In fact, this may be a good time to grab a Laser pointer and try a dark wall or table. Take a moment to consider what happens to the surface when you tilt the laser pointer from an angle perpendicular to the receiving surface (also known as the "normal" in geometry). The vertical angle is called the zero incident angle (θ = 0°). The supplementary angle of this angle (90° minus the incident angle) is called the glancing angle (here, α). Now, tilt the pointer up or down while keeping the same focus on the receiving surface. When you tilt the pointer from the "normal", you will increase the incident angle and decrease the glancing angle. The cosine of the incident angle is proportional to the density of photons on the receiving surface.
Now, place your hand in front of the beam. It creates a shadow and robs the receiver of these precious photons for energy conversion. Sometimes we want shadows (for patio design), sometimes shadows are really harmful to solar conversion (for example in photovoltaic panels). Design teams can use orthogonal projection and Sun chart tools to learn how to predict when and where shadows will appear in the design.
From our small experiment with laser engraver, we have just explored three main geometric methods that serve solar engineering and design goals! As shown in the following sections, the concept of "regional settings" provided to customers is actually a combination of place and time. A certain position on the earth is related to seasons and regional climate, changes in the position of the sun on the sky dome, and the position of SECS north or south of the equator. So, given the tools developed in this chapter and the next, how do we achieve the goals of solar design?
Power density is a measure of how the laser is applied to the material to be processed. It is expressed as Watt/square centimeter-W/cm2, where Watt is the unit of laser power and square centimeter is the area related to the beam size.
In other words, the power density of a blue laser pointer is the amount of power concentrated in a specific space. For example, a 400 watt laser focused to a spot size of 50 microns in diameter will produce a power density of approximately 41 megawatts per square centimeter.