Re: OT: GO SOLAR ! Was: go nuclear. Was: Detecting ETI via CO2
- From: "Rob Dekker" <rob@xxxxxxxxxxx>
- Date: Tue, 26 Jul 2005 09:36:35 GMT
Matt,
Sorry I got a little busy the past few days.
But here are some notes that might clear up some differences.
I'll address the following issues below :
- Solar thermal power plants run at 19%+ efficiency (proven).
- Power distribution over long distances is not a problem at the moment,
and will (have to) be solved in the future any way
"Matt Giwer" <jull43@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:I9EEe.23507$mC.2520@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Rob Dekker wrote:
[...]
> > Let me instead focus on solar-thermal, because you ran the numbers for
that,
> > and I ran the numbers for it, and we came to totally different
conclusions.
> > So lets find out if we have the same numbers. That should be easy.
>
> There are two requirements, no magic and nothing else changes. That is no
massive refitting of
> everything to make use of DC and no superconductors, perfect batteries,
nothing get 100% efficiency
> and things like that. It is our world today with a different source.
>
Fair enough.
[...]
> > For solar power : At 100% efficiency, 250 GW at 1000 W / m^2 requires
250
> > Mm^2 which is an area of about 10x10 miles.
>
> Thermal efficiency must always be considered. I started without other
generating losses and assumed
> 30% efficiency solar cells which was a bit of magic in itself but appears
to be achievable.
So you considered PV cells as the choice for solar-power ?
I did not even consider that at this point.
PV cells might be good for local, personal use, and can even supply
electricity for homes in a isolated places, but as replacement for
major electrical production plants they are (still) rather useless.
Two main disadvantages of PV cells over any other energy source :
(1) They are WAY too expensive (about 5 times more expensive than any
other energy source, including wind energy or nuclear)
(2) Storage (for cloudy moments or night-time operation) would need to be
done with batteries, which are again exceptionally expensive (per kWh).
Point (1) might be solved at some point, with amorf silicon devices, but
point 2 still is not a feasible solution at GW level power production.
We would need some very serious technological break-throughs for PV cells
and battery technology to become a competitor for large-scale electric
production.
And that violate your first paradigm ("no magic and nothing new").
So that's that.
[...]
> > That's nothing, especially since solar-power is best harvested in the
> > deserts (where nothing lives and grows any way, and land is cheap).
>
> But where transmission lines are long and transmission losses are 50% or
so at current distances.
> And the efficiency of converting to HV AC is also a factor. Transmission
from the desert to New York
> might be 5% efficient if that good. I doubt anyone would seriously
consider power transmission over
> 2500 miles.
Yes. Transmission losses are a concern, and probably the only real problem
for wide-scale use of solar-thermal. I admit that. But, for the short-term,
when we do not yet have to replace 100% of electric production, that is not
a problem. We can start in the South-West. Plenty of people (15% of US
population now lives in California), and plenty of remote desert-like area,
and plenty of sunshine. Also Florida has a lot of space and a lot of
people. There, we would need to brace the power plant mirrors for the now
all-so-common hurricanes that rush through.
Longer term, we probably need to solve long distance transmission any way.
No matter which replacement energy source we choose : Wind is best harvested
on the plains of the central US, solar in the SW deserts, and nuclear
requires hard negotiations with locals with every new plant.
For the 250 nuclear plants that we need (remember the 250 GW we are shooting
for), choosing sites for them is going to be a political battle for each one
of these. Nobody wants a nuclear plant in the city, nor their county, and
possibly there are states that want to stay nuclear-free.
Call it Jane Fonda politics, or call it caution, or call it common sense. It
does not matter what the origin is, but it is going to be hard to find
locations for the 250 plants. So they are likely to end up in remote places
(remember the French plants are as far away from Paris as possible ?).
So, we might need to solve the long-distance power transmission problem even
for nuclear power. The key there is increasing voltage. Power grids across
the US and the world have been increasing voltage on their long distance
lines ever since power grids were invented. I think the main standard
voltage is now 500kV. That allows power-transmission with managable losses
up till 500 miles or so. It is likely that the voltage will go up in the
future. Either with new grids which span more and more states, or for
expanding existing grids.
A bit of educated-prediction thinking : It is not unlikely that a
nation-wide 5MV or so power grid will be built in the next 30 years. That
would solve a lot of the energy transmission/distribution problems, and make
it much easier to plan plant locations. Solar plants in Arizona, Nevada and
California could provide power for evening in New York. Wind farms on the
plains provide power to Florida, and Florida nuclear plants provide power to
Vegas on cloudy days. Washington state hydro power plants fill in the gaps.
It's possible. And cost-effective too. It makes economic sense, and since I
trust the American free-market spirit, I'm certain it will become reality in
the future.
Once again, this is not the immediate problem, because we are still 95%+ on
fossil fuel, and it will take a while before that is changing.
> In any event getting it just to California will be at least a 50% loss.
Duh ? We have a lot of desert and open space here in the Golden State, thank
you.
[...]
