Affordable Energy Storage: The Holy Grail Of Clean Energy

Enabling safe, clean energy that will never run out is a key toaverting catastrophic climate change.  Roughly half the “solution” toglobal warming is solar and wind [see "How the world can (and will) stabilize at 350 to 450 ppm"].  Of course, many U.S. concentrated solar plants will use low-cost, high-efficiency thermal storage.  In the longer term, plug-in hybrids and electric carsare likely to play a key role in storage, if issues surrounding batterylife can be solved and/or battery leasing strategies pan out (whichwould also create a large aftermarket for batteries that utilitiescould use).  Another strategy for grid integration is natural gas.  In this repost, guest blogger Craig A. Severance discusses what he learned about available technology from interviews with leading storage firms.  Severanceis co-author of “The Economics of Nuclear and Coal Power” (Praeger1976) and a former Assistant to the Chairman and to Commerce Counsel,Iowa State Commerce Commission.

As the world meets this December toset plans to halt global warming, it is expected America and otherindustrial nations will commit to a daunting task: reduce CO2 emissions80% by 2050.  In just 40 years, a complete revolution in how we useand supply our power must happen, or the world will face catastrophic effects of runaway climate changes.

As a new power plant typically lasts 40-50 years, many scientistsare now arguing we must simply stop building new power systems that usesignificant amounts of fossil fuels.  They argue we must move to a highreliance on the wind and the sun for our electricity.

Abundant Power. The U.S. has enormous wind resources, capable of generating over 20% of U.S. electricity from wind by 2030, according to the U.S. Department of Energy.

The sunlight  falling on our deserts, parking lots, and rooftops has even more power  – enough to supply 69% of U.S. electricity by 2050 according to published studies.

Other renewable power sources — such as geothermal energy, municipalwaste-to-energy, and biomass – will also play a role, but they pale insize compared to the gargantuan resources of wind and sunlight.

How We Use Energy vs. How Nature Provides. Thoughnature provides all the energy we may need, there is a problem. We demand power literally “at the flick of a switch”, not just when thewind is blowing or the sun is shining.

This basic fact about how we use power versus how nature suppliesclean energy has caused many to discount the idea that wind or solarpower can ever supply more than a small fraction of our electricity. Critics of renewable electricity call it “intermittent” and“unreliable”.  They say we can’t “catch the wind”, nor can we commandthe sun to always shine.

These critics see two possible choices for the future. We candevelop more stable supplies of renewable energy by coupling wind andsolar projects with storage.  Failing that, they argue we should giveup on renewables as a primary source of electricity, and instead buildmore nuclear power.

The flaw in the nuclear path, beyond its tremendous cost,long lead times, and imported fuel, is that nuclear is not actually“dispatchable” power.  Nuclear plants are designed to run all the timeat fairly steady output — meaning nuclear power cannot provide the “peaking power” nowprovided by gas turbines.  Thus, a nuclear path would still relyheavily on fossil fuel power plants to “ramp up” on a daily basis toprovide the power needed during these daily swings.

A truly dispatchable system providing over 80% reductions in carbonemissions, therefore, must rely on some form of energy storage.  Theenergy storage can allow us to fully utilize wind and sunlight as ourmain power sources – supplying both “base load” power and dispatchabledaily peaking power with energy from these inexhaustible supplies.

Energy Storage and Today’s Grid.

Despite critics, wind farms and solarphotovoltaics are already feeding zero-fuel-cost power intotoday’s electric grid with little or no energy storage.  At currentlevels, the fluctuations in wind and solar output are backed up by thesame ”load-following” and “peaker” natural gas power plants thatalready must handle wild fluctuations in customers’ demands forelectricity.  Indeed, the DOE’s “20% Wind by 2030? scenario modeled howwind could supply this very significant portion of U.S. electricityneeds even with no storage of the wind power.

As long as natural gas remains cheapand acceptable to use, many argue that developing ways to store wind orsolar energy may be a case of “a solution in search of a problem”. They note natural gas peaking plants are cheap to build and don’t needto operate much more than they already do, to provide firming power torenewables.

“Different sectors like to associate with wind power,” the NY TImes quotedRobert E. Gramlich, policy director at the American Wind EnergyAssociation. “But we don’t want to give anyone the impression thatstorage is needed to integrate wind.  Even growing 20-fold, storageisn’t needed.”

A Better Way. Though wind and solar can beintegrated without storage for a long time to come, energy storageproponents argue that coupling wind or solar power with utility scaleenergy storage is a “Better Way”.  If stored wind or solar energyinstead of natural gas plants can be used to generate power when thewind is not blowing or the sun is not shining, less natural gas willbe burned to provide dispatchable power.

