[ExI] solar power tower

[Damien Broderick]

More Aussie smartness  :)

(Unless some big bad wolf comes by, of course, and blows the thing down 
the moment everyone depends on it.)
........................................................................
<http://www.gizmag.com/enviromission-solar-tower-arizona-clean-energy-renewable/19287/>

Twice the Height of the Empire State - EnviroMission Plans Massive Solar 
Tower for Arizona
LOZ BLAIN - GizMag

Click through to look at the pictures and view the videinterview with 
EnviroMission CEO Roger Davey.

An ambitious solar energy project on a massive scale is about to get 
underway in the Arizona desert. EnviroMission is undergoing land 
acquisition and site-specific engineering to build its first full-scale 
solar tower - and when we say full-scale, we mean it! The mammoth 
800-plus meter (2625 ft) tall tower will instantly become one of the 
world's tallest buildings. Its 200-megawatt power generation capacity 
will reliably feed the grid with enough power for 150,000 US homes, and 
once it's built, it can be expected to more or less sit there producing 
clean, renewable power with virtually no maintenance until it's more 
than 80 years old. In the video after the jump, EnviroMission CEO Roger 
Davey explains the solar tower technology, the Arizona project and why 
he couldn't get it built at home in Australia.

EnviroMission's solar tower: coming to Arizona in 2015
EnviroMission's solar tower: coming to Arizona in 2015
EnviroMission's solar tower: coming to Arizona in 2015
EnviroMission's solar tower: coming to Arizona in 2015
View all

How Solar Towers Work

Enviromission's solar tower is a simple idea taken to gigantic 
proportions. The sun beats down on a large covered greenhouse area at 
the bottom, warming the air underneath it. Hot air wants to rise, so 
there's a central point for it to rush towards and escape; the tower in 
the middle. And there's a bunch of turbines at the base of the tower 
that generate electricity from that natural updraft.

It's hard to envisage that sort of system working effectively until you 
tweak the temperature variables and scale the whole thing up. Put this 
tower in a hot desert area, where the daytime surface temperature sits 
at around 40 degrees Celsius (104 F), and add in the greenhouse effect 
and you've got a temperature under your collector somewhere around 80-90 
degrees (176-194 F). Scale your collector greenhouse out to a several 
hundred-meter radius around the tower, and you're generating a 
substantial volume of hot air.

Then, raise that tower up so that it's hundreds of meters in the air - 
because for every hundred metres you go up from the surface, the ambient 
temperature drops by about 1 degree. The greater the temperature 
differential, the harder the tower sucks up that hot air at the bottom - 
and the more energy you can generate through the turbines.

The advantages of this kind of power source are clear:
-- Because it works on temperature differential, not absolute 
temperature, it works in any weather;
-- Because the heat of the day warms the ground up so much, it continues 
working at night;
-- Because you want large tracts of hot, dry land for best results, you 
can build it on more or less useless land in the desert;
-- It requires virtually no maintenance - apart from a bit of turbine 
servicing now and then, the tower "just works" once it's going, and 
lasts as long as its structure stays standing;
-- It uses no 'feed stock' - no coal, no uranium, nothing but air and 
sunlight;
-- It emits absolutely no pollution - the only emission is warm air at 
the top of the tower. In fact, because you're creating a greenhouse 
underneath, it actually turns out to be remarkably good for growing 
vegetation under there.

The Arizona Project

While this is not the first solar tower that has been built (a 
small-scale test rig in Spain proved the technology more than a decade 
ago) EnviroMission has chosen to build its first full-scale power plant 
in the deserts of Arizona, USA.

The Arizona tower will be a staggering 800 metres or so tall - just 30 
meters shorter than the colossal Burj Khalifa in Dubai, the world's 
tallest man-made structure. To put that in context - it will stand more 
than double the height of the Empire State building in New York City, 
and it'll be as much as 130 meters in diameter at the top. Truly a 
gigantic structure.

Currently undergoing site-specific engineering and land acquisition, 
EnviroMission estimates the tower will cost around US$750 million to 
build. It will generate a peak of 200 megawatts, and run at an 
efficiency of around 60% - vastly more efficient and reliable than other 
renewable energy sources.

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.

Considering that a large city like Los Angeles requires total power in 
the region of 7,200 megawatts, you'd have to build a few dozen solar 
towers up to the same size as the Arizona project if you wanted to 
completely replace the existing, primarily coal-based energy supply for 
that city's 3.7 million-odd residents. So it's not an instant solution - 
but then, its short projected payback period and virtually zero 
operating costs make it a very sound economic proposition that competes 
favorably against other renewable sources.

Under the terms of the pre-purchase agreement, the Arizona tower is due 
to begin delivering power at the start of 2015.