For example, the EST is -5h from UTC, while Central European Time (CET, like Paris) is +1h from UTC. Your standard time zone will tell you the standard meridian ( λ s t d). How do I account for Longitude ( λ ≠ 0 °)? As we demonstrated earlier in the lesson, each standard meridian (a major line of longitude) is spaced 15° apart, beginning with the Prime Meridian ( λ = 0 °) in Greenwich, England, and continuing for 360 degrees, or 24 hours. Because time and angles are all linked together, we cannot escape the sexagesimal (base 60 math) system for geographical locations. We have used lines of longitude, or meridians as a reference for time and position E-W. Our notion of time is also tightly coupled with our system of longitude (the longitude symbol for us is λ). The time that you are used to using on your laptops, phones, and (if you still have them) watches is called Standard Time, and is referenced back to the Coordinated Universal Time (UTC), the primary time standard by which the world regulates clocks and time. Time after solar noon counts forward from ω = 0 °, and so the angles are positive.Ĭorrecting Time for Big Longitude Changes: Standard Meridians.Time before solar noon counts backward from ω = 0 °, and so the angles are negative.The hour angle for solar noon is ω = 0 ° (given the symbol of lowercase omega).Solar noon is defined as the moment when the Sun is at its highest point in the sky.A solar day is 24 hours long, and Solar noon is always used locally as the center of time.The time that we use in solar energy is the apparent time and path of the sun relative to the aperture or collection device, called Solar Time. Your job is to get out of watch time and into thinking in terms of solar time, and the angles those times represent.Īs we see in the reading, time is a critical parameter in solar energy resource assessment, and we use a "different" time from your mobile phone (or if you have one, a watch). Watch time is just a convenient way to get everyone to work at the same time, and to coordinate conference calls. In solar simulation tools like SAM (System Advisor Model), we will only be using solar time, which is the industry norm. watch time (which will be expressed as standard time vs. Pay attention to the use of solar time vs. We will use those angles to later calculate the estimated irradiance and irradiation conditions just outside of the Earth's atmosphere (called Air Mass Zero: AM0). In this continued reading of Chapter 6, you will be focusing on the way that we account for time in solar energy and the relation of time to more spherical angles. SECS, Chapter 6: Sections titled "Time Conversions".
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