a wide range of actually feasible methods of capturing carbon and sequestering it.

“Wait, so why don’t we do those, and just go ahead with what we are doing?”

The flip side of this is that the already feasible level of carbon capture and sequestration is quite dramatically overwhelmed by our current scale of CO2 emissions.

We can, for example, plant short rotation perennials in marginal land, convert them into charcoal, and bury the charcoal. If we worked really hard at it, we could sequester what would sound like a large number. But it wouldn’t be anywhere near as large as the amounts we are presently emitting.

The scale of “realistic direct-from-atmosphere CCS” that we can actually achieve in not entirely clear, in part because political paralysis has prevented us from getting the start at it to learn more about the possibilities from experience.

But that is what I mean by “low/no carbon”. Even if some carbon was emitted somewhere along the way … eg, in the chemical reaction in producing the concrete for the cement foundation of a wind turbine … if that intrinsic emission on a per KWh basis is some small percentage of the runaway CO2 emissions of a Natural Gas or Coal Powered generator, it is far more likely to be in the scale that can be mopped up by a feasible scale of “realistic direct-from-atmosphere CCS”.

Quantities are important in this. People that treat CO2 emissions as a “sin”, and divide the world in a dichotomy of sinners and saved, are at risk of lumping together emission levels when one is twenty, fifty or a hundred times the scale of the other.

And there is a further challenge that a life cycle analysis of the emissions of producing equipment to harvest renewable energy will be analyzing that in the context of an energy supply system that is based primarily on fossil fuels. However, the more equipment we install to harvest renewable energy, the lower the “production” CO2 cost there will be for the next one … and for everything else that is made using that energy source.

How low we have to go is determined by the rate of “realistic direct-from-atmosphere CCS” we are able to achieve. But it would be absurd to wait to start reducing the CO2 cost of everything we reduce until we have an exact reading on where we need to end up. We already know thedirection we need to go, which is “lower”, and we know of a range of technologies which, if rolled out, will take us substantially lower.
The Simple Economics of Existing Nuclear Power Plants

The reason that the existing nuclear power plants are under threat of closure is, at heart, economic. We pretend that coal and natural gas are not using a scarce natural resource when they emit CO2. We do that by not charging for the use of the scarce natural resource … the ability of the natural Carbon cycles of our global ecosystems to sequester carbon that we are adding to the atmosphere.

We are, in fact, not only allowing them to use that scarce natural resource: we are allowing them to use it up, and therefore CO2 concentrations in the atmosphere are increasing at what is a an unprecedented rate during our history as a species. And in the process, we are risking catastrophic climate changes that have the potential of destroying our nation as a society and an industrial economy.

If we charged an adequate price for the use of that scarce resource, given the CO2 concentrations we are already on track to have emitted by the time we could feasibly bring new emissions under control … it would be a price to either prevent the combustion of mineral coal, natural gas and petroleum products in large scale, or else only allow their combustion in large scale if combined with a highly effective carbon capture and sequestration.

And if we charged that price, existing nuclear power plants would be providing quite extremely competitive electrical power, and given that we live in what has been a commercial Republic from its founding, it is very likely they would remain in operation through 2030.

Now, nuclear energy opponents will argue that this is incomplete economics. They will argue that nuclear energy has its own external costs, including for the United States, uninsurable risks of both proliferation of nuclear materials as well as active sabotage of nuclear power plants.

It seems that renewable energy advocates are often in coalition with opponents of nuclear energy. Measures that renewable energy advocates back because they promote renewable energy are often seized upon by nuclear energy opponents as alternatives to nuclear power.

And in some cases, nuclear energy advocates are aggressive opponents to measures to encourage renewable energy. A core argument is that the most widely deployed new renewable energy sources, windpower and solar PhotoVoltaic (solar PV), are variable sources of energy which undermine the earnings of steady producers of power ~ like Nuclear power plants ~ and require readily dispatchable fossil fueled energy sources with relatively low capital costs ~ like Natural Gas powered plants ~ to operate during the time that the renewables aren’t generating.

