Solar Energy the Sensible Way

[Enthalpy]

Hello you all!

 

A nice Solar power plant has just been inaugurated in southern Spain. It's called Gemasolar, efficient browsing keyword:

http://www.torresole...asolar-plant/en

http://www.nrel.gov/...fm/projectID=40

(http www) youtube.com/watch?v=GhV2LT8KVgA

http://www.lemonde.f...#ens_id=1271383 (French)

 

Why the provocative title "the Sensible Way"?

- It converts Sunlight to electricity through heat. The huge light collection area is made of "cheap" mirrors, not of expensive Solar cells.

- A turbine and alternator can have 40% efficiency, as opposed to <10% for affordable Solar cells.

- Heat is stored in a cheap bulk material to produce electricity during night - storing electricity instead would be expensive.

 

How expensive? The produced electricity is bought 0.10-0.20 euro above market price. Which looks good if you consider this plant produces 20MW on average: building it 100 times bigger would slash unit prices in 3 naturally.

240M euros investment for 20MW is six times more than a nuclear power plant (3G euros for 1.5GW) but this plant is the first of this model. Much of this cost is non-recurring (research) and would drop with size as well.

 

How big? Thaaat big: 2 km² for 20MW in a very sunny location. 1GW would need (10km)² so you better have vast empty space. Sahara, Atacama, Namib, Neguev of course - and southern Spain does make sense, as would places in New Mexico for instance.

 

You guessed, I like it...

Edited November 19, 2011 by Enthalpy

[swansont]

Why the provocative title "the Sensible Way"?

- It converts Sunlight to electricity through heat. The huge light collection area is made of "cheap" mirrors, not of expensive Solar cells.

- A turbine and alternator can have 40% efficiency, as opposed to <10% for affordable Solar cells.

 

There are several efficiency terms. What is the efficiency of the light being absorbed by the salt solution? I doubt it's 100% — that represents an efficiency for which you need to account. With mirrors, there is a space efficiency, since the reflected light can't be blocked by other mirrors if it's going to be useful. Solar thermal tends to take up more area than unconcentrated photovoltaic. Land costs money, too. Since you would put this in more remote areas where the land is cheap, you have to account for transmission costs and losses as well.

 

Photovoltaic efficiency ranges from below 10% to above 20%, depending on the material. You have to normalize the cost on the efficiency — a 20% cell that is twice the cost of a 10% cell is just as affordable, since you need half as many for the same power.

 

How expensive? The produced electricity is bought 0.10-0.20 euro above market price. Which looks good if you consider this plant produces 20MW on average: building it 100 times bigger would slash unit prices in 3 naturally.

240M euros investment for 20MW is six times more than a nuclear power plant (3G euros for 1.5GW) but this plant is the first of this model. Much of this cost is non-recurring (research) and would drop with size as well.

 

How big? Thaaat big: 2 km² for 20MW in a very sunny location. 1GW would need (10km)² so you better have vast empty space. Sahara, Atacama, Namib, Neguev of course - and southern Spain does make sense, as would places in New Mexico for instance.

 

It's not obvious why the cost scales the way you claim. The number of mirrors and tracking units, for example, won't scale at all. Why does the price supposedly drop by a factor of three when you go to 2000 MW?

 

Fuente Álamo Solar Power Plant is photovoltaic, also located in Spain and is rated at 26 MW; it takes up just 0.62 km^2 (62 hectares). If you normalize that to the same annual energy output, then it would still need to take up less than 2 km^2. One fifth of the area you require. It's also more than three years old, so a similar plant built today would have more efficient panels — if it's a few percentage points higher, that could represent a 10 or 15% improvement in efficiency and corresponding drop in required area.

http://en.wikipedia.org/wiki/Planta_Solar_Fuente_Alamo

[Enthalpy]

What is the efficiency of the light being absorbed by the salt solution? I doubt it's 100%

-> 98% for instance. Absorbing is never difficult, unless you approach the source's temperature.

