David's recent post on pumped storage attracted enough angry responses that I guess it is time for a more detailed post on energy storage and renewable sources.
Solar and wind energy are variable sources. If we want them to provide more than 20%-40% of our power, we will need some storage method.
Fortunately, long-distance transmission lines can reduce this need. While the sun and wind have gaps at any one spot, if we use long distance HVDC transmission lines to connect sites thousand of kilometers apart, the sun will be shining or wind blowing somewhere almost all the time. As I pointed out in previous posts, connecting wind farms with such lines could provide a 96% reliable firm commitment with only 12 hours of storage, or a 99%+ reliable firm commitment with 22 hours of storage. With an extensive long-distance grid, most supply gaps shrink to a few hours.
Modular pumped storage (MPS) is not only the lowest cost, but lowest ecological impact electricity storage means available to fill this gap. Separate two artificial reservoirs by a difference in elevation. Pump water uphill when you have extra electricity. Run the water downhill through turbines when you need the power back, recovering from 70-85% of what you put into storage.
Note the word "artificial." Don't convert existing rivers, lakes, wetlands, or other water courses for such purposes. Instead, build a closed cycle system with a lined bottom to prevent leakage. Water for this system will essentially be supplied one time, with minor continuing use to replace evaporation and leakage. (If that is still too water intensive, add a cover to minimize evaporation losses.) That way, you don't end up draining and refilling whole rivers or lakes. You are not trapping organic matter to create methane, or endangering fish and wildlife.
No, not every place in the U.S. has suitable differences in elevation. But somewhere along the greatly extended grid we will need to smooth supply variations from these sources, we can also find elevation differences suitable for modular pumped storage systems.
Nor is the land area particularly extensive. If you look in the second tab of the online spreadsheet I created on this subject you will see that such storage will require less than 2000 (revision) square miles to provide about 12 hours of use, less than 4000 square miles to supply 22 hours worth -- assuming at least an average 875 foot elevation. This compares to about 42,000 square miles (compressed DBF database) current hydroelectric dams require. (Note: this download contains no summary information. You have to add up the numbers yourself.) You can also look on it as 56-102 square feet(revised) of pumped storage per U.S. household.
I think you will find similar numbers apply for other nations and other continents. Modular pumped storage could supply the storage for every continent in the world, with around one fiftieth the ecological impact of the dams or coal mines or other dispatchable sources it helped displace.
My next post will go beyond long-distance lines and pumped storage to demand management and thermal storage. But while these can reduce the need for electrical storage, they will not eliminate it. We will have to store some electricity as electricity. Pumped storage is the best way we know how to do this today.
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Comments
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Whiskerfish Posted 7:12 pm
10 Jun 2007
My understanding is that good sites for pumped storage schemes are actually few and far between.
Here in South Africa we have one operational scheme (the Palmiet pumped-storage scheme) that destroyed quite a lot of hugely species-diverse fynbos habitat.
There is a second scheme, currently under construction, that'll damage a unique percolation wetland that happens to be one of only 4 known places on the planet that the endangered White-winged Flufftail (a bird) spends the non-breeding season (the critter breeds in a couple of wetlands in Ethipia and is on the verge of extinction). Google 'Braamhoek Flufftail' to learn more.
Although there might be lots of good things about pumped-storage there's no need to oversell it as a zero-impact option. In South Africa's case, it's coal electricity sent by AC lines that send the water uphill...
Whiskerfish
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planetthoughts Posted 9:06 pm
10 Jun 2007
Other ideas that should require less physical space while not depending on toxic chemicals: what about compressing air? what about spinning flywheels to high speeds to store energy. These must be much more compact. Flywheels, by the way, can be made very efficient and durable.
I believe there have also been some low-toxicity rechargeble battery chemistries that have been developed, as mention in the documentary "Who Killed the Electric Car" - I would like to look closer at those.
David Alexander
PlanetThoughts.org
Love your Planet.
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Charles Barton Posted 10:13 pm
10 Jun 2007
The problem with combining wind and solar power with pump storage is the cost of building, operating and maintaining duplicate (triplicate? quadruplicate?) generating capacity. Your actual costs for a wind + pump storage system would be the costs of the wind system that meets immediate consumer demand + the cost of the wind system that powers the pumps in the pump storage system + the costs of the pump storage system. The same cost situation would be involved with flywheels or any other storage scheme.
A solar electric scheme that used heat storage conceptually would have fewer generators, but it would still require duplicate energy capturing systems. It strikes me that such a system might hold some long term promise, and should be explored. But promising is not the same as deliverable. We need to rely on proven technologies, rather than hoping that an untested scheme will save us. We should also maintain flexibility, so if we start down one road, and find that another is going to be better, that we posses the ability to switch.
