On its own EROEI "energy returned on energy invested" is on use in choosing between energy sources. To be useful, an energy technology just has to produce more energy than it takes to build. The ratio of output to input is meaningless on its own. What you also need to know is how much it costs to build the plant. A low ratio plant is fine, it is cheap to build and operate. As an example, if solar cells are cheap to make (they are made from sand) and run (they run on sunlight), then it is worth making a lot of them, even if they are not very efficient (you can use the energy from the existing solar plants to make more solar panels). What also has to be taken into account in the cost is any pollution caused (burning coal causes carbon dioxide pollution which causes global warming, for example).

How does tidal stack up?

I saw a small tidal plant in Ireland that was some 400 years old; originally it drove a mill but had been converted to drive a generator and charge a bank of batteries.

Peter,
I don't think you get any brownie points for dismissing the thyroid cancers so lightly, even if most are apparently cured. The public should be told the truth about them.
The other subject which you raised, is that of reducing the levels of allowable ionising radiation. To date there is actually no scientific justification for any level. Some would suggest that there is no safe level, others want a higher level than is currently internationally agreed. It is all just about consensus, an argument which the conservatives are winning, a situation which will continue well into the future because of the lack of good scientific evidence to change it. Statistics plays a large part in all this and as we all should know, there are liars, damn liars and statisticians.
David

David,

"The public should be told the truth about them."

I agree the public should be told the truth. They are provided with the best scientific evidence and conclusions available at an time by the authoritative bodies, not by scaremongering journalists and media.

What you read in junk articles is not the truth, even if you accept such nonsense. I'd suggest you do some objective research, put your faith in the authoritative bodoies that have done objective and thorough research using the best authorities available in the relevant field instead of scaremongering.

"To date there is actually no scientific justification for any level. "

Absolute nonsense. More is known about radiation effects on humans than any other pollutant, including smoking.

And, you still haven;t been able to appreciate context: even if the media article is correct, the thyroid cancers may not have been attributable to contamination from the accident (proper studies have to be done to attribute cause to effect), and even if they are they absolutely trivial compared with the counter-factual of the case if Japan had been using coal, gas and oil for the past 45 years instead of nuclear power. I'd urge you to consider context and use perspective.

tomw, I'd recommend you read the original articles and follow the debate on the scientific sites where the in-depth debate has been held. You could short cut it by reading John Morgans response to all the critiques (see link at top of this thread).

However, can I urge you to consider this: why would a rational person, once hes' become informed of the relevant facts and comparisons advocate for renewable energy given that nuclear is far superior at meeting all the important criteria:

1. energy security

2. reliability of supply

3. cost of energy

4. health and safety

5. environmental impacts

Why would any rational person advocate for renewable energy once they are aware of this. If they are not aware, and they are not simply advocates for some cause or ideological belief, why wouldn't they undertake to do their own objective research to find out?

tomw, with battery storage PV's are in deficit EROEI (below 1). Even if it was 1.6 with hydro storage (possible in some cases) do you suggest that a year's world energy from high EROEI production sources should be given over to producing PV's?

We realize that this could not all happen at once, but over what time period do you believe the transition would be completed? Meanwhile, world energy demand won't stand still:
http://en.wikipedia.org/wiki/World_energy_consumption#/media/File:World_primary_energy_consumption_in_quadrillion_Btu_by_region.svg
I have no calculation on this as many realities intervene, but I'm guessing it would be in the order of many more generations than we have to solve the climate problem.

That's why we must look at high EROEI alternatives to renewables.

Luciferase said;
Meanwhile, world energy demand won't stand still:

Well actually it will stand still and a possibility that it will decrease further.
No one knows at this stage, but it is pretty certain
that it will not increase because of high prices, which is what has
got us to where we are now.
Production decline is here now with a 40% decline in drilling rigs in the US.
Any reverse in demand will very quickly lead to higher prices.
The production peak in conventional oil was in 2005 and unconventional is peaking now.

Re ERoEI, some sources say oil is now 10 which accounts for why the
major oil companies are getting such poor results on investment.
I guess we will all know clearly by the end of this year what will happen.