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What is free energy?
If you have an electronic device connected to the internet, you probably have seen something about Free Energy. Free energy seems to be energy derived from breaking the laws of physics. Not going to happen! There is however, plenty of real free energy from the gigantic nuclear furnace parked 93 million miles from home. Plenty close. This source is available almost every day all around the globe, except for along the Wasatch front during the month of December when we descend into the seventh level of inversion hell.
There are many times when you, or your project is not conveniently close to a coal fired power plant and the use of primary batteries is not practical either. The answer that most people turn to in these cases are solar panels. The panel provides power that charges a local storage device, like a rechargeable battery, so that the energy can be used as needed.
If you have not used solar panels before, there are some things that you need to know in order to be successful. For example, how do you orient the panel? Horizontal? Vertical? Facing east, west or south? How big of a panel do you need for your particular application. All of these questions must be addresses, including one more – where on the planet will your project be located? Local conditions greatly impact the amount of available energy for harvesting.
There are some terms about the location of the sun that are needed to fully understand the best way to use solar panels:
Solar Declination: This is the angle between the sun’s rays and an imaginary plan through the equator. The solar declination is only dependent on the day of the year.
Solar Hour Angle: This is the angle between the position of the sun and solar noon, which is simply when the sun is located directly overhead. The angle is considered negative before solar noon and positive after solar noon. The angle is zero at solar noon. The hour angle changes one degree every 4 minutes.
Solar Altitude Angle: This is the angle between the sun and a horizontal plane at the desired location. The angle is zero when it is just rising or setting and 90 degrees when overhead. To calculate the solar altitude, you must know the location (latitude), the solar declination and the hour angle.
Just how much power are we talking about?
The amount of solar radiation hitting a unit area is maximum when that area is normal to the sun’s rays. If that unit area is outside of the earth’s atmosphere the amount is called the solar constant. There is some dispute about the exact amount, but is ranges between 1353 W/m2 and 1394 W/m2 depending on who you talk to. The value of 1367 W/m2 is generally accepted.
The amount of radiation varies due to the varying distance between the earth and the sun, the earths path around the sun being an ellipse. An estimate of the solar flux can be made based on the day of the year using a simple formula.
Now, if you consider the amount of radiation hitting a unit area on the ground, you have to consider the fact that the earth is tipped at 23 ½ degrees, local weather conditions, the amount of water and other gasses that absorb or scatter solar radiation. Fortunately, the National Renewable Energy Laboratory (NREL) conducted a nearly 30-year study of solar radiation (1961-1990) collected at 239 station in the United States and its territories. The data is available for download as a 259-page publication, “Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors.” SLC Utah is listed on page 222.
One of the interesting things highlighted in the study is that the angle of the panels, horizontal (0 degrees), vertical, the same as the latitude and then plus and minus 15 degrees off latitude are reported as monthly and yearly averages. The burning question is what angle is best and that is simply the angle equal to the latitude. To get better performance in winter, when there is less energy falling on a unit area parallel to the earth surface, add 15 degrees to the latitude and set the panel at that angle. To maximize for summer, subtract 15 degrees.
The aforementioned paper gives the average rate of solar radiation for various panel orientations. As an example, the solar radiation for a flat panel set at 40 degrees in Salt Lake City will receive 5.8 kWh/m2/day. Perhaps not today because it is raining, but we will hope for tomorrow.
At Celtic Engineering Solutions we want the sun to always be shining on our clients. Please give us a call and ask us how we can make your tomorrows brighter.
This newsletter is sponsored by Celtic Engineering Solutions LLC, a design engineering firm based out of West Jordan and Murray, Utah, which can be found on the web at: www.celticengineeringsolutions.com. We are also on Facebook, Instagram and Twitter. If we can ever help you with your engineering needs please contact us. You can find the newsletter on the company blog, LinkedIn or in your inbox by subscribing. Send your emails to The Celtic Engineer at: [email protected], with the subject line SUBSCRIBE.
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Sean O’Leary is sometimes known as the Celtic Engineer. He was involved in putting two missions on the space shuttle. He has worked at the Smelter’s Biproducts department of Kennecott Utah Copper. Has helped design ballistic guidance systems for Northrop Grumman. Worked on various DARPA projects, an anti-RPG system known as Iron-Curtain and has been involved with the downhole oil and gas industry. He currently is the owner of Celtic Engineering Solutions a consulting Engineering Company in West Jordan and Murray Utah.