
Twice the height of the Empire State - massive solar tower for AZ - aditiyaa1
http://www.gizmag.com/enviromission-solar-tower-arizona-clean-energy-renewable/19287/
======
ajkessler
Really? Very cool idea, but some of the claims sound downright ridiculous.

First, the zero maintenance claim that is touted at least 3 times by the
article seems suspicious. You can't really leave anything out in the desert
sun and not have to maintain or replace it. Sun will disintegrate a lot of
material, not to mention wind and sand. Anybody have any info or insight into
what material they are using to create the "greenhouse"?

Additionally, the claim that _"In fact, because you're creating a greenhouse
underneath, it actually turns out to be remarkably good for growing vegetation
under there."_ does not seem to jibe at all with the claimed temperatures
("add in the greenhouse effect and you've got a temperature under your
collector somewhere around 80-90 degrees (176-194 F)"). I'm not sure I'm
familiar with any vegetation that grows in near 200 degree temperatures.

Does anyone have any actual experience with this kind of tech?

~~~
geuis
Desert environments are _extremely_ good at preserving things, particularly
technological devices.

[http://maps.google.com/maps?q=Mojave,+CA&hl=en&ll=35...](http://maps.google.com/maps?q=Mojave,+CA&hl=en&ll=35.063795,-118.145009&spn=0.005067,0.009581&sll=37.0625,-95.677068&sspn=40.052282,78.486328&t=h&z=17)

The above link shows an aircraft storage facility in Mojave, California. There
are a number of such facilities in the US, and many more worldwide. It was
discovered some decades ago that you can leave a plane in the desert for years
at a time, and when you come back to it there's very little maintenance that
has to be done to make them airworthy again.

There was a story that I read a few months ago that I sadly can't find a link
to at the moment. Some years back during one war or another, there was a plane
that had engine problems. If I remember correctly, this was in northern
Africa. The crew radioed that they were coming back to base, but they never
made it. They were flying over a desert area.

A lot of years went by, and some prospectors working for an oil company were
driving around the desert looking for places to drill and they came across the
wreck of the plane.

The tail of the plane had broken off during the crash, but otherwise the plane
was in excellent condition. There was still fuel in the tanks and the
batteries were still charged. The oil guys were even able to turn on the
lights and get the engines to turn over (might be wrong about that, but I
think I remember that). If the tail hadn't broken, they likely could have been
able to fly it out of there with not so much work.

So anyway, putting stuff in the desert isn't _no_ maintenance, but it is _low_
maintenance.

I do agree with your assessment about the greenhouse. Deserts are already
pretty hot and plants don't grow well there. I don't think 2-3x the temp will
be a big improvement.

~~~
ajkessler
I'm pretty sure that was part of the plot from The Mummy? :)

In any case, desert is great for preserving stuff in terms of low humidity (ie
things don't rot). Not so good for preserving stuff in terms of them getting
sand blasted. Especially in AZ where winds routinely hit 100mph+ during gusts
and 60mph during windstorms. Not to mention the haboobs.

Also, the prototype of this tower in Spain figured out that the plastics they
were using were "not durable enough". I would imagine that means they
disintegrated? I'm wondering what they're planning on building this thing out
of.

[http://en.wikipedia.org/wiki/Solar_updraft_tower#First_Proto...](http://en.wikipedia.org/wiki/Solar_updraft_tower#First_Prototype_in_Spain)

~~~
pyre

      > I'm pretty sure that was part of the plot
      > from The Mummy? :)
    
    

<http://en.wikipedia.org/wiki/Lady_Be_Good_(aircraft)>

~~~
ajkessler
Ah thanks! Flight of the Phoenix was the movie I was thinking of.

------
kylec

        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.
    

Is there any reason why this can't be constructed to be 831 meters tall to
edge out the Burj Dubai?

~~~
techiferous
I think that Burj Khalifa (formerly known as Burj Dubai) _should_ be the
tallest for economic reasons. The Arizona tower is simply infrastructure, so
its goals are to produce the most energy for the least cost. Adding 31 meters
may upset the cost/benefit ratio. Dubai, on the other hand, is a tourist
destination, and having the tallest building in the world is good marketing.

