# Profit margin for Solar Chimney projects and land power density?

It is said that the Madrid Spain solar chimney project occupies 110 acres land, but only output humble 50 kw: https://en.wikipedia.org/wiki/Solar_updraft_tower

The fact: the average yearly solar power density of above powerplant = 0.11 W/m^2

Interestingly, there are many countries still planning next solar chimney projects, such as the billions dollar project of solar chimney with land coverage of circa 100 square kilometers in the desert of China who is the biggest PV solar panel production country in the world.

Why the harvestable solar power density is so tiny, and still sought-after?

To answer this question, we need a reference frame.

In comparison with planting cash crops, what is the minimal yet profitable power density PD of a land size dependent power generator?

Assuming energy price just as same as Hydro company $0.10/kwh, and given 1 acre = 4047 m^2, harvestable$653/acre/year soybean from USA agriculture statistic data.

Solve from this equation: 0.1 x (4047 x PD x 24 x 365 / 1000) = 653

We get: PD = 0.18 W/m^2

It means that every new invented method of solar energy harvest must have at least 0.18 W/m^2, despite the transient powerful sunshine 1360 W/m^2.

The power density 0.11 W/m^2 of the Spanish project is very close to this threshold, and obviously there is still potential for improvement.

Perhaps that is the possible answer for the question.

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Dale
Mentor
2021 Award
It means that every new invented method of solar energy harvest must have at least 0.18 W/m^2,
Photovoltaic cells seem to exceed that by a factor of 1000 approximately

https://en.m.wikipedia.org/wiki/Solar_panel

russ_watters
Photovoltaic cells seem to exceed that by a factor of 1000 approximately

https://en.m.wikipedia.org/wiki/Solar_panel
Therefore, if a farmer switches to PV power generation, a 1000 times profit than cash-crops can be gained?

But curiously, why my neighboring farmers who installed PV many years ago, they are still unhappy with the supposed 1000 times profit? Even a few of guys dismantled and sold the panels, then re-farm the land with dirty cheap crops.

If PV super good and I were president of china, I would pass some special laws: prohibiting PV export and making full domestic use; reducing crude oil import; switching crops plantation to PV power generation; importing all foods from other countries; ...

anorlunda
Staff Emeritus
Therefore, if a farmer switches to PV power generation, a 1000 times profit than cash-crops can be gained?

No. It means that power density w/m^2 is a poor way to measure the usefulness or the value.

russ_watters and Dale
Dale
Mentor
2021 Award
Therefore, if a farmer switches to PV power generation, a 1000 times profit than cash-crops can be gained?

But curiously, why my neighboring farmers who installed PV many years ago, they are still unhappy with the supposed 1000 times profit?
Probably because they made bad assumptions and are not getting that much profit, despite the power.

Probably because they made bad assumptions and are not getting that much profit, despite the power.
"Too good to be true, I was misguided by bad scientists & government agents, the gain even cannot cover loan interest", some guys complained.

Dale
Mentor
2021 Award
"Too good to be true, I was misguided by bad scientists & government agents, the gain even cannot cover loan interest", some guys complained.
Yes, that sounds right. So going back to your assumptions, what do you think you may have missed?

The old fable: A rabbit and a turtle are racing on a racetrack, unfortunately the winner is the turtle, not the rabbit.
Of course, the rabbit transient "power density" is far greater than the turtle. Why the rabbit is the loser?
Perhaps this may be the same scenario: PV & solar chimney.
PV is too picky on direct sunshine, it outputs zero during long night, even almost zero during dawn & dusk & overcasting weather. Therefore PV hates to be averaged by 365*24 = 8760 hours.
A solar-tracking mechanism is very important to PV. Also in hot weather above 30 Celsius degree, the efficiency will plummet freefally, so cooling system is better to have.

Dale
Mentor
2021 Award
No, that isn’t the issue at all. The problem is that you are looking only at revenue, not costs. Profit is revenue - cost.

Kiwaho Kilowatthour
No, that isn’t the issue at all. The problem is that you are looking only at revenue, not costs. Profit is revenue - cost.
Therefore, the correct math equation for equivalence should be:
0.1 x (4047 x PD x 24 x 365 / 1000) - SystemCost = 653 - PlantingCost ?
Oh, forgot, local government buys back PV energy not $0.1/kwh, but$0.2/kwh for temporary incentive.

