Can Organic Electronics Promise Cleaner Energy?

MargaretHarding said:

Stephen,

You misinterpreted my original comment. I was responding to a comment about concentrating solar that seemed to imply that more energy could be generated from the same space by concentrating light. There is a theoretical maximum beyond which one cannot go without violating fundamental laws of physics. I think that confusion was settled long ago in this chain.

I think 6700 square kilometers is still a great deal of land. It is your claim that there are millions of square kilometers that are unusable and have no other ecological benefit that I am simply accepting. Perhaps in Australia that is true. Here in the US, I have found that one man's wasteland is another's ecologically unique environment that cannot be built upon.

Another acquaintance (project manager for renewables) once said to me. "No site ever seems to be acceptable. Everyone wants renewables, just not here."

I will write a post, but it will of necessity include more considerations to be complete. This is based on very rough basic principles, not on actual in the field working design. Most engineers would have added 30-50% for unknowns and other issues not considered. I did not, in order to give you the minimum required land use. I have not considered any growth in electrical usage, any additional lands for infrastructure needs, nor any margin in capacity. I will also include comparative land use by other generation sources, otherwise, the number is in a vacuum.

You have also proposed an interesting scheme for recovery of the land using bio char. When you get that concept more fully fleshed out, I would be very interested in seeing a post with the details.

StephenGloor said:

Margaret Harding - "I know I'm so difficult, demanding verifiable numbers."

That was not the original comment you made.  In your first comment you seemed to imply that solar energy was somehow against the laws of nature!

"You're not considering some basic laws of nature. ......."

And then you concluded with:

"Vast areas would have to be covered with solar PV or thermal conversion panels."

However the hard numbers you 'demanded' showed that the area required for solar energy is trivial and that there is nothing in the laws of nature that preclude solar energy from providing a significant portion of our energy needs.

So we can finally consider that the land use argument against solar power is finally dead and gone?  If so can you please inform Barry Brook, Peter Lang etc when next you post about it as I am really sick of dealing with it.

RickEngebretson said:

Margaret, may I suggest you subscribe to National Geographic. This month's issue is all about water with a great map.

Corn ethanol is less about fuel and more about feed. Sugar is fed to yeast along with other critical nutrients to create livestock feed. Ethanol is a byproduct looking for a market. I don't remember the biochemistry, but there are CO2 growth limited plants and photon limited plants. Corn is optimized for productivity. We are not really using food for fuel, but we are using other resources. I don't moralize, I just recognize we have a lot of people who want a lot of things.

The hay crop approach is similar. Except hay produces more protein and is a perennial. Hay is the only farm crop that is not processed and so requires a ruminant animal to digest it. There was talk near the end of WWII to process alfalfa for people when nobody knew if Hitler would burn the farm fields in retreat. As you know, the midwest US is serious about agriculture.

All I am trying to do is suggest solar thermal fuels production instead of the enzyme process. As a protein biophysicist I am going against the current. And I don't owe you anything because I'm not asking for anything.

MargaretHarding said:

I know I'm so difficult, demanding verifiable numbers. It's a quirk of mine. However, please recognize that I'm trying to calculate an annual energy output. By doing so, one can ignore seasonal variations. The theory would be that you store excess during high generations periods (either seasonal or diurnal) and use that excess during period where demand exceeds generation. In this way, the arguments about the amount of sun in December vs. July becomes irrelevant. The Spanish plant provides annual output data. I presume that captures the variation that exists in Spain as well.

I thought I was being pretty fair in my analysis. I didn't add additional requirements for the inefficiencies of energy storage. Nor did I add anything for the potential line losses for long transmission from source to use. I also did not make any claims about the relative cost of these systems.

One of my concerns is the conversion of crop land from food production to energy production. So I wince when I hear the suggestion of converting hay crops to methanol or ethanol. I grew up in Iowa (center of much ethanol production in the US) and have questioned the viability of such systems with people involved there. I'm still trying to learn about this.

RickEngebretson said:

You have a very constructive dialog here. I wish I could find more of this.