So we have two no/low carbon alternatives. 100% Renewable and 100% Nuclear.

I think this is confusing legacy technology for technological possibilities. What we have done clearly demonstrates an option, but it just as clearly does not demonstrate all feasible options.

We would have much more freedom of choice if some level of reliance on low/no carbon nuclear energy source was not just compatible with but complementary to som level of reliance on renewable energy.

Well, maybe that is a technological possibility. I am making no warranty of economic feasibility of the nuclear fuel cycle I discuss below, nor any warranty that the scenario I lay out is in the close neighborhood of a cost optimizing no/low carbon portfolio. As I explain, neither of these are actually knowable in advance of further research and development.

I am just exploring one type of scenario where a fleet of so-called “advanced nuclear power plants” acts as a natural complement to a portfolio of both variable and dispatchable renewable energy … in the context of an electrical grid that is far more suited to the integration of variable renewables than the one we have today.
The Distinction between Renewable Energy and Sustainable Low/No Carbon Energy

The first point I want to touch on is that not all renewable energy is sustainable, no or low carbon energy. And it may be that not all sustainable, no or low carbon energy is renewable energy.

For example, lumber harvest for biocoal, whether from old growth forests or from matchstick pine tree plantations, is carbon emitting on a time frame of decades. If its cultivation is a modest carbon consumer then it may well be a low carbon energy source on a  steady state basis. However, if it takes 40 to 100 years to growth the replacement biomass … it takes 40 to 100 years to reach steady state, and it is a carbon emitter (though on a declining basis) for that whole period.

So to be a potentially no or low carbon source on the time scale we need, biomass energy has to be from more rapid growing cycle sources.

At the same time, if its cultivation is energy intensive, whether in fertilizer, the production of poisons (pesticides, herbicides and/or fungicides) that industrialized annual monoculture is heavily dependent upon, in harvest, or in some combination of the three, then it won’t be no or low carbon, no matter how fast the growing cycle.

So the target for sustainable, no/low carbon involves a short-rotation perennial such as short rotation coppice or the Miscanthus perennial grass. Long rotation perennials or high-input annuals are, for distinctive reasons much less likely to qualify as sustainable as well as no/low net carbon emitting over the time scale that we require.

And it is not necessarily the case that all energy sources in an entirely sustainable, no/low energy energy portfolio will be renewable energy. While many anti-nuclear advocates argue for the limited sustainability of the current once-through Light Water Reactor fuel cycles, there are also those that make the case for advanced nuclear energy options such as molten saltthorium fuel cycle (warning: Wikipedia machine entry) reactors. This requires further research and development (which may involve crossing one or both of the two “R&D death valleys” unless there is actively supportive federal policy), but thorium is an energy source that is more abundant than uranium (though information on economically viable reserves is not as clear), and thorium fuel cycles can consume dangerous plutonium and breed uranium.

It is also possible to design a molten salt reactor so that it is passively safe against meltdown. For instance, one approach, for designs where the uranium

A principle challenge with the thorium fuel cycle is that in addition to breeding uranium 233, it also breeds uranium 232, which is a hard gamma emitter. This is, after all, one of the reasons why the US dropped development of the thorium fuel cycle: U232 damages electronics, which limits the usefulness of thorium-bred uranium in nuclear weapons – and at least according  to the Wikipedia machine (but with a supporting link lost to link rot, when the US military tested a U233 bomb, it had a lower destructive yield than anticipated. U233 and U232 cannot be separated by chemical means, so fuel reprocessing for a semi-closed thorium fuel cycle that recycles U233 requires remote control, radiation hardened equipment. However, the presence of U232 also makes it easier to track the transport to and back from the fuel reprocessing plant, to guard against the nuclear proliferation risks of nuclear fuel diversion, and then if diverted requires isotope separation which is made more difficult by the similarity of atomic weight and chemical properties of U232 and U233.

