Archive for electric grid

Visual Comparison of Electricity Generation Technologies

I just put together a couple graphs for a talk I’m giving on Monday to give people a visual feel of the various technologies for generating electricity.  These come with a gigantic caveat: the numbers are far from precise.

With changing technologies, it’s impossible to represent any of this with a single number anyway.  I’m trying to show how the technologies compare to each other, and I used four parameters:

  • Cost ($/MWh),
  • Availability (better the closer the profile of the technology matches a normal demand curve (wind is bad, baseload is okay, dispatchable is best, solar),
  • Emissions (and I count waste storage when it comes to nuclear),
  • Bubble sizes represent the size and durability of the resource (I’ve tried to combine in one number how much power we can get from the resource, but also how long supplies of fuel will last.) 

In both charts, the “best” technologies are in the upper left (low cost, low emissions, and available when we need them.)

I know that I’m going to upset a lot of people because I was too harsh with their favorite technology, so feel free and comment on the numbers I’m using, but also please provide references for where you get your numbers.  Most of these are off the top of my head, so their accuracy is admittedly questionable.   Here are the numbers I used to make the graphs.

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The Psychology of Energy Efficiency

Efficiency is unquestionably the largest, cheapest, and cleanest wedge among the many we need decarbonize our energy economy.  Energy efficiency tends to cost just 1 to 3 cents per kWh saved, far less than even coal-fired generation.   Every renewable technology, from wind to solar, to biomass, has trade-offs.  At the very least, we have to decide if the energy we are using for one purpose is not better used for something else.

Energy efficiency is the exception to this rule: you can not use a kilowatt-hour or a BTU over and over again.  Given these advantages over generation, it’s amazing that energy efficiency is nevertheless so extremely cheap.  Given an even moderately efficient [pun intended] market, you would expect that all the cheap energy efficiency measures would long ago have been taken until the marginal price of the next efficiency measure was above the marginal price of added electricity generation.

So why hasn’t it? 

Why is TXU trying to build a half dozen coal fired power plants in the face of broad opposition from the community when, for a fraction of the cost, they could instead pay to help people insulate their homes, change to more efficient air conditioners, and replace energy efficient lighting and save as much power as they plan to generate with the coal plants without any cost for fuel and harm to the environment from mining and emissions?

For that matter, why don’t TXU’s customers (and the rest of us) take these steps ourselves, when the internal return on investment is many time what we can rationally hope to achieve in the financial markets, and in many cases is even higher than the interest borrowers with the worst credit ratings pay on their credit cards.  (Like most financial advisors, I hate debt, especially credit card debt, but even if you’re drowning in $30,000 of credit card debt at 25% APR, it still makes sense for you to buy a pack of CFL’s at $3 each on that high-interest credit card, and replace every incandescent light bulb in your house that you use more than 2 hours a day.)

Here’s a blog which does a good job outlining the usual answers: lack of financing, perverse incentives, and disinterest on the part of people for whom energy is only a tiny part of the budget (all of which are true.)  He goes on to outline perscriptions that will undoubtably help to break down the barriers to the adoption of many Energy Efficiency measures.

I see other barriers that lie behind these.  Not just a failure of normal market forces, but conceptual problems.   While energy in general is a fuzzy concept to most people, using less energy is even less tangible.  You just can’t drop energy efficiency on your foot.  You’re not even at risk of electricution from it.

The pernicious consequence of systems of measurement is always that things we can’t measure go unnoticed.  If you have a hammer, everything looks like a nail, but even more insidiously, things that will never look like nails no matter how hard you squint dissappear from your vision altogether.  It is this psychological quirk that makes energy efficiency go unnoticed.

What image comes to your mind when I say “wind power”?  If you’re anything like me, you probably had a image of a forest of giant wind turbine blades turning gracefully on the horizon like ballet dancers.  Or, you might be like my wife, who would also have an image of a wind farm, but thinks they are ugly (although not so ugly as the haze from a distant coal plant) despite recognizing their necessity.  She wishes they were painted to camouflage them into the background.   Whatever your attitude towards wind power, you probably saw an image.