~~~
waterlesscloud
I'm willing to bet Burj Khalifa wasn't built tallest for purely economic
reasons. I have a suspicion ego was at least a tiny factor.

~~~
nikcub
and then that ego was bruised when they had to change the name to the guy who
runs the city next door because he bailed you out

------
gavinballard
For any other Aussies that, like me, vaguely remember the plans for building
this near Mildura but can't be bothered watching the video to find out why it
didn't happen, the reason cited is a "complete lack of incentives".

Sad that something like this couldn't get a dime from the Australian
government while the US "welcomed them with open arms" (and, presumably,
truckloads of cash).

~~~
Eliezer
That's not a good sign. I mean, ideally, you'd want the incentive to be, "It
produces power cheaper than coal!"

~~~
cma
Presumably it could if you factor in coal's carbon externalities.

~~~
innes
What makes you think that?

~~~
innes
Not sure why I can't edit my post. Anyway - downvoted for asking for
clarification on an unsupported assertion. HN at its most scientifically
rigorous!

------
Spyro7
I love this technology _a whole lot_ , but this is Hacker News so it is
worthwhile to think critically about this kind of "press release"-style news
posting. This article does a bit of hand waving with the numbers, and, while
this is an amazingly cool project, I think that they are overselling its
benefits.

First, let's get the terminology right. This plant has a capacity of 200 MW.
That does not mean that it produces 200 MWh. The formula for converting MW
into (annual) MWh is the following:

MWh = MWx365x24xCF

In the above formula, CF is the capacity factor. Capacity factor is basically
the amount of energy that a plant is actually able to produce over the course
of a year divided by the total capacity of the plant. Here are some common
capacity factors for various industries (taken from a private document, so no
sources but this stuff is easy enough to google):

* Coal - 65-95%

* Natural Gas - 35-65%

* Hydro - 25-65%

* Solar - 20-35%

* Wind - 20-35%

* Nuclear - 80%+

Capacity factors are never 100% for various reasons:

* Plants may need to be taken offline for refueling, maintenance, or inspection

* For renewables, the wind isn't always going at full speed and the sun isn't always shining

* A whole bunch of other things that I am too tired to list (read the references below, they have some more in them)

Now, let's look at this new project, and one of the claims made in this
article.

According to the article, this plant will be able to provide power for 150,000
homes. According to the EIA, the average household annual energy usage is
10,896 KWh. Given this information and using a more generous solar capacity
factor (35%):

Number of Homes Powered = (200x365x24x.35) / 10.896 = 56,278 homes

Hmm, well that's just a bit less than what the article claimed, so they must
be assuming a really amazing capacity factor for this estimate. Let's solve
the below for cf and see what we get....

(200x365x24xcf)/10.896=150000

cf = approx. 93%

Look, I'm all for scientific advancement and alternative energy, but can we
try to be more sensible than this? This is a highly improbable capacity
factor.

Documents available from Enviro Mission says that the simulated capacity
factor will be more like 50%. When we plug that number into the equation we
get about 80,397 homes, which is pretty sensible. However, we have to remember
that these are only simulated numbers. There are no similar projects currently
available that can be compared to this one, so the actual capacity factor may
be either more or less.

Note: Please keep in mind that efficiency is a totally different concept from
capacity factor. Efficiency is typically used to describe how well a plant
transfers from its energy source into electricity^. The capacity of a plant is
a number that already incorporates the plant's efficiency. The capacity factor
is simply a measure of how much of that capacity is actually used on an annual
basis on average.

^ I am not an electrical engineer. I am an economist, that is the best
definition I can come up with.

Disclaimer: I am incredibly tired right now, so if any errors appear in the
above posting please send me some coffee so that I can correct them before
falling asleep.

References:

\+
[http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3](http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3)

\+
[http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pd...](http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pdf)

\+
[http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CP...](http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CPID=1090)

 _Edit: Formatting was all messed up the first time. Forgot to include some
additional information. Added clarification on efficiency._

~~~
aik
Appreciate the analysis, however I believe you made a fairly significant error
with the solar capacity percentage. Unlike other solar power, the cool thing
about this structure is that it doesn't specifically require constant sunshine
to work effectively being that it works off the temperature differential
through the tower, rather than pulling energy strictly from solar panels.
Because of this, I would imagine capacity to be much nearer to 100% than the
opposite.