Though storage will cost money, burning less natural gas will savemoney on fuel costs.  Also, there are now times when excess wind farmkWh’s have been sold onto the grid at extremely low prices oreven given away, because they occurred in the middle of the night whenthere was very low demand for power.  Storing that wind energy, forsale of kWh’s the next day when prices are higher, would generate more revenue.  While less dramatic, solar power production can also be shifted tohigher-demand periods, from solar noon to late afternoon/early eveningwhen utilities typically experience maximum summer peak demands.

The most important motivator, however, to find a “Better Way” is theneed to achieve phenomenal reductions in CO2 emissions.  While it maytake until 2030 to reach a 20% contribution to the grid, what then? Going beyond this level will require dispatchable renewable power. Twenty years is within the lifetime of any new power plant built today,so storage proponents argue we should already be building toachieve minimum levels of fossil fuel use.

Compressed Air Energy Storage (CAES). A proventechnology, ready to use now, for economical storage of massive amountsof renewable power is to compress air at very high pressures, and storethis compressed air in large underground caverns, depleted wells, oracquifers.  When the wind turbines and solar plants reduce output, andpower is needed,  the compressed air is released and run throughturbines to generate power:

Source: Scientific American

Because the caverns or acquifers are so large,  hundreds of hours ofoutput can be stored, providing the ability to cover very long“doldrum” wind periods or stretches of cloudy days. Most CAES turbinescan also run in natural gas-only mode in the extreme event the cavernbecomes fully depleted.   A reliable, fully dispatchable electricitygeneration system is provided.

CAES has a well established track record at scale.   A 280 MW plantin Hunthorf, Germany has run since 1978, and a 110 MW plant atMcIntosh, Alabama  has been in continuous operation since 1991.

CAES systems use gas turbines almost identical to normal natural gaspeaking turbines.  However, they only use about 1/3 the naturalgas, because 2/3 of the natural gas energy in a regular turbine is usedto compress air before it enters the turbines, and thiscompressed air would now be supplied by the stored air.  Natural gaswould still be needed to heat the air before it enters the turbines.

CO2 Reductions. While not a 100% carbon free power system,a wind or solar coupled CAES power plant system can achieve >80%reductions in fossil fuel use.  A baseload CAES/wind system (designedto provide at least 85% Capacity Factor power to the grid) wouldtypically provide half of its total power directly from the wind farmto the grid, without cycling through the CAES plant.  The other half ofkWh’s supplied to the grid would come from stored energy in the CAES,at about 1/3 normal fossil fuel use.  Total fossil fuel use perdelivered kWh would thus drop to roughly 1/6 of a normal fossil fuelplant, an over 80% reduction in CO2 output.

A carbon-free electric system is also possible, with CAES plantsfitted with thermal storage.   The thermal storage would store heatfrom compressing the air, for later use to heat the air going to theturbines.  Known as “adiabatic” CAES plants, the stored thermalenergy replaces the need for natural gas, causing the entire system torun on renewable power alone.  Because thermal storage is costly, it isnot expected CAES plants installed in the next decade will include it. However, a regular CAES plant can later be retrofitted with thermalstorage, when it becomes more economical or society demands zero-carbonpower.

Geological Formations Suitable for CAES. A nationwidenetwork of CAES plants could use the same types of geologicalformations, and depleted gas wells, as are currently used to store mostof the nation’s natural gas supplies.  Wide areas of the U.S. — mostnotably the wind-rich central states — have these formations anddepleted wells:

Source: Coha and Louks (1991)

Cost of Renewable/CAES Power Systems. Because the caverns, aquifers, and wells are already there, CAES offers very economical energy storage.

Estimates for CAES plants range from $750/kW of generating capacityup to about $1,200/kW, with the difference being primarily the numberof hours of energy storage.  A wind farm/CAES system (taken as a whole)capable of providing baseload capacity factors of 85% could be builtfor around $5,900/kW of equivalent baseload capacity, including thewind farm itself and the CAES facility.  While this is far more than anatural gas plant, it is comparable to a new coal fired power plantand at least 1/3 less costly than the same capacity if added throughnuclear power.

Unlike a nuclear or coal plant, the CAES plant would be fully dispatchablepower, able to increase and decrease its output along with fluctuatingcustomer demand.  This flexibility  is a major advantage for usefulnessto the electric grid.

Total costs/kWh from this system would also be competitive. Estimates indicate that if the wind farm is built with the 30% FederalTax Credit (still available through 2012), a total wind/CAES systemcould deliver baseload power to the grid at about 10.5 cents/kWh.  Thiscost would rise to about 13.0 cents/kWh without the wind TaxCredit. (Effectively, the Tax Credit if used wisely could pay forthe CAES plant to convert an intermittent wind farm into firm,dispatchable power.)

