Does one megawatt of coal fired electricity = one megawatt of wind powered electricty?

@ArishMell Kind of like building a huge nuclear plant and then putting in a fraction of the fuel needed.

@ArishMell

So it takes 10 times more wind turbines to create the same amount of electricity as one lump of coal?

@calicuz The problem with wind is that the wind doesn't always blow. A few weeks ago the wind farms in both Alberta and Saskatchewan had no wind to turn the turbines. Nothing mankind can do about that. However should the coal fire start to die you just throw another lump of coal on the fire.

@calicuz I don't know the figures but it might be the other way round, because even if much more powerful a coal- or oil- fired power-station is probably a lot less efficient in converting its source energy into electrical energy.

It would need 10 times as many wind as steam-turbines for a given power, if an individual machine's optimum output is only a tenth of that from the steam turbo-alternator, [i]but[/i] machine power is [i]not[/i] the same as its efficiency - and of course the wind is free.. Though as Hippyjoe says, when it blows!

@ArishMell Can you give us a definition of efficiency? If a machine has a rated capacity of say 2 MW but usually produces less than 1 through no fault of the operator said machine is extremely inefficient. If a machine has a rated capacity of 10 and reliably produces 10 on a daily basis then that machine is very efficient. Wind is extremely inefficient. The amount of energy available and the amount of energy converted into useful energy is so grossly out of proportion as to make windmills one of the most inefficient sources of power available.

@hippyjoe1955 Efficiency in engineering terms is simply the ratio of useful output energy to input energy. (Or power, but they are different though related things, of course.)

It is usually expressed as a percentage.

So if a certain generator produces 1kW of electrical power if driven by something of 5kW power - be it a wind, water or steam turbine, or an internal-combustion engine - then its efficiency is

(1 / 5) X 100 = 20%.

Most coal-fired power-stations are of little better than 30% overall efficiency, by the conversion of the coal's potential chemical energy to the alternators' electrical energy. Much of the heat energy from the coal is lost up the chimney, despite some recovery by combustion-air and boiler-water pre-heaters in the flue; while more is absorbed within the entire system by a lot of necessary, heavy, auxiliary machinery. I don't know typical wind-turbine efficiency, but those have a much more direct conversion from input to output; albeit with some power taken by the blade-control mechanism.

In both cases, you also have frictional and air-circulating energy losses inherent in any moving machine, and various electrical-energy losses within the alternator: that energy is lost by having been converted to heat of no practical value, possibly even a problem, to the purpose.

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Now, note that this is a measure of the power in / power out; not of the power alone. If the driving energy drops by a half; the output energy drops to a half, if the efficiency remains constant. I think in practice a big drop like that might reduce the efficiency too by making the losses more significant; but that is a side matter.

So the wind turbine is inherently not less [i]efficient[/i] when the wind drops a bit; it just produces less electricity because it has less wind energy available.

You are of course right that the less the wind power, the less the electrical power, produced; but that is not the same as the efficiency. We still need the base-load generators to cope with the calm days!

@ArishMell That is you definition of efficiency. It is not the only definition of efficiency by any stretch. The fact is that windmills are rather useless things prone to failure and hugely expensive to install and maintain. The CO2 emitted in building a windmill far exceeds any reduction of CO2 one might expect from using one to generate electricity. The fact is that wind will never carry the base load of a modern society. It simply can not be done.

@hippyjoe1955 I am not denying your case. I agree with it. I simply defined "efficiency" in its engineering terms; which is not the same as availability.

It does not really count for much if something is as high, let's say 80% efficient as a machine, if its driving force fails! It's like comparing a car managing 30mpg with one that will return 45mpg, for the same journey, only to find the filling-station at the end of the road has closed down.

Wind-power is mechanically and electrically efficient, but only in its optimum conditions - a steady, fairly stiff breeze - and we do still need something to carry the load when the wind drops.

Cost efficiency is a different matter, and I am not an accountant or economist. Even so, I know wind-farms are costly to build and maintain, but so is any power-station. The wind-turbine is at least comparatively simple, with parts that can be replaced easily (in their own terms), and most of the materials can be salvaged. Not so the blades though, as they usually contain a lot of synthetic-resin based materials that cannot be recovered. Ironically, those are made from petroleum derivatives, as are the protective paints, insulating materials and lubricants.

The cost is even more significant when the turbines are off-shore as many of Britain's are. (The largest are out in the North Sea). Those need huge, specially-built ships to erect them, and maintenance access can only be by boat in reasonably calm conditions. At least the winds at sea tend to be steadier and easier to forecast than over land, in the same weather system. On the other hand the British Isles tend to have their generally-lowest winds in Winter. We do have storms then, I believe some with winds too strong for the turbines to operate properly; but often between long high-pressure calms.

I agree too that simply building more "wind farms" (and covering more arable land with solar arrays) will never be enough; but governments seem not to grasp this. Campaigners certainly don't - most are well-meaning but seem not to realise how the slang meaning of "green" applies to them.