For those of you who don’t know Solar Fred, I’m not a solar engineer by any stretch, but I’m a serious solar geek and advocate. Ever since I was as a kid, I’ve been fascinated by how the sun’s energy could be turned into electricity and hot water. That’s why I’m in this business.
So when I asked one of our company founder’s, Gal Moyal, to write some solar technology blog posts, I was really looking forward to some great geeky solar information that would show our readers the power of the sun…and Gal’s engineering know-how. Gal’s first assignment: The Nature of Sunlight and Solar Hot Water, Part 1
What Gal returned to me was a brief course in the nature of sunlight and solar thermal physics. Personally, I’m not sure I understand it all, but if there’s one thing that the Gal show’s our customers is that:
- A great solar installation involves some thoughtful engineering.
- Gal is an engineer.
- Gal is more of a solar geek than I am, and so I’m proud to be a part of Free Hot Water.
So, without further delay, here’s a brief solar lesson from Free Hot Water’s co-founder, Gal Moyal, with some interspersed translation by Solar Fred. Please let him know how much you appreciate it in the comments section, won’t you?
The Nature of Sunlight and Solar Hot Water, Part 1
Solar Insolation and Radiation (Solar Fred Translation: Sunlight and Solar Emitted Heat)
The Sun emits light primarily in the visible spectrum, but it also emits at other wavelengths, in the infrared and ultraviolet regions of the electromagnetic spectrum. (Solar Fred’s translation: The Sun shines rainbows of light and it is good.)
Figure 1
The intensity of solar radiation just outside the earth’s atmosphere (Solar Constant) is approximately 1,368 w/m2. However; the intensity of this radiation is reduced before it reaches the earth’s surface due to absorption by gases, vapors and dust particles in the atmosphere. On average, about 70% of that radiation hits the earth’s surface and can be calculated using the following formula: (Solar Fred translation: 70% of the sun’s warmth and light is responsible for bronze bikini model tans and warming the earth, including our solar hot water panels.)
Insolation: Solar Radiation Striking the Surface
I = S cos Z
I= Insolation
S~ 1000 W/m2 (Clear day solar insolation on a surface perpendicular to incoming solar radiation. This value actually varies greatly due to atmospheric variables.) (Parenthesis, Gal’s)
Z = Zenith Angle (Zenith Angle is the angle from the zenith (point directly overhead) to the Sun’s position in the sky. The zenith angle is dependent upon latitude, solar declination angle, and time of day.) (Parenthesis, Gal’s.)
(Solar Fred translation: Gal is an engineer. There was actually more calculus formulas below this formula, but I edited because I couldn’t translate. and brain started hurting. Please contact Gal if you would like the full formula. Moving on. )
A typical solar insolation intensity of clear day solar radiation on a south-facing surface can be seen in figure 2. One can easily see that the time of the day with the most insolation is at noon when the sun is directly above the equator and most of the insolation is a direct solar radiation. (Solar Fred Translation: Solar panels work best when facing South and get the most sunlight at high noon, which is usually my lunch hour.)
Figure 2
Solar Zenith Angles
The Earth’s axis is tilted from perpendicular to the plane of the ecliptic by 23.45°. This tilting is what gives us the four seasons of the year – and the different insolation intensity during a given year. Summer is warmer than winter (in each hemisphere) because the Sun’s rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer. During the winter, the Sun’s rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth’s axis. (Solar Fred’s translation: Gal explains it pretty well below.)
Practical applications
Based on the above science, when Free Hot Water solar thermal engineers design a system, we need to pay attention to the following:
- For best results, panels should face the equator. Therefore, in the U.S and Canada and most of Europe, the solar panels should face south. While in the Southern hemisphere countries such as Australia and Argentina, solar panels should point north.
- True south does not align with the magnetic south. That magnetic declination can be precisely determined for any location based on latitude and longitude using the calculator at the following Web site: http://www.ngdc.noaa.gov. (Solar Fred Translation: That was part of the calculus I didn’t put in. Sorry.)
- Solar panels tilt for optimal winter performance can be calculated for the specific zone using the following calculator. (Solar Fred Translation: We have a great solar cost estimation calculator. Please use it. Our other co-founder, Paul Burrowes worked very hard on it, and it’s really easy.)