 Now try “energy efficiency.”  It’s a lot trickier, isn’t it?  I think about energy efficiency all the time, the way a teenage boy thinks about sex (okay, maybe not quite that much), and even I can’t settle on an image.  My mind flashes from the act of replacing an incandescent bulb with a compact fluorescent lightbulb (CFL) to an industrial scale combined heat and power facility, to closing the blinds at night to keep the heat in.

Not only is energy efficiency hard to picture, it’s also hard to measure.  To compute the energy savings from any activity, you have to establish a baseline: how much energy would you have used if you had not changed your methods.   Even in the simplest case of replacing a CFL, we don’t really know that the bulb we replace would really have stayed in the socket until the CFL breaks: A CFL can easily last 10 years, and by that time, we may be replacing all our bulbs with LEDs.  And that does not even begin to account for the effects on our HVAC systems.

Is your mind spinning?  That’s my point.  It can be so hard to get our minds around all the impacts of energy efficiency that, for most people, the most people, it may actually be rational to waste a little energy in order to avoid the headache that trying to get their mind around efficiency may entail.

The problem is, that decades of conserving brain power has left us as a society that wastes energy egregiously.

My prescriptions, designed to make thinking about efficiency easier:

  1. Measure energy use at every opportunity.  Many Prius drivers report that the real-time MPG gauge on the dash causes them to change their driving habits to grive more efficiently.  Getting a Kill-a-Watt energy meter makes us think more about our next electronics purchase.   Getting to know your electric meter can also motivate you to track down wasted energy.  A radical idea: on new homes, the electric meter should be inside, along with the circuit breakers.  New meters can be read (and even turned on and off) remotely, so there is no reason any longer to have them on the side of the house where we never see them. 
  2. Another thing we need to measure is when we use our electricity, not just how much.  Wholesale electricity prices can vary from a few cents per kWh to 30 cents or more during peak consumption.  As we move to a grid based on renewable energy supplies, most of which are intermittent and non-dispatchable, we need to get used to paying the real-time price of the energy we’re using.  Wide-spread adoption of time of use metering will drive the invention and adoption of appliances that can adapt themselves to changing prices.  There are direct, immediate benefits to the system by shaving peak loads, but the real benefits will come when people adopt new ways of doing things and new devices that will cause our appliances to run and our devices to charge when electricity is plentiful, and runonly the most essential uses of electricity when it is scarce.   Xcel is currently doing a pilot study on Time of Use Pricing in Colorado.  The preliminary result are that the right pricing scheme encourages customers to change their energy use much more than they had anticipated… but it still would not be “economic” to change out meters for more sophitocated models capable of handling this sort of billing.  Their definition of “economic” almost certainly does not include the benefits of the creativity which realistic pricing would unleash. 
  3. Allowing utilities to profit from selling less rather than more.  This concept, known as decoupling, is covered well here.  It’s important to remove (or even reverse) the incentive of utilites to sell us more electrons when we really want them to help us use less.

Finally, I do call this blog EE/RE Investing, so here are the sectors that I see benefiting from these recommendations as they are adopted:

  1. Companies selling advanced metering devices, and control systems that adapt to changing electric rates.
  2. Companies that sell building management systems.
  3. Energy storage technologies, such as as advanced batteries, flow batteries, and compressed air energy storage.
  4. Broadband over power lines technology, to handle the increased flow of information.

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Xcel Fighting Merchant Coal Plant

On January 18, Xcel Energy filed a motion with the Colorado Public Utilites Commission to reject a merchant coal power plant bid for 2014.   Xcel has been under intense pressure from the Colorado Commission to sign a contract with the project.   The Company also filed a motion for extraordinary protection  for critical parts of the bid report, which means we can’t see the underlying bid info or economic analysis.  While this is unfortunate but expected, the parts of the motion we can see make very interesting reading.

 This docket is a continuation of the competitive bidding process from the company’s 2003 resource plan and the settlement agreement.   

Xcel’s main ground to reject this bid is because it is “not economic.”  Unfortunately, we do not have access to the specific numbers, so we should not use this to say that coal plants are never economic.  I simply want to highlight the fact that this coal plant, according to Xcel, is uneconomic.  If the true cost of externalities of pollution and CO2 emissions were taken into account, the case for any coal plant’s economics becomes much worse.