 

Solar thermal tends to take up more area than unconcentrated photovoltaic

-> 4 times more efficiency means less area.

 

Photovoltaic efficiency ranges from below 10% to above 20%, depending on the material

-> 20% are single-crystal cells, affordable only on spacecraft.

 

 

Why does the price supposedly drop by a factor of three when you go to 2000 MW?

-> Because you build more units.

 

Fuente Álamo Solar Power Plant is photovoltaic, also located in Spain and is rated at 26 MW; it takes up just 0.62 km^2 (62 hectares).

-> Gemasolar indicates a mean power output, which is only 5MW at Fuente Álamo. Gemasolar is hence more area-efficient than Fuente Álamo.

[superball]

Its a very interesting array of mirror reflectors, and the salt solutions after they become molten has insulation properties,for heat retention.

 

The problem I see is it is very inefficient designed.

 

Research, and development was key in getting this idea off the ground, but the concept is still a good one.

 

I would use sunlight, steam power, and the power of hydrogen, and oxygen as the fuel to sustain the energy in the system.

 

1. by a process of super-heating steam for generators.

2. by the use of natural light sources processing superheated steam to its constitute parts even further for use as fuel..

3. by the absorption, and reflective spectrum energies of natural sunlight by acting higher the energy vacuum electron energies, and emissions of the same.

 

 

There is some other very key concepts that validate this idea.

 

I hope it is ok to cut, and paste the information for your review. I cant find the link, here is the hard copy.

 

Absolute Proof that Operational COP>1.0 EM Systems Are Possible and Eventually Practical

 

 

 

Brody, Herb. Victor Klimov in Los Alamos National Laboratory in New Mexico has constructed a solar cell which can absorb the light of a specific wave length in such a way, that one photon can energize more than one electron. As soon as the electron absorbs a photon, it disappears for a very short moment into the quantum field. Being in the virtual state the electron can borrow energy from the vacuum and thereafter appears again in our reality. Now the electron can energize up to 7 other electrons. This leads to a theoretical coefficient of performance (COP) of 700%. A COP = 200% can be readily achieved and it has been. The experiment has also been replicated successfully by the National Renewable Energy Laboratory in Golden Colorado. [Herb Brody, "Solar Power - Seriously Souped Up." New Scientist, May 27, 2006, p 45].

 

Quoting: "Make solar cells as small as a molecule; and you get more than you bargained for. Could this be the route to limitless clean power?"].

 

modnote: deletia

 

AFAICT the entirety of the remainder of the material (now deleted) is located here: http://www.cheniere.org/correspondence/100608.htm

Edited November 20, 2011 by swansont
copyright deletions

[InigoMontoya]

I've not studied solar power tech in great detail, however, as one who lives in one of the best locations in the US for solar power, I would point out that the Spanish plant is not unique. I am aware of two such plants within 150 miles of me (ie, both are in Southern California). There are also SEVERAL power plants that use a distributed boiler system using troughs with long parabolic mirrors rather than the central tower. These distributed systems are apparently easier/cheaper to build/operate, but again, it's not something I've studied in detail.

 

 

Solar One/Two. A tower-based plant that operated as an R&D facility for a number of years (wiki page indicates the Spanish system is a direct descendant of this project).

 

SEGS. The trough based systems mentioned above.

 

Sierra SunTower. The other tower-based system near me. I've driven by it several times while it was in operation. Esolar's page on the plant.

 

Again, those are all within 150 miles of my home. Thermal-based solar in the US has been online for at least 15 years now...

 

 

 

 

edit: The only benefit I think anybody sees with photovoltaics is their ease of use for small installations. Making a solar tower in your back yard is a bit complex. Throwing up a few solar cells? Not so much. So if your installation isn't going to be measured in megawatts, it probably makes sense to use photovoltaic. If megawatts are your desire? Yeah, thermal based makes a lot more sense.

Edited November 19, 2011 by InigoMontoya

[swansont]

-> 98% for instance. Absorbing is never difficult, unless you approach the source's temperature.