"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... Because the heat of the day warms the ground
up so much, it continues working at night;"

As for how the difference in temperature between the surface and 100s of
meters in the air changes throughout the day/night, I don't know.

So according to your equation, at 80% capacity, it could cover 128k homes. At
93.3% capacity it'd reach 150k.

~~~
speleding
It still needs a temperature differential to run, which will not be there at
night, so the best you could get is about 50%. This is the number that Enviro
Mission uses.

~~~
brlewis
The article claims, "Because the heat of the day warms the ground up so much,
it continues working at night"

------
ColinWright
It's a regret that I'm late to the commenting party. This comment won't get
seen, so I won't get any feedback.

However ...

I haven't been able to find out what the upflow airspeed will be. If it's
large enough one could wear a winged suit and freefall in the funnel. That
would be awesome.

------
marvin
This is just so cool. I'm curious about the local weather impact of something
like this. Basically, what these guys are doing is creating a continuous,
artificial thermal, the same type you use for flying hang gliders and
sailplanes. I'm certain the guys have done the math, but I'm wondering if you
won't get cloud formation above the tower due to condensation of the hot air
rising through the tower.

Meteorological theory suggests that you would definitely get this if the
airflow was not contained by the turbines, and cloud formation with the
release of condensation heat would cause even more cloud formation which would
basically result in a giant, permanent thundercloud above the power plant.
This would obviously decrease insolation a lot.

Anyone in here who has done any theory on these kinds of projects? I'm just
guessing based on my knowledge of gliding that a considerable amount of the
energy collected from this power plant actually comes from the temperature
differential between not just the solar energy collected directly underneath
the tower. It isn't just the fact that hot air rises. Due to decreasing
pressure, the air temperature of a mass of air decreases approximately one
degree per hundred meters of altitude gained. But if the atmospheric
temperature distribution due to meteorological conditions is such that the
actual temperature in the atmosphere drops _more_ than one degree per hundred
meters of altitude, you have an untapped energy source; any air mass set in
motion upwards will actually accelerate instead of slowing down.

That we are making large-scale technology to exploit this is so ridiculously
cool I have problems expressing it.

~~~
Daniel_Newby
It's a desert. The air near the ground is usually pretty dry. That's why
radiation cooling makes things cool off so much at night (instead of making
clouds and fog).

------
serichsen
Big toy.

For one, maintenance will _not_ be low. Wind turbines (and nothing else is
used here) do have quite some maintenance costs, and additionally, you need to
keep the greenhouse clean.

The main problem I see is the capacity. 200 MW peak capacity at 60% efficiency
translates to 120 MW peak electric energy. If we assume 50% capacity factor
(which I suspect is _very_ generous), we arrive at 60 MWe average output. You
would need 15 of these to substitute for a single 1 GW nuclear plant.

Big toy.

~~~
adaml_623
Wish I could downvote your post for repetition and for just making up stuff.

'200 MW peak capacity at 60% efficiency translates to 120 MW peak electric
energy'. This sentence makes no sense. They are building a 200MW plant. That
is the amount of electricity it will put out at peak.

You made up the number for 50% capacity figure just then didn't you? You did.
I just saw you. So your final figure is wrong.

~~~
speleding
I agree the 200MW is output, so no efficient factor should be added, but
Enviromission says the capacity factor is 50%:

[http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CP...](http://www.enviromission.com.au/IRM/Company/ShowPage.aspx?CPID=1090)

Makes sense, since half of the time it's night...

~~~
adaml_623
Absolutely correct. Thanks for that link.

------
sliverstorm
60%? Darn. I was hoping for better after the hype earlier in the article.
Don't large steam plants approach 99%?