Some arguments Xcel uses:

  • Electricity demand has not kept up with the demand they assumed in the 2003 LCP.  (Most likely due to increasing prices of fossil-fuel generated power, and a heightened awareness of the problems associated with global warming, both of which spur efforts for conservation.   It is also worth pointing out that our personal efforts to conserve electricity have contributed to the drop in demand, and that drop in demand makes this coal plant less likely to be built.  In this way, everyone can make a difference when it comes to fighting global warming.)
  • Xcel has successfully negotiated with bidders to provide natural gas fired power to lower their prices (p.5), while the coal bidders want to modify the terms of the contracts in a way that may shift environmental risks to Xcel (p.6) (which would then try to shift the environmental risks to ratepayers.).  
  • Coal is very capital intensive, so in order to make coal economically effective, the plant must be running as near constantly as possible.   (The inflexibility of coal and the need to keep the plants running all the time make coal as difficult to integrate into a system faced with variable demand.  In my mind, there is a certain irony in this, because the main argument against wind power is similar: the power supply is not well matched to demand.)
  • (p.27) “Far and away the most influential factor contributing to the reduced value of coal bid is the fact that the bidders increased their bid prices from what they initially offered in May 2005.”  (These increased bids are probably due to higher estimated construction costs, which coal plants are particularly vulnerable to due to the large amount of steel and concrete used in construction, as well as much higher prices for coal.  One of the best arguments for solar and wind generation is the fact that they are immune to escalating fuel costs.)
  • While Coal plants require years to construct, Demand Side Management (DSM aka Energy Efficiency), gas and wind can all be on-line in less than 16 months, making it much easier to match supply with demand.
  • (p.27) The PUC told Xcel to use their 2006 gas forecast prices in this analysis, at the same time as they were told to use their 2005 coal price forecasts.  Even though this artificial imbalance skews the results in favor of coal, it is not sufficient to make the coal bids seem economic.
  • There are substantial costs of added transmission to incorporate these coal bids.  (pp.47-50)  I point this out because wind naysayers often point to the transmission costs of new wind facilities, without taking into account the transmission costs for coal.  I infer from the text that this bid may be a mine mouth coal plant in Wyoming, which would require upgrades along transmission lines from Wyoming to Colorado.  Considering the Wyoming/Colorado border is an area with excellent wind resource, many sites for extensive wind generation would require the upgrades to the same or shorter sections of transmission lines.

I have uploaded Xcel’s filing here.   It will eventually be avialable on the Colorado PUC’s website, under Docket No. 05A-543E.
I’m happy that environmental advocates have this opportunity to build a more constructive relationship with Xcel by joining them in this. 

I also believe that these same arguments that Xcel is using here might be effectively used against some of the 150-odd other coal plants currently being planned in the US by utilites which are less progressive than Xcel (and there are many… TXU in Texas and many Rural Electric Co-ops come to mind.)

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Secrets of the Utility Mind

I feel that many of us renewable energy activists do not understand how utility planners think.  To us, we see wind as cheap electricity, but to them it is the Predator (of movie fame), something that looks benign and friendly, but at any moment will wreak havoc on their grid by turning off unpredictably.

In order to have a constructive conversation with utility planners, I think it is important to understand their point of view.  This is my attempt to do that, with the hope by doing so, we will be able to engage with them more productively.

These are what I see as the underlying principles that shape the utility planning process:

There is no God but Reliability, and Least-Cost is his prophet.

Or, put another way,

The Holy Trinity of electric resource planning: The Baseload, The Cost, and the Holy Reliability.

I use the religious references to make a point: reliability is a religion for utility planners, and people become defensive and angry when you threaten their religion.   If we want to work with the utilities, we need to address their real concerns about intermittent renewable resources such as wind and solar.  And we have to work with utilities if we are going to modernize the way we get and use electricity. 

