• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

Solar thermal Energy

DC

Banned
DC
Joined
Mar 20, 2008
Messages
23,064
Are Solar Thermal Powerplants in combination with molten salt storage a technology for the future?

A very promising technology i think first plants already run.

interesting presentation of the current state of the technology.

 
Solar power has its attractions, but the environmental costs are often over looked.

For example:

US annual power consumption is about 3 x 10^16 W-hr.

Generating that by solar, assuming 300 clear days a year requires 10^11 KW-hr / day.

Assuming 6 hrs / day operation says solar generation needs to collect 1.6 x 10^10 KW.

With 100% efficiency, this would require 1.6 x 10^10 sq meters (solar irradiance is about 1 KW / sq m.)

But no process is 100% efficient. Let's assume 20% system efficiency, which says we need 8 x 10^10 sq meters. This efficiency is arguably a bit low, but we'll ignore the need for extra footprint for support functions.

So going all-solar requires about 30,000 square miles of collector. That's about the area of South Carolina. And not much can grow under these collectors, so it's basically a desert. Now, it's true that desert is exactly where you'd put this stuff, since the air is clear and there isn't much rain, but the Sierra Club would have a cow. And putting everything out west means that supplying places like New England would drag down the system efficiency even more, requiring even more collector area.

None of this means that large-scale solar isn't possible, mind you. It's just that folks don't often think about the scale of construction required and the costs of various kinds that would be incurred.
 
WhatRoughBeast said:
Solar power has its attractions, but the environmental costs are often over looked.

For example:

US annual power consumption is about 3 x 10^16 W-hr.

Generating that by solar, assuming 300 clear days a year requires 10^11 KW-hr / day.

Assuming 6 hrs / day operation says solar generation needs to collect 1.6 x 10^10 KW.

With 100% efficiency, this would require 1.6 x 10^10 sq meters (solar irradiance is about 1 KW / sq m.)

But no process is 100% efficient. Let's assume 20% system efficiency, which says we need 8 x 10^10 sq meters. This efficiency is arguably a bit low, but we'll ignore the need for extra footprint for support functions.

So going all-solar requires about 30,000 square miles of collector. That's about the area of South Carolina. And not much can grow under these collectors, so it's basically a desert. Now, it's true that desert is exactly where you'd put this stuff, since the air is clear and there isn't much rain, but the Sierra Club would have a cow. And putting everything out west means that supplying places like New England would drag down the system efficiency even more, requiring even more collector area.

None of this means that large-scale solar isn't possible, mind you. It's just that folks don't often think about the scale of construction required and the costs of various kinds that would be incurred.
Click to expand...
I'm kinda peeved by all these calculations that assume that the whole of energy production is supposed to be replaced by just one particular proposed technology.

This is not what proponents of alternative energy productions propose, as far as I encountered them. They always assume a mix of different technologies used for those areas where they work particular well, and they always propose a gradual, not abrupt, change away from current technologies.
 
WhatRoughBeast said:
So going all-solar requires about 30,000 square miles of collector. That's about the area of South Carolina.
Click to expand...
As elgarak has just pointed out, "going solar" doesn't necessarily have to equate to "going all solar".

And not much can grow under these collectors, so it's basically a desert.
Click to expand...
"Solar thermal" encompasses a rather broad category of different types of systems. For example, the solar updraft tower involves construction of a very large greenhouse with a roof that gradually slopes up toward a large tower at the center which houses turbines for generating electricity. Growing plants under that glass at the same time is something that can be done, and already has been done with at least one prototype, though my guess is that it would tend to impede airflow somewhat and thereby compromise electrical generating capacity. It might still be an acceptable tradeoff under some circumstances.

That Wiki article mentions one such installation which began operating last December in China's Inner Mongolia Autonomous Region. They put the thing over sand (like they had a choice), and it relies a lot on the heat absorbing potential of that -- an added bonus is that one thing all that covered sand isn't doing is blowing around (they're losing entire cities to encroaching dunes). I don't know how practical it will turn out to be as a way of generating electricity, but it's still a fun idea.
 