 _150,000 US Homes_

Is that a lot? I hate to (continue to) be a cynic, but it doesn't sound like a
lot.

~~~
ianterrell
The Census says there are 110,692,000 occupied homes in the US, so 150k is
0.136% of that.[1] That means that there would need to be 738 of them to meet
demand.

Now, the EIA says there are about 5700 power plants currently operating in the
US [2]. Continuing with the back of the envelope math, that's almost 8 times
as many as would be necessary if they all produced as much as this one. Pick
whatever factor you want for "non-home" energy, but we're dealing with the
right order of magnitude.

Combine that with the clean energy aspect of it, and I don't see a lot of
reason to be cynical.

[1] <http://www.census.gov/hhes/www/housing/ahs/ahsfaq.html> [2]
[http://www.eia.gov/tools/faqs/faq.cfm?id=65&t=2](http://www.eia.gov/tools/faqs/faq.cfm?id=65&t=2)

~~~
tedkimble
So at $750 million a pop, that's a little over $550 billion to power US homes.
Or, roughly 50% of the annual budget of the military to power all US homes for
80 years!

Clearly back of the envelope numbers, but definitely something to be excited
about.

~~~
ahlatimer
Well, you can't only have these things powering US homes because I can't
imagine they work that well at night.

~~~
erikpukinskis
They do actually.

~~~
savramescu
Truth be told, the article doesn't say how well they work at night. I don't
think that it'll work just as good, but that doesn't mean it won't work at
all.

------
Detrus
I don't see it mentioned in the article, but the greenhouse must be colossal.
These updraft towers use land far less efficiently than concentrated solar and
those don't use land efficiently either.

From <http://en.wikipedia.org/wiki/Solar_updraft_tower>

_A 200 MW power plant with the same 1000-metre-high tower would need a
collector 7 kilometres in diameter (total area of about 38 km²). The 38 km²
collecting area is expected to extract about 0.5 percent, or 5 W/m² of 1
kW/m², of the solar power that falls upon it. Note that in comparison,
concentrating thermal (CSP) or photovoltaic (CPV) solar power plants have an
efficiency ranging between 20% to 31.25%_

38 square kilometers, these things don't make sense if you don't use the
greenhouse for something. Hopefully the wiki is outdated and they have a
higher efficiency.

~~~
nitrogen
When you have an almost comedic overabundance of uninhabited desert, a less
efficient but cheaper technology may prove more economically effective. If,
one day, the costs of more efficient technologies fall, or if suitable land
becomes scarce, then efficiency will become a greater concern.

~~~
Detrus
The whole point of these renewable energy projects is to be considerate to the
environment. Covering up the desert, inhabited by tons of species (this is not
the Sahara) in a greenhouse is an environmental disaster in a new skin.

Land use efficiency is a concern now for the environment. If renewable
technologies have to cover up 60,000+ square miles of land not inhabited by
humans, then coal and nuclear are the environmentally friendlier options.

~~~
nitrogen
From a strictly pragmatic perspective, I would argue that the loss of some
desert habitat in an ecosystem that is not significantly linked with those
used by humans for habitation, carbon sequestration, or agriculture is
acceptable compared to the damage to higher-value ecosystems caused by air
pollution from coal power. This assumes that environmental damage that causes
long-term consequences for humans is considered more egregious than
environmental damage that has no negative consequences for humans.

Personally, I think a thorium nuclear power plant in an isolated desert is a
much more environmentally preferable approach than most renewable power
sources.

~~~
Detrus
It's better to make coal powerplants run cleaner too. Thorium will require
serious effort to develop, a decade perhaps, but sure would be nice to have.
Modern uranium is not that bad either.

There was some solar thermal project in California that ran into a lot of
problems trying to use the desert land. Old power companies are paying
environmental groups to protest those sprawling projects. Divide and conquer
those hippies!

High altitude wind is the best source of renewable energy. It's concentrated
and takes up airspace instead of land. They're taking their time though.

------
Luyt
I see two insurmountable problems with this solar tower, in this age of rising
environmental concerns and increasing influence of environmental pressure
groups:

\- The base of the tower covers a huge piece of land, which is now home to
various desert creatures. Changing their habitat is unacceptable from the
environmental protectionists' viewpoint. The precious creatures (probably some
endangered species too) would probably die.

\- Visual pollution. Nobody wants to have ugly structures in his backyard, let
alone a half-a-mile-high tower which will be visible from a huge area. It
detonates with the natural desert views of Arizona.

Because of these two reasons, this solar tower project will face years of
litigation from environmental pressure groups, and in the end the project will
probably stall.