So the potential of molten salt thorium fuel cycle reactors comes with several caveats, involving safe handling and transport of gamma emitting spent fuel for recycling of Uranium 233. And its development requires substantially more new research and development than “mature” Light Water Reactor fuel cycles. However, the “mature” LWR technology present inherentproliferation risks because the technology was selected to be complementary with nuclear weapons production.

It is plausible that there may be advanced nuclear fuel cycles that may be exploited as a sustainable and no/low carbon energy source, even though they consume an abundant but non-renewable resource. Further active research and, especially, development is required to verify that it qualifies … in the same way that further field trials are required to determine both the opportunities and limitations of various potential short rotation perennial bioenergy crops.
But why do we care? Why not depend on wind and solar alone?

Now, why do we care about biomass energy, or nuclear energy, or any other potentially sustainable, no/low carbon energy sources along those lines? Why not power all of the economy with windpower, solar, and run-of-river hdyro?

As previously covered in the Sunday Train (eg, in Variable Renewables and Dispatchable Demand), these abundant renewable energy resources are variable. They are “use it or lose it” resources, which are harvested when available. Even though the sun is shining on some part of the US for much of the day, part of the time it is night across all of the continental US. Even though the wind is always blowing at useful speeds somewhere in the continental US., the total amount that can be harvested by wind turbines varies. Even though many run-of-river hydropower generators are essentially “always on” except when closed for maintenance, the amount of power they generates varies with the strength of the river current.

Now, electrons are “fungible”: the electrical grid does not matter whether a particular electron is being pushed around due to harvest from the wind, or the sun, or from a flowing river. What matters to the electrical grid is the total amount of energy that is harvested. So while each individual piece of energy harvesting equipment is an “intermittent” supplier, which sometimes produces energy and sometimes does not, the total available renewable energy resource is notintermittent. There is always some energy available from a well-diversified portfolio of renewable energy harvesting equipment. However, it IS variable.

And with a portfolio of variable, renewable energy, the problem is as follows:

  • Suppose that a maximum of 80% of installed “nameplate” capacity is available at any given point in time
  • Suppose that an average of 40% of installed “nameplate” capacity is available at any given point in time
  • Take the ratio of the two … in this case, 40%/80% = 0.5
  • When you have that variable renewables installed equal to that fraction of peak demand, then some of the time you are getting all of the energy that you ever require from renewable energy
  • But on average, you are only getting half of the energy that you need from that renewable energy

As discussed in more depth in a previous Sunday Train (Making An Energy Revolution, 7 July 2015), that gap can be made up in various ways, including:

  • Reservoir hydro, but the total resource is less than 10% of total energy demand.
  • Providing dispatchable demands, so that the daily, and possibly weekly, cycle of electricity demand can better match the
  • Providing flexible dispatchable no/low carbon energy other than reservoir hydro, including biomass … and conceivably some form of nuclear energy, to the extent it can be operated in a flexible, load-following manner.
  • Overbuilding variable renewable capacity and spilling it. However, the cost is inversely proportional to the fraction of power used, so with each additional 1% spilled, the average cost of the renewable energy harvested and used increases at an increasing rate.
  • Overbuilding no/low carbon energy capacity and storing it for use at a later time.
    • Grid scale battery and pumped hydro storage would be used more than once a day on average (eg, “400+ cycles per year”) for best cost-effectiveness, and then with rising cost per KWh, as each halving of cycles per year (200 per year, 100 per year, 50 per year) doubles the fixed cost component per KWh.
    • Electrofuels have far lower “round trip storage efficiency” than pumped hydro storage, and have capital costs in proportion to per hour production capacity, but once produced can have much lower storage cost per KWh stored.
    • Because of round-trip energy losses, it’s silly to operate electrofuel production at the time that electrofuel is being used to generate electricity. This means electrofuels for energy storage (as opposed to energy transportability) should ideally be produced most of the time at a steady, and moderate rate, and consumed the balance of the time at a variable and relatively high rate.