How do we deal with people committed to this religion?  By taking their concerns seriously, and helping them find solutions.   In short, when we hear “Wind is so unreliable,” we should say “That’s true.   Here are some ways we can take advantage of the benefits of wind without compromising the integrity of the grid.  We can be allies in getting regulators to approve rates that allow utilities to get a fair rate of return on these measures that improve reliability, while also allowing more wind onto the grid without impacting reliability.”

Why do we expect them to listen?  Because they already have and have to work to deal with a problem that is very similar to unpredictable generation from wind: unpredictable loads.  People and companies turn appliances and whole factories on and off unpredictably, and never once do they think about calling up the utility first to let them know that they should have the necessary capacity ready at the appropriate time.  Instead, we as consumers just flip a switch, and never expect that the lights won’t come on because there is not enough capacity.  If they don’t we get angry.

How do utilities accomplish this seemingly impossible feat of matching supply to capricious demand?  They do it with extensive load modelling, so that they can predict approximately how much  load will be on the system at any given time with a fair degree of accuracy, and by maintaining “Spinning reserves,” which are basically generators which are already up an running under very low power (hence “spinning”) and turning in synchronization with the current of the grid, like a non-hybrid car sitting at idle.

When there is a sudden increase in the necessary load, they can then increase the power produced from the spinning reserves almost instantaneously, like the motorist of our metaphor starting up when a light turns green.

There are many types of generation that can be used as spinning reserves, not only gas turbines.  Hydroelectric dams can work well this way, and can agreements with neighboring utilities to supply power when it is needed, on the theory that two different utilities will not have the same load patterns, and so both utilities can gain by trading power back and forth as needed.

There are many proposals circulating to increase grid reliability and ability to accept more intermittent resources.   As is usual in complex problems, there is no one solution, and in this case it will always be a combination of many of these (and some I don’t know about… please leave comments if you have ideas I’ve left out), and the mix will vary widely depending on the unique situation of any particular utility.

  1. More transmission.  Wind not only needs massive new transmission capacity to get the electricity from windy rural areas to the places that need power, but a more robust grid means that widely dispersed wind farms can all provide power to a single utility.  Since the weather varies in different places, this has the benefit of making the system as a whole a lot less variable.  Denmark sells power to Germany, Norway, and Sweden when their wind farms produce more power than they can use. 
  2. Moving to a national electricity system from the current system of regional grids would also ease the flow of wind power from one region to another.
  3. Time of Use/ time-based pricing.  Time of use pricing allows a utility to charge less or more for power depending on how much power is available at any given time.  Time of use pricing is currently a hodge-podge consisting of none at all for some utilities, and others that offer it (or even mandate it) for/to all customer classes.  Often time of use pricing simply consists of two prices: on- and off-peak, but the ideal goal for this is to actually have real time pricing, which will even depend on that day’s weather forecast (on windy days, electricity should be cheaper than otherwise.)  The ideal goal would be to eventually move all electricity customers to real-time or near real-time electricity pricing, so that customers who are willing to adjust their usage patterns are compensated for the service that they are providing to the system as a whole.
  4. Demand side management goes hand in hand with time of use pricing.  Demand side management involves giving customers incentives to keep their load from peaking too much at any one time.
  5. Dispatchable/Interruptible loads involve allowing the utility a certain amount of control over their customer’s energy use.  The classic example is installing a remote switch on an air conditioner, so that on a hot day, the utility can regulate it so that they don’t all come on a the same time, but rather take turns, lowering the peak demand on the grid.   Utilities typically pay their customers for this right for remote control.
  6. Large scale electricity storage: Pumped hydroelectric, flow batteries, hydrogen and stationary fuel cells, and compressed air energy storage are all ways to store large amounts of power when it is plentiful and cheap (on windy nights, for instance) until it is scarce and expensive (late afternoon and early evening.)
  7. Distributed energy storage, such as plug in hybrid or electric vehicles with vehicle to grid.  Vehicles which charge from the grid can be beneficial even if they are not capale of sending power back to the grid, simply because their owners can charge them only at non-peak times, a practice which is easy to incentivize with time of use pricing.
  8. New forms of generation that can serve as backup power.  Concentrating Solar with thermal storage, landfill gas turbines, and biomass gasification are all possibilities.  One often overlooked advantage of IGCC(“Clean Coal”) is that electric power from IGCC is generated by a gas turbine which burns the syngas product of the gasification step.  While it is quite possible that carbon capture and sequestration may never be made to work with IGCC, this is one reason (along with lower emissions of traditional pollutants and higher efficiency, which reduces carbon emissions for MWh generated) that renewable energy activists should prefer IGCC to old style pulverized coal plants.
  9. Increase energy efficiency, especially in appliances that are often used during peak times.  In most of the United States, peak load usually occurs on hot afternoons and evenings when air conditioners are running, so replacing an air conditioner with a more efficient one not only reduces overall energy use, it also reduced peak demand.  Once again, the institution of time of use pricing would give customers the incentive to upgrade the right appliances for energy efficiency first.   Here are two advances in efficient air conditioning I’m particularly excited about the Delphi HMX (formerly known as Coolerado), and thermally driven dessicant cooling.

