Alternative reduced CO2 wind back up systems

The work of Warren Katzenstein and Jay Apt, Peter Lang, and Peter Hawkins all seems to demonstrate that natural gas beck up of wind generation imposes choices and inefficiencies, that almost or completely the CO2 emissions benefits of wind. It would appear from their work that stand alone natural gas systems using combined cycle gas turbines, are either nearly as efficient at lowering natural gas emissions or actually more efficient as a wind plus open cycle gas turbines. Supporters of wind generation have noted that that wind generators are well matched to hydro-electricity, and indeed that seems to be the case in a few parts of the world, for example Scandinavia where wind generators in Denmark appear to compliment hydroelectricity from Norway and Sweden. In the United States, hydro resources have been almost entirely utilized, and are currently inadequate for wind back up in most high wind areas. Pumped Storage has been suggested, the the high cost of past pumped storage facilities suggest that the cost of nuclear reactors is competitive with the cost of pumped storage facilities with similar rated capacities, while the nuclear facilities would be far more flexible, and produce as much as 2 times as much electricity on an annual basis as pumped storage would. Compressed air energy storage (CAES) is a second form of backup proposed for wind generators. My investigation, however, revealed a surprising problem from CAES, radioactive radon gas would be brought to the surface with returning compressed air. The problem appears to be far more serious than the release of radioactive gases associated with nuclear power generation. My case study of proposed CAES project presented by the Ridge Energy Storage & Grid Services company to Texas State Energy Conservation Office in 2005 showed that 40% of the energy for the project would come from the burning of natural gas. CASE systems are huge geothermal heat pumps, and they return cold air. Humidity in the air freezes, and the ice can damage generator turbines. Heat lost in the CAES process represents lost energy from electricity used to compress the air. In evaluating the cost of wind generated electricity I stipulated

a cost for new West Texas wind of $2250 per name plate KW in 2009. Since the capacity factor of West Texas runs around .40, the adverage output West Texas wind producer can expect to pay $5625 produce KWs of electricity his windmill will average producing. Since only 70% of the electricity entering the CAES facility reaches the consumer, the wind producer must add 30% more capacity to compensate for the energy loss. Thus the price of the wind generated electry entering the CAES facility must compensate the wind producer for something like a $8000 capitol investment for every average kW sold to the CAES facility.

In addition the estimated cost of the Ridge Energy CAES facility was $765 per KW of electrical output, Thus we are looking at an investment of nearly $9000 per kW of electrical capacity and this does not count the cost of new electrical transmission lines from West Texas to energy hungry Dallas. In contrast

the 2008 cost of nuclear power is somewhere between $4000 and $5000 per kW (as opposed to an estimated $8000 to 12,000 figure during the middle of the next decade).

And nuclear plants can be located close to electricity markets. In addition, the nuclear plant would be far more flexible, and would produce more electricity on an annual basis than the wind + CAES combination. In addition I noted an alternative employment of the CAES system that no one seems to have thought of, the used of CAES in in nuclear cooling, that would produce a low cost nuclear CAES combined cycle:

It seems to have escaped the notice of most CASE advocates that CAES casn be teamed with nuclear power plants in innovative ways. Since it is more economical to keep reactors running at full power all night, suplus electricity produced at night could be used to store compressed air. During the day, compressed air can be used to expand the reactors daytime power output by as much as 40%. The air does not have to be heated with natural gas. Indeed the compressed air can be heated from the reactors waste heat, killing two birds with one stone, and conserving the water used for daytime reactor cooling, and the use of compressed air in cooling the reactor, would creat significant water use savings, allowing reactors to run even during drought conditions.

Just a thought, mind you.