WhatRoughBeast said:
Solar power has its attractions, but the environmental costs are often over looked.

For example:

US annual power consumption is about 3 x 10^16 W-hr.

Generating that by solar, assuming 300 clear days a year requires 10^11 KW-hr / day.

Assuming 6 hrs / day operation says solar generation needs to collect 1.6 x 10^10 KW.

With 100% efficiency, this would require 1.6 x 10^10 sq meters (solar irradiance is about 1 KW / sq m.)

But no process is 100% efficient. Let's assume 20% system efficiency, which says we need 8 x 10^10 sq meters. This efficiency is arguably a bit low, but we'll ignore the need for extra footprint for support functions.

So going all-solar requires about 30,000 square miles of collector. That's about the area of South Carolina. And not much can grow under these collectors, so it's basically a desert. Now, it's true that desert is exactly where you'd put this stuff, since the air is clear and there isn't much rain, but the Sierra Club would have a cow. And putting everything out west means that supplying places like New England would drag down the system efficiency even more, requiring even more collector area.

None of this means that large-scale solar isn't possible, mind you. It's just that folks don't often think about the scale of construction required and the costs of various kinds that would be incurred.
Click to expand...

how much space would be needed to replace the worlds electricity production with Solar thermal was actually part of the video.
they think some 240 000 squer miles would be enough to replace today's world prodcution.
 
the most interesting aspect i think is the hot salt storage. This way it even can be a solution for baseload.
 
WhatRoughBeast said:
Solar power has its attractions, but the environmental costs are often over looked.

For example:

US annual power consumption is about 3 x 10^16 W-hr.

Generating that by solar, assuming 300 clear days a year requires 10^11 KW-hr / day.

Assuming 6 hrs / day operation says solar generation needs to collect 1.6 x 10^10 KW.

With 100% efficiency, this would require 1.6 x 10^10 sq meters (solar irradiance is about 1 KW / sq m.)

But no process is 100% efficient. Let's assume 20% system efficiency, which says we need 8 x 10^10 sq meters. This efficiency is arguably a bit low, but we'll ignore the need for extra footprint for support functions.

So going all-solar requires about 30,000 square miles of collector. That's about the area of South Carolina. And not much can grow under these collectors, so it's basically a desert. Now, it's true that desert is exactly where you'd put this stuff, since the air is clear and there isn't much rain, but the Sierra Club would have a cow. And putting everything out west means that supplying places like New England would drag down the system efficiency even more, requiring even more collector area.

None of this means that large-scale solar isn't possible, mind you. It's just that folks don't often think about the scale of construction required and the costs of various kinds that would be incurred.
Click to expand...

Ethan Siegel at Scienceblogs puts the area at 35 miles by 35 miles = 1225 square miles.

In the mean time, I "see" hundreds of square miles of roof tops that could be fitted with solar, but aren't.
 
It's certainly one of the favoured technologies for Desertec. Stick huge solar thermal plants in North Africa and use an HVDC grid to distribute it. Lump in geothermal in Iceland, tidal stream around Wales and Scotland, offshore wind, hydro in Norway, nuke in many of the countries, and you have a fairly sustainable capacity. North Africa benefits from better power generation, and a steady national income.

http://www.desertec.org/
 
DC said:
the most interesting aspect i think is the hot salt storage. This way it even can be a solution for baseload.
Click to expand...

Another good method, where geography permits, is reservoir storage.

During the day (or when it is windy in the case of wind power) you use excess capacity to pump water uphill into a reservoir, and then when you need more than is being produced, the process reverses and the water flows downhill and drives turbines.
 
BenBurch said:
Another good method, where geography permits, is reservoir storage.

During the day (or when it is windy in the case of wind power) you use excess capacity to pump water uphill into a reservoir, and then when you need more than is being produced, the process reverses and the water flows downhill and drives turbines.
Click to expand...

