Namibia to build 25 square km greenhouses!

[JoeReal]

The ultimate greenhouse yet. This is extraordinary in that it attempts to combine both energy and cash crop production literally under one structure. I hope they will succeed. Namibia approved this project and construction will begin this year. Each collector will cover 37.5 km2 (9,266 acres) area and generate 400 MW of electricity with 25 km2 (6177 acres) of that used as greenhouse area. Imagine, 6,177 acres of greenhouse that produces 400 MW of electricity. The chimney would be 920 ft diameter by 4,921 feet tall! A total cost of 600 Million Euros per greenhouse.

I could only imagine what kind of rarefruits I'm dying to plant inside these greenhouses! One important thing to note is that the vegetation inside this structure will increase its overall energy conversion efficiency.

There is no problem with windspeed as the chimney structure can be made strong and yet inexpensive. Moreover, the resonance problem with such a long tube can be solved by putting a lightweight spiral helix around the chimney to break or disrupt the lateral winds to prevent the resonance from building up, similar to the reason why a small wire is wound around your car antenna to prevent the whistling sound.


Here's how the basic tower operates:
Solar updraft tower - Wikipedia, the free encyclopedia

Here's the news that Namibia government approved building such green tower together with greenhouse area:
Solar tower sheds light on little-used technology

And here's the short Executive summary of the project:
GreenTowerGT - Short Executive Summary

Some skeptics say this can't be done, some are bordering their thoughts that this could be a Namibian Scam. But I give the benefit of doubt and sure hope that at least one structure will be built. Truly exciting if true, combining both energy and agriculture literally under one roof.




GREENTOWER TECHNOLOGY AND COST

1. WORKING MECHANISM

Visible radiation from the sun and (overcast) sky heats the air inside the glass covered collector, the buoyancy of which causes an up-draught inside the centrally situated tall chimney flue driving turbine(s) with integrated generator(s) at the chimney foot. Present solar to power efficiency is 4%, theoretical (Carnot) limit = 25%, practical limit = development potential = 14%.

Vegetation inside the greenhouse increases power production according to Stellenbosch University, continuously researching the GT since 1998. The outer 2/3 of the collector’s area is used as a greenhouse and for air heating at the same time. Evaporated water is re-condensed.

2. SPECIFICATIONS

● The concept of the GreenTower® (GT) follows Prof. Schlaich’s Updraft Tower (Solar Chimney), but combines power station + greenhouse (high profits), recent international research results and unique experience in cooling tower design/building by Krätzig & Partner + related German experts.

● Flue height = 1 500m; flue-Æ:180 - 280m; collector-Æ: 6.9km; collector-roof height: 10–30m

● Power rating: 400Mwel (pure solar, emission-free); 32 turbines at flue perimeter with integrated linear generators; plant load factor ³ 89%; availability = 97%

● 6 day full power quick-response thermal energy store + seasonal store Þ power at any time

● Collector area = 37.5km², dry area = 12.5km²; outer ring = greenhouse area = 25km²

● Greenhouse: Drip irrigation + humus soil (12% £ humus £ 25%); high yield-low cost organic agriculture (microbial nitrogen fertilization); composted plant matter buried in soil as humus

● CO2 sequestration per GT + related irrigation schemes » 2 000MWel of coal-fired power emissions

● Design life-span = 160 years, depreciation period ³ 80 years; construct. period = 3 to 4 years

● Capital cost: Dry GT: €475m; greenhouse implements: €90m; glass factory: €35m


for more info:
GreenTowerGT - Short Executive Summary

[broli]

I'd rather have a small and compact solution for independent use than mega structures which serve as an another milk cow for the wealthy. 600 million € per tower is a lot of money.

[JoeReal]

Some projects are economical and able to pay-off when done on such a scale. It is called economies of scale. Agricultural crops in itself are done on massive scales.

For example, let us take the individual solar PV as independent source. Each peak Watt power capacity costs anywhere from $5-$10 installed after rebates. If you total all the household to reach 400 MW, it would have cost $2B to $4B. Thus there is economy of scale in larger setup .

In California for example, super massive arrays of solar PV or dishes are planned to generate several gigawatts power capacity, and each of the project module would be anywhere from 300 to 600 MW capacity, and they cost roughly the same as the solar tower of the same capacity. While costing at par, they don't have the greenhouses to grow your crops. It is single purpose, for production of renewable energy. With the solar tower combined with greenhouse, there is a chance for faster payback. You produce both crops and energy.

After all, plants would normally waste more than 95% of the solar energy it gets, mostly in terms of evaporating the water (requires a lot of energy) and reradiation. With the solar tower, you are able to recover significant amount of what have been lost energy while you still have your crops.

The enclosed structure would allow for organic growing without the use of pesticides, and you get cleaner crops free of insect pests.

Done on a small scale, the solar tower wouldn't have enough wind velocity to power wind turbines, but nonetheless, the solar tower can be used to cool the houses in combination with passive geothermal setup.

[broli]

You are assuming no free energy device would be invented by now and the time this pays off. Don't depend on "economy" to much it has brought the mess the world is in today.

[JoeReal]

Economy and "economies of scale" are two different things. Don't be confused.

[wpage]

All relative

The question of scale in solar energy applied to the natural world...

In the relm of photosynthesis from a simple blade of grass vs the mighty sequoia tree. Same harness of light energy supporting life.

Which is superior life form?

[ANTIQUER]

Hi Joe;

Since this is approx. 3 times the height of the tallest building in the world and I doubt if the government of Namibia has 600M. Euros (or anywhere near it) I'll go with a hoax or practical joke.

Al