3 ms·

the cost of solar array as a function of desired temperature rises In a heliostat-based configuration, I'd assume that it's just the cost of the target of the

by pcl 12y ago

the cost of solar array as a function of desired temperature rises In a heliostat-based configuration, I'd assume that it's just the cost of the target of the array of mirrors that increases, right?

abdullahkhalids 12y ago
To increase temperature you need to increase the power being transferred to the water. There are several ways you can do it. (a) increase size of mirror array (b) increase reflectivity of mirrors (c) improve sun tracking so that mirrors point towards the sun. (d) improve radiation absorption of receiver. Except the first, each of these is a very non linear. eg. taking reflectivity from 90 to 95 percent might double the cost. But then taking it to 97 might double the cost again.
- ndonnellan 12y ago
  In addition, as your design steam temperature rises, your receiver's costs start to go way up. You need to use more expensive, less conductive metals - some (all?) of which are patented. Your radiative heat losses go up exponentially (T^4), so you need to hide as much surface area from the environment as possible (which means you need a cavity receiver). Now that you're a cavity, it becomes harder to concentrate light (smaller target) so your heliostat requirements go up. If I were a betting man, I'd say this goes nowhere. I think PV has already won the "war" versus thermal unless someone can come up with a great solar -> syngas receiver.
  - VLM 12y ago
    Probably meant more conductive because the walls inherently have to be thicker, so if the atmospheric side remains barely below melting, the interior of a thicker wall will be cooler. Rocket engines have the same problem. Thats why no one ships a 50000 PSI chamber pressure rocket engine, it would work great (Well, I wouldn't want to design the pumps...) but we just don't have the metallurgy to make a chamber that wouldn't melt. Aside from the Isp not going up fast enough to make a heavier engine worth it. Although there is also truth in that higher temp materials tend to be bad conductors. Tungsten is like what 4 times worse than copper as an engineering estimate? You don't use pure W or Cu anyway, but the general idea holds.

by pcl 12y ago

the cost of solar array as a function of desired temperature rises In a heliostat-based configuration, I'd assume that it's just the cost of the target of the array of mirrors that increases, right?

abdullahkhalids 12y ago

To increase temperature you need to increase the power being transferred to the water. There are several ways you can do it. (a) increase size of mirror array (b) increase reflectivity of mirrors (c) improve sun tracking so that mirrors point towards the sun. (d) improve radiation absorption of receiver. Except the first, each of these is a very non linear. eg. taking reflectivity from 90 to 95 percent might double the cost. But then taking it to 97 might double the cost again.

ndonnellan 12y ago
In addition, as your design steam temperature rises, your receiver's costs start to go way up. You need to use more expensive, less conductive metals - some (all?) of which are patented. Your radiative heat losses go up exponentially (T^4), so you need to hide as much surface area from the environment as possible (which means you need a cavity receiver). Now that you're a cavity, it becomes harder to concentrate light (smaller target) so your heliostat requirements go up. If I were a betting man, I'd say this goes nowhere. I think PV has already won the "war" versus thermal unless someone can come up with a great solar -> syngas receiver.
- VLM 12y ago
  Probably meant more conductive because the walls inherently have to be thicker, so if the atmospheric side remains barely below melting, the interior of a thicker wall will be cooler. Rocket engines have the same problem. Thats why no one ships a 50000 PSI chamber pressure rocket engine, it would work great (Well, I wouldn't want to design the pumps...) but we just don't have the metallurgy to make a chamber that wouldn't melt. Aside from the Isp not going up fast enough to make a heavier engine worth it. Although there is also truth in that higher temp materials tend to be bad conductors. Tungsten is like what 4 times worse than copper as an engineering estimate? You don't use pure W or Cu anyway, but the general idea holds.