Though more expensive than kWh’s from a new baseload natural gaspower plant (which would probably be about 9 cents/kWh), a wind/CAESsystem would be well protected from future fuel cost increases.  Also,at 10.5-13.0 cents/kWh, the baseload wind/CAES system would only beabout half the cost/kWh  from a new nuclear power plant.

Pump Water Up and Let it Fall Back Down. Pumpedhydro-electric storage is just that simple — when you want to storeenergy, use electricity to pump water to a high level.  Then, wheneverpower is needed, let the water fall through hydroelectric turbines togenerate power.   You don’t get all your electricity back (about 22% islost), but you get it when you need it.  This enables you to acceptpower from renewable sources when not needed, and store it for uselater.

Pumped hydro storage is the largest utility energy storage method inthe world, with 20,800 MW already in use in the U.S.  However,  its usehas slowed because of limited sites for hydroelectric power dams.

Enter Riverbank Power Corporation,with its simple idea:  combine two well-established technologies intoone.  First, use standard deep mining techniques to create a largecavern 2,000 feet deep, under a body of water such as a river orabandoned quarry.  Then, install 4 gigantic 250 MW hyrdroelectricturbines at the bottom of shafts, for a massive 1,000 MW power supplyavailable on demand.  When power is needed, let water fall down theshafts and generate power.  When renewable power is available, pump thewater back up.

Source: Riverbank Power

Riverbank Power is now actively exploring 15 sites in the U.S. andCanada, for selection of its first five 1,000 MW pumped hydro (AquabankTM) facilities. Wiscasset, ME is high on the list, where Riverbank has alreadyperformed successful bore hole tests of the underlying rock.  TheWiscasset site is very symbolic, as it is the home of the former MaineYankee nuclear power plant,  decommissioned more than a decade ago. Aboon to Riverbank Power is the site is still set up to connect directlyto the transmission grid.

Costs. Because Riverbank Power has to dig out its owncavern, its cost to construct is significantly higher than a CAES plant— estimated at $2 Billion for the 1,000 MW facilities, or roughly$2,000/kW. Also, instead of dozens or hundreds of hours of storage,Riverbank plants are designed to run for 6 continuous hours before thewater would need to be pumped back up.  The timetable is good forhour-to-hour or minute-to-minute fluctuations but not long stretcheswith no wind or sun.

Riverbank is confident of its business plan, and is not asking fortaxpayer or utility dollars.  Its turbines use no fossil fuels, and thefacility should last 100 years.  The company plans to buy power atcheap prices, and sell power when it is needed more, at a higher price.

If it does that for 100 years, the Company feels it should pay forthe initial $2 Billion investment many times over, while creating jobsand giving green energy developers a solid market for their power.

Batteries to Store Power When and Where Needed. Whileboth CAES and pumped hydro storage plants hold the promise of verylarge scale economical storage, they both require special siting.  CAES requires an available underground cavern, well, or aquifer, whilepumped hydro requires a water resource.  Batteries, however, can govirtually anywhere, and take almost no lead time compared to the largerprojects.

Xtreme Poweris a company out there today, already selling product, byidentifying customers who have needs and who are willing to pay forsolutions.  The company has a systems approach employing modularbattery packs that can be scaled to provide Mwh of power storage,together with power electronics control systems.

Xtreme Power can shift  4 hours of power to a later time,for roughly 5-10 cents/kWh.  In many electricity markets, thedifference in value between different times of the day can more thanpay for this cost.

The company has some large scale systems going in before the end ofthis year, and plans to deliver at least 75 – 100 Mwh of power storagein 2010, with more that can be delivered.  Most of its customers arelarge solar and wind developers, who are eager for a solution and readyto pay for it now.

NGK Insulators

Sodium Sulfur (NaS) Batteries. Another battery solutionwhich is also already commercially available is sodium sulfur.  XcelEnergy has a 1 MW NaS battery installation underway from NGK Insulatorsto store up to 7.2 Mwh (in other words, over 7 hours of power), of windenergy for use when most needed.  The system will be adjacent to an11-MW wind farm owned by Minwind Energy LLC, in Luverne, Minnesota.

Let’s Not Store These Ideas For Later. Whenrenewable energy was still a long way off, the solution to energystorage seemed to be the unattainable “Holy Grail”.  It was always tobe found, yet never found.

Now, however, the answers are actually here, and they are simplerand plainer than we expected,  Store air.  Pump water.  Use advancedbatteries.   Like Indiana Jones in his Last Crusade, we need to know when the true Grail is right in front of us.

As Michael Breen from Xtreme Power told me, “Let’s stop jabberingabout it, . . We just need more demonstration units so the industry cantalk about this more intelligently.”

This is now happening.  Is the Holy Grail finally found?



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