I've long thought that Concentrating Solar has very little chance of a technical breakthrough to allow the cost to be competitive. Photovoltaic has the potential for the order of magnitude type of breakthrough. But the storage technology also has to exist at a reasonable cost or else we still need a large installation of baseload generation that would either be fossil fuel or nuclear (which I favor but I know most people here don't) and would make solar redundant.

The technology available off the shelf right now does a decent job. Wide scale deployment of current technology will drive economies of scale, competition and inevitable technology improvements.

Take any other technology that has emerged, there has always been a gradual incremental improvement, not step changes. It can't proceed any other way and is really just an extension of evolution / natural selection.

Imagine if people looked at the Wright brothers aeroplane and said "no way that thing is hopeless I'm waiting for a 747". With that attitude there would have never been a 747...

At my last house I had a boring "old tech" 1 kW solar PV grid connect system. It generated about the same kWh as I consumed. In the city I live the system produced peak power coincident with peak demand such that if all the homes in the city had a similar system it would eliminate a coal power station or two. Contrary to misconceptions the system would still produce resonable kWh on very cloudy / rainy days.  

The issue of intermittency could easliy be solved with a combination of solar / wind, a variety of distributed storage technologies like pumped hydro, battery banks, compressed air etc and generally wasting less energy.

Imagine a new paradigm - It's been cloudy  so there's less energy in the smart grid so if I wan't to turn on all the lights in my house I have to buy power from someone who is willing to turn them all off and so on.

We've sequenced the human genome, transplanted organs, put man on the moon blah blah. But we can never ever harness the 6000 times more solar power hitting the earth than the total human power consumption? Puhlease, doing this should be friggin' easy.

A solar revolution in Boston.

The reason I favor requiring coal plants to sequester carbon is NOT because I favor coal. Still less that I prefer it to solar. That's a red herring b/c this isn't an either-or choice.

The reason for carbon sequestration is that:

a. we want the shit to get cleaned up if we are going to have it at all

b.  making utilities pay the price of cleaning it up puts a price on carbon that is not theoretical.

Otherwise our near-term hopes for pricing carbon are based rather unrealistically on getting Congress to tax CO2 and/or implementing complex international cap and trade systems of doubtful integrity and enforceability.

c. the greater cost for scrubbing coal emissions of CO2 will make solar and other alternatives more competitive.

So far from the situation being coal with sequestration VERSUS solar/ renewables/ efficiency, I think these strategies work synergistically.

As for 'intermittency', I think a full-scale, 100 percent renewable energy economy would not  distinguish between 'baseload' vs. 'peakload' as to time of day and season, in the traditional way of looking at the problem.  

If demand exceeded combined solar and wind output at any particular moment, hydroelectric could be the gap filler. So hydro is shifted to a 'topping' cycle, instead of running constantly.  This gives a role for existing large dams should they not be decommissioned.

I would love to see some explanation of how you can get 16 hours of steam storage. I assume you are talking about the AUSRA concept. It still confounds me how this could ever work. The system supposedly stores high temperature, high pressure water and flashes it to steam when needed. The problem, of course, is that energy content of water is much lower than steam and, at feasible temperatures and pressure, only about 1/3 of the water can be flashed. Also, that's at the maximum pressure. As water is flashed, the pressure drops (unless you continue to pump in water, which would cool the stored water) and the yield drops. When you look at the steam throughput in any reasonably large turbine, you quickly find that you need to provide storage for millions of pounds of high pressure, high temperature water. That would be ASME pressure vessel storage. The cost of this scheme would be incredible, which is why the only operating storage systems have used molten salt.

Let's hope for the best, but the storage issue is far from solved.

Also, using hydro to level renewables is a good idea, as far as it goes. However, hydro is, if I remember correctly, only about 8% of total generation so I would guess dedicating hydro to leveling would only allow wind/solar to contribute two or three times that, so renewables would still only be about 30% of total generation.

Ausra is being secretive because they don't have a clue on how to make this work. As a homework assignment get out your old copy of steam tables and calculate how much high pressure hot water (say 1000 psi or 2000 psi) has to be stored to provide 16 hours of steam for a 100 MW steam turbine. The results are shockingly large. Then think about storing at a pressure that you could use in geo structures - maybe 100 or 200 psi. At those pressures it just plain won't work (by first and second laws of thermodynamics).

