The EOS grid-storage system and nuclear power: a marriage made in heaven

EOS Energy Storage is peddling a megawatt-scale, fully containerized energy storage solution based on zinc-air (or zinc-oxygen?) cells.  Self-contained in a standard 40-foot footprint, the cutaway shows blocks for batteries, inverters, and cylindrical objects which seem likely to be some sort of gas storage or perhaps filtering/processing system.  The stated performance figures:

• $1000/kW
• $160/kWh
• 75% round-trip efficiency
• Cycle life 10,000 cycles
• 30-year design calendar life

This appears designed to operate roughly 1 cycle a day for 3 decades.

If they actually deliver at those specs, it's worth thinking about what it could do.  For instance, at $1000/kW output and 75% round-trip efficiency, $300 million invested plus 2400 MWH input over 6 hours (400 MW) yields 1800 MWH output (300 MW) over 6 hours.

Let's try this as a hypothetical example with something else that's already coming:  the AP1000, with 8 currently being constructed worldwide.  This will supply base-load power which can be cycled to follow load, but is most economical if it's run flat-out.  The AP-1000 is rated at 1154 MW(e), and the estimated pricetag per plant of about $8 billion at Vogtle isn't out of line for first-of-a-kind efforts.... batteries not included.

Let's add them.  $300 million for 300 MW of EOS units bumps the pricetag to $8.3 billion.  Charging at full power drops the net output from 1154 MW(e) to 754 MW(e).  Maximum discharge increases the net output to 1454 MW(e), nearly twice the minimum.  (This is considerably greater than the 1.67:1 day/night swing detailed for the eastern provinces of Australia.)

At full cycling, the daily output is (1154*24-600)=27096 MWh, or 1129 MW(e) average.  Other attributes:

• Peaking:  self-supplied (either centralized or distributed)
• Reactive power:  presumably available from the EOS inverter systems, distributed with the storage units.
• Air emissions:  zero.
• Spinning reserve:  as much as 700 MW (the difference between 400 MW maximum charging rate and 300 MW maximum discharging rate).

Amortizing $8.3 billion over 20 years at 7% interest costs $772 million/year; divided over 1129 average MW at 0.9 capacity factor, I get 8.7¢/kWh.  Selling off-peak power at 5¢, mid-demand at 9¢ and peaking power at 15¢ I calculate $913 million annual revenue vs. $772 million annual amortization (salaries and fuel not included).  Even at the extreme first-of-a-kind price of $8 billion for the nuclear unit, this is clearly affordable.  After 20 years the bonds are paid off and the system becomes a cash cow for likely 4 more decades or longer.

The value added by the battery is the difference in purchase (or opportunity) cost of the off-peak power and the sales price of the peaking power.  At the same 0.9 capacity factor I see $49.3 million annual gross revenue from the battery, paying off in just over 8 years.  Plainly the battery is pulling its fiscal weight!  But it will also cut the supply of off-peak power (shifted to charging), so off-peak prices may increase.  This would further improve the economics of the system as a whole.

The impact on unreliables

Would the EOS battery make the dream of an all-renewable grid possible?  That's very doubtful, given the need to tide the system over lulls adding up to days of average output.  48 hours of storage would itself cost $8000/kW, or around 16¢/kWh even if it was cycled continuously (50% capacity factor).  That's over and above the cost of the power to charge it, which is hardly cheap at feed-in tariff rates.  What would people do, looking at that pricetag to go "green"?  They'd go the way of Germany and Poland, and burn coal.  If stored energy comes at caviar prices, we should not be surprised if people decide to eat energy "junk food" instead.

The impact of a carbon tax

Suppose for a moment that the current system of production and investment tax credits is replaced by a simple, non-discriminatory figure of merit:  a straight-up carbon tax.  Let's set this carbon tax at $40/ton of CO2, which matches the 2.2¢/kWh PTC for a gas-fired generator emitting 550 gCO2/kWh.  Coal plants will be assumed to emit 900 gCO2/kWh, with coal at 15 million BTU and $100/ton delivered (average bituminous and sub-bituminous).  Also, with the North American shale-gas investment bubble about to collapse and multiple LNG export terminals ready to push prices up to world levels, wholesale NG delivered to major markets costs $15/mmBTU.

