Why Wind Farms Can Be Relied On For Almost Zero Power

Yes. Wind farms are “fuel savers” and hence, they are “co2 emission reducers”.

Humanity doesn’t need either of these.

We need to eliminate – not merely reduce – co2 emissions, and wind farms can’t do that.

We need nuclear power, the fuel for which does not need to be saved because it is inexhaustible, so we don’t need wind farms to save nuclear fuel.

Who just quoted Feynman to the effect that nature bats last?

Replacing coal with wind and gas backup seems like a big win, carbon-wise. 

Also, a lot of gas is burned for heating when Arctic cold fronts come through, and that is just when wind energy could exceed electricity demand, in which case we might switch from gas to electric heat.

If I had a smart meter telling me electric rates were dirt cheap, I’d switch on the electric space heaters, which are inexpensive devices I have around anyway.

Robert, I’ll dutifully avoid the “N-word” to agree that the environmental contribution of both solar and wind is limited to offsetting fossil generation, and point out that it may well be offset by their environmental impact.

Wait, were you deliberately trolling the nuclear advocates?  Clever.

Of course, with the recent research results showing that methane leaks make natural gas roughly as bad for the climate as coal, and certain admissions that “renewable” energy is mostly gas-powered, it’s pretty much inevitable that nuclear is going to get positive attention.

Robert, environmental impact isn’t limited to atmospheric carbon. This is not research per se, and I can’t vouch for the reputation of the source, so it may be baseless. I’ll let you decide.

Here though is onshore wind’s real problem. Wind farms take up a hell of a lot of space.  Delivering a Hinkley C level of energy from wind farms will require an area of at least 1000 square kilometres to be covered in wind farms.

http://theenergycollective.com/robertwilson190/2140086/hinkley-point-nuc...

Is an evidence-based comparison a “pissing match” just because it amounts to a rout?  We do have the evidence.  The problem is that “Green” isn’t about evidence, it’s a quasi-religious romantic movement.  Part of the evidence for that is that the Green parties in Europe have been far more concerned about eliminating nuclear power than reducing GHG emissions.  You’d think that the utter lack of on-going damage from Chernobyl and the trivial injuries and absence of fatalities from Fukushima would have been a much broader wake-up call than just a few people like George Monbiot.  Instead, the movement is doubling down on failure.

Are “renewables” a means to an end, or an end in themselves?  If they’re a means to an end, then better means are preferable to worse ones.

It wouldn’t work if you had to pay an “environmental fee” on every kWh, regardless of source.

Robert, when you find a way to quantify the value of land lost to windfarms and solar arrays, both aesthetic and purely utilitarian, chime in. Otherwise this train of thought is a hopeless waste of time.

Is that just a consequence of the laws of thermodynamics?

1. You can’t win

2. You can’t break even

3. You can’t quit the game

Its a bit different in the US.  In Texas for example, the wind resource is quite good but does not match load.  Wind is night peaking.  However as EVs proliferate, the load will match quite well, particularly as TOU metering provides a substantial incentive to charge at night.  Tesla already has a built in timer so that it is easy to set it to charge after midnight.   

There are many who oppose renewables and echo the FF talking points that wind has no net benefit because there has to be fossil fuel capacity.  This is the strangest argument I have every heard.  Great Plains wind averages 37% CF with some site reaching 50% and many of the best sites, as yet, untapped.  If there is no curtailment then that would imply a 37% reduction in emissions of the offset FF capacity.  But as is illustrated in the link above, PV is a great match to wind.  That is, it peaks when the wind is least available.  So the primary need for FF backup is during the transition periods when the overlap is insufficient.  At these points peaking plants are already available.  The cost of power during these breif periods is very high, roughly an order of magnitude higher than baseload, but due to their low duty cycle it averages out to a pretty low number.  So the budget for storage should be compared to the cost of peaking plants not baseload.

Another favorite comment by FF advocates is that storage is very expensive.  First of all, if the wind power utilized the peaking plants and increased their duty cycle, the cost of peaking power would drop since the capital cost could be amorized over a larger number of kwhrs. 

Second of all, the silly math that the anti-wind crowd uses to depricate wind power, suggests that the cost for storage should be compared to base load power.  In fact, it should be compared to the peaking power that would be needed.  If that is done there is ample money available that could be used for storage rather than peaking plants.