Let us check with the $9 billion dollar price tagged parabolic trough solar farm in Morocco: https://en.wikipedia.org/wiki/Ouarzazate_Solar_Power_Station Calculate the power density on land: Given official data -- the finished NOOR I stage 450 hectares on land characterized as 2635 kWh/m^2/year, its salable capacity 370 GWh/year. We deduce: 1. Yearly receivable irradiation average power = 2635*1000/(365*24) = 301 W/m^2 It is reasonable, because the solar power density above atmosphere 1360 W/m^2, and the Earth surface area = 4*Pi*Radius^2 = 4 times of central circle area = 4 times sunshine projection area, thus the theoretical average diffused heat power density = 1360/4 = 340 W/m^2. The measured value 301 W/m^2 sounds right. 2. The infact harvested power density = 370 GWh/year / 4500000 m^2 = 370,000,000,000/(365*24)/4,500,000 = 9.4 w/m^2 3. The average efficiency of heat-to-power = 9.4/301 = 3.1% 4. The transient quasi efficiency at noon moment = 9.4/1360 = 0.7%, only this data can be compared with the PV nameplate efficiency 12%. Instant question: now that the transient efficient of this mirror-molten-salt system so tiny 0.7%, why not to use PV? 5. As per previous vague threshold of plantation reference frame 0.18 W/m^2, its power density is 9.4/0.18 = 52 times greater. 6. We can see large gap between adjacent rows of parabolic troughs array. It seems that the power density could be doubled if narrow the gap to almost zero. Is any my calculation wrong? #### Attachments • p04hy3gq.jpg 64.6 KB · Views: 372 Last edited: jbriggs444 Science Advisor Homework Helper 6. We can see large gap between adjacent rows of parabolic troughs array. It seems that the power density could be doubled if narrow the gap to almost zero. You can double the power density when the sun angle is high. The density is not doubled at times of day or seasons of the year when the sun angle is lower. You might also be giving up convenient access for maintenance and repairs. Then there is the question of how increasing density increases profit. If land is cheap and troughs are expensive then density is not an important metric. russ_watters Dale Mentor 2021 Award Is any my calculation wrong? What are you trying to calculate? russ_watters and jbriggs444 What are you trying to calculate? Just wondering why the rich Arab country choose low efficiency mirror-molten-salt system, but not the high efficiency PV farm. russ_watters Mentor Just wondering why the rich Arab country choose low efficiency mirror-molten-salt system, but not the high efficiency PV farm. Why are they building empty cities in the middle of deserts? The Wikipedia says it sells to europe at price tag$0.19 /kWh.
Is this price competitive in europe local energy market?

russ_watters
Mentor
Interestingly, there are many countries still planning next solar chimney projects, such as the billions dollar project of solar chimney with land coverage of circa 100 square kilometers in the desert of China...
Do you have a reference for that? I couldn't find any with a quick google. I find it hard to believe.
Why the harvestable solar power density is so tiny, and still sought-after?
I don't see that it is sought after. As far as I know, there aren't any utility scale solar updtaft plants and we go years between threads on the subject here. If it hasn't been commercialized after 30 year, I think there is probably a reason for that.
In comparison with planting cash crops...
I don't think they are mutually exclusive, are they?

Do you have a reference for that? I couldn't find any with a quick google. I find it hard to believe.

I don't see that it is sought after. As far as I know, there aren't any utility scale solar updtaft plants and we go years between threads on the subject here. If it hasn't been commercialized after 30 year, I think there is probably a reason for that.

I don't think they are mutually exclusive, are they?

There are many reports in Chinese media, but less in English media. The Wikipedia does mention the solar chimney project in China. I will try to collect its photos in Chinese media later.

https://www.china5e.com/news/news-198134-1.html

russ_watters
Mentor
There are many reports in Chinese media, but less in English media. The Wikipedia does mention the solar chimney project in China. I will try to collect its photos in Chinese media later.

https://www.china5e.com/news/news-198134-1.html
I don't see anything about a 100 square km system in that link. And no, the wiki doesn't say anything more than that there is an experimental project.

Dale
Mentor
2021 Award
Just wondering why the rich Arab country choose low efficiency mirror-molten-salt system, but not the high efficiency PV farm.
I don’t think that any calculation will answer that. You might be able to find press releases from the time of the decision that would answer that (assuming that the publicly stated reasons are correct)

russ_watters
anorlunda
Staff Emeritus
I first heard of the solar updraft tower around 1995, when a developer in India asked my firm to do an engineering evaluation of his design, We declined because the proposed scale (500 km diameter at the base) was far beyond engineering experience. But I recall the principle that efficiency of an updraft tower increased with physical scale.

All forms of power production must compete with alternative forms. Solar PV and wind power are both enjoying a period where their costs are decreasing rapidly. In rough numbers, PV cost in $/MW or m^2/MW decreases by a factor of 3 every 3 years. So if a solar updraft tower project will take 9 years to complete, the cost of PV may be 1/25th of today's cost 9 years from now. That is tough competition. On the wind side, GE just announced a 12MW offshore wind turbine (http://reneweconomy.com.au/ge-unveils-massive-new-12mw-wind-turbine-19016/) that will further decrease$/MW and m^2/MW. That is also tough competition.

I'll use the https://en.wikipedia.org/wiki/Ouarzazate_Solar_Power_Station project you liked as an example. Construction began in 2013, and design was probably fixed in 2010. Cost $9 billion and capacity 580MW. That is$15.50/watt. Today's PV panels cost as little at $0.37/watt. 8 years ago and including installation and infrastructure that number may have been close to$15/watt. That is an example of how important just one factor (time) that you did not include can matter.

So, I think that you are trying to oversimplify. The calculations needed to evaluate profit are much more complicated.

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Asymptotic and russ_watters