This was worth working through in detail, so I posted the spreadsheet in both text and downloadable file at ergosphere.wordpress.com.  This spreadsheet assumes a grid capable of delivering 600 GW average, to allow expansion for electrification of transport etc.  I used a 20-year amortization for all RE generation (wind farm lifespan appears to be shorter than that), 30 years for nuclear (licenses are now being extended to 60 years), 7% interest rate, and highly decentralized and interconnected networks for both wind and solar generation.  Without storage the RE must be consumed at the time of generation, so transmission capacity must equal peak generating capacity.  I assumed cost of $2 million per mile for a ±1.2 megavolt, 1000 A (2.4 GW) dual-circuit HVDC line with an average of 1800 miles length between generation and market.  That's enough to get Dakota wind power to the coasts, and Arizona and New Mexico solar power to both Seattle and Georgia.  I also rolled in a $40/tCO2 carbon tax for the fossil-backed options, with emissions of 550 g/kWh for gas and 900 g/kWh for coal.  In the all-RE case, some 2.3 million miles of HVDC line are required.  Some of these may be able to share rights-of-way; some may not.  This many times the total mileage of the Interstate highway system.  I assumed for the sake of simplicity that fossil-backed RE could use DSM to use peak generation productively and would require neither storage nor spillage.

The cost figures for the RE options are all dismal.  Gas-backed is cheapest at $114/MWh (11.4¢/kWh), with coal not far behind.  The gas option emits 122 gCO2/kWh, which is at least twice what we can tolerate in the long term.  Getting this down using storage is staggeringly expensive.  Using the EOS zinc-air system at $167/kWh, total cost soars by a factor of almost 10 and power rises to a prohibitive 90¢/kWh.

The nuclear option comes in best.  Assuming $5000/kW average for a new-build fleet of nuclear reactors (roughly twice China's cost for a new AP1000), and 180 GW (1200 GWh) of EOS battery storage, total capital cost is about $3.3 trillion.  No HVDC network is required.  Amortization over 30 years at 7%/year is $270 million.  Total amortization cost comes to 5.1¢/kWh.  Carbon taxes are zero, so the only unknown is O&M at perhaps 2-3¢/kWh.  CO2 emissions from operations are ZERO.

The nuclear system does not depend on natural energy flows, so it can be expanded when and where desired.  For each new application electrified on this grid, all the carbon it formerly emitted is displaced.  This appears to be a cost-effective way to de-carbonize entire national economies.

This would be anything but a small task.  632 GW of AP1000's is 575 units, not allowing for refueling and repair outages.  Even so, building 30 a year the USA could finish the job in 20 years.  The alternative is to build something like SMRs, where we'd be turning out several a week instead of one every couple of weeks.  That looks doable too.

Conclusion

Trying to de-carbonize the US grid with enough excess to electrify transportation is a massive task.  The cost of the all-renewable scenarios for doing it, with the requirements needed to provide a reliable supply to dark/calm parts of the country, is prohibitive.  Nuclear energy and the energy stockpile of fissile metals eliminates both the long-distance interconnections and massive storage needed for reliance on fickle energy flows.  If we want to go green, nuclear is the only real option we have.

Labels: alternate energy, analysis, batteries, CO2, energy substitution, nuclear power, petroleum dependence

  ¶ 11/30/2013 01:16:00 PM 0 comments

 

Plentiful Energy and the IFR Story

I'd like to call attention to the article with the above name (about 7 years old now) hosted at The Center for Reactor Information.  It lays out the brief history of the Integral Fast Reactor, including how it came within a hair's breadth of surviving the 1994 vote to kill it.  It also gives a brief listing of its selling points, including (contrary to claims often made by anti-nuclear activists) that its fuel cycle is unable to produce weapons-grade material and is effectively proliferation-proof.

This is an article suitable for non-technical readers and ought to be spread widely.  Some of its figures are out of date (wind power is now pushing 2% of US electric supply, not ¼%), but this is good for further analysis to show just how difficult it is to scale up renewable energy to the quantities we need.

Labels: alternate energy, energy, government incompetence, IFR, nuclear power

  ¶ 7/31/2011 10:50:00 PM 0 comments

 

Energetics of cultivation: draft animals vs. combustion engines and the Haber process

Abstract

The energy use by the agricultural sector of the economy has been widely discussed and debated in the peak oil community.  The amount of energy used directly at farms is not very large; typical claims for the fuel required to cover a field with a plow or other implement are in the range of one gallon of diesel per acre per pass.  Assuming seeding, harvesting and 3 other passes per year, the total comes to approximately 750 MJ per acre per year.  Nitrogen fertilizer applied at 200 pounds of nitrogen per acre would account for another 4600 MJ per acre¹.  Residues from many crops such as corn can supply over 20 GJ per acre and energy sources such as wood chips and fuel grasses are even more productive.  Farming operations such as dairies have already become net exporters of energy as electricity.  This suggests that even a mechanized farm can be self-sufficient in energy, and "fast crash" doom scenarios involving the collapse of farming are not very likely.

1    Farming before powered machinery

Before self-powered farm machinery, there were draft animals.  They were slow to reproduce and train, and often dangerous to work.  They were fed using the one quarter to one third of land fallowed as pasture at any given time.  Some grain (such as oats) was also needed as supplemental feed.

