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Solar Energy
Published in Sergio C. Capareda, Introduction to Renewable Energy Conversions, 2019
In calculating the amount of solar energy received at a given location at any given day of the year and time of day, one must keep in mind the concept of solar time. Solar time is defined here as the time based on the apparent angular motion of the sun across the sky with solar noon, the time the sun crosses the meridian of the observer (Duffie and Beckman, 2006). Solar time is not the same as our standard or clock time. The difference is given by Equation 2.2: Solar Time=Standard Time+4×(Lstd−Lloc)+E
The Earth–Sun Relationship
Published in Matt Fajkus, Dason Whitsett, Architectural Science and the Sun, 2018
Because solar geometry calculations employ apparent solar time, it is frequently necessary to convert to or from local time, the official time shown on clocks at a given location. To convert from solar time to local time, two or three adjustments must be made: a constant adjustment due to the position of the location in its time zone, a variable adjustment for the equation of time, and an adjustment for daylight saving time if it is in effect.
Solar Radiation
Published in T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl, Heating and Cooling of Buildings, 2016
T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl
All solar angle calculations should use solar time. Solar time is based on the apparent motion of the sun as seen from a point on the surface of the earth. Universal time, or Greenwich civil time tciv,Gre, is the time along the Greenwich meridian (or longitude), adopted as the reference meridian of zero longitude. This is the time quoted in international TV and radio programs. Three quantities are relevant when specifying the time of day at a specified location: Standard timetstd of the time zone of the specified location is defined by the reference value of the longitude. For instance, in the contiguous United States, the reference meridians for the time zones are 75°W for Eastern, 90°W for Central, 105°W for Mountain, and 120°W for Pacific standard times. Most countries have only one reference meridian; i.e., for India, it is 82.5°E. The standard time is the watch time when daylight savings is not followed.Local civil time tciv,loc is the time at the specific location in question. A constant correction is needed, which accounts for the difference in longitude between the reference meridian and the local meridian. Since one full cycle of a day corresponds to 360° longitude, each degree corresponds to (24 h × 60 min)/360° = (1/15) h = 4 min. In most parts of the world, clocks are set to the same time within a time zone covering approximately 15° of longitude (although the boundaries may be quite irregular).Daylight savings time (DST) is an artificial change adopted by several countries worldwide. From several decades, most parts of western Europe and North America have instituted an advancement of the clock by 1 h during the summer half of the year (the “spring ahead, fall back” rule). The reason for adopting DST is that it improves the match between human activities and the availability of daylight, thereby resulting in humans consuming less energy. It also results in a reduction in overall building energy consumption (such as lighting electricity use).
Developing a model for predicting optimum daily tilt angle of a PV solar system at different geometric, physical and dynamic parameters
Published in Advances in Building Energy Research, 2021
Seyedmohammadreza Heibati, Wahid Maref, Hamed H. Saber
In Equation (3), n is the day of the year. The solar time is based on the apparent angular motion of the sun across the sky with solar noon time that the sun crosses the meridian of the observer. Also, the local standard time (LST) is converted to solar time where there is a constant correction for the difference in longitude between the location and the meridian on which the local time is based (Eastern, 75° W; Central 90° W; Mountain 105° W; Pacific 120° W; Hawaii-Alaska 150° W) (Athienitis, 1994; Hamiltona & Sakazaki, 2017). Note that one degree in longitude is equivalent to 4 min (since 360° is one day).