> > For peak-power :
> > - At 35degrees lattitude (US deserts), the sun is 80 % efficiency on
flat
> > land.
>
> reducing to 50% on Dec 26 when the sun is 23.5 deg further south.
Yes. But note that this does NOT mean that we need more mirrors. Only that
they are spaced a bit further out. So it only costs some more (desert) land.
>
> > - Collecting / concentrating solar, into a high-temp liquid, to
ultra-heated
> > steam : 80 % efficient or so (mostly due to imperfect mirrors and
thermal
> > loss).
> > - Rankine turbine generator efficiency to electricity : 30 %
>
> > Overall peak-power efficiency : about 19 %
> > That is in line with the 25% peak-power effciency of a fossil-fuel
plant,
> > and way better than the 5 % efficiency of solar-electric cells.
>
> The problem will be getting temperatures as high as those used in
fossil-fuel plants. If not the
> efficiency decreases. If I am not mistaken you are talking at least 600
deg C and maybe 800. That is
> not easily achievable as what is heated with mirrors is also a radiator.
So here we are talking
> heating efficiencies which because of radiation are not 100%. The higher
the temperature the less
> efficient due to greater re-radiation. You cannot be talking about a
generator at the collection point.
>
> There is also a problem with what to heat that will absorb heat with high
efficiency. Make it the
> blackest of black you can find and see if it will stay that way for a few
years. 90% absorbing is
> about it. Plain carbon is shiny, lamp black is blacker but it has to be
particulate to be that
> black. But say there is something 90% efficient at aborbing lit with 90%
efficient mirrors meaning
> the process starts with 81% efficient before considering re-radiation of
what is being heated. I
> can't see starting with this part being 80% efficient.
>
> I do not think you have set yourself a simple engineering problem
No, but a lot of work has been done on this already.
Get informed :
The best overview of solar-thermal power is this paper :
http://www.energylan.sandia.gov/sunlab/PDFs/solar_tower.pdf
It's a bit old (about 6 years or so), based on the Solar I / II experimental
plants, so the efficiencies and other numbers will be better by now.
It gives the range of temperature of concentrated solar power : 500-600 C
It takes in detail about thermal heat storage (with liquid salt),
and has a full efficiency analysis : 17-20% solar to electric energy
efficiencies
maintenance costs, and a wealth of other information about solar thermal
energy.
Brief story heat storage using liquid salt (details in the pdf doc above) :
http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm
Here is a great overview of some projects around the world :
http://www.solarpaces.org/TASK_I_1.HTM
(My only problem with this site is that it does not mention commercial
plants)
FYI : Small solar thermal power plants for local (farm) usage :
http://people.linux-gull.ch/rossen/solar/renderings.html
>
> In addition you have to transport megawatts (3MW + thermal losses of heat
per MW of electricity) of
> this heat to a decent sized turbine/generator so there can be efficiencies
of scale in their size.
> But heat is lost with transmission. I have never heard of long distance
transmission of superheated
> steam. This is another major engineering problem. If doable the
maintenance costs will be high.
You would never send super-heated steam through long-distance pipes, you
dumb-ass.
I thought you were smarter than that.
You generate the steam next to the turbine just like fossil fuel plants do.
Transmission/distribution is done via the high-voltage power-grid.
>
> While I can see maintaining such lines inside a power plant I would not
like to take up the project
> of maintaining them in the open desert.
You are loosing it. There is nothing special for maintenance in the desert,
other than that it is dry, hot, and there are dust storms. Ever been to
Vegas ? Hot, dry and there are dust storms sometimes. Cleaning mirrors is in
Vegas is not different than cleaning mirrors on a solar power plant.
Actually, cleaning solar-thermal plant mirrors can easily be done robotic.
>
> It is also going to be interesting to get the millions of gallons of fresh
water per day to the
> desert and see the ecological effects of releasing it as steam. We move
large quantities of water by
> gravity like the Romans. I don't know where it is going to come from.
Again : ever been to Vegas ? Or Los Angeles ? Or the California Central
Valley ? Water goes where people want it to go.
The California Central Valley used to be savanna. Humans transformed it.
There is enough water, and certainly for cooling (which does not actually
'use' much water. It just heats it up and puts it back where it came from).
But you are right : cooling water for solar plants could be in short suppy
in real desert areas.
Continued R&D should help in finding innovative cooling solutions. Maybe use
air cooling (maybe using the massive mirror surfaces that are already in
place) or more efficient cooling using same amounts of water.
>
> > So we would only need 1/.2 = 5 times the collecting area.
> > That's thus now 22x22 miles.
>
> > Of course, can't always run peak power with solar.
> > Two more important factors come to mind :
> > - Sun does not always shine (cloudy days). 70% efficient.
> > - Sun shines only between 10 and 14 hours/day, and also rises and sets.
25 %
> > efficient.
> > That's again another 17% efficiency.
>
> For the shining part of the day is 70.7%, the RMS for a sine wave.And you
have to design for winter
> peak power needs which are now heating when these 35 deg latitude desarts
are 58.5 deg away from the
> sun or cosine 58.5 which means it goes from 80% to 50% in the winter.