So, for example, dispatchable demand that can time-shift 10% of demand to a time of immediately available supply, storage that can time-shift 10% of supply to a time of immediately available supply, and 5% additional variable renewable supply due to capacity that is frequently spilled would (if all three are feasible) allow 75% of supply to be provided from variable renewables, instead of 50%.

Then 15% of supply from flexible dispatchable renewables and 15% from partially load following advanced nuclear power, including 2-3% supply time-shifted through electrofuel production (with, as will be seen below, substantially more peak generating capacity), would be sufficient to close the remaining gap in total supply.

Why did I include that nuclear power share? See above ~ I am exploring the space in between “all renewable” and “all nuclear”, so if I set it at 0%, that would be trouble.

These add up to more than 100%, of course, since if there is no reserve, where you are is on the knife edge of a “brown-out economy”.

These are simply illustrative shares. The actual cost-effective shares depend upon the cost trade-offs … how much does this wind turbine cost per KWh nameplate capacity, and what will its production profile be if placed in this location, and how will its output compare to both immediate and dispatchable demands, and how much of its energy is provided when the solar PV supply from that area is not supplying, and how much does this battery cost per KW capacity and how many cycles does it provide, and what is its efficiency, and etc. and etc.

As implied by discussion above (though from the other side of the argument), the principle weakness of conventional nuclear power for use as a complement to variable renewables is its relatively inflexibility. Current French designs can load-follow for half of their fuel cycle. The General Electric AP1000 Pressurized Water Reactor can load follow on a 100-50-100 daily cycle over 90% of its fuel cycle (pdf, sheet 10), so a fleet of two fueled for two years each, with refueling properly timed, could load follow by over 50% of output during peak seasonal net load.

The “mandatory minimum” with these reactors is a technological issue but its conceivable that new research and development will uncover engineering solutions for technological issues.

For one thing, it is conceivable that a molten salt thorium fuel cycle reactor could be made to be even more flexible. It would operate at prevailing pressure but high temperature, so that it could use another molten salt as the heat transfer medium to the generator, and also as thermal storage. This could effectively decouple the thermal output of the reactor from the power output of the generator, allowing the reactor module, with its relatively higher capital cost per KW capacity, to run relatively continuously, and the generator module, with its lower capital cost per KW capacity, to run in a pure load following manner.

Now, this is a close to ideal energy source for methane as an electrofuel, since part of the heat output of the reactor can be used to heat water used for high temperature steam electrolysis (HTE), increasing the hydrogen output per KWh … and in a combined cycle process, the transfer medium could then be used as a heat source for the catalytic Sabatier process to convert CO2 and Hydrogen into methane and steam … and then perhaps the steam can be recycled to provide some of the water for further electrolysis. According to the Wikipedia Machine, at 100°C HTE has a maximum efficiency of 41%, but at 850°C, HTE has a maximum efficiency of 64%.

And when generating in peak power mode, heat from the exhaust of the gas turbines can be recovered for a second cycle of thermal steam power or for thermal storage using existing capacities of the generation plant, so rather than the 35%-42% efficiency of a single cycle peaker, I will assume 50% efficiency in electrofuel consumption.

This is a scenario I am laying out, so let me lay out some parameters for the scenario. It may be that some are reasonable, it may be that others are not actually cost effective in practice … but of course this is all based on a reactor technology that has not yet been developed, so this is rather a look at what might be rather than a prediction of what shall be. In this scenario:

  • HTE is in practice 60% efficient in generating electrofuel
  • The power generation from electrofuel is 50% efficient (though as discussed below, this can be raised substantially)
  • The reactor is in normal operating mode about 90% of the time
  • The reactor devotes two fifths of its output to electrofuel generation while it is in normal operating model
  • The generator module has 150% of the maximum steady state output of the reactor
  • There is sufficient thermal energy store to convert 60% of nuclear reactor capacity into 0%-150% of generator capacity

This means that the electrofuel plant is operating for about 90% of the hours of the year in normal, load following and electrofuel production mode, and 10% of the hours of the year (but not necessarily 10% of the hours of any given week), the facility is in peaker mode, the electrofuel capacity is shut down, and the methane peaker turbines are online and available to generate.