I also looked at battery backup for wind, that was of course, way too expensive. In fact it was so expensive that I conducted a thought experiment,

Assume that the system operators chose to back up the 1 GW wind system with nuclear power rather than a redundant wind system plus batteries. The cost of the wind system would then drop to $2.7 billion plus $5 billion for nuclear backup or $7.7 billion. Quite obviously the nuclear backup would be cheaper, but now the wind is totally redundant, because the backup system can operate full time for just the added price of fuel. Thus the purely nuclear system would simply be a lower cost than a reliable wind system. The nuclear system would be more reliable, and could be counted on with a fairly high degree of certainty to produce at 100% of its rated capacity during peak electrical demand summer months.

Thus my conclusion was that Pumped Storage, CAES, and battery backups for wind were more expensive, less flexible, and would produce less electricity over time than electricity producing nuclear reactors.

Texas Wind Still More Expensive with CAES than Nuclear

When I presented my cost study of "reliable Texas wind using batteries, several of my critics complained that alternative energy storage systems, for example pump storage or Compressed Air Energy Storage (CAES) . My analysis of the cost of Pumped Storage indicates that the capitol costs were comprable to those of batteries once uncertainties were taken into account.

However, CAES does appear to lower the cost of energy storage, but at the cost of a considerable inefficiency in the use of wind generated electricity, CO2 emissions, and a surprising environmental issue. CAES increases the reliablity of wind generated electricity, but may not greatly increase the value of off peak hours generated electricity to the producer, despite the delivery of more hours of electricity during day time and peak demand hours. Even with its ability to deliver electricity at times when utilities pay for it at optimal rates, CAES systems appear to only bring a modest return to their owners. I will presently argue that CAES could be more profitable without its coupling with wind using an alternative post-carbon energy stratigy.

This assessment is based on "The Economic Impact of CAES on Wind in TX, OK, and NM," by Ridge Energy Storage & Grid Services L.P, for the Texas State Energy Conservation Office. in 2005 .

The Ridge Energy study focused on atwo alternative hypothertical projects invloving the use of CAES thenology coupled to several wind generating facilities in West Texas, Western oklahoma, and New Mexico. These facilities have some of the most reliable wind in the United states, with average capacitiy factors of around .40. In addition, wind generation does not take place symultaniously at all of these facilities, thus coupled together they produce electricity with greater reliability than their average capacity factor might suggest. The use of CAES would enable the ability to guarantee the dispatch of both base electricity, and 16 hour a day week day electricity. The use of CAES would enable wind producers to sell electricity produced at night at day time prices, but with some fairly significant inefficiencies.

A significan amount of heat energy is lost during the air storage of the operation that aas the air decompresses, it comes out of the ground at below 0 C (32 F). Moisture in the decompressed air condensed and freezes. The resulting ice would damage generation turbines, necissitating the heating of the ait by burning natural gas to melt the ice. 40% of the energy converted into electricity in conventional CAES systems comes from burning natural gas. Energy output of CAES systems is .80 of energy inputs. This suggests that there are considerable in efficiencies in the use of wind generated electricity by the wind CAES system, and that 30% of the electrical input is lost to system inefficiencies.

Ridge energy stimatrd that the capital cost of a CAES system would run @$765 per KW, an exceedingly modest sum, but one which should be examined. The capital cost for electricity produced by the Wind cAES system is in fact much higher. Last week I discussed recent wind costs as reported by Bryan Layland, a electrical systems engineer from New Zeeland. Some commenters rejected Leylands cost figures on the wholely irrational grounds that he was a global warming skeptic. Looked for cost figures for North American Wind projects, in order to evaluare Leyland's numbers, and found 4four projects costing between $2200 and $3200 per name plate wind KW. For the sake of simplifying the argument I will stipulate a cost for new West Texas wind of $2250 per name plate KW in 2009. Since the capacity factor of West Texas runs around .40, the adverage output West Texas wind producer can expect to pay $5625 produce KWs of electricity his windmill will average producing. Since only 70% of the electricity entering the CAES facility reaches the consumer, the wind producer must add 30% more capacity to compensate for the energy loss. Thus the price of the wind generated electry entering the CAES facility must compensate the wind producer for something like a $8000 capitol investment for every average KW sold to the CAES facility. When added to the $765 per KW Capital investment in the CAES facility, we get a very ugly picture, of the cost of wind generated electrity. but one which is still less than our battery based system, about which I made some slightly different stipulations, Since the 2008 cost oh nuclear power is somewher between $4000 and $5000 per KW (as opposed to an estimated $8000 to 12,000 figure during the middle of the next decade).

