Brilliant Light Power’s Initial Commercial Launch to be a “Thermal” SunCell

The following post has been submitted by Dr. Mike

Brilliant Light Power’s Initial Commercial Launch to be a “Thermal” SunCell

5/21/2017

According to Brilliant Light Power’s website:  https://brilliantlightpower.com/ , their initial commercial launch will now be a “thermal” SunCell with the electrical SunCell based on concentrator photovoltaic (CPV) cells to follow sometime later.  (Their new plan can be found in the “MONTHLY BRIEFING” section as “May 2017” here: http://brilliantlightpower.com/wp-content/uploads/presentations/May-2017-Briefing-Presentation.pdf.)
Many that have reviewed Brilliant Light Power’s plan for their SunCell development were asking why they didn’t first develop a device that just produces heat.  Although I haven’t seen their plan for connecting the SunCell to a heat exchanger or boiler system, an initial system that delivers heat rather than electricity using CPV cells should eliminate most if not all of the illumination uniformity problems that could adversely affect the output of the CPV cells.  Also, even at 3000ºK the illumination intensity would have been more than 1.5 times higher than the rating of most existing multi-junction CPV cells. Designing, fabricating, and verifying the reliability of CPV cells with a higher intensity rating may have delayed the commercial introduction of an electrical SunCell.
The engineering issues in building the prototype thermal SunCell should be mostly involved with automating the operation of the SunCell by adding sensors and control systems and incorporating a heat exchanger into the design.  However, there may be an issue with the thickness of the graphite blackbody radiator that limits high temperature operation (assuming my calculations are correct).  Although graphite would be considered a fairly good heat conductor at room temperature, its thermal conductivity falls to about 30W/m/ºK (0.3W/cm/ºK) at temperatures in the 3000ºK-3500ºK range.  The temperature difference from the inner to outer surface of the graphite sphere would depend on the thickness of the graphite, which does not appear to be specified on BLP’s website.  From a picture of the graphite sphere on the BLP website it appears that the flange on each half of the graphite sphere is about ½ inches (~1.2cm) thick.  For my initial calculation I will assume that the graphite sphere thickness is about ½ of the flange thickness (0.6cm). The temperature difference between the inside surface of the graphite sphere and the outer surface can be calculated as:

Delta T = P / A * RI / RO * (RO – RI) / κ

Where:

Delta T = the inner to outer temperature difference of the graphite sphere

                      P = the radiative outer power at 3000ºK (330000W)

A = Area of the 6” (15.24cm) diameter sphere (729.7cm2)

RO = outer graphite sphere radius (7.62 cm)

RI = inner graphite sphere radius (7.02cm)

and κ = thermal conductivity of graphite at ~3000ºK (0.3W/cm/ºK)

Delta T = 330000 / 729.7 * 7.02 / 7.62 * (7.62 – 7.02) / 0.3 = 982ºK

To achieve an outer temperature of 3000ºK the inner temperature would have to be 3982ºK (very near the 4000ºK sublimation temperature for graphite) to get sufficient heat flow across the 0.6cm thickness of the graphite sphere.  It seems likely that the thickness of the graphite sphere will be less than 0.6cm to prevent sublimation of the inner graphite surface.  If the graphite thickness is only 0.5 cm thick, the inner graphite sphere temperature would only need to be 3807ºK to support the 330000W heat flow out of a 3000ºK 6-inch diameter graphite blackbody radiator.  This might be enough temperature margin for operating the graphite blackbody radiator at an outer temperature of 3000ºK without concerns about the inner surface subliming.  BLP also has plans for raising the outer graphite blackbody radiator temperature to 3500ºK which would have a radiative output heat flow of about 620000W.  Assuming my calculations are correct, the thickness of the graphite would have to be reduced to about 0.1cm (1mm) to keep the inner surface temperature below 3800ºK.  While the a graphite thickness of 0.5cm seems doable, it seems that it would be difficult to build a structurally sound graphite sphere that is only 1mm thick even if an effort is made to balance the pressures internal and external to the graphite sphere.  It appears that it may be very difficult to achieve a 3500ºK outer temperature on a 6-inch diameter graphite blackbody radiator.

One simple solution to achieve the ~620000W thermal output in a Thermal SunCell would be to increase the size of the graphite blackbody radiator and perhaps even reduce the blackbody temperature.  For example, if the graphite sphere size were increased to 10 inches in diameter (25.4cm) then a radiative output power of ~700000W could be achieved at an operating temperature of just 2800ºK.  The graphite thickness could be 0.8cm thick with the inner sphere temperature kept just a little below 3800ºK; or by reducing the graphite thickness to 0.5cm, the inner surface temperature would only be about 3400ºK (very good margin to prevent sublimation of the graphite). The only problem with this approach to achieving higher thermal output is that this solution would not work for the electrical SunCell without greatly increasing the size (and cost) of the CPV array.

Although there still remain some engineering issues to be resolved on a “thermal” SunCell, it certainly appears that Brilliant Light Power will be able to get a Thermal SunCell to the market much faster than would be possible with an electrical version using CPV cells.  This device should be a direct competitor with all LENR technologies.

 

Dr. Mike

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