Despite use of animal manures as fertilizer, the yields of the time were not very high.  40 bushels of corn (maize) per acre were typical.  Combined with fallowed acreage, net productivity was a fraction of today's averages.  Productivity was also low; a double-furrow plow pulled by 3 or 4 horses could only plow 2.5 acres per day.

2    The transition to modern practices: steam tractors

The change to steam gave several major improvements.  Steam engines could use any fuel which would burn in the fire box; it did not have to be suitable for animal food.  They also did not have to be "fed" when not working.  Last, the productivity went up radically; one man on a steam tractor could plow 25 to 40 acres per day.

The thermal efficiency of open-cycle steam engines is quite low, roughly 5%.  Guessing from the efficiency of modern diesel engines, it would have taken perhaps 1.2 GJ of fuel to make one pass over an acre.  This is about 180 pounds of firewood, or a considerably smaller amount of coal.  Being able to plow several acres with the wood from one tree was a huge improvement over draft animals.

3    Internal combustion engines (ICEs) and their efficiency

Internal combustion engines are much more efficient than piston steam engines, as well as much more convenient to operate.  Thermal efficiency of medium-speed diesel engines runs upwards of 40%, and low-speed marine diesels can top 50%.  Internal combustion engines can also operate on biofuels, with handicaps which depend on the exact fuel fed to the engine.

4    Homegrown ICE fuel supplies

While current vehicles and farm equipment are fairly finicky about their fuel, the generic ICE is quite adaptable.  Spark-ignition ICEs can be run on everything from petroleum to ammonia to carbon monoxide made from partial combustion of charcoal.  Diesel engines are somewhat fussier, but they can be "co-fueled" with some amount of liquid used to ignite a charge of air and a high-octane gaseous fuel.  The addition of gaseous fuel to diesel intake air is called fumigation.  Kits are available to fumigate propane into diesels to improve their power and reduce their smoke emissions.

Most current farm equipment has diesel engines.  One of the features of the fast-crash doom scenario is that there will be little or no time to make major adaptations for different fuel supplies, so the most interesting possibilities are those which can be

• built from common materials and
• retrofitted to existing engines.

Are there significant possibilities out there?  I believe there are.  Here's a short list off the top of my head:

Straight vegetable oil (SVO).  SVO is one step removed from biodiesel, but requires no methanol or other processing.  It can be used directly after pressing so long as it is filtered so as not to clog pumps and injectors.  SVO must be kept hot to thin it enough to atomize, so engines must be fully warm before using it.  This can be accomplished by heating the fuel and coolant externally, or starting and warming up on petroleum diesel or biodiesel.  The fuel system must be flushed of SVO before the engine is allowed to cool off again.

Supplies of SVO are likely to be limited, but if SVO is used for a "pilot injection" to ignite a charge of another fuel it can be stretched considerably.

Fumigated bio-gas.  Bio-gas can be produced from animal wastes and stored in tanks.  Introducing gas into diesel intake air creates a fuel-air charge which ignites and burns when oil is injected by the conventional fuel system.  It is not usable as the sole fuel in a diesel engine, but it can stretch the supply of liquid fuel.  A dual-fuel biomethane bus in the UK expects biomethane to supply 60-80% of its fuel.  As no biomethane is used when the engine is at idle, agricultural equipment could expect to use a higher fraction of biogas than a bus.

The downside of biogas is that it is a gas, and storage cylinders are heavy and bulky.  Materials likely to be on-hand would leave a a great deal to be desired:  low-pressure cylinders such as propane tanks can contain biogas but would hold relatively little fuel even if it is purified to remove CO2.  A 250-gallon propane "pig" pressurized to 250 PSI would hold the equivalent of about 4 gallons of diesel fuel.  It might be possible to get work done this way, but refueling would be very frequent and take a great deal of time away from work.

Fumigated producer gas.  Gas does not have to be delivered to the vehicle; it can be produced on board from solid or liquid fuels.  The technology for using gasogenes to produce fuel gas for a combustion engine was brought to a high level of refinement during previous periods of oil rationing (such as WWII).  Gasogenes were revisited by the USDA during the 70's oil price shocks, and designs created which could be built out of available materials to power tractors in the event of fuel shortages.

Gasogenes can use most any dry combustible matter as fuel.  Wood chips and charcoal are conventional feedstocks.  Dried grass pellets and torrefied biomass are other possibilities.  Combustible liquids may be used also; a liquid fuel which is not suitable for an engine's fuel system may be turned into a gas for fumigation.