Just to throw more fuel on the fire, I hope some added concepts are of interest.

The day cycle and season cycle and weather cycle and geography defy the hard numbers Margaret insists on. But a good farmer cuts a good crop of hay right around the longest day of the year. Hay can be converted to biofuels like methanol.

If methanol or methane (natural gas) is burned, a dominant combustion product is hot water. The quantum mechanical vibration of the OH chemical bond is in the near infrared. Hot water radiates light as it cools. An interesting PV is provided by www.jxcrystals.com. It is a direct band gap semiconductor with very high efficiency in the near infrared. Thus, simply by burning fuel and first collecting the light we can generate electricity with no moving parts. With cogeneration we also achieve nearly 100 percent efficiency.

 Solar fuels and optical fuel cells are plausible.

StephenGloor said:

Bill Woods -" You can see that in the southern part of Australia where most people live, there's almost twice as much energy per unit area in mid-summer as in mid-winter."

However if you look at these graphs:

http://www.bom.gov.au/climate/averages/wind/wrselect.shtml

You can see the same areas have more than twice the wind in winter as summer.  So you can size the total renewable system to provide constant year round energy.  No-one expects solar thermal to do the whole job.

Also the belt around Mildura up past Dubbo has much more constant sunshine that Southern Australia.  All these locations are on the present Eastern Australian electricty grid so CSP plants built here would generate energy for Melbourne and Hobart via Bass Link.

StephenGloor said:

Margaret Harding - "Let's see where these numbers get us for my Australian scenario. I still don't have any good biomass data, so for simplicity I'll just assume no biomass for now and determine land use requirements for 100% electricity generation with solar generation from one of these facilities."

First of all nobody would expect CSP plants to be 100% of the generating capacity.  We also have the world's best wind resources so CSP would only need to be 40% or so with wind at 40% and peaking plants and others at 20%.

Secondly we have MUCH better solar resources that Spain.  The average conditions in Australian are much better than even the best conditions in Spain so solar collectors in Australia would produce much more energy.

Thirdly the CSP plants would have a range of storage amounts.  The 'baseload' plants would have very large collectors and 12 to 16 hours of storage and supplemental boilers. Additionally they are far more likely to be Power Towers rather than troughs.  The smaller Andosol like plants would be load following and phasing in and out in concert with the available wind energy.  They may or may not have supplemental fuel.

Finally as you calculated even if we did get 100% of our energy from Andasol type plants the land use is still trivial confirming it as a complete non-issue.

StephenGloor said:

Bill Woods - " so the average spot can only have 1/4 the insolation of the point directly under the sun — the equivalent of 6 hours of peak sun per day. Latitude matters, so places in the tropics can have average insolation of 24/π ~ 8 hours. But that's not counting the losses in the atmosphere."

Solar power plants track the sun.  It is available at least one hour after sunrise till one hour before sunset for a system that tracks the sun through the sky.  Troughs have a problem because they are very long in one direction.  If you point the long direction to the North-South you can track the sun during the day however you cannot change if for different seasons.  If you point it East-West you can change the tilt for the seasons however you cannot track the sun during the day.  Heliostats do not have this problem.

StephenGloor said:

Margaret - "The graphs of output that I've seen for solar arrays operating in sunny locations in the American Southwest show that even with 10-12 hours of sunlight, optimal output only occurs mid-day for 5-6 hours."

I am sure they are however that depends on how the troughs are aligned:

 "The Luz parabolic trough solar collectors utilize a single northsouth axis orientation to track the sun. Although the more common east-west axis orientation gives a slightly higher and more even annual distribution of electric production, the north-south axis biases summer operation. This allows a higher percentage of the on-peak rate period to be supplied by solar energy. Daylight savings time further shifts solar production to meet summer on-peak hours. The north-south axis also causes the noon time dip in solar
production seen in Fig. 2 during winter months. This dip is due to the path the sun takes through the sky in the winter. In the morning and afternoon the incident angle between the
collector and the sun is smallest. Thus the highest solar flux is absorbed during these times. At solar noon the sun is sitting low in the southern sky, but the parabolic troughs are
facing straight up, resulting in the largest incident angle."

