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Comment: Re:Thermal storage (Score 1) 217

by DanielRavenNest (#48430653) Attached to: Lessons Learned From Google's Green Energy Bust

Dry rock (gravel) can store energy at about $1/kWh. It doesn't get any cheaper than that. How you use that storage capacity is to use a solar concentrator to heat a working fluid (usually water). Some of the steam goes directly to turbines to make electricity. The remaining hot water or steam goes to a heat exchanger, and a fan circulates air through that and the rock bed. When the Sun isn't shining, you reverse the fan, and suck heat out of the rocks to heat water/make steam again.

To keep the rock thermal bed hot, you surround it with "vacuum powder insulation", which has about six times lower thermal conductivity than fiberglass. On a large enough bed, that will stay hot for days. That's because thermal loss goes as the square of the thermal bed size (area), but heat storage goes as the cube (volume). So the bigger it gets, the longer it can store heat.

Batteries are not really a solution for storing power grid amounts of energy. A valley full of water (hydroelectric) or the equivalent of a gravel pit full of rocks (thermal storage) are answers because the raw materials (water or gravel) are really really cheap.

Comment: Re:Yet (Score 2) 217

by DanielRavenNest (#48430497) Attached to: Lessons Learned From Google's Green Energy Bust

Solar-thermal with storage. You get power at night.

The 400 MW Ivanpah solar thermal plant is on the same power line as Hoover Dam (both are near Las Vegas). It didn't need its own storage unit, because the dam already provides huge amounts of storage. Whenever the solar plant is running, the dam can save water for later. Not all locations have an existing dam conveniently near, so solar-thermal will need to build their own storage units on-site. There are several options, and which is best to use is an area of active research.

Comment: Re:Simple (Score 1) 217

by DanielRavenNest (#48430463) Attached to: Lessons Learned From Google's Green Energy Bust

No energy source is truly renewable. Solar comes from fusion in the Sun, which has a finite fuel supply. It's just a really big supply on human time scales. Ultimately all "green" energy sources trace back to nuclear sources, either fusion in the Sun (solar, wind, hydroelectric, biomass, ocean thermal), or radioactive decay in the Earth (geothermal). For that matter, fossil fuels are fossilized sunlight, so are also nuclear-based also. They just have a more limited inventory.

What renewable means is there is a constant flow of energy that can be tapped - the Sun shines every day. New fossil fuels aren't being created anywhere near the rate we are burning them, and new nuclear ores aren't being created at all.

Comment: Re:What it means (Score 1) 217

by DanielRavenNest (#48430425) Attached to: Lessons Learned From Google's Green Energy Bust

Sorry, but you are quite wrong about that:


Like anyone who has more than a smidgeon of understanding about power grids, Google understands that no single power source can satisfy varying demand. So they are investing in a variety of sources:

Comment: Re:ShirtStorm (Score 1) 337

by DanielRavenNest (#48393815) Attached to: Philae's Batteries Have Drained; Comet Lander Sleeps

> Santa Claus isn't real.

Saint Nicholas of Myra is quite real. His bones are buried in two places in Italy (long story). He's the original whose story and image have been mutated over the centuries. The modern mall Santa image comes from Clement Clark Moore's poem, the Saturday Evening Post, and Coca Cola ( The modern version incorporates no small amount of pagan imagery.

Comment: Re:Value in Space (Score 1) 337

by DanielRavenNest (#48393699) Attached to: Philae's Batteries Have Drained; Comet Lander Sleeps

> The only thing of value in space: water.

You have a very limited view of what is valuable. The amount of solar energy passing the Earth, closer than the Moon's orbit, is equal to the whole world's known fossil fuel reserves every minute. Tapping even a tiny fraction of that could power our entire civilization. What's that worth?

Comment: Re:Space Guns (Score 2) 337

by DanielRavenNest (#48393657) Attached to: Philae's Batteries Have Drained; Comet Lander Sleeps

I was manager at Boeing on a Gun-Launch propellant delivery system study, and using them for space launch is quite feasible. They have been used in hypersonic research for decades, like this one at Arnold Engineering Development Center: You just need to make one somewhat larger, and install it on a mountain with the right slope.

Gas guns are preferred over electromagnetic ones for low launch rates. The power supply for a space launch gun would be immense, because the power draw is very high for a short time. High pressure gas can be stored in a tank, and released all at once. Electromagnetic would be more efficient in the long run, but you need to overcome the high initial cost.

For humans and spacecraft equipment (as opposed to bulk items like fuel and structural parts), you are limited to about 6 g's (60 m/s^2). There are a few locations on Earth where you can install a 20 km pipe, which lets you reach about Mach 5. The gas pressure for that level of acceleration is surprisingly low, about what is put in vehicle tires.

Comment: Re:Great idea, but some concerns... (Score 1) 108

> but Bitcoin doesn't have any sort of "chargeback" system.

The first Silk Road solved this problem by "escrowing" bitcoin payments. Drug buyer sent funds to the Silk Road, who held them until the buyer got his goods and was satisfied. When he posted a positive review/reputation score, the funds were released to the seller. With the distributed "OpenBazaar" system, you just need neutral third parties to supply the escrow service.

Comment: Obvious to Engineers (Score 5, Informative) 185

Any engineer who has studied thermodynamics knows that water has about four times the specific heat as air. The mass of the oceans is about 260 times that of the atmosphere. Combine these facts, and you find the oceans have about 1000 times the heat capacity of the atmosphere. Thus it should be obvious that in any scenario of temperature change, the oceans will play a big, if not dominant part.

In regards to Chipmunk100's summary, greenhouse gases affect the heat input to the planet. The oceans represent a vast amount of thermal storage capacity. One is the current rate of change, the other is the integrated total of the changes over a number of centuries. Different units with different dimensions. A change in greenhouse gases today will take a long time to show up as an overall change in ocean temperature.

Comment: Re:Solar Could be 50+% of production, but... (Score 1) 167

by DanielRavenNest (#48065521) Attached to: Solar Could Lead In Power Production By 2050

Areas of the country that are very cloudy tend to have more wind and hydro energy, cause clouds tend to be associated with storm fronts. You are correct that solar varies in usability by location, but typically other renewables compensate. Hydro in Seattle, solar in Phoenix. And grid operators know this. They aren't stupid.

Did you know that for the price of a 280-Z you can buy two Z-80's? -- P.J. Plauger