Massive Solar Tower Planned For Arizona

inkscapee writes "It's simple, clean, low-maintenance, and cost-effective: using hot air on a large scale to generate electricity. No, this not a plan to use Congress to generate power, though that would certainly be an endless supply — EnviroMission will use air rising up a tall tower to generate 200 megawatts of electricity. The concept is simple: a giant greenhouse at the base of the tower warms the air. The warmed air rises through the tower and turns turbines, which generate electricity. The taller the tower, the faster the air moves, which increases power output. This structure will be a monster at over 2600 feet tall. It works in all weather, and if there is a feasible water source, food could be grown in the greenhouse."

Decent idea.

[Lance Dearnis]

This is, by far, the kind of tech we need to be investing in, preferably starting a decade ago. Genuine renewable, reliable power - are deserts hot? Yes? Let's make power from it! It'll be terribly uneconomical at first, of course, but it can improve given time. And it's worth trying out. It might not pan out, but it's sure as hell a better investment then 1.1 million in legal fees trying to surpress video games or whatever other legal action is popular at the moment.

So even if it's silly, go for it, Arizona - this is a much better investment then your immigration laws. In fact, triple your budget for this.

Re:Decent idea.

[nschubach]

FTA:

The output has already been pre-sold - the Southern California Public Power Authority recently signed a 30-year power purchase agreement with EnviroMission that will effectively allow the tower to provide enough energy for an estimated 150,000 US homes. Financial modelling projects that the tower will pay off its purchase price in just 11 years - and the engineering team are shooting for a structure that will stand for 80 years or more.

The only thing taller..

[molo]

This is a ridiculous idea. The only structure that is taller than 2600 ft is the Burj Khalifa (Burj Dubai), which is 2717 ft.

http://en.wikipedia.org/wiki/List_of_tallest_structures_in_the_world [wikipedia.org]

The idea that we would build the 2nd tallest structure in the world for 200 MW is ridiculous. This doesn't even come CLOSE to being a top producer of energy per power plant. The top 10 power plants in the world all produce more than 6000 MW. Even the largest biofuel, geothermal and tidal plants currently exceed 200MW.

http://en.wikipedia.org/wiki/List_of_largest_power_stations_in_the_world [wikipedia.org]

-molo

Re:Decent idea.

[AdmiralXyz]

lots of moving parts

Maybe in absolute terms, but virtually any other means of electrical power generation has more. The only moving parts here are the turbines. Not only do we have plenty of experience with running turbines (since every other power source uses them), but they should all be independent from one another, so a failure of one doesn't lead to damage or require a shutdown, it just means you're putting out a little less power.

Re:They should catch it on the way back down

[adonoman]

They aren't "lifting tons of air mass" against gravity. Gravity pushing down on the surrounding air is what is pushing the air up in the first place. This tower is a way to focus that downward push of cool air onto a narrow tube of hot air that then floats up and runs the turbines. This isn't any different than boiling small amounts of water at the bottom of a lake. The bubbles will rise quickly and that energy could be harnessed, but it would be pretty useless to try and harness the energy of the resulting water vapour eventually drifting back to the bottom of the lake.

Re:Decent idea.

[necro81]

Sigh... I have a pen, anyone have an envelope?

The tower is rated for 200 MW, with an estimated utilization of 60%. So the average power output is about 120 MW.

Wholesale electricity prices in the United States are 40-100 $ / MWhr. This should be able to provide most of its power during peak usage, which is great from a business model. Plus they can command a bit of a premium from the California ISO because it is renewable, and California has a 33% renewable mandate. Let's assume 60 $/MWhr.

In each year there are 24 * 365 = 8760 hours. So the company's annual revenue should be in the ballpark of $65 M/yr.

The estimated cost to build the thing is $750M, and their estimated payback period is 11 years. That doesn't quite jive with the numbers I've come up with, and doesn't take into account net-present-value calculations, financing costs, operating expenses, etc. But, even so, you should certainly be able to pay for the thing over its many-decades-long lifetime.

Re:Decent idea.

[nschubach]

It's kind of like putting a hose in a tub, running it out the window and sucking on the hose a bit to get the water started.

The hot air raising up the tube creates a vacuum that pulls in more cold air around the base which is heated by the sun through the glass. The higher it goes, the more air it needs to pull in the bottom. If you cut the tube off, the vacuum is reduced because the hot air is not being used fully and being released too soon.

Re:Sounds great in theory

[Dare nMc]

I am guessing you have never spent the night outside in the Desert.
I live in the AZ desert, and have a green house for 3 reasons. 1) the birds, rabbits, etc even eat the hot pepper plant northern rabbits wont touch. 2) Cold nights, day to night swings of 30F are the norm, northern plants seam confused by this, and don't grow (but don't die either.) 3) Humidity, normal plants lose way too much humidity without a enclosure. My roof panels auto open at 90 degrees, and the misters turn on at 95 then close up to maintain overnight.
#1 seams to apply here, #2, probably be good dual purpose for Nov to March.#3 the moisture should settle out on the way up as it gets cooled. Thus if captured would be available. However I would guess the cooling affect of the water down low, would reduce the efficiency, and thus not be desired.