Since today we don't have much
> electric home heating the peak power demand may become higher than it is
today.
Actually peak demand in the US is highest in the summer, for AC cooling. So
we probably don't need to compensate for the lower 'winter' dip.
But again : the lattitude, or 'hight' of the sun only determines the spacing
of the mirrors. Not the mirror collecting area itself.
>
> > Important to understand is that storage of heat is easy (liquid salt
> > containers), and can be done virtually without heat loss.
> > Thus this 17% efficiency of the sun not always shining only affects the
size
> > of the mirror-field.
>
> It is not clear what you are envisioning here. You want moving mirrors in
acre sized sets to point
> at a collection tower?
Yes. Or the 'trough' design of some commercial plants :
http://www.powerfromthesun.net/chapter1/Chapter1.htm
> Who cleans the dust off of them? How are they built to survive storm
winds?
See previous links. Cleaning and protecting for foul weather is not a
problem.
> You still have to transport this heat to the actual generators. What is
pumping liquid salt like and
> has it been done? And mirrors are only about 90% efficient unless very
expensive.
Yes, it has been done, and yes mirrors should not have to be more than 90%
efficient.
The less efficient, the more mirror space you need.
The more mirror space, the more expensive the plant.
So the hunt is out for low-cost , rotatable, mirrors (heliostats) !!
Experimental mirrors (heliostats) were about $250/m^2.
Later designs brought this number down to about $80/m^2 today.
Some claim heliostats of $50/m^2 can be made with milar surfaces.
To be commercially really attrative, and create electric power at $5ct / kWh
(lower than nuclear), heliostats need to be less than about $60/m^2.
So, we are getting there !
>
> > The cost of the power-train remains the same, because
> > with heat storage, the turbines can continue to run through the night
(if
> > needed).
>
> Of course they have to run at night. No magic batteries that store AC.
Yeah. But they don't need to run very hard. Night-time electric usage is way
below day-time usage. So storage does not need to really be for full-power
all night long.
Also, in combination with other energy sources (wind, bio, hydro and
nuclear), there would be even less requirements on storage. It just becomes
a cost-calculation issue. Hydro has great storage capacity, and could run at
night. Solar during the day.
It becomes an overall engineering problem of capacity and risk and engineers
are really good in finding the optimal solution...
Any way, heat storage is not a problem. See the links.
>
> > Overall collecting area, considering all these efficiencies, has now
grown
> > to 52x52 miles.
>
> > That might seem a lot, but it's only a tiny fraction of US desert areas.
> > It's even only a small part of San Bernadino county for example.
>
> > And don't forget that we are talking about ALL the US electrical needs !
> > So collecting area is NOT the problem.
>
> Nor did I find it a problem to get all this electricity where it is not
needed. If fact it was the
> almost flippant assertion of how little land it would take that caused me
to investigate the issue.
Thank you !
Did this change your thought about the viability of solar energy ?
Does solar energy have a place in your energy picture of the future ?
If not, than I suspect you are choosing nuclear option only out of
principle.
> And you have missed several of the basic losses while requiring major
engineering accomplishments
> such as hundreds of miles very well insulated pipes moving superheated
water. Starting with very
> efficient solar cells avoided all these engineering challenges.
I think we are beyond this now ?
>
[...]
[...]
> If you are talking anything like the systems which have gone to the
experimental stage mirrors are
> the cheapest part.
Mmm. No.
Mirrors (heliostats) are by far the biggest capital investment of a solar
power plant.
It's in the range of 45% of overall plant cost.
Remember that the rest of the plant is just like a fossil-fuel plant
(Rankine turbine and all that), so the heliostat cost is really the
replacement cost of the fossil fuel itself.
Thus, bringing down heliostat costs linearly increase its cometitiveness
with fossil fuel.
And fossil fuel will go up in price, while heliostat engineering will bring
costs down.
The cross-over point I think has been reached already, or will be reached
within a year or two.
>
> > Cooling water sometimes not easily available in desert areas.
>
> Sometimes? If it were easily available it would not be called desert.
Remember Las Vegas and Los Angeles.
>
> > Still, the benefits seem to far outweight the disadvantages.
> > So I wonder why there is so little attention paid to this.
>
> It has been and the problems are as I touch on them above. There are other
problems of course.
Like ?
[...]
> After dismissing the desert aproach for the power being in the wrong place
There is no wrong place to farm energy.
Most Californians lives within 100 miles of desert or desert-like land which
can be transformed into (energy) farm land. We might have to give-up alfafa
and rice farming in the Central Valley, but that uses more water than a
nuclear power plant any way. I can do without alfafa. Can't do without
electricity...
Think of it as farming. Energy farming. How much space do we use for beef ?
How much for corn ? How much for grain ? So, why so little for energy ? Why
fight wars in far-away countries with people that don't like us, while we
pay top-dollar for their black gold ? All this just for energy ? While
energy shines on our head at 1000 W/m^2 ? Lets farm it !
Rob
.
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