 

High absorption means a high emissivity, but that also means it radiates efficiently, and that means losses. "For instance" sounds like you are making up the number. And the numbers don't jibe here.

 

-> 4 times more efficiency means less area.

 

You haven't demonstrated 4x the efficiency. You are citing the turbine efficiency, which is only one component. The mirrors don't reflect all of the light, not all the light gets absorbed to heat the transport solution, and there are heat losses before you get to the turbine. You have accounted for NONE of that. The photovoltaic efficiency is electrical power out/sun power in. You have to compare this system using the same analysis or else it's garbage.

 

-> 20% are single-crystal cells, affordable only on spacecraft.

 

Not true. SunPower, for example, makes commercial-market cells that are >20% efficient.

http://www.greentechmedia.com/articles/read/sunpower-announces-efficiency-record-is-the-end-near/

 

-> Because you build more units.

 

Where does the factor of three come from? Without explanation, "you build more units" is indistinguishable from "it's magic". Not everything scales. What scales in this case? Has it been demonstrated?

 

-> Gemasolar indicates a mean power output, which is only 5MW at Fuente Álamo. Gemasolar is hence more area-efficient than Fuente Álamo.

 

But the total energy output is given. 110 GWh/yr on 185 hectares is 0.6 GWh/hectare for Gemasolar. Fuente Álamo produces 44 GWh/yr on 62 hectares, which is 0.71 GWh/hectare. So Gemasolar is not as efficient in terms of area. Which is why your 40% vs 10% efficiency number has to be wrong. The numbers don't add up.

 

 

——————

 

 

I hope it is ok to cut, and paste the information for your review. I cant find the link, here is the hard copy.

 

!

Moderator Note

It depends. Fair-use copying is OK. Large swaths of text, with no link to the original? No, that's not OK. Going OT with speculative material is also not OK — discussion of tapping vacuum energy should be discussed elsewhere. The topic of this thread was the solar-thermal plant.

 

To be clear: The conclusions drawn about getting energy from the vacuum are crap.

[Enthalpy]

High absorption means a high emissivity

No, because the collector's temperature hence the wavelength differ from the Sun's surface.

And even is absorptivity equalled emissivity, the T⁴ dependence would give >98% ratio.

Figure that, I had such reasons to give the number.

 

You haven't demonstrated 4x the efficiency. You are citing the turbine efficiency, which is only one component.

>40% is for existing complete thermal plants, which includes all the losses you imagined.

By the way, on a power plant, the turbines have widely over 90% efficiency.

 

Price does scale with the number os units. I don't feel the need to explain that.

 

But the total energy output is given. 110 GWh/yr on 185 hectares is 0.6 GWh/hectare for Gemasolar. Fuente Álamo produces 44 GWh/yr on 62 hectares, which is 0.71 GWh/hectare. So Gemasolar is not as efficient in terms of area. Which is why your 40% vs 10% efficiency number has to be wrong. The numbers don't add up.

Compute it again.

[insane_alien]

>40% is for existing complete thermal plants, which includes all the losses you imagined.

By the way, on a power plant, the turbines have widely over 90% efficiency.

 

turbines can now exceed ideal thermal efficiency? when did we break thermodynamics and what has replaced it? this is exceedingly important in my job.

[swansont]

No, because the collector's temperature hence the wavelength differ from the Sun's surface.

And even is absorptivity equalled emissivity, the T⁴ dependence would give >98% ratio.

Figure that, I had such reasons to give the number.

 

Either it absorbs or it reflects. If it absorbs, the emissivity is high. If it reflects, the emissivity is low. In either event, there are losses. It reflects light and it radiates because it is hot. It's a matter of how much. Even if the emissivity is 1, the system will lose energy to radiation.

 

Price does scale with the number os units. I don't feel the need to explain that.

 

In general, yes. But you quoted specific numbers, as if there is some scaling law involved. Did you just make them up, or is there reasoning behind them?

 

Compute it again.

 

I did. Got the same answer. Do you get a different answer or is this just bluster?

