Figure 11: Types of DIY solar air heaters (Rimstar, 2005)
These designs shown in Figures 10 and 11 are all similar where cool air enters from the bottom, heats the air as it moves through the painted-black system (to absorb as much solar heat as possible), and then the hot air exits at the top to heat the room. The image to the left of Figure 11 is a screen design, where the air enters at the bottom of the system and moves in front of the black screen. The air exits at the top as it rises when heated by the sun-heated screen. In the ‘back pass with baffles’ system in Figure 11, the air enters at the bottom hole and is heated as it moves under a black screen in the direction of the exit hole as it is diverted. The last two images in Figure 11 indicate where the air enters the system and is heated as it moves through black painted cans (which are connected through holes at the bottom and top of the cans), or when moving through a black painted downspout. 2.4.6 Light through water The law of refraction (or Snell’s Law) was discovered in the fifteenth century by a Dutch mathematician and geodesist Willebrord Snel van Royen. Figure 12 illustrates the refraction of a light ray as it hits the water.
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