An East West alignment of troughs will take a long time to start up as the sun has to get high enough however facing then North-South means a faster startup but less output in winter.  Of course the Power Tower plants of eSolar and Solar reserve do not have this problem as each individual heliostat tracks in 2 axis so no matter where the sun is in the sky it reflects the sun onto the tower.

"Unfortunately, I've never seen reliable numbers on the land use requirements, output, and capacity factors. I've looked for it on the websites for that facility in Spain."

No neither have I however the message I am trying to get across is that the land use no matter what the storage requirements are are trivial compared to the land use for agriculture.  Basically land use is a complete non-issue and I am at a loss why nuclear power advocates keep banging on about it.

"You are going to grow salt resistant plants on this salty farmland, then burn the plants and create biochar."

This is actually something I thought of - I have not seen it anywhere else.  I have seen plans for biomass supplemental fuel however the connection between rehabilitating slat affected land is my idea only so far.  You also do not burn the plants.  To produce biochar you have to subject the biomass to slow pyrolysis assisted by solar energy.  However you can just gasify it and store the syngas - there are a number of options.  The reason you use CSP plants is to minimise the cost and problems involved with biomass.  Make the biomass problem as small as possible as photosythesis is only <3% efficient.  I would rather generate the bulk of the electricity with highly efficient CSP plants rather than low efficiency agriculture.

MargaretHarding said:

Bill Woods,

Thanks! I don't know why I never found this website. I tend to ignore cost numbers. Too much of it is speculation and hidden subsidies. I like to just look at the actual physics and see what answers I get. Many times, that discussion alone can make clear what the realities are.

Let's see where these numbers get us for my Australian scenario. I still don't have any good biomass data, so for simplicity I'll just assume no biomass for now and determine land use requirements for 100% electricity generation with solar generation from one of these facilities.

180 GWH per year per plant means that to generate 237 billion KWH we would need over 1300 of these plants. at 510 000 sqm per plant (the second website has a slightly higher figure that may account for the other land needs) that means you would need more than 67 000 hectares of land or about 6 700 square kilometers. Given earlier statements about millions of hectares of unusable land with no other value, this is at least physically feasible.

Now, the questions about energy storage, peak demand, cost of transmission and other questions come into play. Those, I do not profess to have sufficient knowledge to comment further.

Stuart21 said:

I think charcoal for biochar is not a wise use where it could offset fossil fuels - esp oil or petrol, as these lose so much just in processing. 

BillWoods said:

Margaret Harding: "Unfortunately, I've never seen reliable numbers on the land use requirements, output, and capacity factors. I've looked for it on the websites for that facility in Spain."

According to www.flagsol-gmbh.com/flagsol/cms/front_content.php?idcat=25

• ~ 500.000 sqm of collector area (>70 soccer fields) per [50 MW] plant
• Annual electricity generation of around 180 GWh/a (160GWh net) per plant

The total land is larger than the collector, of course. 

According to social.csptoday.com/news/lower-cost-production-actually-product-andasol-1s-energy-storage

The developers say Andasol 1's electricity will cost ... 271 euros per MWh [36 US¢/kW·h]. 

Dunno if that's before or after subsidies.

MargaretHarding said:

I wasn't complaining about not having sun 24/7. I was simply stating a fact. I'm a numbers kind of girl and like to see these discussions around hard data. Yes, solar has dozens of design configurations, some of them make great sense, some of them do not. As I've said to my students, do not bring me a solution in search of a problem. Make sure you have your problem well understood, then look for an optimal solution.

BillWoods said:

Stephen Gloor: "As you can see the sun hours for site varies.  Some site in Australia have an yearly average of 10+ sun hours per day."