[CaptainPanic]

Either it absorbs or it reflects. If it absorbs, the emissivity is high. If it reflects, the emissivity is low.

 

Selective coatings exist (used on industrial scale in solar boilers) that are good at absorbing sunlight, and emit little in the IR spectrum (which is what they aim at, because they are used to make hot water).

 

Obviously, if you do not remove the hot water (i.e. there is no flow), then soon enough every solar boiler (and in fact every object in the universe) will increase in temperature until at some point the emissions are equal to the absorption (although not necessarily the same wavelength). Equilibrium must be reached, because otherwise it would heat up indefinitely... and the goal of the solar power thing in Spain is to get as far away from that situation as possible.

 

So, the solar boiler absorbs light, but will emit little IR radiation, and thereby converts a lot of light into heat (up to 74% according to wikipedia). Naturally, an ordinary solar boiler is not the same as this molten salt thing in Spain. Most importantly: the surface area which is exposed to the outside (where there is no insulation) is relatively small in the Spanish molten salt thing. Therefore, radiation gets little chance.

 

It is vitally important that you make a heat balance for this discussion, and you cannot dismiss the flow of molten salt. Most of the material which is heated by the mirrors is nowhere near a location where it can emit much.

[swansont]

Selective coatings exist (used on industrial scale in solar boilers) that are good at absorbing sunlight, and emit little in the IR spectrum (which is what they aim at, because they are used to make hot water).

 

Obviously, if you do not remove the hot water (i.e. there is no flow), then soon enough every solar boiler (and in fact every object in the universe) will increase in temperature until at some point the emissions are equal to the absorption (although not necessarily the same wavelength). Equilibrium must be reached, because otherwise it would heat up indefinitely... and the goal of the solar power thing in Spain is to get as far away from that situation as possible.

 

So, the solar boiler absorbs light, but will emit little IR radiation, and thereby converts a lot of light into heat (up to 74% according to wikipedia). Naturally, an ordinary solar boiler is not the same as this molten salt thing in Spain. Most importantly: the surface area which is exposed to the outside (where there is no insulation) is relatively small in the Spanish molten salt thing. Therefore, radiation gets little chance.

 

It is vitally important that you make a heat balance for this discussion, and you cannot dismiss the flow of molten salt. Most of the material which is heated by the mirrors is nowhere near a location where it can emit much.

 

I have no problem with any of this, and I will note that 74% is not 98%, which is my point. There are losses, and I think they have not been accounted for in the analysis. This is a two-stage loop, going from molten salt to boil water, and you'd be limited by the Carnot efficiency for each. 40% sounds — at best — like the efficiency of a single stage of boiling water and driving a turbine. I'd like the claims to be backed up.

[CaptainPanic]

I have no problem with any of this, and I will note that 74% is not 98%, which is my point. There are losses, and I think they have not been accounted for in the analysis. This is a two-stage loop, going from molten salt to boil water, and you'd be limited by the Carnot efficiency for each. 40% sounds — at best — like the efficiency of a single stage of boiling water and driving a turbine. I'd like the claims to be backed up.

The molten salt loop obtains heat from the sun, and transfers that to water (and forms steam). That part is not limited by the Carnot efficiency. In fact, it has a theoretical maximum of 100% efficiency. With enough insulation and negligible friction in tubes and equipment, every single Joule of absorbed radiation can be transferred to the water/steam. The salt only transfers the heat, because it is not practical to place a boiler in a tower, and because molten salt can store a lot more energy (heat) than steam, which is practical in the night when the sun does not shine. The 40% efficiency comes from the only Carnot efficiency (there is only 1), which is found in the steam cycle.

 

Also, with 565°C of the molten salt, you should be able to make steam of at least 500°C. It's a liquid-liquid heat exchanger, and it should be pretty efficicient. And that means that your Carnot efficiency is:

 

[math]\eta=\frac{W}{Q_H}=1-\frac{T_C}{T_H}=1-\frac{273+50}{273+500}=0.58[/math], or 58%

I've assumed a cold reservior at 50°C because we're in Spain in the desert, not at a moderate area where a much colder reservior would be possible.

