5 ms·

Please keep in mind that efficiency in itself does not mean much. The variable you have to optimize is cost per unit of energy. Supercritical steam is useful f

Please keep in mind that efficiency in itself does not mean much. The variable you have to optimize is cost per unit of energy. Supercritical steam is useful for fossil fuel generation because it is relatively easy to make closed off systems which can withstand high temperatures/pressures. The optimum for solar power might lie at the much lower temperature. Why? Because the cost of solar array as a function of desired temperature rises much faster than that of a fossil fuel generator.

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.
illumen 12y ago
They address cost in the article. "So instead of relying on burning coal to produce supercritical steam, this method demonstrates that the power plants of the future could be using the zero emission energy of the sun to reach peak efficiency levels – and at a cheaper price." They also say that it is not ready to be used commercially. But this organisation is quite good at making things commercially viable. Rather than just doing research for tax breaks. From one of the researchers: “Steam flowed at around 330kg/hr , which equates to a little over 300kW of adsorbed solar energy. The experiments were designed to represent a single element of large scale design, so scale up is related more to multiplicity than redefining heat and mass fluxes.” This experiment was done so they could scale up production of power by just adding more of these.
- tankenmate 12y ago
  Actually the CSIRO (Commonwealth Science and Industry Research Organisation) is owned by the Australian Government; so research for tax breaks isn't the reason. The CSIRO has a largely good reputation amongst scientists and researchers in Australia. And they have a reasonably good commercialisation rate as well; their WiFi patents (most of which have recently expired if I remember correctly) have earned the Australian government nearly one half a billion dollars.
  - dwd 12y ago
    And the current pro-coal/oil/gas Abbott government is cutting funding to ARENA (Australian Renewable Energy Agency), who funded this project, by $435 million in the new budget.

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.

illumen 12y ago

They address cost in the article. "So instead of relying on burning coal to produce supercritical steam, this method demonstrates that the power plants of the future could be using the zero emission energy of the sun to reach peak efficiency levels – and at a cheaper price." They also say that it is not ready to be used commercially. But this organisation is quite good at making things commercially viable. Rather than just doing research for tax breaks. From one of the researchers: “Steam flowed at around 330kg/hr , which equates to a little over 300kW of adsorbed solar energy. The experiments were designed to represent a single element of large scale design, so scale up is related more to multiplicity than redefining heat and mass fluxes.” This experiment was done so they could scale up production of power by just adding more of these.

tankenmate 12y ago
Actually the CSIRO (Commonwealth Science and Industry Research Organisation) is owned by the Australian Government; so research for tax breaks isn't the reason. The CSIRO has a largely good reputation amongst scientists and researchers in Australia. And they have a reasonably good commercialisation rate as well; their WiFi patents (most of which have recently expired if I remember correctly) have earned the Australian government nearly one half a billion dollars.
- dwd 12y ago
  And the current pro-coal/oil/gas Abbott government is cutting funding to ARENA (Australian Renewable Energy Agency), who funded this project, by $435 million in the new budget.