I don't know what definition of 'sun hour' they're using, but simple geometry shows that the Earth has a cross-section of π r² and a surface of 4π r², so the average spot can only have 1/4 the insolation of the point directly under the sun — the equivalent of 6 hours of peak sun per day. Latitude matters, so places in the tropics can have average insolation of 24/π ~ 8 hours. But that's not counting the losses in the atmosphere.

It also doesn't consider seasonal variation. This set of maps is better since it's measuring energy in MJ/m²: www.bom.gov.au/jsp/ncc/climate_averages/solar-exposure/index.jsp You can see that in the southern part of Australia where most people live, there's almost twice as much energy per unit area in mid-summer as in mid-winter. So if you build a solar power plant with a capacity of 1 GW, and size the collector array and storage to generate 1GW x 24 hr/day in July, you'll have to throw away a lot of potential power in December. Alternately, if you size it to generate 24 GW·hr/day in December, you'll only be generating ~15 in July. 

RickEngebretson said:

Not "all thermal power plants." A solar cycle allows heat management. As Margaret complained, solar plants don't produce 24/7. You folks sure work hard to criticize.

In another paradigm shift consider what "off peak" means for solar. Resistive loads like hot water and warm homes can be in the daytime instead of after midnight.

We're trying to innovate here. We need reliable energy resources for a global market in uncertain times. Solar energy works in dozens of design configurations for a thousand situations. It always has.

WilmotMcCutchen said:

All thermal power plants, including nuclear and coal as well as CSP, consume large amounts of water in evaporative (wet) cooling of turbine exhaust steam.  Dry (air) cooling is of limited capacity due to the wimpy heat flux (<1 W/cm^2) through the air-cooled surface of the steam condenser.  And since the condensing surface is out in the sun, it is acting as a collector at the same time it is trying to reject heat to the atmosphere.  So I hope the CSP designers have got something for drought-parched Australia that doesn't involve wet cooling or unrealistic expectations of dry cooling.  Free convection air cooling has a heat flux of only 0.05 W/cm^2, and adding blowers to produce air impingement cooling only gets it up to a maximum of ~1 W/cm^2.  Forced convection boiling is the best cooling method of all, with a heat flux of 100 W/cm^2. 

MargaretHarding said:

Thank you. I had not seen this map of Australia's daily sun. Is this optimal sun? or total sun? That does make a difference to the determination of total output of a solar array. The graphs of output that I've seen for solar arrays operating in sunny locations in the American Southwest show that even with 10-12 hours of sunlight, optimal output only occurs mid-day for 5-6 hours. Dr. Chu presented such data at the SmartGrid conference last fall. That is what I am basing my numbers on.

I understand the principal of thermal storage. However, I have not seen the total generation capacity of such systems to be able to use any hard numbers in my calculations. Do you have any data on these systems?

Physics tells me that if you are storing some energy, you are not producing as much from the facility. Which, in turn, means that the facility would be larger to produce the same amount of electricity, but would produce more constant electricity. That is what I account for with a lower capacity factor. A thermal storage facility might have a 100% capacity factor, but would require a greater amount of land in order to store some energy while it produces some. Unfortunately, I've never seen reliable numbers on the land use requirements, output, and capacity factors. I've looked for it on the websites for that facility in Spain.

I don't understand your comment relating to biomass. You are going to grow salt resistant plants on this salty farmland, then burn the plants and create biochar. Return it to the farmland and make it usable again? Sounds like an excellent idea. Is there somewhere that I can read more about it? Seems like you should skip the solar arrays and do 100% this type of generation. You get more reliable energy and eventually return the farmland to usable crops.

StephenGloor said:

Margaret Harding - "1) energy use in Australia - 237 billion kwh in 2006 - comes from the US DOE EIA website."

Not dispusting this.

"2) land use requirement for solar array - http://www.energy.ca.gov/sitingcases/ivanpah/index.html"

Not disputing this at all - simply pointing out that the land required is trivial compared to even the salt affected areas of most countries.  If we can cover truly vast areas of solar collectors now (plants) why should a small increase matter at all?