Robert,

you pretty much missed the point.  First, I think that the information is documented pretty well.  No I do not have time to fish out the daily numbers.  But at 50% CF and not much of that happening in the daytime I think it is safe to say that there is a pretty reliable supply at night.  You are making up the 1 week lul, but for the sake of discussion lets say that it occurs.  With great plains high CF wind power it will be a rarity and the peaking power plants can run then.  That does not negate the emissions reduction value of the wind power and the peaking plants are already there so we don’t need to build out massive amounts.

I have read enough of your stuff to know that you know the difference between load shifting and V2G.  I am talking about load shifting.  You can have the other argument with someone else.

Good article leading to an easy-to-understand conclusion that wind farms are fuel savers. The attractiveness of wind farms is therefore directly linked to the type of fuel they displace. If they displace uranium, it is pretty much a useless exercise, but if they displace natural gas, things become more interesting. 

System level analyses like Lion Hirth’s work or the IEA’s recent “power of transformation” often talk about the scenarios of legacy (current capital stock) and transformed (capital stock tailored especially towards integration of variable renewables). The attractiveness of the transformed scenario is always much greater as it contains much more gas (high fuel and low capital costs) as opposed to coal and nuclear (low fuel and high capital costs).

Going from the legacy to the transformed scenario will take decades and will be a big commitment to intermittent “fuel saver” renewables. We should be quite sure about this commitment as the costs of changing our minds half way would be high in terms of time, money and CO2. 

Robert, your points on the impacts of variable, non-dispatchable wind power covers some of the obvious performance factors including the need for backup, fully dispatchable power (primarily natural gas and hydropower pumped storage under ideal conditions) and the primary benefit of reducing the fossil fuels consumption and associated carbon emissions from displaced baseload and intermediate coal/oil/natural gas capacity.  Another factor rarely highlighted is the fact that wind power capacity factors are most often ‘maximized’ by being given operating capacity priority over all other power generation sources (including hydro & nuclear in some cases).  The benefit of this operating practice is good for renewable power operators, but comes at a cost for consumers.  Besides the need for backup intermediate/peaking power capacity (often from fossil fuels), another less beneficial factor is the impact on fossil fuel power generation plant efficiencies; i.e. fuel consumption and carbon emissions per unit net power generation.  If wind power generation results in totally ‘shutting down’ equivalent amounts of average fossil fuels generation, the carbon emissions will be minimized and this benefit maximize.  However, all fossil fuel power plants have maximum designed efficiency levels of operation.  If the wind power merely reduces a natural gas power plant toward minimum rates (i.e. towards hot spinning reserve operation with minimal net power generation), the plant’s thermal efficiencies can drop towards half of design maximums.  Under this condition fuel consumption per KWh increases proportionally and the claimed/estimated carbon reductions by the wind power generator can be inflated considerably.

I reread your article.  My bad, overall I agree with your points.

However, I think EVs offer a great load shift opportunity that can enable higher penetration of wind particularly in night peaking areas which are common.  No smart grids required, just set the timer in the car for night time.  However, one would hope that the PUCs would require utilities to share the savings and incentivise a scenario that is lower carbon by installing TOU metering.  This is old technology, for example they have been doing it with electric hot water for decades now.

Gibson;

 A stock tank is a storage device that can store a week or two of water.

Please reference some wind farms that have buildings full of batteries that can store a week or two of average output. What do those kWhr’s cost?

Should every home have a shed with a ton of lead acid batteries, inverters and chargers? Do you have one? What would the cost and environmental impact of that be?

Let’s tell it like it is.  Global nuclear capacity has leveled off and renewables are growing at 15%+ CAGR’s.

Global nuclear electricity production reached a max of around ~2600 TWh between 2006-2010 but has declined since then.

The more fun question is : When will global wind electricity production PLUS global solar PV electricity production surpass 2600 TWh?  Can it?

I believe it can and will and sooner than most think, but then most people are blind to a paradigm shift / exponential change mechanisms.

I think EVs offer a great load shift opportunity that can enable higher penetration of wind particularly in night peaking areas which are common.

The problem with wind is that it can’t be varied to follow demand.  Peaking at night is only part of it.

No smart grids required, just set the timer in the car for night time.