With the main generating plant at 150% of reactor capacity:

  • About 90% of the time, two fifths of the reactor heat generation is used to generate methane electrofuel
  • The same 90% of the time, the generator produces between 0% and 150% of reactor capacity, using three fifths of reactor heat generation
  • About 10% of the time, all of the reactor capacity is used to produce power, electrofuel is used to produce an additional 100% of reactor power generating capacity, and thermal stored power is used to produce up to 50% of reactor capacity, and

Now, after stepping through it, you may wonder why bother with the electrofuel. After all, that 100% of extra generating capacity cost the equivalent of 360% of reactor output. However:

  • In terms of capital cost per additional KWh storage, it is much cheaper to store energy in methane for a week or a month or a year than in batteries or in pump hydro storage. For inter-monthly or inter-seasonal balancing, natural gas may be stored in depleted gas formations as well as aquifers … and, indeed, you will note 0% natural gas consumption for electricity in this scenario, so the legacy natural gas pipeline and storage system may be used for part of this … so co-location with a long term methane storage facility is not required. During off-peak hours of peak demand periods, the natural gas may be transferred from long term storage into tank storage if necessary backed by salt caverns, for more rapid extraction during the actual turbine generation periods;
  • During a pedal-to-the-metal transition to low carbon power, the natural gas peaker plants already exist, and are the natural gas generating capacity with the greatest GHG emissions. Also, due to the inefficiency of single cycle turbines and their restricted number of hours used per year, even if Natural Gas industrial scale Carbon Capture and Storage turns out to be economically feasible (which the scenario does not rely upon happening), the peaker plants are by far the least economic for conversion to Natural Gas carbon capture and sequester.
  • And in terms of peak net-load, two and a half times total reactor capacity is a lot of energy, when the reactor capacity is 15% of average energy supply.

This last point is perhaps more confusing for experienced professionals than for novices. The novice says, “yes, two and a half times 15% is 37.5%, that does seem like a healthy slice of power.” The professional says, “wait a minute, you are confusing average power output with peak load. Peak loads by definition must be substantially above average load, by definition. “Peak to Average” ratios, the ratio of peak demand to average demand, average between 1.7 and 1.8 in the Mid-Atlantic region of the “PJM” electricity interconnect, and in 2006 hit 1.82.

Except that is pointing to today’s fossil-fuel powered grid, which does not have our (assumed) ability to time shift 10% of total energy demand, nor our (assumed) ability to time shift 10% of total energy supply. That is a grid that is able to level out the most commonly experienced daily peaks.
A Bridge Over Troubled Water

I’ve been loosely using the term “peak operation” for these hypothetical nuclear power plants, and in so doing I will have been confusing our hypothetical expert … which is probably unavoidable … but also likely confusing you, my dear readers.

For a dispatchable unit in our no/low carbon electricity generating portfolio,its peak operation is not necessarily about an underlying peak demand for electricity. After all, we have variable renewable generating capacity providing on average 75% of total energy consumed. And with our 2:1 ratio between maximum and average renewable energy harvest, during some periods, it might be generating 150% of average energy consumed.

And typical hour to hour swings in power demand during the day are the least expensive to cover with storage and demand shifting, because the annual capital costs are spread out over hundreds of annual uses.

Then there are the expected seasonal swings in both energy demand and variable renewables production. At a level of a feasible solution, these are also straightforward to cope with … fire up a fleet of biomass powered generators.

Now, it is not guaranteed that this is a solution that we can pursue sustainably at a price that we wish to pay, nor that it is necessarily the cost optimizing solution, but it is a solution that is feasible at some cost that we could pay without crashing our entire economy.