~~~
corprew
On the other hand, this is probably precisely why this is being built in
Arizona and not in California.

~~~
geni08
I agree.

------
nhebb
If anyone was curious about the funding for this (I was), EnviroMission has a
press release on their site [1]. _"The Southern California Public Power
Authority (SCPPA) has taken a call option to purchase the first of two
EnviroMission 200MW Solar Tower power stations planned for development in La
Paz County, Arizona."_ It does seem odd, though, that they are building these
in Arizona when California has its own deserts.

[1]
[http://www.enviromission.com.au/EVM/Company/ShowPage.aspx/PD...](http://www.enviromission.com.au/EVM/Company/ShowPage.aspx/PDFs/1281-79414176/USPowerAuthorityTakesCallOptiononSolarTower)

~~~
corprew
If I were to guess, the regulatory burden of putting something up like this in
Arizona is probably way lower than putting it up in California. So, not that
odd given that both sides are plugged into the grid and California already
buys power from far away (like the Pacific NW.)

------
mark_l_watson
Even if this type of project only provides a small fraction of the energy we
need, it is great to see funding and construction because experience building
systems like the one in the article will lead to more effective systems in the
future.

My wife and I live in Arizona (in the mountains) and we are having solar
panels installed on our roof in 2 weeks that will furnish 100% or more of our
electricity needs for about 10 months a year (and we will often make a little
money back selling back power to our utility company) and cover about 50% of
our needs the two months a year that we run our air conditioning.

A few friends have been critical of our decision for monetary reasons, and
they may be right, but it is something we wanted to do. Also, if prices for
energy, food, etc. increase dramatically, then we will break even on costs
sooner rather than the anticipated 6 or 7 year time frame.

------
ForrestN
Wonderful if it works as described! That's quite a bit of power. I'd be very
interested to know comparisons in terms of how long a traditional power plant
takes to become profitable, and also how much initial investment this project
is requiring.

~~~
snowwindwaves
750 million, payback in 11 years.

for comparison, hydro electric costs about $2 million per megawatt so a 200MW
hydro plant would be $400 million, but with associated environmental concerns.

------
Groxx
You mean they're actually going through with it? Awesome! I hope it works as
well as planned.

I'm _extremely_ interested in the aftermath of all this. The building itself
is clever and all, but what will the ecological impact be? Wind farms kill
birds and bats and there's evidence the sound drives many more off,
concentrated solar has a nasty habit of significantly heating the air around
the plant and hydro-dams are _enormously_ destructive no matter how you look
at it. What's a 1/2-mile-tall heat pump going to do?

------
waterlesscloud
Since this seems to work on temperature differentials, could you run it up the
side of a mountain? Seems you could get height differences of 5-7k feet in a
lot of places with that approach...

~~~
snowwindwaves
unless you had a perfectly vertical mountain your tower would end up being
longer and costing more. if you did have a perfectly vertical mountain it
would still be somewhat difficult to build on the side of a cliff.

I suppose you'd need a mountain in the desert as well.

~~~
techiferous
The mountain would also provide unwanted shade.

~~~
waterlesscloud
Not necessarily. Depends on directional facing. A south facing spur up the
mountain may provide no shade at all to the base.

And longer, yes, but not in need of vertical support.

------
nixy
This is a question out of pure curiosity, I'm not very well read on these
subjects, so please forgive me if this is a dumb one.

Is there any reason why this can't be built as an underground structure? If
it's working on temperature differentials, shouldn't you be able to achieve a
more constant capacity by plugging it into earth where temperatures change
less?

~~~
Luyt
The sun doesn't shine underground...

~~~
nixy
But it shines on the ground, so instead of putting the heat source at the
bottom of the cylinder, you put it on top and see temperatures drop as you go
further down underground.

------
vonSeckendorff
The article insists on the plant's low maintenance costs, so this may be a
stupid question, but won't the greenhouse* have to be washed regularly of
dust? I imagine the accumulation of detritus would significantly impact power
production.