What happens if the wind is down when the chargers come on, then comes up again as they’re shutting off?  You really do need that smart grid after all.  If the daily and hourly forecasts are good you could use EV chargers to follow wind production, and schedule the least amount of other generation required to get everything filled up by morning.  Again, this takes coordination, which takes smarts.

Average electric demand in the USA is almost 1500 watts per capita, 24/7/365.  A Leaf-class EV has a 24 kWh battery, only able to buffer a partial day’s worth of per-capita demand.  To make EVs a real contender in grid storage you need a nation-full of Teslas.  That will be a while coming.

Edit:  I can’t believe this appeared in minutes, but I’m still waiting for my top-level placeholder comment to be approved so I can get the HTML edit button I need to format my long comment correctly.

A disturbing implication of this article is its impact on grid construction in developing nations.  It means that energy-hungry places like China and India must fully deploy fossil fuel power plants and the supply chains to fuel them, regardless of the amount of wind power they deploy.

Wouldn’t it be preferrable for developing nations to leap-frog fossil fuel technologies and deploy sustainable energy infrastructure that does not require a fully redundant fossil fuel energy system?

—

This article also suggests that we should replace our concept of “grid parity” for variable renewables with the more appropriate objective, “fuel cost parity” (which even the much praised wind power of the US central plains can not achieve without subsidies, when transmission costs are included, whether costed against coal or frac’d gas). 

Robert,

I think the term you are looking for with this piece is “capacity value” or “capacity credit.”  Capacity value is an established protocol for determining the probability of wind power in meeting load. It has been established in many (probably all) regions, and it is always more than zero.  In MISO for example it is 14.7%, in ERCOT it is 8.7% but is likely to be revised up as more East Texas wind is developed with better coincidence with peak.

 I was surprised that neither you nor any commenter mentioned it.  There is much discussion about “capacity factors” but that is not the same thing.

There are a number of “how to” papers online for determining capacity value:

http://www.nerc.com/docs/pc/ivgtf/ieee-capacity-value-task-force-confide...(2).pdf

http://www.science.smith.edu/~jcardell/Courses/EGR325/Readings/CapValu_U...

And so on.

– Ben Paulos

Ben, what “capacity value” sounds like is an established protocol of the wind industry to dodge the nagging fact there are times, at an individual windfarm, it’s completely unavailable. Checked out, out to lunch, down for the count.

This definition from the typically self-serving NREL is an interesting one.

Capacity value refers to the contribution of a power plant to reliably meet demand.

http://www.nrel.gov/docs/fy13osti/57582.pdf

In that case it’s easy to determine the capacity value of any windfarm or solar plant: zero. None can reliably meet demand, and no amount of statistical legerdemain can change that fact.

Who are you, “Engineer-Poet”? If you are interested in a pissing match, perhaps you could supply your real name.

Why?  So you can doxx me to get me to shut up?  Shall we do the adult thing, and discuss facts instead?  I’ll try to make the rest of this comment a link-fest, so you can be totally assured that none of what I’m about to tell you is my own unsupported opinion.  What I’m writing here would be as true and valid (or not) regardless of the name attached.

“Utter lack of ongoing damage”, Fukushima “trivial”. Either you are paid to say such things or you are a truly heartless individual. Which is it?

No one pays me to say anything (though I wish someone would, I can use the money), and you might note that I provided support for my claims.  (Conca’s piece is worth reading for the playful use of language alone.)  As for “heartless”, what would you call someone who wants the public reduced to energy poverty “for their own good”, as so many Greens explicitly say they want?

Have you ever read Shaw’s play, “Pygmalion”?  I recall a scene where Eliza Doolittle, in her tiny room after receiving her windfall in Act I, splurges and puts extra money into her coin-operated gas lamp to give herself the luxury of another hour or so of artificial light (this vignette may have been an adaptation, it’s not in the script I can find on-line).  I have enough heart to want such days never to return.  I also want a world that remembers and cherishes the work of George Bernard Shaw (as well as the Mona Lisa and the Venus de Milo), which a return to agrarian living cannot do.

On Chernobyl:  The Chernobyl babushkas who returned to their homes have reportedly done better than the evacuees:

One refrain I heard often was, ‘Those who left are worse off now. They are all dying of sadness.’ What sounds like faith may actually be fact. According to reports by the United Nations Development Programme and the United Nations Children’s Fund, many of those who were relocated after the accident now suffer from anxiety, depression and disrupted social networks, the traumas of displaced people everywhere.