For another well thought out perspective on energy storage, hop on over the the Ergosphere for the Engineer-Poet’s thoughts.

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Vehicle to Grid, without the Vehicle

There’s been a lot of talk recently about how plug-in hybrids will change the economics of wind.  The idea is that they con be programmed to charge when there is surplus capacity on the electric grid (at night, and especially when the wind is blowing), and even act to do a little peak shaving by providing back up power during peak times, a technology referred to as Vehicle-to-Grid or V2G.   Hybrids-Plus of Boulder has even teamed up  with Colorado’s Office of Energy Management and Conservationand others to build a demonstration Prius+ with V2G capability.

 This is a great idea, and it is likely to both speed the adoption of plug-in hybrids (because the energy management services a car with V2G capability can offer are valuable to a utility, and so some utilities will probably be persuaded to provide a rebate to buyers in their service area) and the adoption of wind power (because the intermittent power from can be used more effectively by plug-in-hybrids than it can by the current gird.

Unfortunately, it will be at least 5 years and probably a lot more before we see mass production plug-in-hybrid or electric vehicles with V2G, given the long lead times needed to introduce new models and technology in the automotive industry.  This got me thinking: why does the V2G concept have to be limited to cars?  Don’t we have lots of electronic equipment that has internal batteries for portable use, but which we often leave plugged in to the grid? 

The answer, of course, is right in front of me: my laptop.  There are lots of them, they all have batteries, and they’re usually plugged in (mine is, at least.)

Uninterruptible power supplies(UPS) are less common, but perhaps even better candidates, because there is no weight constraint imposed by the fact that we often lug our laptops around with us, and are always plugged in.  If an electric utility were to offer relatively large rebates (through a Demand Side Management program) to customers who bought a special UPS that the could signal to only charge when there was surplus power was available on the grid, and to supply high-value power to the grid at peak, many businesses and individuals for whom a battery backup was only a matter of convenience rather than necessity might buy them.  Such an upgraded UPS would likely extensive additions to the electronics, because they already have electronics to regulate voltage drops and spikes for the devices plugged into them.  I’m no electrical engineer, but it seems to be that it would not be too difficult to reconfigure a UPS to provide regulation and virtual spinning reserves for the grid as a whole.

The great advantage of this approach is that a V2G UPS could be available to the public much sooner than a V2G plug-in hybrid.  This would allow utilities the opportunity to evaluate the effects of fairly large scale deployment of V2G plug-in hybrids, without nearly as much expense, and years sooner than could happen with cars.

Is there an investment opportunity which would benefit from this idea?  A lot of the same companies that are likely to benefit from the grid upgrades we need anyway.  The extra demand for batteries will help battery makers, as well as makers of other electricity storage devices such as ultracapacitors and flywheels.  Other industries that might benefit are makers of UPS systems and laptop power supplies; power electronics in general, but especially companies that build small scale and consumer power supplies and regulation devices.  The whole point of the idea is that the cost is spread out to lots of consumers who are buying these devices for reasons unrelated to making the grid function better, but that they are much cheaper because of this added benefit to the utility.

