Efficient Solar Power Using Stirling Engines

tscola writes "The EE Times is reporting that the U.S. Energy department believes it can make solar collectors that generate electricity at efficiency levels that rival other methods. Instead of using photovoltaics, they want to use Stirling engines to convert the heat of the sun into electricity."

Comments

Why so big scale?

[BigZaphod]

In the article they mention that with 6 dishes they could power about 40 homes. Why so big scale? Couldn't the size and stuff be scaled down a bit, mass produced, and then homes could have their own sundish or a sundish shared in small community groups? Like shared water wells and such. That'd eliminate the middle man.

One of the issues they have is startup energy

[foniksonik]

From the article:

"Since each dish draws about 10 amps from the power grid for a few milliseconds when it starts up in the morning, startup must be staggered if a large dish farm is to avoid causing a blackout."

Question:

Why not add a fuel cell or battery to each dish that would be charged as needed during operation for use as a starter?

This would enable each dish to start up under it's own power without affecting the grid at all... and for a very small price in terms of daily output.

Any reason why not?

Re:where's the...

[Anonymous Coward]

I read somewhere ( sorry, best I can do citation wise ) that hydrogen is more valuable for other uses, like upgrading existing petroleum stocks for it to be economical to waste hydrogen by burning it as fuel. Also, it seems hydrogen, being the smallest atom, leaks like a bastard, and requires super high pressure tankage to store. Gasoline requires only a thin walled tank, and does not need to be stored under pressure, making it a better, safer fuel. Why carry 500 lbs of hydrogen tanks in your trunk when a 20 lb tank can hold 10 gallons of gasoline? Why mess with high pressure fittings when a liquid fuel allows for a relatively forgiving station pump? Mythbusters even busted the myth that cell phones can cause gasoline fumes to ignite. Wouldn't we be better off using the hydrogen to make gasoline out of say tar, than trying to burn it directly?

Land prices always kill this...

[human bean]

The problem with solar power conversion has always been the high Total Cost of Ownership. You have to figure the cost of the real estate these items sit on, versus what other purposes the land could be used for.

In the case of other power technologies, the land use is relatively concentrated. Mines, transport routes, powerplants, refineries, etc. don't take up nearly as much space. In a number of cases the land surface can be used for dual purposes, as in ranging cattle on scrub land sitting on top of an oil patch, or growing crops on reclaim land.

There is cheap land available for this, but it's often located some distance from the use points, and energy doesn't store well and transport is expensive. Figure in the TCO of building that intertie to your solar farm in the middle of nowhere, and the pickings start looking a lot smaller.

Grid transients in general are an issue

[Engineer-Poet]

Even if you managed the system such that one dish started off the grid and further dishes started off the ones already running (exponential progression), you'd still have an issue with the grid balance. Typical grid demand fluctuates by a few megawatts on the time-scale of seconds; if you fired up a 100 MW dish farm over 5 seconds you'd have generation increasing by 20 MW/second for some time. Unless you also had demand, reactive power, transformer taps etc. scheduled in synchrony with this, it would make a lot more sense to leave dishes pointed off-sun until you could guarantee demand and had down-regulation capacity ready to handle any excess. It might make more sense to fire up big farms over 15 minutes or more (unless you can start generating with the weak morning sunlight and eliminate transient issues by following the curve of incoming sunlight).

Misleading - Coal isn't "cheap"

[Red Rocket]

While it would be nice to get away from coal, there are two things stopping this. First, coal is cheap. Second, in recent years they have done a pretty solid job at cleaning up the health risks associated with coal.

First, coal is not cheap. The price is low because the mining and electricity corporations export every cost they can get away with onto the public at large. Mountaintop removal/valley fill mining practices illegally destroy thousands of acres of Appalachian hardwood forests and hundreds of miles of streams. Electricity generation plants dump millions of tons of CO2 into the atmosphere altering its composition with unpredictable consequences, create acid fog and rain that destroy forests, lakes, and streams, and dump hundreds of pounds of mercury into the environment where it ends up damaging our brains. If mining and generating corporations were forced to be good citizens and not force us to surreptitiously pay for their products' hidden costs then other energy sources would be economically competitive. Instead, they prefer to stuff pennies into the fuse boxes of capitalism and bitchslap any more responsible initiatives with their ill-gotten capital.
Second, BWAH HAH HAH HAH. That would be hilarious about the "pretty solid job at cleaning up the health risks" if it weren't so tragic what is happening. Granted, they are better than they used to be, but those gains come from laws passed in the '70s and '80s which are being rolled back now. (See the "Clear Skies Initiative")

Re:Flywheels instead of hydrogen cells?

[bluGill]

You ever try to mount a flywheel? Some of the old mainframe disk drives needed a special foundation because if left loose they would move in relation to the earths rotation. Enough energy in flywheels to run the US overnight? I think you would push the earth off orbit if you tried it.

I'm not sure if this is funny or insightful. Anyone care to do the physics?

Something that I have mentioned before...

[cr0sh]

Stirling engines do not "run on heat", rather, they take their energy from "heat differentials" - as long as there is a difference in temperature, a Stirling engine will run (in theory, at least - I have never seen a Stirling engine run on say, liquid hydrogen on the "cold" plate, and liquid nitrogen on the "hot" plate - but in theory it would work). This leads to interesting design possibilities, much more so than other conventional heat engines.

One such design, which some of you here are familiar with, is known as an "OTEC" - or "Ocean Thermal Energy Conversion". Pushed greatly by the book "The Millenium Project" - OTECs are devices, sitting on ocean-based platforms, which use the thermal gradients in the ocean at different depths to drive a Stirling-type engine which runs a generator to generate electricity (for a variety of uses in the book). These are actual devices, which have been built and tested (I am not sure if they are in real production or not). This is a very interesting use of stored (in the ocean) solar energy - the amount of energy taken out by OTECs would be miniscule, and would very likely not cause harm to flora and fauna (the ocean is HUGE).