I would next like to turn to what might be considered a suprising consequence of the use of CAES technology, that is a radiation problem. The same problem also exists, largely unrecognized with all gas fired electrical generating systems. The origin of the problem comes from the more or less uniform pressence of U238 and Th-232 isotopes in more or less uniform amoumnts in crustal rocks. Both isotopes are slighltly radioactive, and as they breakdown through alpha partical radiation, they under go nuclear mutations that eventually leads to the production of radsio-active radon gas. Radon present in rocks is known to escape with natural gas, and wiyh other gases, trapped underground, Salt is known to be relatively impermniable to the transportation of radioisotopes. And there is no uranium or thorium in salt domes. Thus air drawn from sali caverns should not posae radiation danger, as long as the salt has not been evaculated to the rock walls of the cavern. However there would be some question of radon pollutionof stored air in natural caverns, or in mines. There is an even more significant radon danger in deep underground aquifers, which have also been proposed for CAES. Greens, of course, will not see the sligest danger from radon escaping through the operation of CASES fascilities even though they would see far less radon escaping from reactors as an extreme and very dangerous environmental hazard. Radiation is not radiation if it comes from "natural" sources in the Green propoganda. Of course green advocates of CAES technology, all of whom are total hypocrites on radiation issues, have totally ignored the radon problem with natural gas and with many proposed CAES systems.

It is possible to recover at least some of the waste hear usually lost to cavern walls in CAES storage. Compressed air can be run through heast exchanges, just like air from super chargers is sometimes run through intercoolers to cool it before it enters an engine. Heat storage systems using rocks, mineral oil, or molten salt would have to be fairly masive, and would add complexity to the CAES system. While they might lesson the amount of heat lost to cavern walls, heat storage systems do not repeal the second law of thermodynamics, and at least 25% of the energy used to compress the air, is still lost in the process. It is not at all clear that the added capital expense of heat capture and release systems would cost less than the cost of the added wind capacity necessitated by CAES inefficiency.

Finally, it ought to be noted that a potential day carbon free power system for producing day time power with CAES without windmills is possible. It seems to have escaped the notice of most CASE advocates that CAES casn be teamed with nuclear power plants in innovative ways. Since it is more economical to keep reactors running at full power all night, suplus electricity produced at night could be used to store compressed air. During the day, compressed air can be used to expand the reactors daytime power output by as much as 40%. The air does not have to be heated with natural gas. Indeed the compressed air can be heated from the reactors waste heat, killing two birds with one stone, and conserving the water used for daytime reactor cooling, and the use of compressed air in cooling the reactor, would creat significant water use savings, allowing reactors to run even during drought conditions.

Underground compressed air storage, geothermal power and radiation from radon

During the recent Oil Drum debate on Nuclear EROEI, "Cyril R." a frequent commenter on energy related blogs made a case for "Compressed Air Energy Storage" (CAES).

In a response to a comment concerning the low capacity factor for wind, "Cyril R." stated
"the capacity factor you referenced is very low, good locations in the US get 30-40%, which is close to the average capacity factor in the US. Moreover, consider the correlation with the load to be more indicative than capacity factor. Not good for wind, but with CAES this can be cost-effectively dealt with; the CAES equipment is similar to NG turbines, i.e. they have low materials input so this won't fundamentally increase the materials input for wind."

Cyril R proposed compressed air storage in salt domes and saline aquifers which he argued were adjacent to areas of high-quality wind resources.

