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Comment by sliverstorm | Hacker News Reader

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 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

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.

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

They do actually.

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.

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...

99%? No. The Carnot limit is much lower than that for the temperatures at which steam turbines operate.

Besides, the thermodynamic efficiency isn't particularly relevant for technologies like this anyway - you're not paying for the input, after all. The efficiencies you care about here are watt/area, energy payback time and, ultimately, $/watt.

thermodynamic efficiency should correlate pretty strongly to watt/area because the device harvests sunlight.

For this technology, but not for the competitors that you'd want to compare them with.

60% was a plant factor, meaning that the 200 MW plant output will be 200 * .6 when averaged over the course of a year, presumably because some turbines will be down for maintenance some of the time, and the temperature difference will be less at times, so it can't always put out maximum power.

And there will be transmission line outages some times too.

60% has nothing to do with the efficiency of the transfer of energy.

He says in the video coal plants run 80% plant factor, nuclear plants would be even higher, probably putting out over 90% of their rated power.

It claims 200MW/150,000 homes = 1.3KW for a US home !!!! So homes in Arizona don't have AC or electrical appliances and are all owned by eco-warriors

all of the appliances are not on all the time, sometimes more power is used, sometimes less. 1.3 kw per hour for every hour in the year is the average.

the top comment right now has a reference to the EIA which states that the average homes uses 10,896 KWh in a year. divide by 8,760 and you get 1.24 KW average

Checked the figures and 1.3Kw is the average (24*365) for Arizona.

Surprising - when I lived in Houston you needed AC running 24x7 for 6months of the year and all the other appliances where electric.

I assume, being in the desert, Arizona is cooler at night and they use propane/oil heating in the winter?

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