"3) Simple physics - optimal sunlight is available on average (ignoring cloudy days) for 6 hours per day."

Here are some hard numbers.  Have a look at this solar map of Australia from the Bureau of Meteorology

http://www.bom.gov.au/climate/averages/climatology/sunshine_hours/map_gi...

As you can see the sun hours for site varies.  Some site in Australia have an yearly average of 10+ sun hours per day.  A CSP plant here would have a theoretical CF all year round of 40%.  So these hard numbers completely invalidate your assumption of 6 hours sun per day means a CF of 25%.

Finally CSP plant with thermal storage like the ones being built in Spain now have oversized collectors that can store thermal energy and generate electricity at the same time.  This thermal energy is stored in molten salts and recovered if it is needed when the sun is not shining to generate electricity.

Biomass is supplemental fuel not storage.  Sometimes the storage is empty and the sun is not shining so CSP plants use a supplemental fuel for these times if it is required.  Right now they use natural gas which is not carbon neutral.  Using biomass means the supplemental fuel is carbon neutral and if salt resistant plants are used and the ashes are returned as biochar then the supplemental fuel could be benficial rather than harmful.

"I am asking you for is the courtesy of providing specific numbers and your method of calculation, not simply blasting me because you do not like the calculations I have done."

I am not 'blasting" you because I do not like the results of your calculations.  I am pointing out where you have made false assumptions which invalidate your calculations.  So in turn can you now provide hard numbers to back up your calculations.

MargaretHarding said:

You are making a number of claims here. I am asking you for hard numbers of the same nature I have provided.

1) energy use in Australia - 237 billion kwh in 2006 - comes from the US DOE EIA website.

2) land use requirement for solar array - http://www.energy.ca.gov/sitingcases/ivanpah/index.html

3) Simple physics - optimal sunlight is available on average (ignoring cloudy days) for 6 hours per day.

My calculations account for storing energy from the solar arrays to provide electricity while the sun is not shining. You have to generate more energy while the sun is shining in order to have something to store. I assumed that you would use batterys, or pumped storage and ignored the amount of land that might be required. If you want to use biomass as your storage technique, great, give me the numbers. How many acres of land must be dedicated to growing biomass and how much energy will it produce?

Unlike some of my compatriots in the nuclear world, I believe that all energy options should be explored, but I believe that we should be realistic in evaluating how much energy will be produced and what resources it will take. All I am asking you for is the courtesy of providing specific numbers and your method of calculation, not simply blasting me because you do not like the calculations I have done.

StephenGloor said:

Margaret - "1 GW of solar is not the same as 1 GW of coal, nuclear, or natural gas. Solar only operates about 6 hours a day at a 1GW nameplate rating. You really have to go back to the kwh consumed in a year and calculate the amount of installed GW based on realistic capacity factors (25% being a reasonable maximum for solar)."

Of course it is.  1GW is 1GW no matter what generates it.  Nuclear operates at 90% CF because everything else is shut down to keep it running.  Natural gas peaking plants can run at 20%CF as this is all that is required.

You realistic CF for solar is completely wrong.  CSP plants without storage operate at 25%CF maybe however often that is all that is required for the market they sell electricty into.  A solar thermal plant with storage and an auxilary boiler burning biomass can generate power 24X7 if that is what is required.  When dinosaur baseload only plants are finally retired most plant can operate at a CF of 70% to 80% which solar plant can achieve easily.

So you calculations are based on a false assumption.  The 237 billion kWhr of electricity can be generated by a mixture of wind and solar thermal.  If the CSP is required to operate at 90%CF then it can.  However the average CF of power plants in Australia is around 70% so 12 hours of strorage coupled with our extremely good solar conditions should enable CSP to easilly achieve this with minimal supplemental fuel.

BTW after several lost posts on this blog I have got into the habit of copying my posts after writing them into the clipboard so when they get lost I can just go back into the thread and paste the comment straight back in.