Alone, this is not a good reason to buy power electronics companies, so the thing to do is to research the industry, and find companies you think are worth buying anyway.  The possibility of widespread Laptop-2-Grid, UPS-2-Grid, rechargeable flashlight-2-Grid, and so on are just an added possible benefit on the upside, and perhaps some incentive to look at the industry in the first place.

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Conversation with a wind skeptic

I’ve been having a long conversation with a wind skeptic who responded to my Gust Ceiling entry.    While the rest of us are thinking about ways to overcome the intermittentcy problem with wind, this Rucio is dismissing it out of hand because of that problem. 

 See the comments for our conversation.  We RE enthusiasts need people like this Rucio/Eric Rosenbloom to make sure that we’re not the ones in la-la land.  To paraphrase Paul Newman, if you look around and can’t tell who the lunatic fringe is, you’re it.

I’d like to point out that I jumped to a couple of conclusions myself, which he points out… I left these comments in, even though they do not make me look great.  They are there because I want people who are trying to make up their mind to know that I have not just invented myself a straw man in order to look good.

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The Gust Ceiling: How much wind is too much?

On Dec 13, the Midwest Wind Integration Study, (see article) which was required by the Minnesota legislature in 2005 to evaluate reliability and other impacts of higher levels of wind generation and carried out independently by EnerNex Corporation and WindLogics, found that the total integration cost for up to 25% wind energy delivered to all Minnesota customers is less than one-half cent ($0.0045 cents) per kWh of wind generation.  Great news, but it’s a little bit anticlimactic (as well as “anti-climatic change”) compared to the announcement on Dec 5 that Denmark plans to increase wind powerfrom 20% today to over 50% by 2025.  (All penetration rates are given as percentage of power supplied, as opposed to nameplate capacity, a measure which would make wind penetration rates seem even higher.)

That’s not to say this report is a total yawn.  First, Europe has a much more robust electric grid than the US (as the Northeast found out in 2003), and the fact that the study was sanctioned by a government body, rather than a renewable energy or environmental group gives it added weight.  Finally, by using extensive simulation, they came up with some relatively hard numbers on what it would cost to reach various levels of penetration.

 The study concludes that the total integration operating cost for up to 25%wind energy delivered to Minnesota customers is less than $4.50 per MWh of wind generation, or less than 1/2 of 1 cent per kWh.  Put another way, this is less than 10% of the average cost per kWh of wind energy.

As I alluded to before, when talking about Europe, we need to be careful when we generalize from one utility grid to another as to the costs of integration: Europe’s grid is not the same as America’s, and Colorado’s grid is not the same as Minnesota’s.  Costs for integrating wind into Colorado’s grid are likely to be higher than in Minnesota, because we are behind the rest of the country in terms of how robust and well integrated our grid is to the rest of the country.  Because of the limitations of out grid, all of the major wind farms now in Colorado or under construction have had to be scaled back.

 Nevertheless, the study is great ground for hope.  Colorado desperately needs to upgrade our transmission anyway, and the Minnesota study only takes advantage of one of the many possibile strategies that helps firm up the capacity factor of wind: geographical diversification: “the wind is always blowing somewhere.”

Other strategies not considered:

  • Time of use pricing, which can be used to shift demand to times when the wind is blowing.
  • Plug in Hybrids, which can be programmed to be charged when power is cheap, or even supply peaking capacity to the grid.
  • Energy storage, such as the Wind-to-Hydrogen project recently unveiled at NREL’s Wind Technology Center (in partnership with Xcel Energy.)  One interesting aspect of this project that did not make most of the articles on the center is that they are experimenting with directly connecting the wind turbine to the electrolyzer, without the intermediate step of a transformer which has to be used to convert the wild AC power from a wind turbine the regulated AC power used by the grid. 

In short, I see 25% as a good start, but given that wind power has already shown itself to be cheap, safe for the environment (despite claims to the contrary, wind kills far fewer birds than coal; just ask the Audobon society), and is proving much easier to integrate into the grid than skeptics imagine, we need to start thinking like Denmark, and aim for numbers much higher than 25%.  It will take creative thinking, and serious investment not only in wind farms, but also in our grid, and even behavioral changes on the part of consumers. 