Water in pipe at 600F, 42.4 lb/ft^3  1.51 BTU/lb F.  100MW(e) ~ 300MW(t) 16 hr = 1,280,000 ft^3  200,000 wells without hot sand contribution.

Biogas can be stored for backup for the few times when the system is lacking enough renewable power.

Smart grid low temperature heat storage, it needs some computer modeling.  But it stands to reason that everyone could get the power they need, just not on any timetable.  

100% dispatchability  is what that old style grid feature is called.  The central power plant is built big enough to cover all the freezers, pumps, heaters, lights all being turned on at once.

A smart grid runs your freezer to cool it for the next 12 hours.  Then it runs the neighbors freezer..and so forth.  It manages the load, while still keeping the food cold and the home warm.

Backup from biogas is only needed for emergency back ground load.  Lights, phones, computers.  maybe a few time a year everything would go on that emergency mode.  So what, it's better than blackouts, like the normal grid has.  or massive storm outage.

A distributed renewable smart grid is self healing.  It won't just go out in whole regions from storms.  It is more reliable than the normal grid.  

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

There are a couple of problems with your estimates.

First, 700 degree F water has a saturation pressure of 3090 psia. Therefore your 6 inch pipe has a required design pressure of 3500 psi or greater. That is not garden variety piping. I think the wall thickness is 1 inch or greater and the material is exotic. There will be several tons of steel in each well. Also, it would fall under ASME boiler code and require code safety valves. Add in drilling and I would wager your wells are closer to $100,000 each than $1000. $1000 won't even pay for the steel ingots from the foundry.

Your calculation of energy available also doesn't work. 700 degree water has an enthalpy of 823 BTU/lb. If you release steam (initially at very high pressure) the steam flashes by transferring energy from the water as it depressurizes. Eventually you end up with a tank that's still full but full of water at atmospheric pressure and 212 F plus enough steam at 212 F to fill the rest of the tank. So a lot of the water is still in the tank. Yes, you released steam but initially it was released at 3000 psi but the pressure quickly dropped and the steam you released at 1000 psi or 500 psi was significantly less efficient in driving the turbine. You only get 500 F steam until the pressure drops to 680 psia which will happen very quickly in this system.

There is s tendency for people to look at these things as big hot water heaters. This would be a very sophisticated energy transfer system.

People working on 16 hour storage are using a hybrid approach of molten salts, ceramics, well casings, and small diameter pipes for high-pressure in-situ steam formation.   They want to avoid moving the salts through valve packings and pumps.  24 hour solar thermal power is possible.  Engineering will improve cost envelopes.

Watch for some wonderful things coming out of universities...

Steam pipes are embedded in a large insulated mass of an inexpensive solid material like concrete.

Excess steam generated while the sun is shining heats the concrete to 300-400ºC. At night, or low insolation water or heat transfer oil is pumped through the concrete blocks to generate steam to run the turbines.

Concrete has a reasonably high volumetric heat capacity so it can store large amounts of energy in a relatively small space. There is some info here: concrete storage

Concerns about high pressure steam are unfounded. Most steam turbines run at 6000 kPa (880 psi) / 400ºC which means there are thousands of conventional power plants with 1000's of km of piping running under these conditions.

"using hydro to level renewables is a good idea, as far as it goes. However, hydro is, if I remember correctly, only about 8% of total generation so I would guess dedicating hydro to leveling would only allow wind/solar to contribute two or three times that, so renewables would still only be about 30% of total generation."

Interesting observation about the limits of using hydro to level out fluctuating wind and solar. How does Ken figure what the proportions of hydro to other renewables would need to be?

Another renewable supply possibility that seems large is 'dry rock' geothermal. This involves pumping water down a well and using steam that is so generated to turn a turbine.  This is distinct from tapping into 'hot water' stored in a geologic formation -- a la geysers  -- which is a far more limited resource, both geographically and in amount.

MIT recently did a study of the potential. The western US is the best, with certain areas of very hot volcanic rock lying close to the surface.  However, the potential is there all over if you can drill deep enough. The costs were reported to be seemingly within reach of other conventional power options.

Is this also a possible "instant-on" gap filler that could function during the times when the solar or wind output dies down?

Hot rock does look good for both source and storage.

The sun is the only permanent energy source. At some point in time it will be the only energy source reliably available, and what are fossil fuels but stored sunlight?