Edit: I previously had written mirrors. The concept art looked misleadingly
shiny.

~~~
dangrossman
Compared to the cost of buying coal or natural gas and keeping all the
machinery that moves and burns that clean, cleaning out the dust and debris
this building takes in should cost relatively little.

------
mcdaid
I wonder what effect this could have on the local climate. Pumping out hot air
into cool air at height of 800 metres has got to have some affect.

Now if the base is used area is used for growing plants then the air emitted
at the top would be moist, which I imagine would cause cloud formation as it
meets the cold air.

~~~
cturner
I'm having lots of thoughts about climates within the rings.

I'd expect the temperature ranges to change at different distances frmo the
centre. It may be that you could do agriculture at some points underneath.

On the other hand, it's likely that for best efficiency they'll need to create
as much momentum as possible from the device.

But - the venturi effect will be significant underneath and they might need to
shape the land in sections under the rings. Is it possible you could hide
crops within glass casings that improve that effect?

Will water vapour collect at any point in particular?

I'm considering a science fiction plot based around people who live in housing
built around energy towers like this.

When this is built, I'd be interested to do a roadtrip to see it.

------
mkr-hn
This brings up an interesting possibility. What's stopping us from engineering
these towers on to buildings once the technology is proven?

~~~
Symmetry
The huge area of glass enclosed space that needs to spread out from around the
tower.

------
adaml_623
I've been following Enviromission for quite a while now (maybe since 2001?). I
check out their website once a year or so to see how they are going. They have
been championing this technology for quite a while.

I think it's sad that there are so many people doing back of the envelope
calculations and wasting time typing them into Hacker News. There are 100s of
millions of dollars involved people. Someone qualified will check the figures.
And really it's not rocket science.

~~~
nitrogen
_I think it's sad that there are so many people doing back of the envelope
calculations and wasting time typing them into Hacker News. There are 100s of
millions of dollars involved people. Someone qualified will check the
figures._

I think it's sad that you think that. One of the fundamental qualities of
science is that it can be independently verified, and one of the fundamental
qualities of hackers is that they don't typically trust "someone qualified"
with "100s of millions of dollars" to do the verification when they can get a
rough idea themselves. Hackers aren't here to let the "qualified" people just
do their thing. We're here to learn, inspect, disassemble, discover, and most
importantly, to create.

~~~
adaml_623
You're absolutely correct and I should have chosen my words more carefully.

So I'll change my words to say: I think it's sad that there are so many
educated and capable people doing back of the envelope calculations on Hacker
News. Half of us are capable of hunting down the original papers on solar
towers and running the numbers through the proper calculations.

Also why are we just typing out the equations using text. It's the 21st
century! We need a better way to discuss technical matters.

------
46Bit
Surely building the tower is going to offset a non-insignificant amount of
it's CO2 'savings' vs Fossils?

------
meow
Why does it have to be that tall ? is it because the top end becomes much
cooler with more height ?

~~~
meow
Looks like that is the case from the article..

------
Jach
For just $2trillion, we could build enough of these to supply power for 300m
homes!

------
crizCraig
After I saw this story, I posted it to Facebook and my friend whose a
journalist at Arizona's local news station picked it up and did a full blown
story. [http://www.azfamily.com/news/Massive-solar-tower-in-
Arizona-...](http://www.azfamily.com/news/Massive-solar-tower-in-Arizona-to-
be-worlds-second-largest-building-126157183.html)

------
awarzzkktsyfj
The Empire State is New York State:
<http://en.wikipedia.org/wiki/Empire_State>

Or did the article headline really mean the empire state BUILDING?
<http://en.wikipedia.org/wiki/Empire_State_Building>

~~~
awarzzkktsyfj
Lovely, downvotes. Guess we don't have too many New Yorkers in the readership
here. FYI, you can't shorten the Chrysler Building to 'Chrysler' either.
That's a corporation.

~~~
cbs
No, it's because you're splitting hairs when the message was obvious. They
used 'height' not 'elevation', and it is common knowledge that the Empire
State (Building) was once the tallest building in the world.

~~~
awarzzkktsyfj
'building' is not optional.

~~~
knieveltech
Your burning karma thinks otherwise. Go find another hill to die on.

~~~
mtogo
From <http://ycombinator.com/newsguidelines.html> :

Be civil. Don't say things you wouldn't say in a face to face conversation.