My initial response was to observe:

"The last time I checked, the expansion of compressed gasses has a cooling effect. If the gases contain humidity the cooling can produce condensation and even freezing. The Grand Solar Scheme recognized the problem and proposed to burn natural gas in the released air stream to reheat it. There are two problems with this approach. First as we all know natural gas is not a sustainable resource, so it is not a sustainable solution. Secondly, burning natural gas produces CO2, and thus a CAES solution would contribute to global warming."

Cyril R. responded:

". . . using biomass derived fuel for heating in combination with hydrogen. In this instance, the use of hydrogen would be interesting because of the higher thermodynamic efficiency. In adittion, there is the AACAES approach which is hardly rocket science. Just add thermal oil storage (proven industrial technology) to store the heat created during the compression stages and use it later to deal with the cooling effect of expansion."

"Cyril R.'s" burning biomass suggestion is problematic from a number of views. The collection and transportation of large amounts of biomass would be energy intensive, the use of a technology involving the extraction of large amounts of heat from compressed air into mineral oil, and then the discharge of that heat into expanding air would be an added expense to a CAES system.

In addition to "Cyril R.'s" CAES scheme, the January Scientific American, published an article on a "A Grand Solar Plan" that proposed a CAES scheme involving caves.

Following the debate an interesting problem with the CAES system occurred to me. Any CAES project involving the release of compressed air from underground storage in salt domes and saline aquifers would probably transport radon to the surface.

Let us examine the problem. Radon is a colorless, chemically inert, radioactive gas produced by the radioactive decay of thorium and uranium in the earths crust, Because it is a gas radon can be drawn into the lungs. There it produces a radioactive multiple whammy. Radon 222, if it decays in the lungs, produces a long and deadly decay chain. (222Rn (3.82 days) → 218Po (3.1 min) → 218At (1.5 s) → 218Rn (35 ms) → 214Pb (26.8 min) → 214Bi (19.7 min) → 214Po (164 µs) → 210Pb (22.3 yr) → 210Bi (5.01 days) → 210Po (138 days) → 206Pb (stable). Each isotope in the chain releases more radiation into the lungs triggering more and more carsenogenic lung tissue damage. Radon is considered to be next to smoking the second leading cause of Lung cancer for Americans. Radon exposure greatly increases the lung cancer danger for smokers.

While salt domes generally contain virtually no radon, surrounding rock does. Critics of nuclear power have long argued that radioisotopes from "nuclear waste" placed in salt domes can be transported out of them through a variety of mechanisms. Similar mechanisms could transported radon from surrounding rocks into salt dome cavities used to store compressed air. The method of creation of salt dome cavities together with the effect of compressed air on the surrounding salt and rock might tend to open up channels for radon transport from radioactive rocks into the compressed air cavity. These would include the use of water to form the original cavity, the heat and humidity of the compressed air, together with the the effects of highly pressured air on the flaws and imperfections in the salt structure surrounding the cavity. All these forces could tend to open up transport channels between surrounding radioactive rocks, and the salt dome cavity. The fluxuating air pressure, caused by compression and decompression could pump the radon from the surrounding rock into the cavity. The release of compressed air from the cavity would force radon to the surface.

The use of saline aquifers for compressed air storage is even more problematic. A recent Geotimes report, "Rooting Out Radioactive Groundwater" focus on the problem of radon in all aquifers. It states:

"Groundwater from deep aquifers is typically oxygen-depleted and has a very slow flow rate, and marginal water typically has high salinity. These alternative water resources may therefore also have high radium concentrations."

Thus it would appear that significant atmospheric radon release associated with CAES energy storage in saline aquifers is very likely, and in the case of salt dome storage is quite possible.

The presence of radon in geothermal hot water and steam used in the generation of geothermal power has also been ignored, although high concentrations of radon could be expected from molten and hot rocks. Geothermal power techniques involved in the insertion of large amounts of water into hot sub surface rocks, would almost certainly lead to the transport of large amounts of radon to the surface with hot water and steam