It is by no means clear at present that any alternative energy scheme using existing technology is competitive with nuclear power generation when the costs of reliability is thrown into the cost calculation.
Charles Barton
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Billhook Posted 10:49 pm
10 Jun 2007
Quoting me, you wrote :
>Energy storage may, perhaps, assist the commercial viability of intermittent options such as wind and solar, but it is wholly irrelevant to geo-thermal, forest biomass, current turbines, hydro great & small, etc.>
And commented :
>Currently we know how to do sun and wind on a large scale, though one can argue about the economics. No one has demonstrated a commercial current turbine. Undeveloped hydro great and small represents a very tiny potential. There are strong limits on what we can get from sustainable biomass. Geothermal electricity we can currently tap again represents a very small number, though potential breakthroughs may change this.
As to renewable energy saving a barrel of oil. While the Alaska wind example I posted about recently, wind electricity is directly placing diesel fuel consumption.<
These comments seem to me a bit hasty and decidedly Yank-o-centric.
In theory we know how to do various energy techs "on a large scale"
but in practice only biomass, followed by mega hydro,
has any significant scale globally.
You seem to be getting different info in the US to what we learn here in UK -
for instance the first commercial Current Turbines are being installed right now in the Bristol Channel.
Sustainable Biomass, like any tech on a finite planet, has limits to it, while it also offers unparralelled ecological, economic and social benefits if well designed.
Geo-thermal has very great potential indeed, given the investment,
while your suggestion that Hydro large & small offer only a tiny potential
utterly wrecks your claims of the easy viability of pumped storage for electricity.
Given that you lack suitable hills, let alone suitable reservoir sites,
across much of the US, just as we do in the rest of the world.
a global reliance on intermittent Wind & Solar backed by pumped storage
would not only require the massive new HVDC grid and steel pylons across the landscapes,
it would also entail vast earthworks to provide the elevated reservoir sites.
All of which seems to me a non starter on any serious scale.
Maybe you could do a couple of trial projects on ideal sites in the Rockies ?
Beside acknowledging that we require energy supplies that offer Power-on-demand,
we also need to recognize that the most intermittent options, being Solar & Wind,
are not only those most easily dominated by the corporations,
they are also the most potent in terms of demanding full-scale conventional back-up supply which, under GW's threat,
is a potent argument for additional nuclear capacity.
It is to be hoped that US activists will be alert to this tactic of the status quo,
and will support the development of those sustainable energies that can offer both local legitimacy and global replicability,
rather than primarily those which the corporations see as profitable.
Regards,
Bill
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GreyFlcn Posted 10:58 pm
10 Jun 2007
Concrete puts up a considerable ammount of CO2.
Luckily they are figuring out ways to reduce this.
http://web.mit.edu/newsoffice/2007/concrete.html
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GreyFlcn Posted 11:05 pm
10 Jun 2007
One reliable resource to take advantage of is "Ocean Current Energy"
Runs 24/7
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GRLCowan Posted 11:58 pm
10 Jun 2007
Here's what I said on EnergyPulse 13 months ago:
Is a megawatt-hour a lot of energy to store?
It's less than some American cars have in their tanks. A megawatt-hour's worth of boron, in two equal lumps with good handles, you could probably lift. But to store the megawatt-hour in high-up water takes huge masses, far up: 370 kilotonne-metres. That could be 370,000 tonnes elevated one metre, or 3700 tonnes, which would fill a 20-m spherical tank, elevated 100 metres.
That's a lot of stuff that doesn't care about you.
It should not be surprising that our Canadian hydropower experience includes some minor fatalities. I think here in Ontario we tend intuitively to think of nuclear power stations as the same sort of thing as dams -- massive concrete dreaming in the sun -- but nuclear reactions cannot shrug aside or bypass the concrete the way water can. Thus, that one slipup in one province killed more neighbours than all the uranium mines, uranium enrichment plants, nuclear fuel fabrication plants, nuclear power plants, and spent fuel storage sites in the whole world in the past 20 years. I don't know if Banks is looking for some more statistical kind of evidence, but in this case, a single incident captures the truth.
--- G. R. L. Cowan, former hydrogen-energy fan
Oxygen expands around boron fire, car goes
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Carptracker Posted 12:12 am
11 Jun 2007
The links take you to pictures of the pump storage reservoir that failed, doing tremendous damage to a well-loved State Park below. There were no fatalities, due largely to failure during the winter when the park is little-used. They did pull the park ranger and his family out of trees afterward, and some were in intensive care for a while.
http://mcmcweb.er.usgs.gov/mcgsc/Taum_Sauk_reservoir/aeri ...
http://www.showmenews.com/2005/Dec/1218SunEdit.gif
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GreyFlcn Posted 12:35 am
11 Jun 2007
Either way, one could ask if we have all those aquifers that we were thinking of plugging up with CO2, couldn't we just plug them up with compressed air instead?