And these conditions seem to have health effects as real as those caused by radiation. The journalist Alexander Anisimov, who spent his career studying the self-settler community, claimed that the women who returned to their ancestral homes in the zone outlived those who left by a decade.

The Japanese seem to have an even worse problem, due to an intense national phobia of radiation (which strangely does not extend to radon-rich hot springs and the like, which are as popular as ever).  The symptoms of “radiation syndrome” described by a member of one of my circles (this is the only anecdata I’ll put here) are practically a list of problems caused by chronic stress.  These people are not being poisoned by radiation, but stress hormones from fear… fear whipped up by activists and media.

The Japanese are being directly hurt by radiation phobia.  The political inability to re-start their nuclear plants has caused a balance of payments deficit, energy poverty and a shrinking economy.  This is in addition to those who died during the hasty evacuation, and those suffering from the continued exclusion from their homes.

We have a vast amount of epidemiological evidence that low-intensity radiation is harmless up to a certain threshold, and that threshold is a large fraction of a Sievert per year.  Airline crews are exposed to much higher cosmic radiation than anyone gets on the ground, and those who overfly the North Pole get the most of all.  There’s no evidence of higher rates of leukemia or other cancers in this group save for melanoma… which is what you’d expect from using free travel to vacation on sunny beaches a lot.

There’s plenty of evidence for radiation hormesis, actual positive effects from moderate doses at low dose rates.  I suggest reading Jerry Cuttler’s paper in Dose-Response (which is itself a link-fest) to understand the biology and the politics better.  This would help explain the durability of the Chernobyl babushkas; it’s only partly that their evacuated compatriots were worse off, those in the zone may actually have been better off.

Cuttler quotes the UNSCEAR re Fukushima:  “no health effects attributable to radiation were observed”.  In other words, there is zero evidence that anyone outside the plant received the slightest bit of harm from radiation (there were 3 workers in the plant who received beta burns in the early days of the accident).  The harm from the Fukushima meltdowns, such as it is, is from policy:  the on-going and needless evacuation from the area.  There is one very small strip in which radiation levels are high enough to be of real concern.  This is the red area you see in all the maps, extending northwest of the plant.  The rest should have been declared safe years ago.

Am I “heartless” for suggesting that people shouldn’t be terrorized by propaganda, and encouraged to go back to their homes (which evidence suggests were only hazardous for weeks, or days, if at all)?  That they should rebuild their lives, rather than being well-paid refugees… and that the attention spent on them would be better applied to tsunami refugees who are still without housing?

So there you have it:  my conclusion, and a good sampling of the evidence which underlies it.  If I’m wrong, there’s some error in that stuff.  Show it to me and I’ll change my tune.  I have before.  Just don’t try to convert me to Greenism; that’s guaranteed to fail.

It is precisely this predictable “cost of changing our minds” which is what makes the concept of intermittent RE firmed-up by inefficiënt fossil fuel burning so attractive to those who stand to benefit from it.

They know this concept will not eliminate greenhouse gas emissions, and that is why they stress that this concept will “reduce” emissions (rather than eliminate them). Far from eliminating emissions, the predictable recourse to the use of simple cycle peakers to firm wind comes with double the emissions per kWh, erasing much of the emissions (and fuel) saved by the wind in the first place. All this is part of the plan.

They also know that this concept is only threatened by one alternative – nuclear power – which is why they are always spreading lies about nuclear. If the manage to keep fear alive for a decade or so more, they’ll win.

They already have the obtuse environmental groups on board. You’ll never find a Greenpeace or FoE activist protesting a natural gas plant. (They’ve hardly begun protesting coal for that matter!).

The short end of the stick is firmly in the hands of the public and future generations. But have things ever been otherwise?

The Giga factory is designed for 500,000 cars per year and 50GWhr of batteries per year.  That suggests that the typical EV as they mainstream will be coming in at about 100kWhr.  So yes, still a lot of cars but far fewer than you sugges.  Leaf is an early adoptor vehicle.  You cannot mainstream EVs with the current Leaf’s range. 

About a year ago I was considered pretty optimistic to suggest that batteries would come in under $100 by 2029.  Now Musk is suggesting $100 / kWhr in less than a decade. 

