Economist stuff

Posted by David Roberts at 11:18 AM on 02 Aug 2007

Read more about: energy | renewable energy | wind power | electricity grid

Two short articles of interest in The Economist. One describes the nascent attempts to conceive and build a network of high-voltage DC power lines across Europe, which would enable wind and solar to play the role of baseload power. The other is about compressed-air storage. This is nifty, but confusing:

Meanwhile, General Compression, a small firm based in Attleboro, Massachusetts, is taking another approach. Its windmill compresses air directly. This has the advantage of eliminating two wasteful steps: the conversion of the mechanical power of a windmill into electricity and its subsequent reconversion into mechanical power in a compressor. But an air-compressing windmill, while fine for storing energy, cannot transmit electricity directly to the grid.

Why compress air just for the hell of it? Gar, you out there? Explain this.

For story: Economist stuff
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Monbiot

Poor guy has been walloped in most green communities, but Monbiot has been touting these DC lines for quite some time. Personally, I hate the thought of Edison ultimately triumphing over Tesla, but if the last engineering hurdles can be overcome, this gives a HUGE boost to the matter of today's awesome post by Dave (mandated renewables).

by Tod at 12:22 PM on 02 Aug 2007

Not sure I buy this as a renewable play

Pumped storage has been around for a while and plays the spark spread between on and off-peak power prices, but it's not a renewable issue. Windmills are going to run when it's windy, and will always be the lowest cost stuff to run (0 on the margin, essentially the same as hydro). This means that the wind turbines will always have a profitable home for their power - might not always be at the capital recovery target they set, but always profitable. Adding compressed air to this is therefore highly unlikely to make money for anyone other than the compressed air guy who's trying to arbitrage a price difference. And since it also inserts an efficiency penalty on the cycle, it means that proportionally less of our energy comes from wind.

When all is said and done, the compressed air piece of this looks more like PR for the CA crowd (who realized they could use wind as a way to "green up") rather than something environmentally beneficial. But perhaps others see something here that I don't?

by Sean Casten at 1:45 PM on 02 Aug 2007

promises

The General Compression homepage has a nifty animation that explains how their system works. This page explains the benefits of compressed air energy storage, and this white paper explains how the system is competitive with other sources of energy. They claim:

Dispatchable Wind is competitive with all generation sources in most wind sites of Class 4 and above. Our technology will allow us to penetrate electric grids at rates approaching 50%.

and that

the same footprint that generates a 100 MW wind farm with conventional technology is a 400 MW wind farm with General Compression technology.

Ped Shed Blog

by Laurence Aurbach at 2:21 PM on 02 Aug 2007

white paper

Here's the General Compression white paper: Making Wind Power Sustainable

Ped Shed Blog

by Laurence Aurbach at 2:23 PM on 02 Aug 2007

General Compression the only rational wind

The problems with conventional wind are enormous - wind almsot universally blows the least during peak power, which akes any installation of windmills totally pointless in a situation like ours or increasing energy demands - those wind turbines would contribute nothing and can not be counted in the power requiremnts of the grid. Turbines are also exorbitantly excessive in terms of installation costs , easily 5 to 7 times more expensive than nuclear (disregard those bogus DOE figures given- they don't measure actual power produced nor lifespan of the facilities or turbines and are totally misleading). General Compression attached the turbine's blades to air compressors, not generators, allowing it to operate at much greater wind velocities than
regular turbines, which must feather or shut down their turbines as the winds become strong (pretty stupid, huh?). Thus dispatchable (sort of)
power. And subsidies for wind turbines must require that the turbines be dispatchable. What is out there now is almost totally irrelevant - turbines produce only 33% of their claimed capacity, less than 1/2 of 1 percent of capacity.
Our demand grows as 2% per yesar and will do so for the next 20 years. Wind is a total waste of money that could be spent to make a difference elsewhere. It's a national disgrace.

by theBike45 at 3:02 PM on 02 Aug 2007

Compressors

Just to give the short version: The air is not compressed just for the hell of it. But ONLY the compressed air is used to generate electricity. In other words the way we normally think of storage is that the if the wind generator happens to produce electricity when it is needed, it is fed directly to the grid, if it produces electricity at a time of lower demand then we use storage.

In this case the wind generators NEVER directly produce electricity. They always transmit mechanical energy to transmit directly to the the compressor, and the compressors then produce electricity as needed.

I would worry about thermodynamic losses from compression (about 60% of the power from the the blades) and also additional capital cost from mechanical transmission down the towers. But maybe being able to run the generators on the ground makes up for this. I'll have to read the white papers.

by Gar Lipow at 3:18 PM on 02 Aug 2007

Re:Compressors

Oh I see. The are on top of the tower, so you are using compressed air as the transmission means from storage to tank,

Really interesting.

by Gar Lipow at 3:21 PM on 02 Aug 2007
[ Parent ]

To reiterate

So you are saying that there's a compressor ontop of the wind turbine, and that the wind is being used to drive a mechanical process?

i.e. There's no generator involved inbetween the Wind and the Compression process?