 

There really is no point in creating a molten salt of 565°C if you do not intend to make steam of a very high temperature too. I know that 500°C is in the supercritical range, and that's why I've added a link (here) to an article about supercritical heat cycles in coal power plants... anticipating a question to show that's normal technology...

 

So, to arrive at 40% overall efficiency, with a Carnot cycle that has a theoretical maximum efficiency of 58% (I know that it's lower in reality), we should get a minimum of 69% (0.69*0.58=0.4). When reality is taken into account in the Carnot cycle, we must conclude that the actual efficiency of the molten salt cycle must at least be higher than 69%, (the only alternative is that we call these people a bunch of liars optimists). This in turn means that the absorption efficiency of the heated surface is very likely higher than the maximum of the solar boilers (74%) that I posted earlier. Sure, it is not 100%... but it's pretty high nonetheless.

[swansont]

Thank you for the analysis. That's along the lines of what I wanted to see.

 

One of the things that's going to reduce the overall efficiency is the intent to produce electricity when there is not sun, by using the energy still contained in the salt solution, which will be cooling down. Part of the time you will be using salts that have cooled down, lowering the overall efficiency.

 

The energy production numbers still don't add up, though. 0.6 GWh/hectare for Gemasolar and almost 20% higher for a 3-yeal-old photovoltaic plant. I don't see any mention of the mirror coverage, but it's got to be less than 50%

 

edit: finally found the key number buried in a pdf: 120 MWt

 

20 MWe/120MWt is under 17%

[CaptainPanic]

Thank you for the analysis. That's along the lines of what I wanted to see.

 

One of the things that's going to reduce the overall efficiency is the intent to produce electricity when there is not sun, by using the energy still contained in the salt solution, which will be cooling down. Part of the time you will be using salts that have cooled down, lowering the overall efficiency.

Although it's undeniable that it will cool down, this is for sure negligible. In the pdf that you supplied, we can read that the tanks can contain up to 800 MWh (2.88*10^12 J) of energy (in the form of hot molten salts). If you want to lose 1% (2.88*10^10 J) of that heat into the surrounding air, you would need to heat nearly 30 million m3 of air by a degree. If you do that over the course of 1 day, you heat up 333 m3/s by 1 degree.

 

I just don't think so. I can't prove it, but I think losses are way less than 1%.

 

The energy production numbers still don't add up, though. 0.6 GWh/hectare for Gemasolar and almost 20% higher for a 3-yeal-old photovoltaic plant. I don't see any mention of the mirror coverage, but it's got to be less than 50%

In fact, it's only 17%. The reflective area is 304750 m2, on a total field area of 185 ha. And the mirror coverage might well be less than that of the 3-year-old plant.

edit: finally found the key number buried in a pdf: 120 MWt

 

20 MWe/120MWt is under 17%

Are you sure that 120 MWt is the 24-hour-average? Because if it is peak power (and that makes more sense to me), you need to put that into your little calculation too:

 

20 MWe / ( 120 MWt*(percentage of time that the tower receives light)) = 20/(120*0.5) = 33%

 

The 120 MWt is a very ambiguous number... it can mean many things. It can mean peak power (highest power at the sunniest day). It can mean an average day power. It can mean the average power during hours of sunshine. In a coal power plant, MWt is simple, but those have a continuous process... this does not.

[swansont]

 

Are you sure that 120 MWt is the 24-hour-average? Because if it is peak power (and that makes more sense to me), you need to put that into your little calculation too:

 

20 MWe / ( 120 MWt*(percentage of time that the tower receives light)) = 20/(120*0.5) = 33%

 

The 120 MWt is a very ambiguous number... it can mean many things. It can mean peak power (highest power at the sunniest day). It can mean an average day power. It can mean the average power during hours of sunshine. In a coal power plant, MWt is simple, but those have a continuous process... this does not.

