I see desert based concentrating solar thermal with storage barely makes the cut yet the International Energy Agency thinks it will save us by 2050. Apart from the energy trickle down effect in the pyramid so-called renewable energy seems to need power dense inputs. For example most sub-electronic grade silicon is apparently made by mixing sand with coal derived coke and zapping it in an arc furnace with electricity mostly made by burning coal. If silicon panels lose performance after 20-25 years that process has to be repeated.

Another big hope is that PV + batteries will power suburban homes and electric cars. I guess there are no poor people or rainy weeks in that vision of the future. A lot of our realtime or embodied energy will have to come from large, high yielding plants like smelters and power stations. As the years go by we'll have to ask why most of them don't go away.

"Alternative energy is so expensive that it can barely pay for itself, let alone support a civilisation."
You're dead right there, Do. Luckily, people are starting to realise.

My paper here: compares the costs of a mostly nuclear power versus mostly nuclear energy electricity system for eastern Australia: http://oznucforum.customer.netspace.net.au/TP4PLang.pdf
See Figure 6 for a summary cost comparison. It compares four renewables scenarios and on nuclear scenario on the basis of capital cost, wholesale cost of electricity, and CO2 abatement cost. Figure 5 shows that the mostly nuclear option would avoid about 90% emissions from electricity (same as France), whereas the mostly renewables option would avoid about 70% - but at about 2 to 3 times higher cost then the mostly nuclear option!

The CSIRO 'MyPower' calculator and the CSIRO eFuture' calculators allow people to confirm the huge cost of renewable energy. They also confirm that nuclear power is by th cheapest way to reduce emissions.

Of course, as many who read the posts and comments on Online Opinion would know by now, nuclear energy is also the safest way to generate electricity and would save over a million avoidable fatalities per year is it replaced coal fired generators now.
http://nextbigfuture.com/2012/06/deaths-by-energy-source-in-forbes.html
Also Wade Allison's excellent articles on Online Opinion, and this excellent video:
http://www.youtube.com/watch?v=YZ6aL3wv4v0

A good article. Whatever the criticisms of the particular options, it is clear that, in order to have a *rational* discussion of whether alternative energy is worth it, there need to be a comparison of the *ratio* of inputs to outputs.

This question of rationality is basic and should be obvious in the current debate over renewables, although I am constantly surprised at the number and proportion of people pushing renewables who obviously either don't understand or don't care about the need for rationality in order to make sense.

Too many vague unsubstantiated assertions Don. You havent spent much time on research. Re electric cars it took me about 10 minutes to google this one from a US university:
http://pubs.acs.org/doi/full/10.1021/es702178s
It says plug in Hybrids (PHEV's) are about 30% less carbon emissions intensive than petrol powered cars assuming an electricity emissions intensity of 670 g CO2/ kWh. But if you charge them using your own PV panels (emissions intensity less than 100 g CO2/ kWh), then of course it's a different story - they would emit less than 15% of the CO2 of an equivalent IC car over its lifetime. Incidentally Li Ion battery is less than 5% of the embodied emissions of making the PHEV

Good to have an article highlighting the importance of EROI. But once again, do some better research, Don. This table is from Wikipedia. http://en.wikipedia.org/wiki/Energy_returned_on_energy_invested

EROI of PV is 6.8, wind is 18, hydro 100 - all non-polluting renewable resources. The high values for coal and nuclear of course do not reflect the fact that non-renewable polluting resources are being used. Note also how the figures for oil and gas are rapidly declining as they become harder to extract; tar sands only 3. Note also that fuels are only 25-35% efficient in converting their thermal energy to mechanical energy whereas electricity is >85%.

EROI (for US) Fuel
1.3 Biodiesel
3.0 Bitumen tar sands
80.0 Coal
1.3 Ethanol corn
5.0 Ethanol sugarcane
100.0 Hydro
10.0 Natural gas 2005
50-75 Nuclear (with centrifuge enrichment)
10.0 Nuclear (with diffusion enrichment)
30.0 Oil and gas 1970
14.5 Oil and gas 2005
8.0 Oil discoveries
35.0 Oil imports 1990
18.0 Oil imports 2005
12.0 Oil imports 2007
20.0 Oil production
6.8 Photovoltaic
5.0 Shale oil
1.6 Solar collector
1.9 Solar flat plate
18.0 Wind

Embrace it or there won`t be a civilisation.