Comment by gus_massa | Hacker News Reader

Comment by gus_massa | Hacker News Reader

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I agree, more details.

> The new material can also withstand temperatures greater than 700 degrees Celsius and survive many years outdoors in spite of exposure to air and humidity.

For simplicity, lets assume that it's 723°C (1333°F), and there is a nice summer afternoon and the environment temperature is 23°C (73°F). In Kelvin, we have 1000K and 300K.

By the second law of thermodynamics, we have that Q_in/T_in < Q_out/T_out,

so Q_in/1000K < Q_out/300K

then Q_out > 3/10 Q_in.

At least the 30% of the heat that enters has to be released to the environment in some type of cooler. So the efficiency of the heat to electricity conversion is at most 70%. If we multiply that by the 90% efficiency of the light to heat conversion, we get at most 63%. (65% in a cool winter morning :) ).

The Wikipedia article is not very clear ( http://en.wikipedia.org/wiki/Energy_conversion_efficiency ), but I guess that in a real power plant, we'd get at most a 40% or 60% heat to electricity conversion efficiency instead of the theoretical 70%.

From a quick search, most solar panels I can find are 15-20% efficient, so (from a quick look) this seems like a noticeable improvement, no?

It's a noticeable improvement once you reach that scale of operations. But that's not all that easy. Solar panels are nicely decentralized.

On the other hand, the output of concentrated solar power can be much more constant.

The concentrated solar power facilities have more efficiency (but you can't put one of them on your rooftop). From http://en.wikipedia.org/wiki/Concentrated_solar_power

> As of 2008, the world record for solar to electric efficiency was set at 31.25% by SES dishes at the National Solar Thermal Test Facility (NSTTF).

The 90% * 60% number is probably very optimistic.

The Wikipedia article is also interesting, because it discuss that when the temperature is too high the heat receiver is an important heat emitter. I didn't thought about that.

15%-20% is for photovoltaic solar cells (http://en.wikipedia.org/wiki/Photovoltaics): where sunlight is converted directly into an electical current. The article here talks about converting solar irradiation into pure heat.

Yeah, but gus_massa calculated the upper bound of the sunlight->electric current conversion using the material we were talking about, which seems like an improvement to me. However I don't know what the ballpark efficiency of solar heat plants is, so it could turn out to be not that big of a deal if current modern plants achieve similar levels of efficiency.

It's not a noticeable improvement in efficiency for solar heating. Solar heating was already ~70% efficient at converting incident sunlight to heat for water heating [0]. So it's important to note that this efficiency includes losses for circulating the water within the storage system.

[0] http://en.wikipedia.org/wiki/Solar_water_heating#Economics.2...

The heat rejection can't be done at ambient temperature, the heat exchanger would have to be infinite in size.

Though raising the heat exhaust to say 40 C only slightly changes the efficiency, from 70% to 68%.

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