Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Twice the height of the Empire State - massive solar tower for AZ

gizmag.com

Post reply on HN
Print view View original

81–90 of 132 posts

Re: Twice the height of the Empire State - massive solar tower for AZ

#81

Post by estel »

ianterrell wrote: post #6
sliverstorm wrote: post #3

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.

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 f…

The other aspect you're missing is the probably somewhat larger energy consumption from non-residential properties.

Wikipedia [1] says that the energy consumption of the US is 25,000 TWh per annum. Looking at the top rated comment and picking instead a CF between the two (I used 0.6); we're looking at this tower producing in the region of 1TWh.

So you'd actually need about 25,000 of these towers to provide for the energy requirements of the US. Ouch.

Edit: obviously, this is for the complete replacement of all existing energy use with clean renewable electricity. The gross US electricity production is given [2] as 4344 TWh (2008).

[1] http://en.wikipedia.org/wiki/Energy_in_the_United_States [2] http://en.wikipedia.org/wiki/Electricity_sector_of_the_Unite...

Re: Twice the height of the Empire State - massive solar tower for AZ

#82

Post by 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.

Re: Twice the height of the Empire State - massive solar tower for AZ

#83

Post by dalke »

erikpukinskis wrote: post #67
dalke wrote: post #65

Earlier quoted context omitted.

It also means less power generation in the morning. The thermal inertia in the base means it lags behind the air temperature, so there will be times when the base and top are the same temperature.

Not necessarily. Lets say the lows at the top of the tower are maybe 40 degrees F. They're heating up the base to 180 degrees F during the heat of the day. Whether the thermal gradient ever inverts depends on whether the ambient nighttime temperatures are able to bring that 180 degree thermal mass (concrete? dirt?) down to 40 degrees in the time available before the sun comes back up. You'd have to do the math.

What you say is correct. If there's energy production at night using stored heat then it's pulling out power from the heat reserve and cooling it down. If, say, the system was 10% efficient at producing power directly and put 25% into heat reserves which are 80% efficient at releasing that heat and turing it into power, then yes, the bottom would, excepting rare cases (strange weather?), be warmer than the top.

I don't believe that is the case for two hand-waving reasons. The desert in northern New Mexico (where I lived) gets a thermal inversions. You can see that smoke from morning fires rises, hits the inversion layer, and goes horizontal. I believe this is common in deserts, at least those with mountains. From http://www.srh.noaa.gov/media/abq/LocalStudies/ABQthermalinv... there's an 5.8C difference for shallow (~155m thick) inversions, which occurs throughout the year, and there were "130 inversion cases" in that year. Thus, the "1 degree per 100 meters" rule of thumb only applies during the day. A power system would have to work against the inversion.

Second, power extraction is more efficient with higher differentials. It would, I believe, be better to extract more power during the day (when the difference is high and demand for cooling is also high) than to store it for energy production at night.

The previous comment proposed the "capacity to be much nearer to 100% than the opposite." I just don't see that as being likely.

Re: Twice the height of the Empire State - massive solar tower for AZ

#84

Post by coldarchon »

Spyro7 wrote: post #40

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…

I could be wrong, what why is it called a solar tower when it's mainly based on Bernoulli?

Re: Twice the height of the Empire State - massive solar tower for AZ

#85

Post by corprew »

nhebb wrote: post #31

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…

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.)

Re: Twice the height of the Empire State - massive solar tower for AZ

#86

Post by corprew »

Luyt wrote: post #73

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 pr…

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

Re: Twice the height of the Empire State - massive solar tower for AZ

#87

Post by rnadna »

Spyro7 wrote: post #40

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…

Um, regarding "MWh = MWx365x24xCF", isn't an hour 3600 seconds, so isn't the factor 3600? You seem to be converting using days in year and hours in day, yielding a factor-of-ten error.

Re: Twice the height of the Empire State - massive solar tower for AZ

#88

Post by nitrogen »

adaml_623 wrote: post #80

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 wil…

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.

Re: Twice the height of the Empire State - massive solar tower for AZ

#89

Post by nitrogen »

Detrus wrote: post #42

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 exp…

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.

Re: Twice the height of the Empire State - massive solar tower for AZ

#90

Post by streety »

rnadna wrote: post #87
Spyro7 wrote: post #40

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…

Um, regarding "MWh = MWx365x24xCF", isn't an hour 3600 seconds, so isn't the factor 3600? You seem to be converting using days in year and hours in day, yielding a factor-of-ten error.

With the numbers supplied the calculation is correct. As written it is ambiguous though.

Think of it as: MWh/year = MWh/h x 365 x 24 x CF

Post reply on HN