5    Biofuel energy requirements

For the sake of argument, let's start with a sub-optimal energy system.  Dried biomass loses very little of the original energy (though biomass may not remain dry unless it is stored correctly).  Torrefaction retains roughly 90% of the energy of the original biomass in the product.  Pyrolysis oil retains about 70%.  Production of charcoal may yield about 50% in the solid product (the remainder comes off as gas and heat).  Therefore, let's assume the use of charcoal as the fuel product.

Next, let's assume conversion of charcoal to producer gas in a gasogene.  The fuel portion of charcoal is almost entirely carbon.  Carbon has a heat of combustion of 93960 cal/mol, while carbon monoxide has 68560 cal/mol; 73% of the energy of carbon is retained in the gas product of the gasogene, not including any CO₂ from the exhaust gas recycled to CO using excess heat.  The hypothetical conversion efficiency from biomass through charcoal to fuel gas in the vehicle is thus 37% (not including any productive use of heat or off-gas created in the production of the charcoal).

If the vehicle is a farm tractor or combine which requires 1 gallon-equivalent of energy per acre per pass, of which 90% is coming from fuel gas produced from charcoal, 5 passes per season requires 1.7 million BTU of biomass.  A further 10% of liquid fuel, or 700 kBTU/ac/year, is needed for pilot ignition; since this is relatively small I'll just count it at volume parity with petroleum diesel.  This comes to 0.5 gallon per acre per year.

6    Biofuel feedstock availability

The amount of available feedstock depends on the productivity of the crop and the fraction which winds up as byproducts, but we can get some estimates.  At a yield of 150 bushels per acre, corn (maize) produces roughly 1.5 dry tons of excess stover (not needed for erosion control) per acre, of which 15-20% (0.22-0.3 tons) is cobs.  At 17.4 million BTU per ton, the actual fuel requirement is less than 0.1 tons of biomass.  Corn would in fact yield a very large excess of biomass energy beyond the needs for farm machinery working the field.

Oil for ignition can also come from corn.  At 0.5 gal/ac/yr, the ignition requirements can be met by the oil from about 2.5 bushels/acre of corn (0.2 gal/bu).  The byproduct of pressing is also usable as food.

Other crops also appear to produce sufficient byproduct biomass.  The yield of wheat straw from winter wheat is over 2 tons per acre.

If the main crop does not yield oil, some small amount of land can be devoted to oilseeds.  Sunflowers or canola will do for this.  At a yield of 77 gallons per acre, one acre of canola would supply ignition fuel to till and harvest 150 acres.  Such a modest amount of oil would be easy to produce locally.

These figures suggest that the energy situation of most farms is not nearly as bad as some paint it.  Even assuming the least-efficient pathway for converting biomass to vehicle fuel (charcoal), farms still appear to generate much more energy as non-food biomass than they need to run machinery.  Machinery has the virtues of not having to be bred up from small initial stocks, requires no animal training and no major changes in farm practices and skills, and certainly is not going to be stolen and eaten.

6    Biofuel energy excess and nitrogen fixation

The amount of excess energy from crop byproducts suggests that they might be exchanged for other necessary farm inputs.  For instance, bio-oil (pyrolysis oil) can be produced from almost any finely-divided dry biomass.  It preserves about 70% of the energy of the biomass, and is a relatively dense liquid which seems fairly easy to handle.  One ton per acre of corn stover would yield about 12.2 million BTU of bio-oil.  If this were used as a natural gas substitute in an ammonia plant, it would suffice to produce roughly 680 pounds of ammonia, containing 560 pounds of nitrogen.  Most nitrogen application rates for corn are under 200 pounds per acre (some recommendations as little as ~50 lb/ac), so corn would be enough to provide a large excess of nitrogen fertilizer also.

This analysis does not look at the energy economy of livestock operations.  Anaerobic digestion of manure from cattle, chickens and swine produces more fuel gas than many of them can use; already many farms have turned into net producers of electricity generated from biogas.  While the excess is small on the scale of society, it does suggest that rural farming areas may be able to keep the lights on without purchasing energy.

Conclusions

Some have suggested that shortages of petroleum could produce a collapse of mechanized farming in the near term, with all that implies.  This scenario does not appear to be realistic.  Known methods appear to be able to keep farm machinery operational using only the energy produced on farms themselves, mostly using food byproducts rather than dedicated fuel crops; this is considerably better than the food requirements of draft animals.  The superiority of machinery over animal power, both for productivity and economy and reliability of energy supply, guarantees that it would continue to be maintained and used for some time even if the "fast crash" scenarios come to pass.

Endnotes

1 Assuming 1150 m³ of natural gas per metric ton ammonia and 37 MJ/m³ natural gas, ammonia requires approximately 43 GJ/tonne, or about 23 MJ per pound of nitrogen.

Labels: agriculture, alternate energy, biofuels, energy, energy substitution, peak oil

  ¶ 9/19/2009 01:52:00 PM 0 comments