[rbanffy]

I originally argued against the statement that we will have a "lower energy budget" in 90 years.

Given increasing population, how much more energy do you expect to be able to use? While true we may be able to increase our energy usage, I doubt most of mankind will be able to use as much as we do.

Also, do you realize how much effort (and energy expenditure) would it be to manufacture 10 square meters for every human being alive? Count 10 billion people - that's 100 billion square meters, not counting replacing damaged solar cells.

Nuclear fission is also a point that could be much improved, but it is pretty much a dead end unless we discover some new laws of physics. Nuclear facilities are horrendously expensive to build and to safely manage. There are safer designs, but how much safe is safe in a world you have to guard nuclear fuel (and waste) and keep if from people who are willing to blow themselves up?

As for fusion, you could add the chances of success if they were completely different approaches, but they are not. Also, giving them even a 10% chance of success is very optimistic.

There is no reason to panic, but there is reason to proceed carefully and think through what we are doing and what we are going to do.

[berntb]

>>Also, do you realize how much effort (and energy expenditure) would it be to manufacture 10 square meters for every human being alive?

Please think before writing.

Even today, much less energy is used making solar cells than they create... For material, the latest thin film is not a heavy weight per square meter... (also a hint, we're not running out of silicon for glass...).

In fact, this would take very little resources compared to what a person need to live.

If you want to make a coherent point, you'd note that my "energy budget" didn't include transportation or industry.

We can apply all the clean energy sources we will have in twenty years, for that.

Note that I'm just arguing known sources in one-two decades, assuming the remaining decades are without developments! And you can't answer even that.

Let us assume space based solar in twenty years... 90? I can't even guess.

http://www.npr.org/templates/story/story.php?storyId=1215313...

Did you have any counter arguments against Thorium reactors? Or you're silent because you lack arguments?

>>100 billion square meters [is a lot of area, sic]

You must be unique on this site to never have thought about how many square meters go into a square km. :-)

10 km X 10 km == 100 million square meters. Enough to give 10 square meter to 10 million people, a BIG city. Go check a map, that area is less than the area of the roofs of such a city...

(Most people will live in cities, it seems.)

Enough of the pre-high school math lesson...

>>As for fusion, you could add the chances of success if they were completely different approaches, but they are not.

I don't think you know what you're talking about.

Please explain how a known success/failure of one of the three projects I mentioned would influence the likelihood of the others? I can honestly not see how you could argue that.

I am sorry, but I wonder if you're a troll. I can't be bothered with the rest.

[rbanffy]

Thorium produced in breeder reactors are object of research for many decades, but very few (if any) commercial examples exist. I remember something out of India, but I am not quite sure. There has been some movement around them in China lately, IIRC, but it must be something on a tech demonstration level or we would all be hearing a lot about it. I believe that when someone pull this off, they will brag about it all over the media.

The General Fusion, TriAlpha and Polywell are all a bit far-fetched. GF's thingie has a couple practical problems, like, for instance, extracting tritium from their liquid lead-lithium mix. There are a lot of problems with liquid-metal heat exchange itself, specially on a scale like the one they propose. Radioactive liquid alkali metal exchangers elevate the NIMBY complains to a whole new level. I would give them a 1%. The TriAlpha approach requires higher temperatures than Hydrogen-Deuterium fusion. I would give it about 0.5% chance of success in the next 100 years. If the conditions the GF machine are to operate can be called extreme, I lack superlatives to name what happens inside a Tri Alpha device. As for Polywell... I am an optimist. I would give them a 5% chance. There are some issues on the geometry of the fields (they had some leaks in the "corners") but I expect them to improve steadily enough for sustained operation.

But we are not aiming at technology demonstrators running sustainable reactions. We are aiming at commercial production on megawatt-scale generators. It's not just rescaling your AutoCAD model, even if you don't consider your whole supply chain.