Furthermore, the nuclear resource is grossly overstated by nuclear huggers. There might be enough uranium for "thousands of years", but how much of the planets surface needs to be overturned to get at it?

Solar and it's manifestation as wind/wave/hydro/biomass is the only millenial energy source. Everything else will be depleted within the blink of a geolocical eye.

The whole system is in balance, with the amount of heat being lost at the surface balanced by heat slowly flowing up from the core at a constant rate. If we inject water down into hot rocks to create steam, and effectively move heat from the rocks to the surface at a rate greater than the natural equilibrium the rocks will cool because the heat flowing from the core is constant and no longer sufficient to maintain the higher temperature because the heat flow to the surface has increased.

Every time you drill a geothermal well, the rocks will cool and steam production will drop and eventually cease. You then have to move to a new well and repeat. Eventually the old well will reheat when the natural heat balance is restored but I'm not sure how fast this occurs and whether is is practical to drill enough wells so that they can be rotated and whether there is in fact enough heat flow that can be practically exploited on a scale large enough for all of civilisations energy needs.

There are other geothermal resources that produce heat by decay of radioactive species rather than core heat - these are definitely finite.

Solar = ~1000W per projected square meter at the surface forever. I think geothermal power density is much lower and therefore less abundant and more difficult exploit than is immediately obvious.

Deep geothermal may prove to be not worth it, unless it's close to the surface, but I think it's worth exploring.

If MIT is correct then solar is cheaper than coal and more accessible than hot rocks.

I hope hot rocks steam as described by MIT becomes a proven global energy source less expensive than coal.  Federal research and development is urgently needed.

I'm curious what concern elbarto has about deep fractures?  Lubrication possibly causing small earthquake swarms?  I believe those have been observed, don't know if the magnitude is sufficient to cause alarm.  I guess I would stay away from major active faults.

I've wondered about the effect greater adoption of geoexchange (aka geothermal heatpump) would have on the near-surface heat profile.  I would expect that with prolonged use the heat pumped in during summer would tend to raise temperatures, reducing efficiency (more pronounced, say, in the South where heat withdrawl during winter would be much less).

Interesting fact:  near-surface profiles of temperature vs. depth (say the upper 10-30 m or so?) at undisturbed locations can be inverted to give a history of surface climate, tending to smooth out short time scale variations.  As one might expect, they provide further evidence of recent warming.

We know the solar resource is 250W per square meter of total surface (1000W projected surface) but what is the geothermal heat flow from the core to the surface in W per square meter?

My guess is not very much because if the sun went out the Earth would freeze solid in no time.

W/meter squared might give some indication of which is a better resource solar or geothermal.

A study of heat transfer through a spherical shell might shed some light as to why the geothermal resource might not be that useful.

I could be wrong but think it's fools gold and another pipe dream diversion from what actually needs to be done to secure a clean and reliable energy system for civilisation for future millenia.

Egyptians build pyramids to last for millenia and they actually did. Why can't we look beyond the next few decades and put in place a paradigm that will get us well beyond the next energy crises.

Solar is the only energy source that can realistically provide enough energy for long enough without major planetary modification and creation of dangerous legacies like nuclear, geo, fossil etc all require.

Certainly, we should be going full tilt with wind and solar at the same time we look into geothermal, it should not be either/or, if the mainstream conversation turned to that, it would be a sign that some power group was scheming, because the technologies should complement each other, assuming deep geothermal can work to some extent.

One question with deep geothermal is the extent to which is would be centralized, say in Nevada, vs say, each metropolitan area having its own deep geothermal plant -- which might be a good way to dispose of other baseload generators, say, if it could advantageously replace nuclear, or even some destructive hydro.  I think that decentralizing energy to be as close to the use as possible should be a "law" of renewable energy scenarios, so in that sense the megaprojects of putting solar in the southwest and wind in North Dakota don't stack up too well (I mean, at the extreme we could generate all the world's electricity from solar thermal farms in the Sahara, as some have proposed, which doesn't sound appealling either).

But at this point, I think we should explore all possibilities; we should be able to play with various scenarios, and be able to explore various combinations of all of these technologies.  The difficulty of building such scenarios is that they will be locality-specific -- it won't simply be a case of putting in a standard coal or gas-fired plant where demand is, but understanding the solar/wind and even geothermal potential of each area.