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Erik Hoffner Posted 2:06 am
11 Jun 2007
Wikipedia has a map here:
http://en.wikipedia.org/wiki/Northfield_Mountain
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GRLCowan Posted 2:08 am
11 Jun 2007
The spreadsheet says 8,590,000,000 kWh of storage is enough. Supposing that to be true, how high is that high-up water stacked, supposing its average head is 100 metres?
8.59 million MWh times 3700 tonnes per MWh makes ... but I see he says 800 feet average head. OK, that reduces the water requirement per MWh to 1,520 tonnes, so 13 billion tonnes must be elevated, and on 50 mi^2 that works out to a vertical extent of 101 metres.
Is this correct, then: the 50 square miles, 130 square kilometres, of high-up reservoir would have average depth 101 m, i.e. 330 feet, if their sides were vertical? Somewhat more for more typically round-bottomed dips in high terrain?
--- G. R. L. Cowan, former hydrogen-energy fan
Oxygen expands around boron fire, car goes
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Gar Lipow Posted 2:47 am
11 Jun 2007
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Gar Lipow Posted 3:11 am
11 Jun 2007
Will answer some later. Worldwide hydro potential is low, but that is because hydro needs not only a difference in elevation but a continuous water source -- a river. Modular pumped storage needs only a difference in elevation. So hydro potential is not the same as pumped storage potential. So I repeat undeveloped hydro potential is nowhere near current demand. Undeveloped pumped storage could easily meet current demand. As to current turbines: the Bristol example is tidal current, not deep ocean current. Tidal potential is both lower than deep ocean and also less suitable for base load. Similarly, worldwide geothermal potential with today's technology is pretty widely agreed to to be tiny compared to todays consumption, while under half a percent. The UK is no better off than the U.S. in this respect. There are maybe two nations in the world where this does not apply. There is some new tech that might change this, but it is not yet mature let alone commerical.
Whiskerfish. I'm pretty sure I did not say "zero" impact. The two examples you mentioned are using natural water courses. I agree we have to be careful where we locate them, but both of these examples sound like conventional pumped storage.
But even done right I'm not claiming it is zero impact. I'm only claiming it is something we can live with, and better than the alternatives. Part of this is the lower impact per reservoir. The other part is the small square footage required. Less than 14-28 square feet per household (not person).
Greyfcln: ocean current turbines have not yet been demonstrated. Tidal turbines have been demonstrated, by nature they are not constant, and anyway there is very limited worldwide potential. In terms of concrete -- Geopolymeric concrete reduces CO2 emissions now, at about double the cost of normal concrete. But the again we are talking about 14-28 square feet for every household in the U.S. (to continue with yank centricism). Even given that dams take a lot concrete per square foot, this is an embedded co2 cost you could get back quickly if it let you (say) replace all existing coal plants with wind plants.
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Gar Lipow Posted 3:37 am
11 Jun 2007
Compressed air. Currently all systems that recover compressed air for electricity storage do so by using the compressed air to boost the efficiency of a natural gas turbine. So you continue burning natural gas for power, the efficiency with which you recover power ranges from 50%-65%, and you around half the power produced by the turbines still comes from natural gas. About three to five times as expensive as pumped storage
fly wheels - high efficiency, more expensive than compressed air. Problem, if the power is not tapped quickly it vanishes. Generally you lose all the power in a flywheel in three to six days.
supercapacitors, batteries, flow batteries and such- very expensive. Also the toxic materials use to create them have their own enviromental costs. Yes some existing batteries are suitable for electric cars and PHEV. But that is because the economics of electric vehicles support higher costs than utilities. For example $350 per kWh of capacity for an auto battery that will last 2000 cycles is a good price for an electric car. For utility power it would multiply your power costs many times. Also a lot of articles about advanced car batteries are based on press releases for batteries not on sale today.
We may expect breakthroughs in such things. Battery prices will come down, maybe very soon. There a great deal of work being done on storing the heat of compression when you compress air, eliminating the need for natural gas as part of the system. But right now modular pumped storage is the most economical and most ecologically sound means to store electricity.
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GRLCowan Posted 3:38 am
11 Jun 2007
420 watt-hours per cubic foot of water would imply an elevation change of 5,445 metres.