RickEngebretson said:

Stephen, biomass gasification has gained a lot of interest here in Minnesota, USA. Using solar thermal for gasification you actually accumulate solar energy into the product fuel; "solar fuel." Physicists are leading this effort since the thermodynamics is obscure to many. The oil companies seem to have jumped on this. However, hay crops seem better than wood biomass. A protein rich livestock feed can be extracted along with cellulose. Wood has lignin which is a problem. I'm rebuilding an old barn and silo for this and hope to be done by the time I'm 100. Many prefer alfalfa, a deep rooted legume. Hay crops put carbon into the soil for a negative carbon footprint. Very attractive carbon offset fuel.

Nathan, many companies are working on solar windows. Most use a coating. But I think a set of blinds are easier to manage the optics with light pipes. That was my original reference to "refractive index" since that is how light pipes work.

Margaret, with climate change we have more fuel in Minnesota than we know what to do with. If you want to dig a mile deep under mountains and oceans to extract muck go ahead.

Nathan Wilson said:

Rick, yes it is possible to build concentrator based solar power systems.  Solar thermal of course uses concentrators, but perhaps you meant concentrated PV?

For CPV, there are a few companies offering/developing CPV products.  For example see  www.amonix.com/  and www.solfocus.com.

As you suggested, these concentrated PV systems use very small PV cells, and high (400x) concentration.  This makes them much more complex than flat plate PV, as 2-axis sun tracking is required as is effective heat-spreading for the cells.   A remarkable fact is that they use space-probe type tripple junction cells, which at 40% efficient, are double the efficiency of normal silicon cells.  The bad news is that they are only barely cost competative with flat plate.  And flat plate is better suited to residential roof-tops (most of the market).

MargaretHarding said:

Well, I made a lengthy response to everyone that didn't post here.

@Russ, I'm a realist. I like to have numbers that add up and make sense and don't violate the laws of physics as I understand them.

@Rick, Do I understand you correctly? Are you advocating using solar panels in smaller applications, like appliances, computers, etc. Interesting, but not a huge impact. The main pull for electricity in the home is HVAC, Refrigeration, and clothes dryers. Are you suggesting systems that will run these devices? I'd like to know more.

@Stephen,

You have quoted my numbers out of context. I was thinking about the original comment of "why do you discuss large amounts of real estate" with a comparative basic physics of sunlight on the planet's surface.

1 GW of solar is not the same as 1 GW of coal, nuclear, or natural gas. Solar only operates about 6 hours a day at a 1GW nameplate rating. You really have to go back to the kwh consumed in a year and calculate the amount of installed GW based on realistic capacity factors (25% being a reasonable maximum for solar). According to the EIA, Australia consumed about 237 billion KWh in 2006. Using that as a basis, you would have to install about 110 GW of solar (plus storage facilities and the associated losses related to energy conversion, but we'll ignore that). Last I read, a 400 MW solar facility would take about 3200 acres (1300 hectares) of land. So 110 GW of installed solar would require about 350,000 hectares of land.

I applaud your efforts to return land to usable farm land. Just not sure that solar facilities alone will provide sufficient power.

StephenGloor said:

I made a mistake here.  Australia could be powered by a square of collectors of 40 sq km not 40km X 40km.  This would be a square approx 7km on a side.  Gives you an idea of how little land is actually required.

Also this salt affected land has to be rehabilitated somehow.  One plan in Australia is to use short rotation trees:

www.aciar.gov.au/system/files/sites/aciar/files/.../IAS51+part+A.pdf

 "The impact-assessment study has found that, although the research clearly demonstrated that growing shortrotation trees can result in reclamation of abandoned land, adoption of the outcomes has not been high."

Short term cropping of Mallee trees which are ideal for gasification could actually help rehabilitate the land around the Solar Thermal Plant.  Large areas of nano scale, self replicating solar collectors (plants) could be planted to provide fuel for the CSP plant to be burnt in a gasification cycle that would also yield biochar if it was done correctly.  This biochar would then be placed in the soil enriching it.

Solar Thermal in these salt affected areas could end up returning thousands of hectares of valuable farmland in many countries such as Pakistan and Thailand where salt is a real problem.