Assuming we can expand reservoir hydro to 7% of capacity, the balance of that 15% dispatchable renewables may be assumed to be some form of biomass. And we can can observe some points about the long term economics of this seasonal back-up biopower.

  • Being sourced by biomass, we have to have a biomass crop production system. For the best prospects of being ecologically sustainable as well as a no/low carbon energy source, any biomass produced in excess of sustainably available wastes should be based on a short rotation perennial energy crop. And perennial crop production does not “turn on a dime”.
  • The most thermodynamically efficient biomass seems likely to be biocoal ~ charcoal produced by some variety of flash carbonization under pressure in a sealed carbonization chamber, include treatment of exhaust for pollutants and using the exhaust for co-generation of distributed electrical power.
  • Whether generating power from legacy coal power plants or from direct carbon fuel cells, energy efficiency will be the greatest if run at steadily at the optimal rate, and given a relatively inflexible annual budget, energy efficiency is an important factor.
  • Being seasonal back up power, its capacity factor can be factored into the fraction of the year that it is put into use, and the capacity utilization when it is in use.
  • Roughly half the year, variable renewables will be producing more than average, and roughly half the year, less than average
  • Whatever the make-up of the back-up seasonal power, we will be wanting to start up the most efficient units first, and the least efficient units last.
  • If any are used about half of the time, and all are used some of the time, the average capacity utilization seems likely to be around 20%-30%, so for simplicity I will peg it to 25% in this scenario.

Now, 25% capacity utilization and 8% of total power supply implies a capacity of about 32% of average energy consumption. If average hydropower capacity utilization remains in the neighborhood of 40%, then 7% of total power supply from reservoir hydro implies a capacity of about 17% of average energy consumption.

Now, remember if we are looking at a national portfolio of renewable energy sources offering an average of 75% of annual energy consumption, there is always going to be some supply from somewhere, but it is by no means going to always be 75%. Suppose that the minimum yield is 40% of average yield. Then during the lowest yield period, renewable energy is yielding about 30% of average supply.

Lets add those together … 32+17+30=79%. Even with emergency demand response measures, on top of regular daily-life dispatchable demands, what we have here is a brownout … and, especially if average daily demand at this period is above the annual average, perhaps rolling black-outs.

What this portfolio needs is something that can:

  • Act as a load-following supply under normal circumstances
    • Smooth anticipated hour to hour swings in load net of variable renewables supply plus whatever seasonal back-up power is in operation;
    • Cover expected swings in daily demand that are not expected to last long enough to justify turning on or off biomass back-up power plants; and
    • Provide hour to hour reserve to cover for unexpected drawn-downs of reservoir, battery or PHS stored power.
  • And during both steep, unanticipated drops in variable renewables supply (which will happen), and during the steepest annual peaks in load net of variable renewables supply, act as a firming reserve.

And that is what our hypothetical molten salt reactor, coupled molten salt generator, and electrofuel production plant give us. With breathing room on top.

That breathing room on top is important, since if we get far enough ahead on biocoal supplies … we can bury the biocoal, which is high concentration carbon in a much more stable form than CO2.

And on the other hand, if there is a renewable energy “drought” … whether affecting hydro, the variable renewables, the biomass, or several in combination … that breathing room is our margin for error as we ramp up biomass production … which, for perennials, is a process that rolls out over several years.

And on the other hand, if there is a renewable energy “drought” … whether affecting hydro, the variable renewables, the biomass, or several in combination … that breathing room is our margin for error as we ramp up biomass production … which, for perennials, is a process that rolls out over several years.
But Wait, There’s More

Now, if the round trip inefficiency of the electrofuel to store electrical energy gets you down … there’s a final point which I have left to one side.

That is Combined Heat and Power.

The thermodynamic efficiency of conventional heat engines is limited by the difference in temperature between the heat source and the heat sink. Natural Gas combined cycle generators get their efficiency increase by using the exhaust of the turbine to water for a steam generation phase, so that the combustion of natural gas in a turbine provides the original heat source and the coolant for the steam phase provides the final heat sink.