As for solar, you seriously propose replacing the roofs of every home in the planet with solar panels. I live in an apartment, on a 50's building that's not very tall. There are 40 people living in the same building that has about 200 m2 of roof. That's 4 square meters per person on a not very dense arrangement. It's one of the least dense blocks in my region. Most of my friends live on 1 square-meter of roof per person or less zones (taller, newer buildings). This math will hardly work out. As it is, we have a pretty green energy matrix - mostly hydro. Even our cars run on sugarcane ethanol, but, still, ethanol production takes up a lot of land that could be used to grow food and that may be needed for that if the climate goes south and agriculture takes a hit.

You are more optimistic than I am. Things change, but they change slowly. Unless there is a huge political drive behind this, I don't believe we will see much of it before it's too late.

We need politicians who can focus on periods longer than their terms. I am not sure where to find them.

[berntb]

You claimed: "As for fusion, you could add the chances of success if they were completely different approaches, but they are not."

1. I asked for support: "Please explain how a known success/failure of one of the three projects I mentioned would influence the likelihood of the others? I can honestly not see how you could argue that."

A basic presentation about the projects is NOT supporting that...

You back away from that, now that you have read up on the basics. Is that your standard method when you have guessed about something you don't know anything about?

2. The only "real" thing we know about TriAlpha is that they got large investments from people that presumably got more info. (They claim to publish more in 2010.) There is data on a previous project and IIRC, they talked about FRCs.

So on what do you base your claim about probabilites for TriAlpha?!

Note: AFAIK, to breed tritium is quite common for all fusion DT plans.

3. I haven't looked into the subject about extracting hydrogen from the lead/litium -- why do you claim it to be hard?

>>But we are not aiming at technology demonstrators running sustainable reactions

AGAIN: You made a claim 90 years in the future. These will be built (if one works) inside 20. And deployed inside 30. So your comment was totally irrelevant for my thesis. But you knew that.

>>As for solar, you seriously propose replacing the roofs of every home in the planet with solar panels.

Sigh, do I have to quote the BBC reference I gave:

http://news.bbc.co.uk/2/hi/8386460.stm

A key goal for solar is what is known as grid parity. That is the point when it is as cheap for someone to generate power on their homes as it is to buy it from the grid.

It varies from country to country depending on electricity prices, but the institute estimates that Italy - which has a combination of sunny weather and relatively high electricity prices - should reach grid parity next year. Half of Europe should be enjoying grid parity by 2020, it estimates.

So in ONE decade, half of Europe are expected to start plastering everything with solar cells -- there would need to be a reason NOT to put solar cells on a roof (or south facing side of a house).

I already explained about pre-high scool math. But AGAIN:

10 x 10 km of solar cells is enough for ten million people. That is nothing, considering that you can take unwanted land 50-100 km from the city, if you really need more.

Are you trolling?

That will happen in 10-20 years. Consider how much cheaper/better solar cells will be in 30 years...

http://www.technologyreview.com/energy/24240/

Now go up to 90...

>>Unless there is a huge political drive behind this,

AGAIN: See BBC reference. Solar cells will generate energy cheaper than today's normal price for many countries -- already in less than 1-2 decades. And they seem to keep falling in price.

Why would politicians be involved -- except wanting to tax solar cells?

>> [Thorium]

Active research subject today, India is building a prototype. Not totally trivial, but there is afaik no known show stoppers for deployment inside 90 years(!). Do you know of any?

[berntb]

>>[About General Fusion] Radioactive liquid alkali metal exchangers

The last time I checked the periodic system, lead was NOT an alkali metal. Lithium? Hell, they talk about using sodium in newer nuclear power plants... (and have some going since long.)

[Edit: I googled for you. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi... ]

[Edit: Some discussion about sodium and lead in nuclear reactors. Lithium is hardly worse than sodium. http://www.world-nuclear.org/info/inf32.html ]

(FYI, the main criticism of GF I've seen has been about the mechanical building of the pistons.)