Monday, March 19, 2012

Solar Pants Almost On Fire, and the Smart Power Grid

It's not a big news item, but it's an item just the same, and one that caught my eye in particular for this one guy's quote.

Santago Arias, technical director of Torresol Energy in Spain, said "It is the first station in the world that works 24 hours a day, a solar power station that works day and night!"  He's right in the details - it is indeed the first solar power station that works 'round the clock.  But the first solar power station that could keep working beyond sunset was right here in the US: Solar Two, converted from its predecessor Solar One.

Mr. Arias is talking about the Gemasolar station, a huge (about 3/4 of a square mile of collecting area) installation that bounces sunlight from a tremendous array of flat mirrors, up to a single receiving collector on a tower in the center of the array.  Needless to say, the temperatures generated at the receiving station are tremendous.  The receiver dumps all that heat into circulating heat transfer fluid (maybe water, not sure), which in turn heats water to generate steam to operate power generating turbines.

But how does it operate during the night?

Easy.  You can't store AC electricity.  You CAN store heat.  In this case, the excess heat from the system is dumped into gigantic vats of molten salts.  The salts absorb a staggering amount of heat energy by melting from a solid to a liquid state - the change of phase in itself absorbs a lot of energy, and releases it right back again when it changes back from a liquid to a solid.  And after the sun goes down the heat collector in the middle of the mirror field is out of the loop; the transfer loop that was dumping heat into the salt vats earlier is now picking up heat from the salt vats, and conveying it to the steam turbines.  The steam turbines just keep working.  Stored heat, generated heat, it's all the same to them.  They just work.

But it's not entirely the first of its kind.  Let's talk about Solar Two.

Solar Two was Solar One for a while, but was expanded and added storage capacity and an integer to its name.  By adding storage capacity - the same molten salt scheme as Gemasolar is using - Solar Two in Barstow CA was able to keep operating as much as three hours after sundown.  The salt tanks also kept the plant operating at full capacity through periods of cloudiness, a big boon to be sure.

Now let's talk a little about why that's such a big boon.  The national electrical grid is kind of fragile.  It's designed to do one thing: deliver power from the generators to the consumers.  One thing it doesn't do is respond quickly to changes.  California has discovered just how difficult that makes things, having suffered the brunt of manufactured shortages via Enron, and discovered that the existing grid cannot easily handle added loads.  That's why it makes you such a popular customer in California if you sign up with the utility's "smart" or "responsive" grid program, which gives the utility the capacity to reduce or even turn your power off during high-usage periods.  You get a nicer rate on your bill for being willing to be in the dark for a while when the temperature spikes.

That responsive grid is part of what the issue is.  Solar and wind, they're a little sketchy.  They come and go.  The sun's output is at least predictable in that we know to the minute when the sun will come up, and we have a good idea of what the weather will be.  But wind, well.  That's even less reliable than the sun.  It might blow, it might not.  You might have years of data saying that there's an average wind speed of thus-and-such many miles per hour per day at one location, but that doesn't tell you anything about today.

The storage-enhanced solar plant is everything you could hope it would be.  It's power 'round the clock.  Where I live there's a big coal-fired plant down the road that's running 'round the clock, and a medium-small hydroelectric dam running 'round the clock.  But the coal plant contributes to acid rain, which is Bad.  The dam is continually drawing down on the lake, which for every extra foot of depth generates about an extra million dollars per week in revenue.  Losing the depth is Bad.  How then, if we could have a gigantic structure somewhere that reaped the sunlight and converted that into energy and also set some aside for use all night long?  Then we could close the dam's gates for a few hours and gain some depth.  We could leave the coal plant off for a few hours, just ticking over, ready to fire up to full power to generate a surge of power if needed.  How about we make the renewable, freely falling sunlight the steady-state power source, and have the dirty or detractive technologies on standby?

Or we have big enough solar storage that the storage is the standby, and we can close the coal plant entirely?  That would be cool.

It wouldn't even have to put all those coal plant workers out of business.  The technology on the turbine side is exactly the same, half those guys working at the coal plant could be lifted out of the coal plant, dropped into the solar plant, and know exactly what was what, and work effectively with minimal retraining, if any.

The coal miners might complain.  They could get work reconstructing all those mountaintops back to where they belong.  Then they could get jobs levelling landfills and whatnot into solar reflector fields.

Just a few thoughts.  A big solar plant like Spain's takes up almost a square mile, but what if you don't make it contiguous?  What if there's a patch of reflectors here and a few more over there and another batch on top of the new Wal-Mart?  Give up a few percentage points of efficiency, but you put the power close to where it's going to be used.

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