Pumped hydro is one of the more efficient storage solutions (which may seem strange to some), unfortunately there aren't many places where it's feasible. And you can sometimes get this :p
 
elgarak said:
I'm kinda peeved by all these calculations that assume that the whole of energy production is supposed to be replaced by just one particular proposed technology.

This is not what proponents of alternative energy productions propose, as far as I encountered them. They always assume a mix of different technologies used for those areas where they work particular well, and they always propose a gradual, not abrupt, change away from current technologies.
Click to expand...

Oh, come on. Give me a break.

I used the assumption of all-solar just to give a clear target for the calculations, and to let folks see the scale of things.

Fine. Only half the energy comes from solar. The area is now 16,000 square miles. Somewhere between Maryland and West Virginia. Is that really better?

While it's true that most alternative energy types propose a mix of technologies, who is to say that that is what will happen? These things are under the thumb of the political process, and consider the following:

Nukes cause radiation.
Wind turbines kill birds.
Biomass has low efficiency and low density.
Wave generators kill plankton and mess with fish.

And the list goes on. Every technology has costs, and every cost has a community of opponents. And every community can hire lobbyists. So there is no guarantee that there will be any mix of technologies that you or I agree with.

Also, I recommend the OP video. It's nearly an hour, but it addresses a lot.

Just as a starter, consider the amount of energy theoretically available for each technology (video 09:30 and 47:30). There's a _lot_ more solar power available than anything else.

daenku32 said:
Ethan Siegel at Scienceblogs puts the area at 35 miles by 35 miles = 1225 square miles.

In the mean time, I "see" hundreds of square miles of roof tops that could be fitted with solar, but aren't.
Click to expand...

With all due respect to Ethan, he's dropped at least 2 decimal places. Do the math yourself. Also keep in mind that Ethan says his area provides power regardless of weather, which in the short term doesn't work. The video (43:00) says 10% of the BLM holdings in Nevada. That's a whole lot more that Ethan's 1200 square miles. Although keep in mind that Ethan and the video talk about electrical energy, and my numbers are all power (with no allowances for efficiencies).

The video makes the point that putting solar panels on roofs is very bad economically. It's 3 times more expensive than building from scratch. (video 49:00). That's for power only, but the video says power/heat/cooling combos may make sense. And if you want to add storage capacity, the video makes it clear that energy storage works much better at large scale. For thermal storage, for instance, the square-cube law really points to big. Notice in the video, 37:00, where a molten salt unit uses 28 kilotons of material.
 
Last edited:
WhatRoughBeast said:
Oh, come on. Give me a break.

I used the assumption of all-solar just to give a clear target for the calculations, and to let folks see the scale of things.

Fine. Only half the energy comes from solar. The area is now 16,000 square miles. Somewhere between Maryland and West Virginia. Is that really better?

While it's true that most alternative energy types propose a mix of technologies, who is to say that that is what will happen? These things are under the thumb of the political process, and consider the following:

Nukes cause radiation.
Wind turbines kill birds.
Biomass has low efficiency and low density.
Wave generators kill plankton and mess with fish.

And the list goes on. Every technology has costs, and every cost has a community of opponents. And every community can hire lobbyists. So there is no guarantee that there will be any mix of technologies that you or I agree with.

Also, I recommend the OP video. It's nearly an hour, but it addresses a lot.

Just as a starter, consider the amount of energy theoretically available for each technology (video 09:30 and 47:30). There's a _lot_ more solar power available than anything else.



With all due respect to Ethan, he's dropped at least 2 decimal places. Do the math yourself. Also keep in mind that Ethan says his area provides power regardless of weather, which in the short term doesn't work. The video (43:00) says 10% of the BLM holdings in Nevada. That's a whole lot more that Ethan's 1200 square miles. Although keep in mind that Ethan and the video talk about electrical energy, and my numbers are all power (with no allowances for efficiencies).