--- G. R. L. Cowan, former hydrogen-energy fan
Oxygen expands around boron fire, car goes
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caniscandida Posted 3:42 am
11 Jun 2007
The park ranger and family pulled out of trees sounds like a scene from a "Fitzcarraldo"-ish vision, if only everyone were unharmed.
Chickens are our cousins!
So are other sensitive animals!
Enough is enough!
No more factory farms!
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Gar Lipow Posted 3:49 am
11 Jun 2007
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Nucbuddy Posted 3:56 am
11 Jun 2007
The remains of the Taum Sauk pumped storage plant are located in the St. François mountain region of the Missouri Ozarks approximately 90 miles (145 km) south of St. Louis near Lesterville, Missouri.
[...]
That the Taum Sauk reservoir remains (37d32m10s N, 90d49m05s W) are atop Proffit Mountain and not Taum Sauk Mountain (37d34m13s N, 90d43m40s W) is often a source of confusion to tourists seeking to visit the site. Taum Sauk Mountain, the highest point in Missouri, is about five miles (8 km) east of Proffit Mountain and hosts a state park, not a reservoir. The reservoir is plainly visible from the lookout tower on Taum Sauk Mountain adjacent to the state park. Before the failure of the upper Reservoir visitors could usually drive to the top of Proffit Mountain and walk a ramp to an observation deck at the top of the reservoir.
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Gar Lipow Posted 4:15 am
11 Jun 2007
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Kelpie Posted 4:16 am
11 Jun 2007
Apparently India is rolling out a compressed air car next year.
Here's a couple of links to check out:
http://www.popularmechanics.com/automotive/new_cars/42170 ...
http://www.inhabitat.com/2007/06/01/tata-motors-air-car/
Check out my ecothriller novel Primal Tears at amazon.com and other booksellers.
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Nucbuddy Posted 4:49 am
11 Jun 2007
Based solely on what you and Graham (GRL Cowan) have been writing to each other, it seems to me that your numbers are simply off by a factor of exactly 100. (I have not yet checked the details, though.) Playing with some of the figures in the comments, I came up with a density of 6,333.33 pounds per cubic foot of water -- off exactly by a factor of 100, since the real figure is ~63 pounds.
google.com/search?q=water+density+cubic+foot+pounds
Gar Lipow wrote: It looks like it would take more like a thousand square miles than 50.
My guess is: exactly 5,000 square miles. (If round-bottomness of the reservoirs has not yet been taken into account, then factoring that in would raise the number further.)
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Rune Posted 4:56 am
11 Jun 2007
Meanwhile, Tata, the Indian company is getting bogged down in a nasty turn of human right abuses and even murder as the government with which it is collaborating uses thuggish tactics to clear the way for their new auto factory. I can just imagine how peaceful and reliable that plant is going to be, even if they ever get an MDI engine that can power an overblown go-cart with a body made out of surfboard materials more than 20 miles. But that doesn't stop lots of people from reading the failure of journalism published in a recent issue of Popular Science and dreaming of the remarkable air car (even though the article did note that it is unlikely that the car will ever make it to the U.S. for safety reasons alone). Everyone likes a good story, especially when reality is so much more challenging.
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Sean Casten Posted 6:35 am
14 Jun 2007
The pumped storage facilities in operation - and indeed, all storage facilities - exist to take advantage of differential pricing between on-peak and off-peak electricity. From batteries to reversible fuel cells to pumped hydro, the relevant number for all of them is the "round trip efficiency", which simply measures the total kWh out as compared to the total kWh in. Apropos of this discussion the relevant point is that the round trip efficiency is always <100% (70 - 80% is fairly typical).
Thus, the economic play is straightforward. If I have an 80% round trip efficiency, and I can buy off-peak power at <80% of what I can get selling it on-peak, then I can make money arbitraging the differential. Economically, this can be a good thing, since it lowers the daytime electric rate, putting supply on the grid that is cheaper than that which we otherwise would have had to produce.
As a practical matter, the single biggest beneficiary of pumped storage from a generation perspective though is coal. Nuclear power is now very close to baseloaded, with most nuke facilities producing full load 24/7. Hydro also runs as close as it can get to baseloaded (e.g., as long as there's upstream water, it will run), since nothing else is cheaper. Coal is the next cheapest power source on the dispatch curve, but it curtails production at night for the simple reason that sometimes the total system demand exceeds the total production capacity of the nuclear+hydro+coal resource base. As the most expensive source on that list (albeit cheaper than the gas-fired generation at the margin), coal is the first to curtail production in the evenings.
So - watch what happens if you start deploying lots of pumped storage on the grid. More nighttime load = less need to curtail coal = more coal combustion. As I said, this may well lead to lower power costs in some areas, but it is the exact opposite of a renewable play.
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