This states an average global geothermal heat flux of 0.075 W/meter square.  

Sure there's a few hot spots around that have much higher flux but in the end solar dominates.

I'm fairly sure you cant just drill down 10km anywhere on Earth and tap core heat. High flux sites are very limited.

Solar/wind farms wont be the answer either unless there is a massive reduction in energy consumption.

I believe a contraction of settlements plus massive deployment of solar PV might be viable for the long term.

Geothermal with closed cycle refrigerant as a turbine proplellant is too expensive to compete with wind and solar.

All this worry about storage and baseload power has become irrelevant with studies on diversely located wind and smart grid power management.  It is a holdover from anti-renewable talking points, somehow internalized by environmentalists.

I think that we argued about it for so long that the wrong headed objections about dispatchability and so forth took on a life of their own.  That and the ocasional uninformed visitors that didn't realize storage was not the huge problem everyone seemed to think it was a few years ago, keeps these discussions going.

The really rough part about touting solar at under a few  dollars per watt to compete with other sources on price, has always been that the sun only shines around 2 to 4 thousand hours per year, brightly and directly enough to produce power.  Depending on location and climate.

That means every watt of solar produces around 2 to 4 kwh of electric power per year.  2 to 4 kwh is worth 22 to 44 cents retail.  So the payback period on $1 per watt solar is around 2 1/2 to 5 years.  

Boost that with a 10 cent per kwh subsidy, diverted from big fossil, nuclear, and agribizz energy corporations, and the payback would be cut nearly in half.  A great investment!

But actual installed solar will be closer to $2 or $3 per watt, even with the $1 per watt PV cell manufacturing cost.  But that's around 3 to 8 years payback period.  Still not a bad investment.  Free power after 8 years?  

Plus there is enough roof space suitable for solar, that with conservation (like geo heat exchange cooling/heating) and cogeneration of solar heat from PV panels, that most power needs, even enough to power plugin hybrids can be provided by roof and wall mounted solar.

Then of course there is  solar furnace and large scale wind to power energy intensive manufacturing and electric mass transportation.

And biogas for distributed backup power.

This is all practical now, we are only waiting on subsidy shifting to get it off the ground. Of course this is far from common knowledge.  Our leading hope for this energy policy is Barack and I doubt he has heard of most of it at all.

He needs illumination. Let's have a revolution.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

A conventional power plant has a very limited amount of high pressure piping from the feedwater pumps to the boiler tubes to the high pressure turbine. In a 1000 MW coal plant there are a large number of small diameter boiler tubes but these have almost constant structural support and are isolated from people. The other high pressure piping is measured in hundreds of feet, not kilometers.

Miles and miles of high pressure piping out in the open in a solar facility is a major problem.

Making power and 24 hour power is a policy/political issue.  Using solar is a green marketing issue.  Producing solar is a manufacturing issue.

Ongoing MIT dialog stimulated by Grist...

The Swedes told me their seasonal heat storage was low cost because they pulled the well casing back out allowing the earth to collapse around their half inch pvc hot water loop.  Their 100 foot deep wells and top manifold system is buried under 10 feet of earth.  We can not use plastic for high temperatures but could use hot oil in half inch steel pipe.

The trough people could not afford to maintain their expensive receivers so they used hot oil in steel and those systems have been proven very durable at high temperatures.  Probably the same issues with the Spanish pipes buried in concrete.  So, I am leaning towards a hot oil system with recovered well casings.  Low cost and zero maintenance.

Baseload high temperature steam applications are distant long-term markets.  At least we are ready for the cynics that retort solar does not work at night.  Wet steam when the sun shines is the best market -- simple, low risk, excellent ROI.

The interaction between sources and loads, timed to smooth everything out, produces reliable renewable energy.  Without complicated, expensive storage and backup in each building.

But I think that the only way this is going to get done is in blocks of stable smart grid enabled buildings.  Starting with one home or factory.  Then more, then...Excel has a 1000 home smart grid project in Colorado now.

Prove the stability of renewables in one home, like Amory Lovins has (I know he should use biogas instead of propane as a backup, no one is perfect), then in a neighborhood, then a county/city, then a state..  and so forth.

This is irresistable asdvertising too.  Neighbors tell neighbors, everyone wants it.  Given Grist and Youtube and other internet media, it can go viral..  jumping around to neighborhoods all over the planet.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin