Desert solar energy vs Solar Power Satellite

[neilzero]

I did this analysis to indicate that desert solar electricity is only about 1/10th as good as GEO or Solarsychronous SPS = solar power satellite. One half gigawatt is enough power for a large city. Very large cities need several gigawatts. Lets consider 12 square kilometers = 3 kilometers, East and West by 4 kilometers, North and South. There is a solar power tower close to the Southeast and Southwest corners of the property. They are about 200 meters tall. The land slopes up about 2% from South to North, but is otherwise quite flat. More slope would be better, but more is almost always hilly which is bad. You can see ideal sites are rare. Homes and ranches are practical except very close to the two solar power towers, but maximum height of trees and structures is typically 4 meters, but only 2 or 3 meters in a few spots. Exceptions are the 50,000 steerable mirror towers which range from 12 to 20 meters tall, a few of them with a wind turbine above the mirror. The mirrors average 100 square meters and produce an average of 400 watts per square meter in late June at 1 pm in their beam of sunlight. The heat exchangers near the top of the twin towers absorb an average of 2 gigawatts, and delivers 1.9 gigawatt to the steam turbines. Some additional energy comes from steam super heaters also on the tower. Electrical output is 0.5 gigawatts. With good luck the wind turbines and some photovoltaic panels produce 0.01 gigawatts for a total of 0.51 gigawatt put on the grid. Typically the grid accepts a bit less, so some heat energy is stored in the molton sodium-potassium nitrate in the heat exchanger, and a reserve tank. Sometimes this is sufficient to power the Southwest turbine at reduced power until an hour after sunset which is about the end of the peak demand period. Some additional mirrors may be located to the East of the towers to catch the late afternoon sun. While this would produce some evening reserve, it is likely not cost effective as the towers would be on private property.
As you can imagine, 50,000 mirror towers on 12 square kilometers, is near the limit to prevent shading each other in the late afternoon, especially in December when the sun is low in the sky. Shading is rather severe shortly after sunrise, but that is not very important as the wholesale price of electricity is low mid morning, and it does take about two hours to warm the sodium-potassium nitrate to optimum operating temperature each morning/3 hours typically in December. The installation cannot be enlarged except at diminishing returns, as a 4 kilometer beam produces an illuminated spot bigger than the heat exchanger, even if the mirror is minutely concave. A precision concave mirror is much more costly than plain mirrors and a 500 square meter heat exchanger has considerable heat loss in a high wind. I suppose transparent shutters would help on windy days, and the heat exchanger could be a bit larger than 500 square meters.
The start up crew arrives before sunrise, each morning at the SE tower, for the startup procedure. Typically they leave one technician to monitor, then go to the Southwest tower which will be in a poor position to receive energy until late morning. If there are no problems, all but two are off duty by one pm.
Perhaps ten employees, including two trainees, are needed as the towers need to be observed during start up on Saturday, Sunday, sickdays and holidays as well as week days, so payroll is not a trivial expense, even with the systems highly automated. Please embellish, refute and/or comment. Neil

w says: A receiver and rectenna almost as big would be needed for the microwaves from a solar power satellite. Both would also need operators and repairmen.

Me: w is correct. The satellite and desert 1/2 gigawatt are a bit easier to operate and maintain if they use space mature solar panels without mirrors, turbines and generators, but the huge microwave source and huge antenna will be essentually new technology which likely cannot be fully automated until we have a decade of operating experience. This is another good reason to operate the first several SPS in LEO, so that technicians can live on the satellite. The temperature cycling is likely more severe in LEO than in the desert and it will be an 88 minute cycle instead of a 24 hour cycle. LEO is, however, mostly spared the weather and seasonal cycles, and a semipolar orbit allows beaming to most of the countries of Earth, during part of the peak demand period with as few as ten satellites, I think. Neil

[KaiYeves]

Well, shouldn't we do both and get the maximum amount of clean energy?

[neilzero]

I agree, do both. Some of what we learn from large desert solar will be helpful in building SPS, called SSP by www.spacesolarpower.com If the SSP uses laser diodes instead of microwaves, existing large solar sites can receive the energy instead of building rectennas to receive microwaves. Neil

[KaiYeves]

And nanocables can efficiently carry the energy from the solar desert "farms" to towns and cities, according to National Geographic.

[danscope]

I did this analysis to indicate that desert solar electricity is only about 1/10th as good as GEO or Solarsychronous SPS = solar power satellite. One half gigawatt is enough power for a large city. Very large cities need several gigawatts. Lets consider 12 square kilometers = 3 kilometers, East and West by 4 kilometers, North and South. There is a solar power tower close to the Southeast and Southwest corners of the property. They are about 200 meters tall. The land slopes up about 2% from South to North, but is otherwise quite flat. More slope would be better, but more is almost always hilly which is bad. You can see ideal sites are rare. Homes and ranches are practical except very close to the two solar power towers, but maximum height of trees and structures is typically 4 meters, but only 2 or 3 meters in a few spots. Exceptions are the 50,000 steerable mirror towers which range from 12 to 20 meters tall, a few of them with a wind turbine above the mirror. The mirrors average 100 square meters and produce an average of 400 watts per square meter in late June at 1 pm in their beam of sunlight. The heat exchangers near the top of the twin towers absorb an average of 2 gigawatts, and delivers 1.9 gigawatt to the steam turbines. Some additional energy comes from steam super heaters also on the tower. Electrical output is 0.5 gigawatts. With good luck the wind turbines and some photovoltaic panels produce 0.01 gigawatts for a total of 0.51 gigawatt put on the grid. Typically the grid accepts a bit less, so some heat energy is stored in the molton sodium-potassium nitrate in the heat exchanger, and a reserve tank. Sometimes this is sufficient to power the Southwest turbine at reduced power until an hour after sunset which is about the end of the peak demand period. Some additional mirrors may be located to the East of the towers to catch the late afternoon sun. While this would produce some evening reserve, it is likely not cost effective as the towers would be on private property.
As you can imagine, 50,000 mirror towers on 12 square kilometers, is near the limit to prevent shading each other in the late afternoon, especially in December when the sun is low in the sky. Shading is rather severe shortly after sunrise, but that is not very important as the wholesale price of electricity is low mid morning, and it does take about two hours to warm the sodium-potassium nitrate to optimum operating temperature each morning/3 hours typically in December. The installation cannot be enlarged except at diminishing returns, as a 4 kilometer beam produces an illuminated spot bigger than the heat exchanger, even if the mirror is minutely concave. A precision concave mirror is much more costly than plain mirrors and a 500 square meter heat exchanger has considerable heat loss in a high wind. I suppose transparent shutters would help on windy days, and the heat exchanger could be a bit larger than 500 square meters.
The start up crew arrives before sunrise, each morning at the SE tower, for the startup procedure. Typically they leave one technician to monitor, then go to the Southwest tower which will be in a poor position to receive energy until late morning. If there are no problems, all but two are off duty by one pm.
Perhaps ten employees, including two trainees, are needed as the towers need to be observed during start up on Saturday, Sunday, sickdays and holidays as well as week days, so payroll is not a trivial expense, even with the systems highly automated. Please embellish, refute and/or comment. Neil

w says: A receiver and rectenna almost as big would be needed for the microwaves from a solar power satellite. Both would also need operators and repairmen.

Me: w is correct. The satellite and desert 1/2 gigawatt are a bit easier to operate and maintain if they use space mature solar panels without mirrors, turbines and generators, but the huge microwave source and huge antenna will be essentually new technology which likely cannot be fully automated until we have a decade of operating experience. This is another good reason to operate the first several SPS in LEO, so that technicians can live on the satellite. The temperature cycling is likely more severe in LEO than in the desert and it will be an 88 minute cycle instead of a 24 hour cycle. LEO is, however, mostly spared the weather and seasonal cycles, and a semipolar orbit allows beaming to most of the countries of Earth, during part of the peak demand period with as few as ten satellites, I think. Neil

*****************
Hi, Who do you fry when that RF Beam goes astray? Pick a state.....
any state.......even many states.
Sir: local solar and wind is adequate. We need a change of mind set.
Best regards, Dan

[samkent]

Doesn’t cost effeteness come into the equation? The equivalent number of acres of photovoltaic arrays doesn’t require new technology. Plus you have built in redundancy unlike the other plans. Repairs and normal maintenance are very easy by comparison. Anyone who has traveled the western areas of the US know there is a ton of land that has no other usefull purpose.

If you want it to work right in the long term it has to be simple. KISS

[Noclevername]

*****************
Hi, Who do you fry when that RF Beam goes astray?

Well, since you, me and everyone on Earth currently have radio waves passing through them and are not dead, why do anything? But for worry-warts, a simple negative feedback loop is easy enough to engineer. Beam goes off course, beam no longer receives signal from Earthside receiver, beam shuts down.

Sir: local solar and wind is adequate. We need a change of mind set.
Best regards, Dan

Adequate for what, and by whose measurements?

[Van Rijn]

The Glaser/O'Neill SPS proposals in the '70s assumed an SPS in geosync orbit with a low energy density receiver on the ground. A person or a bird going through the "microwave beam" might notice a slight warming, but that was about it. It wouldn't be much of a death ray. The advantage of the SPS was that it could be placed in an orbit that would almost always be in sunlight, and ground based rectennas could be quite efficient (80% or so), simple in construction, and could be placed anywhere in view of the SPS (that would leave out locations close to the poles, but would cover most of the planet).

The big problem with SPS, and with ground based PV solar for that matter, is cost. Ground based solar also has to deal with power storage: You need to consider night time and weather.

[Noclevername]

A statite positioned above each pole could cover those regions, and be in sunlight full-time.

[Larry Jacks]

A statite positioned above each pole could cover those regions, and be in sunlight full-time.

Except that's physically impossible.

A satellite in a geostationary orbit is in sunlight almost 100% of the time. The only times it isn't fully exposed to the sun is during eclipse season. This happens twice a year centered on the equinoxes. The longest period for an eclipse is 72 minutes for a satellite at 0 degrees inclination. Eclipse season starts a few weeks before an equinox and lasts for a few weeks afterwards. The first few are just a few minutes long and typically aren't even full eclipses. There is an occassional lunar eclipse that can last longer than 72 minutes but those are fairly rare.

[Noclevername]

A statite positioned above each pole could cover those regions, and be in sunlight full-time.

Except that's physically impossible.

A satellite in a geostationary orbit is in sunlight almost 100% of the time. The only times it isn't fully exposed to the sun is during eclipse season. This happens twice a year centered on the equinoxes. The longest period for an eclipse is 72 minutes for a satellite at 0 degrees inclination. Eclipse season starts a few weeks before an equinox and lasts for a few weeks afterwards. The first few are just a few minutes long and typically aren't even full eclipses. There is an occassional lunar eclipse that can last longer than 72 minutes but those are fairly rare.

Statite, not to be confused with satellite.

[Chuck]

Solar panels will kill us all. Light that would normally be reflected back into space will be converted into electricity and then into heat as the electricity does work. More global warming. What we really need is population reduction. Nothing else will solve the problem. People using energy will produce heat no matter where the power comes from.

[Van Rijn]

Solar panels will kill us all. Light that would normally be reflected back into space will be converted into electricity and then into heat as the electricity does work. More global warming. What we really need is population reduction. Nothing else will solve the problem. People using energy will produce heat no matter where the power comes from.

The amount is trivial. Somewhere I saw a calculation, but unfortunately I don't remember the details, assuming all energy came from fission, fusion, or was beamed in from space. There would be direct heat input, but no greenhouse gas effects. Anyway, it took the entire world population using energy at many times that of per capita use in industrialized countries before it started to have a significant effect.

[Ivan Viehoff]

I did this analysis to indicate that desert solar electricity is only about 1/10th as good as GEO or Solarsychronous SPS = solar power satellite.

I looked somewhere in your analysis to find the demonstration that the latter cost 10 times less per useful delivered kWh, but I didn't find it.

There are huge amounts of desert spaces in places like Mauretania and Algeria, etc, where we could get huge amounts of electricity by putting only a small proportion of it to work, and with very limited environmental impact. The only question is how much does it cost to generate and how much does it cost to transport the energy to places of high demand. Within a broad range, absolute efficiency of such facilities is not important, except inasmuch as it affects the cost.

Your analysis talks about taking 2-3 hours heating something up to operating temperature. Perhaps it makes sense to pre-heat it with some stored energy.

[Chuck]

The amount is trivial. Somewhere I saw a calculation, but unfortunately I don't remember the details, assuming all energy came from fission, fusion, or was beamed in from space. There would be direct heat input, but no greenhouse gas effects. Anyway, it took the entire world population using energy at many times that of per capita use in industrialized countries before it started to have a significant effect.

The amount of heat might be trivial for the amount of electricity we're using now but we're not very good at knowing when to quit. We'll be wanting more power per person in the future and will have more people making this demand.

[Argos]

Now this is cool. Seville solar power station.

[Noclevername]

The amount of heat might be trivial for the amount of electricity we're using now but we're not very good at knowing when to quit. We'll be wanting more power per person in the future and will have more people making this demand.

Or we may follow the current trend of becoming more efficient in our use of energy. Thus greatly reducing the amount used per person.

[Ivan Viehoff]

Now this is cool. Seville solar power station.

I presumed that was roughly what OP had in mind. The article quoted talks about energy costing about 3 times as much as fossil fuel. That's quite a premium.

[Delvo]

I find it sociologically/politically/economically interesting that the main "resource" that's abundant in the Middle East, other than oil, happens to potentially be a fairly direct replacement for it: lots of sunlight and land that's not really good for anything but collecting sunlight with.

[Noclevername]

Just because desert isn't useful to humans doesn't mean it's not useful. In fact I don't know of any studies that consider what the effects of putting shade over large amounts of desert land would do. More condensation? Will we need to plant ground cover to prevent sudden erosion of soil from under our solar collectors?

[Ivan Viehoff]

Just because desert isn't useful to humans doesn't mean it's not useful. In fact I don't know of any studies that consider what the effects of putting shade over large amounts of desert land would do. More condensation? Will we need to plant ground cover to prevent sudden erosion of soil from under our solar collectors?

I presume you are talking about the wind-scour that results from the wind-channelling arising from a support pillar being installed. This results in the foundations being self-excavating, if installed on loose material. You can do what oil-platforms do to avoid precisely this problem, which is drape some fabrics around the base of the pillar. This causes the pillar to collect rather than excavate loose material.

Shading the land ought to reduce evaporation, and hence promote plant growth on balance in these sorts of places. But I think you will discover that the proportion of land that is shaded in these schemes is quite low.

I was led to believe from the dimensions (2km2) and eventual output (50MW)of Seville that you get about 25 MW/km2. Assuming it can only run at 40% the load factor of conventional plant (that's different and a lot worse than saying 40% load factor), then it replaces 10MW of conventional plant. From that, you need about 7,500km2 to deliver the installed electricity capacity of the UK (75,000MW), which is a comfortingly low 3% of our land area (not that our land is very suitable for it, being at high latitude and cloudy). UK has about 1% of the world's population, so even at UK levels of energy consumption, then that can be delivered with 750,000km2 of solar thermal, which is 3 times the area of the UK, or about 8% of the Sahara desert, or just a little more than Texas.

In contrast, I calculated that growing miscanthus grass for bio-mass power stations, which is the most efficient use of land for biomass in moderate temperate climates, would require us to put about 30% of the UK under miscanthus cultivation, just to replace electricity. For our entire energy demand, you'd need the whole country. In fact I think I once calculated that to replace the world's energy demand with biomass would probably require an area of land similar to the entire present agricultural land of the planet. The Swedes, Finns, Russians and Canadians can get on with biomass electricity because they have sparse populations and plenty of land that may as well grow trees or grass for burning. But most of the rest of us who have land scarcity for growing things will find solar thermal much more practical, when it comes to looking for a genuine large-scale alternative to fossil fuel for electricity.

[DyerWolf]

Doesn’t cost effeteness come into the equation?

I'm much more comfortable with robust cost evaluations myself...

[Noclevername]

Originally Posted by samkent
Doesn’t cost effeteness come into the equation?

I'm much more comfortable with robust cost evaluations myself...

He must be using the C-3PO actuarial software...

[danscope]

When it comes to solar energy, one of the biggest chips in the game is Windpower. Scandinavian countries are getting 30% of their power from wind.
It can be done. It makes jobs and power and no polution.
Now you think about that......

[galacsi]

Doesn’t cost effeteness come into the equation? The equivalent number of acres of photovoltaic arrays doesn’t require new technology. Plus you have built in redundancy unlike the other plans. Repairs and normal maintenance are very easy by comparison. Anyone who has traveled the western areas of the US know there is a ton of land that has no other usefull purpose.

If you want it to work right in the long term it has to be simple. KISS

You are right , photovoltaic panels are simpler , can be continually and easily upgraded and repaired and yield much more electricity within 12 KM2 , that the solar towers.
And more , they can be put on every flat roof of supermarkets , factories and warehouses and so on.And so you can have your energy produced just near where it is needed. Another good point !

Also they can be both big and small projects.

First time i learned about these solar towers , i was enthusiast, but now i know better. IMO it more like engineer megalomania.

[Delvo]

...but what does it take to produce that much surface area of those panels?

[KaiYeves]

...but what does it take to produce that much surface area of those panels?

Assuming that they are traditional panels, lots. But they will probably be the new thin-as-a-coat-of-paint nanotech panels, which are much cheaper.

[Chuck]

Or we may follow the current trend of becoming more efficient in our use of energy. Thus greatly reducing the amount used per person.

That would slow down the warming but not stop it. We can't reduce our power consumption per person to zero but we can increase our population to disaster no matter how little each person uses.

[Noclevername]

That would slow down the warming but not stop it. We can't reduce our power consumption per person to zero but we can increase our population to disaster no matter how little each person uses.

Increasing population is a problem, yes, but it need not be a disaster. Nor do we need to reduce our energy usage to zero or anything close to it; just low enough to match what is available from renewable sources. Which is certainly feasible given current and near-term advances in technology. Even with no new advances, just updating existing equipment will greatly improve efficiency in many industries.