Back to the primary point.  EVs with night charging will improve the grid ecosystem for wind and allow the support of more of it.  How much more is debatable.  If time of use rates like those in Indiana were put into place load following would occur nicely.  If we get smarter controls then we can get better results.  The point is that simply charging at night with a night peaking source allows for increased use of that source.  How much more is debatable for sure. 

As the  references in Robert Wilson’s aritcle indicate, wind generation does indeed drop to near zero for hours at a time. These outages are often rejoined by RE advocates with pointers to either supposed complementary solar,  existing or theoretical pumped storage, or other short term grid scale storage, supposedly soon to be affordable.  

The problem with these responses is that wind (and solar) outages can be much longer, and over very wide areas.   For instance, over the last five days generation from the ~4.5 GW nameplate of wind capacity of the US northwest’s Bonneville Power Association has been essentially none existent:

BPA Total Wind Generation, 12 Nov to 19 Nov

http://oi62.tinypic.com/5vad7c.jpg

It’s a debate worth having, and resolving, because resolving it means that a solution to co2 emissions has been found.

No other debate (certainly not the typical RE versus FF debate, where nuclear is arbitrarily assumed to not exist) can plausibly result in such a conclusion.

The only conclusion of the decades-long RE vs FF debate is that RE can potentially reduce (but never eliminate) FF emissions, a conclusion which promises to create and increase totally unnecessary self-loathing, self-destruction, hypocricy, waste and conflict, forever.

Personally, I get physically sick when I am confronted with talented young adults in university who have put all the pieces together (except for the nuclear option) and blankly say that solving climate change is impossible and that ‘sustainability’ is a just stupid illusion. Such dispair and cynicism at such a young age breaks my heart, and drives my (unpaid) advocacy for nuclear power.

I agree with both points. The economics are important and pretending nuclear doesn’t exist is odd. One effect of wind is to reduce the capacity factor of nuclear when they exist on the same grid; at sufficiently low capacity factor, the nuclear plant will be shut down because it is not economical or it will not be built in the first place; building wind could increase carbon emissions in this situation.

One can imagine the following scenario. We spend lots of money and time building lots of windmills. As noted in the post, we then also need to build, or to retain, lots of fossil fuel back up, almost 100% of peak capacity. So we end up with two expensive sets of infrastructures sitting around – wind and fossil – one working when the other is not. Then say a few decades down the road, when the negative effects of a rapidly warming world really start to hit home, we realize that reducing our carbon emissions by 30 or 40 or 50% is not nearly good enough – we need to reduce them to zero. What do we do then? Build out nuclear, so that we now have three expensive and overlapping sets of generation? With unlimited money and time, we could take that route; in reality, we are short of both; installing large amounts of wind and gas will very likely preclude us from a carbon complete solution because we will have wasted huge amounts of money on partial solutions. This is why we as a society need to have a very clear idea of where we want to end up with regard to carbon emissions; where we can end up with different energy investment policies; and why the idea – which underlies a lot of thinking on renewables – that installing renewable capacity is an unequivocal ‘good’ because it reduces some fossil fuel consumption (or is “a step in the right direction”) needs to be thought through very, very carefully. (Hirth’s paper on the ‘Optimal Share of Variable Renewables’ is instructive in this regard.)

You could profile two American states in particular, Iowa and Minnesota. I believe Iowa will be at 40% wind by end of 2016 and Minnesota with a new commerce department study confirms that Minnesota can generate a minimum of 40% of power use from renewables with some transmission upgrades.While 100% nuclear grid is a sure way to eliminate co2 emissions, I’m not at all sure that it can deal economically  with load following or manage the political, economic and environmental issues on an equal basis as renewable with robust transmission, load control, minimal backup/storage and high levels of efficiency. 

Don’t know what the thermal load is for Europe at 6pm compared to non optional appliances such as a TV or hair drier, but some cheap thermal storage could go a long way towards spanning that wind gap.

For that to work, the “environmental fees” which make electricity so much more expensive than natural gas would have to be waived for excess RE generation, and the FITs would have to be scaled back too.

As this map shows, BPA is not where the wind is.  If we choose to make wind a major component of our grid then it needs to be in the great plains, Great lakes and offshore off of the atlantic seaboard where the capacity factors are much higher.  This post andhttp://handlemanpost.wordpress.com/2014/01/22/with-50-capacity-factors-w... offer a good deal of information on the primary areas in the US and their potential. 