On a similar note, I have, in the past, proposed here on Slashdot the idea of a "reverse OTEC" - which I proposed for be called a DTEC/GTEC/TTEC, for "Desert Thermal Energy Conversion" (or, alternatively, "Ground"/"Terra"). The idea being that we use the energy differential that exists between a few inches under the soil (hot side), and several feet down (cold side). Alternatively, we could bury the "hot" side of the collector in the concrete/asphault that makes up our roadways and parking lots (as well as place them on roofs). We could then gain heat from the sun, increasing the temperature differential (in the winter, when the ground is frozen in some areas - or at night, when surface temperatures drop, these engines would still work - the temperature gradient is still there, just smaller (or inverted in the winter) and not as large).

Using Sterling engine technology in this way helps to offset the "land use" argument - your land actually becomes more valuable, because not only does it provide parking or roads, but energy as well! The tradeoff being that road/parking lot construction and repair would become waaay more complicated, and probably more expensive. These issues would need to be studied. It could very well be that the economics don't work out for this and other reasons. Perhaps the issue then is to design better roadways and parking lots that don't fall apart in a few years, and instead last for a very long time (so you don't have to repair them as often).

I think such a design for Stirling engine use, coupled with more traditional solar heat panels (to drive the Stirlings as well), where they can be used (perhaps putting the panels on the rooftops would be better?) could easily help supplement the energy usage needs of many large urban sites, like malls and office complexes, as well as possibly neighborhoods.

Still no RTFA?

[IBitOBear]

(I see your bullshit and raise you unnecessary use of attitude.)

They discus the economies of scale (somewhat) by talking first about the "daytime only" nature of the power, and by _coincidence_ the fact that daytime is peak power demand time, where near-term provision will do a lot of good.

The blockquoted text is part of an "not addressed at this time" conjecture. Just liek the part where they talk about a "100 square mile generation system" not as if they are proposing one be built, but as if they were trying to convey the issues of scale and return.

At least it was clear to me when I read the article, and appreciated the "dumbed down explinations" presented, that they were trying to get effecient solar power working instead of wrapping themselves around the *POINTLESS* axle of "what about at night?".

As for the pumping water up a hill (e.g. the "gravity battery" of potential energy) I think you over-estimate the effecency of hydro-power rather a bit as well. Granted the elements are well understood, but I don't think you get the whole "pump head" issue of volume vs lift vs return potential very clearly, otherwise you would not imagine for a moment that the driect mechanical output of the systems in question were "well suted" to running the kinds of pumps you'd need, just because the striling enginges turn and so do pumps.

(_Directly_ using the mechanical energy of the small Stirling Engines to move "enough" water high "enough" to be useful in filling a resivour big "enough" to turn meaningfully sized turbans or water wheels to generate "enough" nightime electricity is a laughable debacle _before_ you consider laminar flow resistance (rising and falling), evaporation loss, pump maintenance (clogging), seeapage loss, providing source water in the first place, simple acreage or water-tower shadows, and so forth.)

The fact remains that cutting N% off our fossil fuel and polution problems is pretty much a win of N%. If we could replace 50% of the runtime on the nations fill-in generators, that would be *huge*. _TEN_ percent would be huge too.

The article and the investigators are trying to solve *their* part, what are you trying to solve by bitching about their off-hand mention of hydrogen?

The fact remains that the "energy storage" problem remians no matter what the generation system. "Batteries" for electric cars, holding solar, wind, or tidal power for return when those are not at peak. That sort of thing will remain no matter what.

The "don't bother with solar until you solve the nightime issues" frame of mind is defeatest as hell and so not terribly useful.

I suspect, were I to have to prognosticate, that we will need to revive nuclear power. Invent better batteries/fuel cells, look into _sonic_ (as opposed to electical) separation of water into hydrogen and oxygen [very promising but not often mentioned], and biomass-fuels, and all sorts of things to "solve" the current problems.

Meanwhile, if we could learn to turn off the freaking lights when we leave the room (guilty here more often than I'd like 8-) and learn to wear a sweater instead of heating the house to 75F (which I *am* good about 8-), and all sorts of simple stuff things will be "Better."

And better is... better.

Or just don't send that power out all at once

[IBitOBear]

The "steadly increasing" 20MW/second isn't that problematical if you don't put it on the grid right then but instead wait till it was needed, or use it to charge a (whatever) storage battery to span lulls and, I don't know make the hydrogen for the on-site matenence vehicles or something.

There is a complete non-issue about how to cut in this power source (compared to any other kind of generator).

How not to "waste" the power generated when you aren't cut in is a "what to do with the gravy" kind of issue for the most part.

Since they have to get up to the (230,000-volt was it?) levels to get menaingfully onto the grid in the first place I suspect that a giant bank of capacitors and a fast switching doodad are pretty much mandatory. The plant's start-up cascade should be private anyway as they could go "on-sun" exponentially before they cut in.

Of course, the larger problems of the power grid are larger problems. Especially with deregulation and "known bad places" as per the recent blackout. So wer are borrowing problems here anyway.

Re:Close, but not there yet

[budgenator]

Snow never really bothered my satelite tv dish, any snow just fell off it. Basicaly the dish points at a point the sun will cross, even got "sunfade" twice a year as the sun passed into the dish-satelite axis. As far as lubricating the engine, there are synthetic oils that will do it pretty easily especialy the dibasic class of ester based oils