Storing Solar Power Efficiently

What do you object to in the clause: "Solar-power startup Ausra, based in Palo Alto, thinks it has the solution..."

An intelligent reply would ignore semantics, grammar and incidental rhetoric to focus on the merit of the content. While certainly not the Holy Grail of energy solutions, this storage solution should be welcomed as one of many. When combined with other solutions such as PV and wind power. they will free this country from oil based energy dependence.

What a troll you are!
Though I don't agree with everything printed here, I find this "rag" generally useful, informative, and interesting.
If you think you can do better, start your own technology emag.  Put up or shut up.

How thought-provoking!  But what about the following:

Solar Thermal is only economical on a grid-level power plant basis.  Distributed electricity generation is better done by Solar PV.  There are efforts underway to use Solar Thermal on a much smaller scale, but it's generally for heating and cooling large buildings and complexes.

Well, it sounds low tech - but it's really the high-tech equipment design that makes it so cheap and attractive.

This is the perfect example of why it's important to invest development in promising technologies - the only way they've been able to bring down the costs is through the existing Mojave desert system which they've used as a test bed for the last 30 years.

Regarding your comment on energy storage for Wind Farms, the industry is not serious about electrochem batteries, at least for the time being. Cost and reliability are the main issues.  Compressed air energy storage (CAES) has had some recent interest here, and some historical success.  A peaker plant in Alabama has been using CAES since the early 90's. Recently, an Iowa farm cooperative has decided to pursue a Wind-CAES project based on successful trials with natural salt cavity formation in Iowa, and even more recently General Compression, a start-up in MA is pursuing a turbine/farm technology that facilitates Wind-CAES.

New technology is why it's suddenly much cheaper and viable.  We've had 30 years to learn from similar systems in the Mojave.  Three things that really drive down costs:
1) Dewar tubes that contain the working fluid are much more robust and reliable.
2) Heat Storage technology has improved dramatically.
3) Using water for the working fluid and generating the steam directly.  Until now they used salts or oil, then used the salts and oil in a heat x-fer to generate water steam inside the plant.  They've bypassed that step in this system.

Maybe cheaper, but less efficient. You need some way to convert the energy from heat to mechanical energy. You'll get substantial second-law conversion loss, however you do that conversion. I guess that's the attraction of molten salts; high temperature, higher efficiencies.

None of these "heat storage" devices is anywhere near as efficient as storing potential energy through gravity, something like pushing water uphill to a reservoir.

See Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass by
David Tilman:
http://www.sciencemag.org/cgi/content/abstract/314/5805/1598

Yes, this is good stuff.  However, photosynthesis is usually 1-7% efficient, and conversion of biomass to electricity or liquid fuel reduces that further.  In comparison, solar thermal is 30% efficient, one needs a lot less land to power the U.S.  There is likely a place for LIHD biomass, but I think most of our energy will come more directly from the sun than taking it through plants.

Compete? If CLFR also gets that 80 percent subsidy that the nukes will get, it would be considerably cheaper than nuclear.

In fact, it would be considerably cheaper than coal.

But not really of course. Because it's taxpayers' money. Fiscal deception at it's best. Or socialism. Take your pick.

If you want more nuclear power, go live in France.

Think I already answered this in my other comments above.

Biofuels only remove CO2 from the atmosphere temporarily.  As soon you burn the ethanol or biodiesel, the CO2 is back.  Solar thermal doesn't remove CO2 from the atmosphere, but using the energy doesn't put any back either.

Biofuels take too much land area to be viable.  The recent PNAS article on switchgrass gave 7100 kg/ha, 0.38 L/kg, giving 2698 L/ha.  Assuming you're powering a fleet of vehicles that get 35 MPG on gasoline, the new CAFE standards, it would take 633,000 mi^2 to produce the ethanol.  How green is that?  The equivalent Stirling Energy Systems dishes in the desert take 3,607 mi^2.  Which do you think is greener, 633,000 mi^2 of stolen habitat, or 3,607 mi^2 of mirrors in the desert?

As for your queries:
(1) You write, "Exactly what sort of area of land do you expect to cover with solar reflectors ?" It takes 3,607 mi^2 for powering the 2.7 trillion vehicle miles traveled in 2005 in passenger vehicles.  I see no "pure fantasy" here.  NREL estimates there are 6,091 mi^2 of "premium" and "excellent" CSP potential in the U.S. West.  There is more in lesser rated tiers.
(2) You write, "Do you realise (sic) the area of agricultural and forestry land avilable (sic) for storing carbon and for producing fuel ?"  Yes, I know the mi^2 for these.  Do you?  What do you plan to eat if you use cropland for fuel production?
(3) You write, "Your (sic) certainly not going to build solar power stations on that sort of land": no, you're going to build it in high insolation areas, such as found on NREL's survey maps.
(4) You write, "AS far your question about how much energy can be stored as biofuel , far more than you can store in batteries ."  Have you done the calculation?  The number of passenger cars in 2004 was estimated at 136 million, with 6 million motorcycles, and 92 million non-car 2-axle vehicles (mostly light trucks and SUVs), or 234 million vehicles.  Let's ignore the motorcycles, and say the passenger cars have 40KWh battery packs, giving 19.6 PJ of energy storage.  The SUVs have 55kWh battery packs giving 18.2 PJ.  Total 37.8 PJ.  Used once a day for a year, that's 13.8 EJ.  At 60 GJ/ha for ethanol from switchgrass, you  would need 230 million ha (887,842 mi^2) to produce that much energy per year.

You should do your own calculations instead of just hand-waving.

Biofuels are a horribly inefficient way to produce energy, and throwing more land into the mix doesn't do enough to offset that.   You still have to harvest it, which kills your theory of tons of land being available to use.

If it can be harvested, guess what else can be there... ya... solar or wind power.  Beyond that, your method of increasing power output destroys your theoretical negative carbon offset and pollutes the environments the biofuel is grown... real green huh.

Research and tech into biofuels, sure... we need to explore it.  But advocating the construction of support infrastructure for a proven bad source of energy is horrible.

Solar works, wing works, nuclear temporarily works, biofuel does not.

As you can see in my formula above, it makes sense to go for a number of solutions that complement each other.

For example: solar thermal with daily storage (load following) + solar PV (additional peaking) + wind (winter peaking)+ bio-energy (dispatchability, backup, filling in the gaps of the others) = a very powerful combination, worth considerably more than the sum of it's parts.

Adding more, such as geothermal, wave, tidal, small hydro etc. might improve the balance even more.

A floating island on the ocean is far from the ideal location for a lot of these technologies.  Besides the power in having a porfolio of technologies is to fit them to the best suited environment, not cram them all into the same environment and then loose energy through distribution losses.

However combining wind, wave, & underwater-current generators does make sense.  If merely for the sharing of a common power line.

Compressed air similar to what CLFR Solar uses anyway to store energy, except that it uses compressed steam instead of compressed air.  When the compressed steam is released to produce electricity it works similar to how these compressed-air engines work.