*Average* wind speed is beside the point of my post (or of the orginal article), which was instead about the possibility of days or month long wind outages over large areas. Absent the development of some economic long term storage, the existing thermal power fleet must largely remain in place at the ready to cover the outages of a large wind fleet.  In which case, why wind?

Dear Hans, Boccard did research and wrote an article that was solid enough to be published in Energy Policy. In that light it seems inaccurate to claim the topic was just “a passing fanvy” for him.

Thanks for the links Ben.  I could only get the second one to work.  Could you double check the first one and repost if there is an error?

Thanks

Robert,

It’s also the case that as impressive as the Danish model might be, Denmark is a tiny country with just over 1% of the population of the EU. The Danish wind experience is only relevant when linked to much larger, more resilient grids.

I thought the key line in this post was, “they displace electricity generation from fossil fuel power plants, but not the power plants themselves.” This should be required reading for all policy makers, and it is even conveniently soundbite-sized.

While it’s possible to imagine a world powered mainly by intermittent/cyclical renewables with storage buffering their intra-day variability, it would look very different than ours, because buffering the inter-day and seasonal variations of wind and solar power would require storage on a massively greater–and massively less economical–scale, or else the kind of total system transformation to other energy carriers, as suggested in Mr. Schmidt’s comment.

I agree that corners can’t be cut in nuclear as it is designed today. The mastery of fission requires a reactor type that can be left alone and without an external source for cooling- indifinitely, such as a design based on Alvin Weinberg’s MSR, or similar. Following is an equation I came up with.

Embodied energy of total system as a percentage of output is equal to

(1/CF)+1/Esoi(1/CF-1)

__________________   (100)  = %

           Eroei

I’m not too good with math but what I’m trying to say is, for a constant power output (without fossil fueled backup) we need to build up about four times the amount of wind (assuming 25% Capacity Factor) and store three parts of that. If the wind has an Energy Returned On Energy Invested of 20 and the clean liquid fuel has an Energy Stored On Investment of just 0.3, then 70% of the energy available would have to be put back into the system in order to make itself. Clearly, this is not enough energy gain (of 1.43) to grow itself and power a growing world.

We could store it in pumped hydro (with Esoi of say, 100), then just 20.15%, or almost five times the energy is still available to replace fossil fuels with. However, massive amounts of land are required. Perhaps there is a better and cheaper mass storage with little embodied energy?

Closed cycle nuclear should have an Eroei of at least 100 (if not thousands) and a CF of say, just 80%. If the storage is in clean liquid fuels at 0.3 Esoi, still, just over 2% is required, giving a gain of 48 multiples of the energy input!

Clearly, the higher the numbers in the system, the easier for it to grow itself and power the already growing world.

Can all the states combined provide like 95% of the power – 24/7? I believe the overbuild required for multiday storage (and the storage itself) would actually consume much of the power just to grow itself (see my post above). The object is to NOT burn fossil fuels.

The only way to make wind energy reliable is to be able to exchange energy over great distances; this implies a continental scale supergrid. One needs a grid big enouh to have parts of it in at least three differerent weather systems. My own calculations show this would be cost effective once completed, but it is at present politically impossible in the US. One key problem with using a supergrid to aggregate wind is that you don’t get the full benefits until the system is nearly complete. And when it is complete, the capacity factor for transmission will be highly variable day to day, hour to hour…just like the underlying variability of wind & solar. I still think though that a continental scale supergrid is an absolute requirement to enable wind & solar to supply most of our electricity.

There are steps along the way to get us to a supergrid. Dale Osborn of Midwest ISO has been leading the effort from within the utility industry to move towars HVDC “overlays” for years. These overlays make wind power more viable over the region served, but the biggest economic benefits come from reducing required reserve margins.There are several classes of reserves, including spinning reserves, and reserves capable and ready to be started up on variou time scales (these can be grouped as “ready reserves”). The main economic benefit for wide area “HVDC transmission overlays” at present is from deferred capital for construction of new generation capacity,but a side benefit is to enable sharing wind generation capacity over a wide area. I have always felt that the wind industry needs to face up to its intermittency, and start advocating for a supergrid. Among other things, this would open up large new areas where pumped storage could be economically built.