Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Man, very cool set of data.

And yes, the devil is in the demand variation. I've been looking around dimensioning for replacing everything by nuclear power plants since your previous diary and the problem is just absolutely maddening (in my case, it's made worse by the fact that I'm trying to replace everything, not just change the existing electrical power plants, so current models of electricity demand are not applicable).

As electricity cannot be stored, the power generation capacity must be dimensioned as a function of peak demand. And the peak to mean ratio is huge.

Just for a rule of thumb for a substitution on existing capacity: according to EIA, in 2004, total annual net production was 3,971,000 GWh for a total generating capacity of 1,050 GW. If all power plants had been running at full capacity all year round with no maintenance stops, the total annual production in 2004 would have been around 1,050 GW x 1 yr = 9,198,000 GWh. So the peak to mean production ratio is 9,198,000 / 3,971,000 = 2.31. This ratio is not directly applicable down to the last decimal : power plant availability is different (and really bad for windmills), seasonal effects are different (thermal power plants are less efficient in hot weather), etc, etc.

But still, 2.31 ... ouch! And for a large share of production capacity in windmills with little backup from gas or coal plants, the ratio is likely to be much worse. 3? 4? May be more?

Also, the pumping stations are OK are intraday smoothing but not so OK for seasonal smoothing. Let's say we want to store 20 GW of capacity during 6 months to deliver 20 GW during the other 6 months. 20 GW seems like a lot but by the scale of the total energy demand of the Great Lakes region - where your example is located - it is actually not that much. You need to store:
  • 20 x 10^9 W x 365/2 x 24 x 3,600 s = 315.36 x 10^15 J

Assuming 2 reservoirs with a 100 m difference and assuming 100% energy restitution (I'm being very nice there) and assuming density of water is 1,000 kg/m^3. Between winter and summer, the quantity of water you need to pump up-hill is:
  • 315.36 x 10^15 J / (9.81 m/s^2 x 100 m) = 321.46 10^12 kg ~ 321.46 10^9 m^3 of water = 321.46 km^3

Let's say Lake Michigan is the lower reservoir (57,800 km^2). Just pumping this water means moving the level of Lake Michigan between summer and winter by:
  • 321.46 km^3 / 57,800 km^2 = 0.00556 km = 5.56 m = 18.2 ft...

I don't know how much the level of Lake Michigan naturally moves between seasons but some lake-shore neighbors may be a tiny bit upset.

So, not even considering actual geographic opportunities, pumping stations don't seem a good option for seasonal smoothing beyond anything but the most marginal contribution.

I'd rather look into [yes] hydrogen, with water electrolysis for production, underground geological storage of the produced hydrogen and the usual combination of combined-cycle and simple-cycle gas turbine power plants which would burn the hydrogen instead of the usual natural gas. The CCGT plants for the bulk of the production can achieve 55% efficiency, may be 60%. Simple-cycle plants (just a gas turbine, no steam turbine) only reach 40% efficiency but are only used for the maximum peaks, once in a blue moon and are really cheap. So factoring electrolysis inefficiencies, storage losses, etc, I'd guess you can get close to 50% restitution.

The economics are probably fairly lousy (you need a lot of electrolysis cells and CCGT plants aren't that cheap) but if, as for a wind-mill, your off-peak hours electricity is virtually free, it may make sense... Upside, now, if you route most of your production through this cycle, it is this part of the electricity production you need to dimension for peak hours, not the windmills, and every hours of wind are actually used. Other upside, the pure oxygen from electrolysis has plenty of nifty usages so this side of the process is not a complete loss either.

I have another objection regarding intraday variations (of electricity demand and wind) but it's really late for me (and I need to sleep) and anyway I'm not sure it's completely relevant if you assume a large intraday storage capacity either pumping stations or my aforementioned hydrogen cycle.
by Francois in Paris on Wed Mar 8th, 2006 at 09:13:19 PM EST
[ Parent ]
I'm thinking that pumped storage might be more useful on the spot market, the very limited market where you can get 100 times the normal price for electrcity.  Stored hydro would have to be principally for this spot market during summer months.  

And I think that pumping from Lake Michigan would have to be limited.  Lake Superior has almost 3 times the volume of Lake Michigan (12,100 km2 for Superior compared to 4,920 km2 for Lake Michigan.) As well, I think that there's a lot of hydropower potential in Ontario and Quebec.

As for hydrogen, I think that it's only a matter of time until it becomes cost competitve. And for geological areas suitable for large scale storage, how about a giant, abandoned salt mine beneath the city of Detroit.  With Detroit being the center of the American auto industry, the implication of having a huge hydrogen supply in close proximity to the vast majority of US auto construction should be obvious.

And I'll give my consent to any government that does not deny a man a living wage-Billy Bragg

by ManfromMiddletown (manfrommiddletown at lycos dot com) on Wed Mar 8th, 2006 at 10:25:38 PM EST
[ Parent ]
I'm afraid this one is no longer fully abandoned but, yes, salt structures are nice for gas storage: very low looses, low cushion, high throughput.
by Francois in Paris on Thu Mar 9th, 2006 at 03:56:04 PM EST
[ Parent ]
for a large share of production capacity in windmills with little backup from gas or coal plants, the ratio is likely to be much worse. 3? 4? May be more?

Around 4 is about right. A month or two ago I showed a calculation that about an eighth of the 21% of the US land area suitable for wind power development 80 m above ground would be needed with this capacity factor. (More if long-distance transmission is to be used heavily for balancing.)

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Mar 9th, 2006 at 07:13:19 AM EST
[ Parent ]


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