The Prepper info is always fun. However did you ever notice how many of them seem to live in Arizona and West Texas. If I lived in that wasteland is would be prepping every day too.

Actually, while this concept sounds great, mathematically it does not work for most regions that are excessively cold. You would have to calculate the angle of the roof for your location. The picture shows 39-degrees relative to the surface, but that would only work where your latitude is 11 N (someone standing in Honduras or Panama would have this latitude – not in the North American area).

There is an equation you must use to find your solar perpendicular point for Solstice. I will explain it, then give you the equation, and you can test it by using the Artic Circle as the proof.

90-degrees is the point straight overhead, known as ‘Zenith’. To correct a plane so that the sun achieves Zenith perpendicular to a plane, you have to know what angle you are first positioned at, then what angle the sun is at. If you don’t know your Latitude (your position), that’s ok, you can either Google it, or at 2 times of year, measure it directly. Let’s google ‘Los Angeles Latitude’. It is 34-degrees North. Ok, now knowing the earth’s ’tilt’ is 23.5 degrees, and that it swings a total of 47 degrees (+23.5 degrees to -23.5 degrees) during the year, then we know that our position is affected by this amount of tilt. That said, it means that in the Summer, the highest above you that the sun can rise (the closest it can approach Zenith), is 90-(34-23.5)=79.5 degrees. In the Winter, when the sun is ‘low’ in the sky, the sun is south of the Equator, so then you calculate low point by compounding latitude and ’tilt’. In LA, the lowest the sun will ever reach at midday is 90-(34+23.5)=32.5 degrees in the sky. The difference should always work out to be 47-degrees, Summer vs Winter.

Now, since you want to build a greenhouse with a perpendicular roof to the sun’s Zenith on Winter Solstice, you would want to be perpendicular to a sun sitting at 32.5 degrees. That’s 90-32.5 = 57.5 degrees. That is a roof which runs more vertical than horizontal “”. As you go further north, that slope further increases. At the edge of the Artic Circle, it would be a vertical wall facing South (don’t forget to face your roof towards true South!).

Yes, this is all accurate – test it with any point on the Artic Circle (66.56 N Lat.). You will see, the equations I have given are correct (I did round, for planet tilt). Now, if you are below 45-degrees N. Latitude (the U.S.), you in theory could take advantage of this equation and the greenhouse roof-slope idea to have a nice home or greenhouse. The concept is valid – as long as you use the proper math to calculate it first.