Reflected Light Nano Materials and Better Solar Panels

Fig 1:  Albedo Values of materials
Source: http://en.wikipedia.org/wiki/White_roof

                    Human built environments have a nasty habit of becoming too hot in the summer time.  A combination of materials that love to convert visible light into heat, large blocks of materials like concrete retaining said heat, and air conditioners dumping their heat into the air around residents.  One solution for mitigating the thermal gain of urban environments is to increase the albedo, or the ability to reflect sunlight (this should not be confused with libido).  Increasing the albedo of an area can be done in a myriad of ways the most popular being painting rooftops a reflective color such as white.  An extremely cool (no pun here) version of the white roof has been developed by graduate students and faculty at Stanford University, they have created a material made out of intricate nano-structures that pull double duty for cooling.  First the material works as an extremely reflective material increasing the albedo of the region that it is placed.  The second and by far more sci-fi sounding feature of this composite is that it is designed to emit thermal radiation in a frequency that our atmosphere is generally transparent to (for people who like thermal dynamics this is really impressive.)

                Other members of Stanford's faculty believe that it is more worthwhile to install solar panels, as the solar cells are generally more reflective than traditional black tar rooftops found on many large buildings and allow for electricity production.  To them I ask ----------------------->

             Recent research has indicated that the snows of winter can actually improve the performance of a solar panel, so long as it isn't covered in snow.  The snow acts as a reflector concentrating more sunlight onto a solar panel, while the cold temperatures of winter can increase the overall efficiency of the system.  Merging this thought with the properties of the Stanford nano-material, which I will call Silver-Surfer for the remainder of this post, one potential design solution came to mind.  Place a solar panel on an easily mounted structure that has Silver-Surfer placed in such a way to suck heat away from the solar cell and reflect a certain amount of incident radiation back towards the solar cell.

Fig 2:  Straight on view of Collector Reflector

The initial configuration would operate as an angled trough with the solar cell at the bottom and Silver-Surfer angling out in such a way that the reflective/emissive surface is maximized without interfering with the ability of the panel to gain sunlight.

Figure 3: Θ and the panel

One critical consideration, if this approach is considered a rational choice, would be determining the angle at which the solar cell and the Silver-Surfer are mounted relative to each other (assuming a non-tracking array). Figure 3 Highlights the angle of interaction, in the case of the quick model Θ (theta) was set at 30 degrees arbitrarily.  The actual angle would be a balancing act of potential shadows cast during day time operations (particularly early morning and evening), increased solar reflection onto a given area of solar panel, and cooling benefits as a result of the area of the Silver-Surfer sub assembly. The trump considerations, deserving their own sentence, would be the impact of cost of materials, installation, and maintenance.  A lower theta value would most likely indicate a lower life time cost of operation relative to net energy production/savings.

Fig 4: Panels on roof top

As an installed platform the array could look something like figure 4, where the collectors create a direct route for precipitation to slough off.  Placing the panels horizontally is possible and may make sense in regions with accommodating climates, it would also allow for the panels to have much larger theta value, increasing the cooling surface.  Other panel orientations should not be ruled out as they could find a sweet spot between dealing with local weather and maximizing the cooling energy generating/saving potential of the system.

One final note, it should not be ignored that in addition to working as a passive generating platform there is the potential for adding piping or ducts into the system.  During the day the system would most likely operate in a similar fashion to the more passive design suggested above, but at night the Silver-Surfer elements could be used to help chillers to produce ice to further offset day time HVAC needs.  This kind of approach would be targeted at facilities like server farms that tend to produce tremendous amounts of heat, even before thermal gain is considered.  Domestic installations would be unlikely to benefit from a more active system as the Gizmag article on Silver-Surfer stated that an average 1 family 1 floor home could achieve a 35% reduction of air conditioning needs by installing Silver Surfer on 10% of the area of a house's roof top.