 

800 MWH of thermal storage is less than 7 hours of daylight production at 120 MWt. The implication is that this excess is available in the summer, so you don't have 20 MWe available 24 hours a day the whole year. (But one of the nice things about solar is that it produces more energy when you have more demand for cooling, which is why it's such a good alternative). But even so, the efficiency is probably less than 33%.

 

Which makes the numbers start to make sense. You have about twice the conversion efficiency as a photovoltaic system but cover less than half the area.

[CaptainPanic]

You have about twice the conversion efficiency as a photovoltaic system but cover less than half the area.

Exactly. If you have enough sunlight (direct, not diffuse) and space, this thing is brilliant.

 

I wonder if you can look at the tower without sunglasses? I guess not. What is it like to have such a bright light (in addition to the already bright sun itself) as your neighbor?

[swansont]

Exactly. If you have enough sunlight (direct, not diffuse) and space, this thing is brilliant.

 

I wonder if you can look at the tower without sunglasses? I guess not. What is it like to have such a bright light (in addition to the already bright sun itself) as your neighbor?

 

The pictures in the pdf show it being white and messing with photo's contrast, so it's got to be quite bright. It looks like a great option for (presumably cheap) desert areas if you can send the power efficiently to where it's needed.

[CaptainPanic]

The pictures in the pdf show it being white and messing with photo's contrast, so it's got to be quite bright. It looks like a great option for (presumably cheap) desert areas if you can send the power efficiently to where it's needed.

You can transfer power without too much losses through DC lines over long distances (the longest line at the moment is 580 km, from Norway to the Netherlands).

 

In the case of this solar tower, it's just 50 km from Seville (Spain). I guess that's close enough to go straight to AC and just put it on the regular grid.

[Enthalpy]

turbines can now exceed ideal thermal efficiency? when did we break thermodynamics and what has replaced it? this is exceedingly important in my job.

 

What you have to learn is that turbine efficiency refers to the available enthalpy drop, as computed from the available pressures, not to the input heat.

And independently of any theory, existing thermal power plants have efficiencies like 42%, look for data.

 

To arrive at 40% overall efficiency, with a Carnot cycle that has a theoretical maximum efficiency of 58%, we should get a minimum of 69% (0.69*0.58=0.4).

 

Yes, that's the kind of figures common in usual thermal power plants. Coal produces vapour at a temperature not much hotter than 560°C because turbine blades aren't cooled and though shall last for very long. Though, the whole plant achieves 42% efficiency, or even better. Which does require heat exchangers and pre-heaters everywhere.

 

20 MWe/120MWt is under 17%

 

You mixed an average day/night output with a peak power.

 

Either it absorbs or it reflects. If it absorbs, the emissivity is high. If it reflects, the emissivity is low.

 

You still have to understand that radiation by the absorber is not at the same wavelength as the absorbed light, and emissivity depends on the wavelength.

In addition, emissivity only multiplies the T⁴ dependency. Alone the Sun's 5950K compared with <900K give a factor of 1900.

So : building a light absorber is easy if one needs only 600°C. Unless someone botches his job, efficiency is very high.

 

As well, a tower with its more complicated mirror steering brings the advantage that light concentration can be optimum, as opposed to the simpler cylindrical or parabolic concentrators.

 

You can transfer power without too much losses through DC lines over long distances (the longest line at the moment is 580 km, from Norway to the Netherlands).

580km must be the longest underwater line. Aerial transmission between Itaipú and São Paulo is 800km long and both lines carry together over 13GW now.

http://en.wikipedia....iki/HVDC_Itaipu

Which is an admirable achievement, because they finished the lines in 1984 and designed them much earlier.

At that time, no IGBT nor GTO existed. They made every conversion AC -> DC -> AC with diodes and gate turn on thyristors (SCR).

 

Even longer, but with consumers spread over the length:

http://en.wikipedia....nd_Transmission

Bay James to New England, a long trip, several GW as well.

Edited November 24, 2011 by Enthalpy