But now you have heated your final heat sink, and have to either replace it with a new source of coolant (so-called “once-through” cooling), or you have to cool it back down again. Because you have … steam or very hot water. And what could you possibly do with a supply of steam or very hot water?

Well, you could run it through pipes built into a heat exchanger with pipes contained a cooler supply of water, and then run those pipes to buildings. During cold times of the year, those buildings could put some of that water through radiators that emit heat into cold rooms … in the process cooling the water in the radiator. Some of that water could be run through another heat exchanger to help heat a supply of hot water. During hot and humid times of the year, some of that water could be run through a dessicant dehumidifier, to release humidity from the dessicant into an exhaust air stream so that humidity can be removed from the internal air supply, raising the threshold comfort level temperatures of the building and reducing energy demand for air conditioning. Given sufficient hot water in the pipes, and sufficient dessicant, outside air can be super-dehumidified, and then cooled with a swamp cooler, to further reduce (or in some climates, eliminate) the need for electrically powered air conditioning.

And of course, industrial and commercial processes that require heat can use the hot water in the pipes to either provide the required temperature, or else to pre-heat to reduce the energy cost of providing the required temperature.

The thing about CHP is … all of those uses are doing the work of a conventional cooling tower. A cooling tower may still be needed … there is no guarantee that demand for electricity and demand for heat through the water pipes will always be in synchronization. But to the extent that the CHP turns the “waste heat” of the second cycle into useful heat for those connected to the CHP steam pipes, then it replaces the alternative source of that heat … and the round trip efficiency of the stored electrofuel got an appreciable kick. If the total efficiency of the consumption of electrofuel is increased to about 80%, then the round trip efficiency rises from about 30% to about 50%.

And that may not be as cool as a Bass-O-Matic, but its nothing to sneeze at.
A Spirited Defence of Nuclear Power

I leave this part to be filled in by advocates for Nuclear Power. I am not mode-advocating here, I am exploring technologies to move to a no/low carbon electricity supply. However, do be careful to be specific about what nuclear power technology you are advocating for. Just as advocating for a passenger HSR train between Houston and Dallas is a quite different animal from advocating for a steam train as commuter rail between San Diego and downtown LA, advocating for each of conventional pressurized LWR, so-called “modular” LWR, and various advanced nuclear reactors ought to, in reality, involve distinctive arguments. If the arguments cannot distinguish between which are more and which are less preferable, it may strike the undecided as simple cheerleading.
A Scathing Indictment of Nuclear Power

Again, to be filled in by opponents of Nuclear Power. I am not mode-advocating here, I am exploring technologies to move to a no/low carbon electricity supply. However, do be careful to be specific about what nuclear power technology you are advocating against. Just as opposition to a passenger HSR train between Houston and Dallas is a quite different animal from opposition to a steam train as a commuter between San Diego and downtown LA, opposition to each of conventional pressurized LWR, so-called “modular” LWR, and various advanced nuclear reactors ought to, in reality, involve distinctive arguments. If the arguments cannot distinguish between which is the lesser and which is the greater evil, it may strike the undecided as simple naysaying.
Conclusions and Conversations

I post this with great trepidation, since in energy discussions, there are often few troll parties like a renewable energy versus nuclear energy party.

But on the other hand, I have just spent two weeks with me 5 month old grandson, and I don’t want him to grow up in an economy continuing to risk catastrophic climate change suicide.

As I have discussed in previous Sunday Trains, we are facing two renewable energy transitions. One of these is the one immediately ahead of us, in which we can roll-out the capacity to tap some 25% or more of our average energy supply from a range of renewable energy sources. That can be done in the context of the energy system we presently have. There will be headaches and difficulties along the way, there could be a wrong turn or two, but in broad outline, that energy transition has already started, and so long as we keep pressing against the defenders of the status quo, we are taking advantage of a downhill push.

