"IN the early hours of Saturday morning, two weeks ago, Denmark achieved something that makes John Howard's goals for lifting the use of renewable energy in Australia look pretty modest.

"At 12.17am, as steady winds swept in from the North Sea and most Danes were in their beds, the nation's wind farms churned out 70 per cent of the electricity being consumed across the country."

That's how The Australian's European correspondent Peter Wilson began a glowing piece on wind energy last week.

Where do I sign? Hallelujah! The world is saved. Just roll out the turbines. A future of clean, green, carbon-free electricity beckons.

Well, actually no. Wilson didn't manage to get around to detailing how barely 48 hours later, those wind farms were supplying all of 2 per cent of the electricity being consumed across Denmark.

From a bracing 2300MWh/h or so -- the output of two largish conventional power plants -- to less than 100 MWh/h, barely enough to keep the night lights burning. When the wind don't blow, the power don't flow.

So when that happened, where did the electricity come from? From Norway, from Sweden and from Germany.

All up, around 1500MWh/h for some hours. In effect, the three neighbours jointly running a very large conventional power station just to keep the lights on in Denmark.

There, in a nutshell, is the twin problem with wind. On average, across a year, you might get 30 per cent of its theoretical capacity, but often you get zero or so close to zero as not to matter. It happens frequently and at any time; and when the wind chooses, not you.

"Somebody", therefore, has to keep unused surplus capacity in some other form of generation equivalent to all the wind generation capacity. And keep it either operating, or able to at the flick of a switch.

Now, no, I didn't have those figures fed to me by the "competing power industries like coal and nuclear power", as Wilson's piece asserted, attacking an earlier critique I had written on wind power.

I have spoken to no one from the coal or nuclear industry, or indeed any other lobbyist, or indeed had any communication, before writing.

In contrast, Wilson quoted no fewer than four spinmeisters for wind and the huge taxpayer and consumer dollars that flow so evenly and strongly to the industry around the world, unlike the electricity flowing from it.

They were Anders Dalegaard, a project manager at the Danish Wind Industry Association; Isabelle Valentiny, communications director of the European Wind Energy Association; Stefan Gsaenger, secretary general of the World Wind Energy Association; and "(wind) industry association spokesman" Peter Rae.

Surprisingly, all of them thought wind was the absolute bee's knees.

Analyse the data on the Danish power network's website -- energinet.dk -- and you should be able to see clearly the two problems with wind power. The first is its low capacity factor.

As I had earlier noted, Germany's biggest power grid operator, E.ON Netz, over the year got an average of just 18 per cent of the rated capacity of its wind network.

This produced an interesting response from one of the windmeisters: the German windmills weren't in the right places. In contrast, other networks were over 30 per cent, with Denmark claiming 45 per cent for its offshore turbines.

The much bigger problem, which the wind-meisters neatly sidestepped, is that at times you get almost zero power out of the entire network.

As noted, 2500MWh/h one minute, less than 100MWh/h two days later. Another example, less than 10MWh/h -- effectively zero -- across all of Denmark for four hours straight. Back in February, less than 100MWh/h for 36 hours straight. If you were relying on wind, a day and a half with no power.

The obvious point about this is that power has to come from somewhere else to make up the difference. The less obvious but far more crucial point is that you need permanent surplus power-generating capacity somewhere for the full wind capacity. In your own grid or one to which you are hooked up.

So if, say, in Australia we opted for the next 10,000MWh/h from wind, we wouldn't just have to build 7000MWh/h of coal or nuclear or gas to "cover" for the 70 per cent on average that wind doesn't provide relative to its sticker capacity.

We would have to build the full 10,000 MWh/h of conventional power generation anyway, for when the wind doesn't blow at all! You can't rely on the wind blowing "somewhere"' to cover for the wind not blowing somewhere else.

Alternative gas power could be turned on when needed, but if you went for coal and nuclear they would essentially have to be ticking over all the time anyway. You can't just fire up the boilers the moment the wind stops blowing. Now, obviously, some games could be played at the margin. We mightn't need the full 10,000 MWh/h of conventional, we could probably get by with, say, 7000MWh/h -- another three Loy Yangs. We'd still essentially be getting one power station for the price of at least two.

Denmark has the biggest wind component in its power generation in the world. The reason it sort of works in Denmark, price aside, but can work only in Denmark, is that the country is small and connected to Norway, Sweden and Germany.

Indeed, Denmark's wind works rather well joined to Norway's hydro, because the hydro can be turned on and off.

But if the wind don't blow, it's still drawing power from Sweden's hydro and nuclear and Germany's coal and nuclear.

The key point is that extra power Denmark might need at points in time could be huge in its own terms -- 40 or even 50 per cent of total consumption.

But it will be tiny when spread around Norway, Sweden and Germany. They can accommodate a small neighbour hooked on wind. But there's no way they could accommodate a Germany with the same wind intensity. Without someone building surplus conventional power stations.

Indeed, when the wind doesn't blow in Germany -- which now gets high single digits of its total power from wind -- it goes to nuclear France.

And none of this touches on the grid challenges from having 2000MWh/h suddenly dropping to, say, 10MWh/h.

Nor does it explain how it would "work" in Australia. Yes, you can connect all the state grids; but if you had a huge investment in wind in, say, Victoria, you would still need equivalent coal/nuclear/gas somewhere -- as essentially idle surplus capacity.

Unless you were prepared to literally turn off the lights, and everything else, when the wind didn't blow.

Yes, Denmark's wind story has a huge lesson for Australia. That there is no way wind can make a sensible major contribution to mainstream power generation in Australia.

Or even to the very objective it is purportedly directed at, greenhouse gas abatement. It is just an expensive, feel-good vanity.