The video makes the point that putting solar panels on roofs is very bad economically. It's 3 times more expensive than building from scratch. (video 49:00). That's for power only, but the video says power/heat/cooling combos may make sense. And if you want to add storage capacity, the video makes it clear that energy storage works much better at large scale. For thermal storage, for instance, the square-cube law really points to big. Notice in the video, 37:00, where a molten salt unit uses 28 kilotons of material.
Click to expand...

what is the source for your squaremiles calculations? they are very different from numbers form experts in the field.
 
DC said:
what is the source for your squaremiles calculations? they are very different from numbers form experts in the field.
Click to expand...


The base total energy number (29 x 10^15 W-hr) comes from http://en.wikipedia.org/wiki/Energy_in_the_United_States. I rounded up a hair to allow for population growth.
And no, they're not that different. Again, note that mine are for all US energy, not just current electrical use. From http://en.wikipedia.org/wiki/Electricity_sector_in_the_United_States the electrical production is about 4 x 10^15 W-hr, so the total energy use is about 7 times the electrical. The OP video (10:50) calculates about 8400 square miles for electricity, so their estimate for replacing all energy with solar thermal would be about 59,000 square miles (assuming, as noted before, no conversion losses). That's within a factor of 2 of my estimate, and I don't know what they're assuming for system efficiency.

Presumably the video estimate is better than mine, but I was just trying for a ballpark estimate.

Close enough for government work.
 
WhatRoughBeast said:
The base total energy number (29 x 10^15 W-hr) comes from http://en.wikipedia.org/wiki/Energy_in_the_United_States. I rounded up a hair to allow for population growth.
And no, they're not that different. Again, note that mine are for all US energy, not just current electrical use. From http://en.wikipedia.org/wiki/Electricity_sector_in_the_United_States the electrical production is about 4 x 10^15 W-hr, so the total energy use is about 7 times the electrical. The OP video (10:50) calculates about 8400 square miles for electricity, so their estimate for replacing all energy with solar thermal would be about 59,000 square miles (assuming, as noted before, no conversion losses). That's within a factor of 2 of my estimate, and I don't know what they're assuming for system efficiency.

Presumably the video estimate is better than mine, but I was just trying for a ballpark estimate.

Close enough for government work.
Click to expand...

ah ok total energy. its not much space it needs then.
 
Regrets.

I worked on the Solar One plant in Barstow; it was a 10 Mw pilot plant built by (then) Martin Marietta, Solar Power Division. There were three projects being worked on at the same time - Solar One, a tube heating system for Elmira Spain, and a third I can no longer remember much about. The Elmira plant used molten salt, with underground insulated storage tanks and cloud sensors to drain the collectors into the underground tanks when clouds were detected.

The Solar One plant used an array of 1200 heliostats, each one individually controlled by a microprocessor, and fed sun position and polled for data once every eight seconds. Martin had a plant built in Pueblo, CO for building the heliostats, each one had 9 six ft square mirrors.

That was when solar was booming, in Carter's presidency. The week after Regan won the election, rumors started circulating about people being moved off solar to other projects. Two Regan staffers came to look at what we were doing; two months later Martin closed its Pueblo plant and dropped all further work on solar. After the plants contracted for were delivered, Martin closed the division. Solar One ran at Barstow for ten years, was reworked as he described (I was gone from Martin by then) , and then decommissioned in the early 90s. It's still there; look at http://maps.google.com/?ie=UTF8&ll=34.871954,-116.833248&spn=0.009066,0.01929&t=h&z=16 . The pilot tube plant, much newer, is right next door.

I imagine Martin Lockheed wishes they had continued pursuing it. Regan was so happy about oil prices coming back down.

Mainland China gleefully displays one of the solar water heaters which Carter had installed on the WhiteHouse and Regan had pulled back down, at one of their solar plants.
 
Last edited:
You must log in or register to reply here.

Back
Top Bottom