Other references

http://cyllene.uwa.edu.au/~dpannell/dp0403.htm

http://www.reuters.com/article/idUSN1139875020080612

 

StephenGloor said:

Margaret - " I don't care if it is roof tops or acres of insolated desert, it still requires at least 1 million square meters."

Sounds like a lot doesn't it?  However 1 million square meters is 1km X 1km which is less than the area of many suburban car parks.  In Australia we can power  our approx 40GW of demand with a square 40km X 40km which is less than 0.03% of the area currently under agriculture.  In Australia we have 2.4 million hectares (24 000sq km) of land affected by salt that cannot be farmed.  Even if only 10% of this land was in good sun areas we still have 2 400 sq km of land that cannot be used for any other purpose which is more than enough and this is only the salt affected land.

 

RickEngebretson said:

I posted a lengthy comment that evaporated into virtual space.

A KW/sq m is a lot of power. Electricity is a low entropy, high value energy, so you will never get 1KW/sq m of solar electricity, as you say. But the 1KW is still there as heat and illumination, things people often wastefully derive from electricity. Thermodynamics.

So put the device where these different energy sources are consumed, in your home. Everybody likes a window.

Of course, you are roughly a 1KW machine, too. You eat food to fuel that machine. And that is equally impossible to many.

russbailey said:

@Margaret - You are obviously not green enough! The truly green group seems to believe that all things are possible if you just believe - the laws of nature, science and engineering are often not taken into account.

MargaretHarding said:

Rick,

I'm not a PhD in anything, but I'm a fairly intelligent person who would like to learn. You have concentrated light into an optic fiber. I'm impressed, but last I checked, nature still has some basic rules. Your response doesn't explain what I have missed with my three laws of nature. So, I'll be more explicit in my statements in the hopes that you will provide either a reference or an explanation I can read.

1) Sunlight hits the earth's surface at 1 kw per square meter. Simple mathematics tell me that at a minimum with a 100% efficient system, to generate 1 GW of electricity requires 1 million square meters. I don't care if it is roof tops or acres of insolated desert, it still requires at least 1 million square meters.

2) The sun does not shine 24 hours a day. It averages over the course of a year, 12 hours per day. Ignoring issues with energy storage efficiency and less optimal sun conditions for several of those 12 hours, that means that to get 1 GW continuously, you would need to cover 2 million square meters of roof tops, or desert, or what have you.

3) It is my understanding that no system will perfectly convert energy from one form to another. Thus, sunlight to electrical is not 100% efficient. Most systems are, at best, less than 30% efficient, thus requiring at least 6 million square meters.

If you can concentrate the light after it has arrived at the earth, and make the conversion to electricity more efficient then you get to change the ratios in my third assumption. What do I not understand here?
 

RickEngebretson said:

Margaret, after describing protein electronics in my Biophysics Ph. D. work (before the word "nanotechnology") I worked to concentrate light into an optical fiber. Some early advocates in the internet included my friend who invented digital electronics. Solar energy and solar fuels have worked for a few billion years. Nature is just more clever than we are.

MargaretHarding said:

Rick,

You're not considering some basic laws of nature.

1) Sunlight hits the earth's surface at an average of about 1 kw/square meter. You cannot concentrate solar power beyond that immutable fact.

2) The sun does not shine 24 hours/day, so additional energy must be generated and stored. At most, the average optimal sun is about 6 hours/day.

3) No energy conversion process is 100% efficient. Converting sunlight to electricity is another energy conversion process. 

When these three immutable facts of nature are properly understood, then one can fully appreciate solar energy's dilema in generating significant power for the country. Vast areas would have to be covered with solar PV or thermal conversion panels.

RickEngebretson said:

Electronics has evolved to accomplish more with less real estate. I don't understand why the insistence on large area PVs. Concentrators can be scaled from the very small to very large. Perhaps a better use of organic polymers is an "active refractive index element" as opposed to an "active circuit element."