In a large system, one year high-temperature deep ground storage is possible.

That said, near-term storage will not be required for the first $200 billion solar thermal deployments.

an electrical megawatt-month? I suppose that would have to be five or six or seven thermal gigawatt-days ...

For "gigawatt-days" please read "megawatt-months". I  put in two references to the larger unit, then thought, that's an opening for him to say gigawatts are an outmoded, corporatist concept -- or some such thing -- and tried to change them all, without immediate success.

3 numbers I'm interested in.  

What is the ERORI of the best (which would be the cheapest) Concentrated Solar Power Plant.   Energy Returned on Energy Invested, would tell you how much we got to put into these things to get our energy back.   I think I remember reading onetime it's 4 to 1, which is really bad.   What if the thing runs 30 years, it would take 7 years to get the energy back?   That seems way to low.  I'm looking.   I wish I keep those links.

What is the ratio of wind in the summer compared to the winter in the midwest?   I think it is 70 percent.   (winter more wind than summer)

What is the ratio of sun for the winter compared to the summer in CSP areas, (CA.AZ.NM.TX)  that might be somewhere around that 70 percent or lower.  

Anyway, the place I would go with this is wind power from the windy states combined with solar power for the sun states, would be a good combination for year round power.   Sure, there would be gaps, but just because there are gaps that would have to be filled with Fossil fuel plants, doesn't mean the combination couldn't be the majority of electrical power.  

As I have read, 3 states, North Dakota, Kansas and Texas wind could replace all of the fossil fuel used for electricity.   An area the size of Indiana or half of North Dakota in wind turbine area (1 1/2 percent of lower 48 states area) with 400 000 wind turbines at 2.5 MWatts each.

Does that make sense or not?   Just hook the whole combo together at New Mexico and Kansas.

All prospectors need is a ream of blank paper and sharp pencils.

and in the fog from a 20 mile Sound kayak adventure.

If this mornings calcs are correct then sand 100 feet deep by 500 x 500 feet square at a delta temperature 250 degrees F. (750 - 500 F.) equals 4 gigawatt-years thermal.  

ERORI of less than one year would definitely be good.   I think I did see ERORI of 4 for CSP, but that may have been someone trying to be negative to CSP and be pushing some other form of energy.   It's so hard to get real numbers for stuff.  Of course, who measures it has something to do with it as well, some might include the energy of workers to drive to work.   Depends on what you want to do with the numbers.

I've read that wind turbines are 3 months to 9 months.

Photovoltaics are 2 years, hence their cost.

I am not an engineer and was only projecting from 90 C. Swedish systems.  The 100 foot depth comes from typical pile driving depth of wells.  The field circumference is often a polygon.  The heat exchange is serial, starting (or ending depending on direction) at the edge and working inward towards the center.  Dry sand has poor heat transfer, requiring more wells.  Rock is ideal but more expensive to drill.  High temperature storage needs intensive engineering followed by hard data on cost and performance measured from prototypes.  Currently, it is just an old concept, a possibility.

I purchased a mothballed 700 psi pressure tank from the Satsop nuclear plant, 10 feet wide, 40 feet long, 2.5 inches thick, stainless lined, weighs 45 tons, cost $500,000 when new.  If that is what the solar-thermal company Ausra is using for high-pressure high-temperature storage, then that would be both expensive and dangerous.  I wonder how adding big expensive storage tanks reduces cost from $0.10/kWh to $0.08/kWh.  Perhaps it is because they get better capacity factors from expensive heat engines.  But, to get to those numbers, their heat engines would need to be really cheap.  Those solar thermal numbers are possible, just difficult, especially for line-focus single-axis tracking concentrators and mid-temperature heat engines.  Ausra sounds aspirational to me.

We need the solar thermal budget restored at NREL, ASAP.

So I dropped it.  In round numbers from my failing memory -- One pound of sand is 0.2 Btu/F.  One cubic foot is 100 pounds.  3413 Btu=1 kWh(t).  At a temperature change of 250 F. 1 ft3 sand = 1.465 kWh(t).  100 x 500 x 500 feet = 35 GWh(t) = 4 MW(t) years.  If used for 16 hour power at night then the power is 2 GW(t).  If $1000 heat wells are every 10 ft2 surface then the cost is $25 million, $0.01 per  Watt(t).  Sounds wild.

Baseload winter solar power has sexy political connotations but it is not relevant for big markets, does not wag my tail.  There might be a niche market after the first $ trillion has been deployed for 24 hour solar power.  District heating/cooling with seasonal heat storage makes more economic/political sense.

I am not convinced seasonal solar power storage is useful.  If the solar system is double sized for power and storage input then it is big enough for winter power output without storage.  Middle ground?  Three months of supplemental heat storage might cost $1/Watt(t).  If solar HIPV costs $1/Watt(e) then it might be more profitable to oversize the solar power plant for summer conditions.  It all depends on technology cost/benefit and market demand/supply.  I suspect winter loads are less due to summer electric air conditioners.

I agree that EROEI isn't the most important measure.   It was just an indication of whether it is worth doing.   Like ethanol, which is only worth doing politically, not for the energy gotten out of it.

I've read that if coal plants were required to buy all the coal they needed 30 years ahead of time, that would make them uneconomical.  (not hard to imagine)   That's what a solar or wind plant has to do, basically buy all their costs upfront in more material and design costs in machines that harvests the sunshine or wind.  

Also their value as reliable power, whether peak, shoulder, base or none of these.

I could imagine that if some of these get built and the claim of cheaper power is working, they still could be combined with the CSP's that have the higher working temperature.   It's important at the turbine to get as high a temp as possible and the combination of the lower cost, lower temp collectors as a step to the higher cost, higher temp collectors might make for a better system.  But they still have to get them to work for now.

Reducing cost is the challenge, the fun.  No matter how cheap solar gets, it can always get cheaper.  Remove one bolt, one dollar, and you make a million on a million collectors.  Cost engineering requires discipline for simplicity.  Like simplifying writing, simplifying technology requires thought, time, and effort.

Low temperature systems do not cost less than high temperature systems.  Flat plate collectors cost more than line-focus collectors, which cost more than point-focus collectors.  It is materials intensity, not temperatures, that drive costs.  Other significant variables include ground support v. steel support, system lifetime, O&M, annual energy performance, tooling, indigenous scale-up, labor skills, cost of capital, and overhead.    The $40 million for Ausra will generate an overhead ache for cost reduction.  I can not imagine why they need so much money.

Storage can be used to keep the power output stable and maybe extend a little but until the majority of daytime needs around the country are met, storage won't be needed. This can be used once coal and other dirty sources are being used only for night time generation. Then it can finish phasing them out.

Ground solar thermal storage should start taking off for home heating any day.