For instance
Wind -> Compression -> Decompression -> Turbine -> Electricity

Is that whats going on?

-David Ahlport

by GreyFlcn at 3:28 PM on 02 Aug 2007
[ Parent ]

Re:Compressors

OK - figured it out. If you compress air and then use that compressed to generator electricity, without adding back heat, you get back about 40% of the mechanical energy you put in the form of electricity. Done this way, you would more than double the number of wind turbines needed to make a kWh. What they are doing is using the usual CAES trick of getting heat from somewhere else - natural gas or waste head. Doing that you get most of the energy you put into compressing the air back - but of course you are also inputting additional energy in the form of heat. You are doing somewhat better thermodynamically. Counting both heat and mechanical energy used for compression you can get back 50% or 60% of what you put in. And most of the input energy will have come from wind. So basically you are cutting emissions from natural gas plants at least in half, and maybe by two thirds.

What is being studied in Europe is storing the waste heat from compressing air, and the using it when decompressing it to run a power plant. At that point you will be able to get 60% to 70% of the energy put put in back. That has not been demonstrated yet. There are commercial products out there for storing electricity via compressed air, but they accept the 60% loss, and make up for some of it using the "waste cold" created when the air decompresses for cooling or desalinization purposes. Given that you have a process where 60% of your energy ends up either as waste heat or waste cold, it would be interesting to see if someone could come up with a combined heat and power system using both.

by Gar Lipow at 3:31 PM on 02 Aug 2007
[ Parent ]

To reiterate:

>So you are saying that there's a compressor ontop of the wind turbine, and that the wind is being used to drive a mechanical process?

>i.e. There's no generator involved inbetween the Wind and the Compression process?

>For instance
Wind -> Compression -> Decompression -> Turbine -> Electricity

>Is that whats going on?

Yep. And with some major thermodynamic losses.

by Gar Lipow at 3:32 PM on 02 Aug 2007

But considering

But considering wind is roughly a third the cost of modern coal, even if it did cost double, wouldn't that still be worth it?

-David Ahlport

by GreyFlcn at 3:35 PM on 02 Aug 2007
[ Parent ]

Never mind

Third the cost
But the wind only blows about a third the time.

-David Ahlport

by GreyFlcn at 3:36 PM on 02 Aug 2007
[ Parent ]

Wind Cost

OK a different issue. The usual cost given for wind is between 4 cents and 6 cents per kWh. That already takes into consideration the roughly one third use of capacity factor. If it used 60% of capacity factor that would be 2 cents to 3 cents per kWh; 70% (as coal does) 1.7 to 2.6 cents per kWh.

And no, I'm not at all sure that a 60% reduction in the portion of power that is coming from the wind is worth what they are doing. But it looks like most of their capital cost is in the natural gas generators turbines they would have to use anyway. In other worlds you are increasing the capital cost of a natural gas peaker power plant in order to save between half and 2/3rds of the fuel. In a natural gas peaker power plant, natural gas has to be at least half the total cost, cause natural gas is not cheap anymore. So if even doubling your capital cost probably pays for itself; tripling it may pay for itself depending on how close to the high end of savings you get, and how expensive natural gas gets.

by Gar Lipow at 4:36 PM on 02 Aug 2007

Use the compressed air to run air cars

Compressed air can be used to run cars directly.

A prototype car - the Air Car - has already been built and mass production is about to begin.

Imagine petrol stations being converted to air stations. In many places high pressure pipes from nearby hills fitted with windmills could enable compressed air to be generated locally.

I have no idea how much compressed energy a high pressure tanker could carry, but it would great if the tankers could both carry the air and simultaneously run their engines with it.

There is a bunch more info here.

And finally, I'd like to note that whereas wind power might not be available close to many major cities, wave power is. And this company will soon be producing submerged wave energy harvesters that pump compressed water ashore. If water pressure is used to compress air, then a large number of coastal cities could use compressed air for vehicles and for many other purposes.

by picoallen at 5:18 PM on 02 Aug 2007

oops

Water, of course, cannot be compressed. The Ceto wave energy device pumps pressurised water ashore, not compressed water. So water pressure would be used to compress air, which would then be used to run cars, buses or trains.

by picoallen at 6:43 PM on 02 Aug 2007
[ Parent ]

Except that

Using the compressed air at the source of the wind turbine, which may or may not be on land, would be a logistical nightmare.

-David Ahlport

by GreyFlcn at 6:59 PM on 02 Aug 2007
[ Parent ]

Besides which

If you went
Electricity -> Compression -> Car -> Engine.
The system efficiency is only about 45%

Electricity can get roughly double that.

-David Ahlport

by GreyFlcn at 7:01 PM on 02 Aug 2007
[ Parent ]

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