The simple facts are that solar power must have a base load back up generating sustem. And it follows that if a solar system is to work to its maximum potential then the back up system will be working at a great deal less than its own potential.

The economics of any sort of major infrastructure is primarily determined by maximising the number of productive hours it is used each year. That has always been the competetive advantage of machines over human labour and it remains the advantage of coal power over solar and wind.

Humans are generally only good for 1800 hours a year while machines operated in shifts by humans are capable of up to 8,000 hours. But it is the reduced hours of major demand for power that define the basic cost structures of power generating plant.

There is a morning peak of 3 hours, a day time base load and an evening peak of 5 hours. So a coal or gas power station is already only operating at near full capacity for about 2800 hours each year. And as there is usually a number of stations in a grid, most shut down during the day and later evening leaving one, in a rotation, to operate at full capacity.

And this is where wind and solar power actually destroy the efficiencies of base load power stations. Most sea breezes come up in the afternoon and are strongest in the early evening. And when combined with the daytime solar power, it reduces the operating time of the expensive base load generators to a point where the limited use does not cover the overheads.

Solar generators only have about 5 hours of peak output and that is only for a bit more than half the year. At about 1000 hours of useful work each year they can never compete on efficiency grounds.

It is wrong to say "solar power must have a base load back up generating sustem" if that means backup by complete 'fossil' generating plants.

With 'concentrating solar power' (CSP), mirrors concentrate sunlight to create heat and the heat may be used to raise steam and drive turbines and generators in the conventional way. Apart from the collection of solar heat, the power plant is exactly like a conventional power plant.

A nice feature of this system is that it is possible to store solar heat in melted salt or other substance so that electricity generation may continue through the night or on cloudy days. This largely eliminates the need for backup from fossil fuels.

However, because most of a CSP plant is the same as conventional power plant, it is very easy to provide something like gas as a source of heat for the relatively infrequent occasions when there is a long succession of cloudy days. Only the gas burner is needed: the rest of the generating system is already in place.

Although wind power at any one spot is variable, it is very much less variable across a wide area like Australia. By connecting wind farms via a highly-efficient 'HVDC' transmission grid, problems arising from variability largely disappear. A Europe-wide system of this kind has been proposed by Airtricity. Australia should look at it too.

5 hrs where you live? Heard Island

Gerry, the spreading of a network of wind farms does not improve the efficiency of the generating system. It only improves the reliability of supply. A dispersed system actually factors in the down time of some of the turbines into the cost structure of the whole system. And the storage of energy in salt water etc adds another cost to the system that is generally higher than the marginal cost of operating a back up system.

Increased use of solar and wind power will only impair the efficiency of our existing investments in generating capacity. And when the costs of those inefficiencies are added to the costs of solar and wind technology they simply do not stack up.

I seem to recall that one of the key principles of sustainability is the "proper pricing of natural resources" and that principle cannot simply be abused to only apply to the full costing of coal etc while leaving out the full costing of so-called alternatives.

Seditious -

How are coal and uranium sustainable? I think you are right that wind turbines and solar power will be more expensive than coal (nuclear on the other hand has costs that are difficult to estimate because nobody has ever safely disposed of nuclear waste for 10,000 years, etc). I think you are also right that there are challenges to improving efficiency with wind and/or solar as a significant part of the grid, but you seem to be making the point that since solar and wind are more expensive, they are NOT sustainable and because coal is cheap, it is sustainable.

If your idea is that the present generations simply use up the non-renewables and let future generations fend for themselves, then fair enough. That is certainly the current government's and probably the majority of Australian voter's view, but don't call it sustainable.

Secondly, where does the cost of global warming impacts come in? If there is 20% less rainfall in Australian farming areas, how many farms are no longer viable? How much less food gets produced? Who pays that cost? If the population increases and rainfall decreases, we will pay more for water. Will the coal burning, power industry chip in to pay for the extra costs of water for urban and rural users? Unlikely. If insurance premium's continue to increase due to climate change, will cheaper power offset the cost?

Certainly let's add up all the costs of producing power, but not just today's costs, also the costs in the future. Let's see if there are better ways to do things that will be truly sustainable.

Seditious is quite wrong to say "the spreading of a network of wind farms does not improve the efficiency of the generating system. It only improves the reliability of supply". Without a large-scale transmission grid, electricity sources of all kinds are much less efficient than otherwise. Why? For the simple reason that, if there is a surplus of electricity in one area it can be transmitted to places where there is a shortage. Without a grid, surplus electricity in any one place is simply wasted.

The "proper pricing of natural resources" is indeed a principle of sustainability and that includes the costs arising from releasing fossil carbon into the atmosphere. It is now abundantly clear that this cannot be allowed to continue. If coal-fired electricity generation can be achieved in a way that prevents the resulting CO2 from *ever* being released into the atmosphere and if it can be done at a cost that is competitive with concentrating solar power, then it may be used.

But before making a judgement about that, listed to a talk by the legendary venture capitalist Vinod Khosla (go to http://www.trec-uk.org.uk/resources.htm and scroll down to the bottom of the page)