However, once we complete that energy transition, we have another one. Armed in part with information presently at our disposal, but primarily with information we will learn along the way during the first transition, we will have to plot out the transition to a completely no/low energy economy. That includes transport energy, industrial energy, residential energy and commercial energy, and it includes the energy we presently consume as electricity and the energy we presently consume through the direct combustion of fossil fuels.

Some pathways that seem plausible today may turn out to be dead-ends. Some pathways that seem to be dead-ends today may turn out to be real pathways. But the more real, feasible options we have available to us at the time that we make that transition, the greater the prospects we have for actually navigating the second transition … as opposed to allowing our nation and economy to collapse before the end of the current century.

So, what do you think?


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About the Author

... is an obscure development economist living and teaching in Northeast Ohio. He writes about the rails and public transit.

  • Todd

    Very good article about a very complex topic. When one sees how very dominant fossil fuels are globally in energy production, we need to have all the low/no carbon emitting energy sources on the table. An article about how much more energy we need today and considering UN states 9.7 billion by mid century

    Seems the NREL agrees with this article

    Page 390 of the latest Quadrennial Energy Review from Dep’t of Energy discusses constraints of raw materials, so we need to make the most of the raw materials we mine out of the earth. (page 102 compares 2010 and 2014 electricity capacity and generation for various sources)

    The reactor that is not mentioned in this article is the Integral Fast Reactor, cancelled during the Clinton administration, but orderable today and

  • AuldLochinvar

    Wind turbines and fractural gas turbines are very good friends. If you desire 300 MW of totally reliable response to peak demand, you can build 300 MW of gas turbine capacity. If you then add 300 MW of wind turbine capacity, and throttle back (but do not stop) your gas turbines to match the wind power available, you might save a quarter of the gas consumption. But in spite of the fact that the average production factor may go as high as 30% in some locations, there is no chance that building 1000 MW of wind farm “caoacity” will guarantee that a mere 300 MW of wind will be available when you need it.
    On the other hand, modern designs of both the IFR and the MSR reactors are not plagued by the iodine 135 to xenon 135 neutron-capture pit. They could follow the wandering behaviour of wind electric production.
    _But why bother?_ Reducing the reactivity in the reactor probably costs more in operator attention than the minuscule savings, if any, in fuel.

  • AuldLochinvar

    The least risky energy source per kWh delivered _when required_ is nuclear.
    The so-called renewables from solar (wind, rain, snow, PV, mirror-concentrated heat) totally require backup. Rain and Snow? Yes, they depend upon the previous weather too. The governor of California was recalled on account of a scandalous rise in the price of electricity, because the previous winter’s snowpack was insufficient to supply peak demand from the water impoundments.

    Suppose you have 800 MW of gas turbine capacity, you can meet any demand up to 800 MW. If you supplement that with 800 MW of wind turbine nameplate capacity, then at times, say 20% to 30% of the annual demand, you can get “free” energy from the wind and throttle back gas turbines to be idling at the rotational speed that matches the grid AC frequency.Note that you dare not shut them down.

    But if you have 800 MW of nuclear electric capacity, what’s the point of throttling it back? It is already as clean as the wind turbines, except when the wind is too strong to use them, when their rotation must be stopped, but the nacelle stil requires power for the motors that keep it turned to face the wind. Then nuclear power is cleaner than the wind.
    Fourth generation nuclear power is as nimble at following load, as gas turbines. So it has been shown (or if you like, claimed) in studies that nuclear can back up the solar origin “renewables”, and they can be “friends”. What nonsense!
    If a power source as clean as a breeder reactor can follow your demand, you save nothing by having an equal amount of wind or solar.
    The maximum load demand that 1000 MW of gas, coal, or nuclear plus N thousand MW of wind and solar can RELIABLY meet, is 1000 MW.
    When the sun don’t shine an’ the wind don’t blow, it doesn’t matter how much “renewable capacity” you’ve got.

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