[neilzero]

Some people at www.realclimate.org were concerned that a million square kilometers of solar panels two or three meters above above the world's deserts would distroy the ecology of our deserts. The concentrating mirrors would be worse short term, but better long term, if they rarely needed repairs, and cleaning. One square kilometer would only produce about 20 megawatt average in late December = 20,000 gigawatts = 20 terrawats, from a million square kilometers, unless technology improves.
Some designs of receiving sites (of the beam from the SSP) would be better for the ecology, but not a lot better.
Beam density will be low enough for early SSP, that a human would notice only a slightly warm feeling, but higher beam density might be used in war zone, emergency and in 22nd century SSP.
The high efficiency photovoltaic panels are not being mass produced yet and may cost lots more when they are mass produced. The steam turbines are old technology and not likely to improve much. The concentrating mirrors can be used with both towers and photovoltaic panels which may be available next year. If so, hybrid will likely be best. Steerable mirrors are best as they work reasonably well all day except very close to sunrise and sunset. They also let about 3/4 of the light reach the surface, and may be 20 times better than nonsteerable in Alberta, Canada in December.That is because the sun is close to the horizon 7 hours per day in Alberta and below the horizon the other 17 hours per day in late December. I posted the following on www.realclimate.org
I’ve been collecting details on SSP = space solar power for about 2 decades. It clearly is not competitive with coal before 2030 unless we assign huge amounts of collateral damage to coal. Since coal likely puts more radiation in Earth’s atmosphere than nuclear power by the KWH, and has other collateral damage it causes, huge may be prudent. If we spend 80 billion on SSP, before 2030, we have no guarantee that SSP will look good after 2030, but that is true of all our other options, so I am urging a demonstration SSP by 2012, sooner, if we can get reasonably organized. http://spacesolarpower.wordpress.com
The 80? billion invested in wind power so far seems to have a good shot at being money well spent, so I recommend another 80 billion for wind power before 2012.
We need to make an 80 billion dollar commitment to photovoltaic in the next year or two or the manufacturing capacity for photovoltaic won’t be available in 2013 for the next scale up of SSP.
While present heavy lift is ok for a demonstration SSP, we won’t have a practical way to get the 2013 larger SSP even to LEO = Low Earth Orbit, unless we invest another $80 billion plus in heavy lift. Perhaps this amount has already been appropriated.
Three of my other favorites are www.liftport.com www.skywindpower.com and very large high altitude balloons, which each need a few million dollars near term to make progress.
Wind turbines produce more kilowatt hours per square kilometer, than the very best photovoltaic locations, and are less costly until cheap photovoltaic is available. Only about 1% of land area is sutable for wind turbines, so they likely can supply no more than 1% of our energy needs in some counties and states.
I’ve given medium amounts of thought on most of these topics. I suppose the USA could come up with 8 billion as it’s share of 80 billion world wide, but I have seen little detail on how the money would, or should be spent. I suspect half of the species loss is in Brazil. Purchasing land there as bio preserves is reasonable, but will surely be regarded as meddling in Brazil’s internal affairs if we buy up several billion dollars worth of Brazil’s land. Also how can we be reasonably assured that good jugement will be used in selecting the pieces of land to purchase? How can we be assured that the land will remain an effective biodiversity preserve long term? Are details available? I’m suspicious that this is another scam to make a few people rich.
I’ve been collecting details on SSP = space solar power for about 2 decades. It clearly is not competitive with coal before 2030 unless we assign huge amounts of collateral damage to coal. Since coal likely puts more radiation in Earth’s atmosphere than nuclear power by the KWH, and has other collateral damage it causes, huge may be prudent. If we spend 80 billion on SSP, before 2030, we have no guarantee that SSP will look good after 2030, but that is true of all our other options, so I am urging a demonstration SSP by 2012, sooner, if we can get reasonably organized. http://spacesolarpower.wordpress.com
The 80? billion invested in wind power so far seems to have a good shot at being money well spent, so I recommend another 80 billion for wind power before 2012.
We need to make an 80 billion dollar commitment to photovoltaic in the next year or two or the manufacturing capacity for photovoltaic won’t be available in 2013 for the next scale up of SSP.
While present heavy lift is ok for a demonstration SSP, we won’t have a practical way to get the 2013 larger SSP even to LEO = Low Earth Orbit, unless we invest another $80 billion plus in heavy lift. Perhaps this amount has already been appropriated.
Three of my other favorites are www.liftport.com www.skywindpower.com and very large high altitude balloons, which each need a few million dollars near term to make progress. Neil