The small sacrifices we will need to make in terms of our behavior to get large penetrations of wind onto the grid, such as checking our time of use meter before we start the dishwasher or dryer, are much smaller, in my mind, than the giant sacrifices we are currently making to coal fired generation in terms of the effects of pollution and global warming on ourselves and our children.  We just don’t see the current sacrifices, because we have become used to the death from a thousand cuts in the form of mercury and other pollutants, and the incremental year on year warming of our planet, lost in the noise of large local and seasonal variations.

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Large Scale Electricity Storage.

One of the biggest barriers to the adoption of wind and solar electricity generation is the lack of storage technology with the capacity to handle the hundreds or megawatt hours necessary.    

Large scale electricity storage technology also allows utilities to flatten their demand, and defer construction of expensive new generation. 

Here’s a quick rundown of some of the technologies vying to meet this need.  Most of this is information is drawn from the Electricity Storage Association website.

Technology

Description

Comments

$/kWh; efficiency

Investment opportunities?

Pumped Hydro: Reservoir to Reservoir

Energy is stored by pumping water from a low reservoir to a higher one, and recovered by running the water back out through a turbine.  This system can be easily retrofitted into existing reservoirs, but has limitations due to water regulations.  First used in 1890.

The cheapest and most developed technology, pumped hydro is nevertheless limited by the availability of suitable sites.

$3-$50 per kWh;

70% to 85%

The major supplier in the business is private.  Could look for opportunities in utilities that have good potential projects.

Compressed Air Storage (CAES)

Energy stored by compressing air into large underground caverns.  Air combined with natural gas on exit and burned in turbine.  The gas compensates for the cooling as air decompresses. 

Gas used is about 40% of the amount used in comparable peaking turbine.  First built in 1978.

70% to 80% efficient; $30-$100 per kWh

 

Underground Pumped Hydro

As above, but water is pumped between an aquifer and an above ground reservoir.

More sites available, developing application.  Might have some water quality issues.

Costs Low

75% to 85% expected efficiency.

Small turbine/pump makers.

Polysulfide Bromide battery

A regenerative fuel cell based battery technology (aka “Flow Battery.)  Seems have run into difficulties due to the toxicity of the chemicals involved.  

15 MW demonstration project in 2003; more recent projects canceled.

75%, unknown cost;

Regenysis, the owner of this technology, was a subsidiary of
Germany’s RWE.  No recent activity; the program may have been wound down.

Molten Sodium-Sulfur (NaS) Battery

Molten battery technology.  “Safety concerns addressed in

30 sites in
Japan, mostly for peak shaving.  Largest is 6 MW for
Tokyo electric

Cost “High” compares to BrS and hydro/ CAES.

NGK, Japanese power equipment supplier focused.  Can be bought by US investors on the Pink Sheets NGKIF.PK

Regenerative Fuel Cell (Hydrogen)

Fuel cells can be run in reverse for electrolysis, with the hydrogen stored in large tanks.

First pilot project 2004

“much less” than 80%

Fuel cell manufactures: Ballard, FCEL, and others.

All these technologies except hydrogen are dealt with very well on the Electricity Storage Association site.  They have some great technology comparison graphs which deal with a lot more variables than I have here in their technology comparison section.

Cost Comparisions

Click to enlargeClick to enlarge

Efficiency/Quality Comparisons:

Click to enlargeClick to enlarge

Of these technologies, Pumped Hydro and CAES are the only ones ready for near term, large scale deployment (with NaS and Flow Batteries applicable in some markets highly constrained markets.)

The major downside for pumped hydro is siting, part of which problem can be solved with the smaller scale reservoir to aquifer option.   For CAES, the downside is the need to use gas to run the turbine, albeit a very efficient one.  One option might be to substitute for the natural gas used in CAES with hydrogen from electrolysis, allowing the system to work at locations remote from natural gas supply, and, for wind energy storage systems, be 100% renewable.

 10/20/06- Article about a flow battery from VRB power systems for an Irish wind farm.

8/5/07: Here’s an article I just wrote about two potential investments in utility scale electricity storage.

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