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Solar Insolation
Published in Dorothy Gerring, Renewable Energy Systems for Building Designers, 2023
The height of the sun in the sky is called altitude (easy to remember because we know altitude is a height measurement) and the sun’s location along the horizon is called azimuth. This is shown in figure 5.3. Solar noon is when the sun is directly overhead, at the highest altitude for that day. Azimuth can be measured as degrees to the east and west of south or north, or on a scale of 360° starting from north as 0°. Azimuth can be applied to your collector as well. If your collector is fixed, it should be within 15° of south (northern hemisphere) or north (southern hemisphere) for optimal collection. The sun moves across the sky at 15° per hour, so facing your collector toward solar noon maximizes your ability to catch the solar radiation.
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
Another source of deviation between solar time and local civil time is due to the nature of the earth’s orbital motion around the sun. The elliptical orbit induces changes in the orbital angular speed of the earth (according to Kepler’s laws). Solar noon is the time when the sun reaches the highest point in the sky; it can differ from noon of local civil time by as much as one-quarter hour. The difference between solar noon and noon of local civil time is called the “equation of time” Et. It is a function of the time of year (plotted in Figure 4.3) and can be approximated by Et=9.87×sin2B−7.53×cosB−1.5×sinB(min)withB=360°×n−81364fornthdayofyear
The Sun
Published in Roger Messenger, Homayoon “Amir” Abtahi, Photovoltaic Systems Engineering, 2017
Roger Messenger, Homayoon “Amir” Abtahi
It is also important to be able to determine the clock time at which solar noon occurs. Solar noon occurs at 12 noon clock time at only one longitude, L1, within any time zone. At longitudes east of L1, solar noon will occur before 12 noon, and at longitudes west of L1, solar noon will occur after 12 noon. On a sunny day, solar noon can be determined as that time when a shadow points directly north or directly south, depending on the latitude. Note that in the tropics, part of the year the shadow will point north and the rest of the year the shadow will point south.
Performance of inclined heliostat solar field with solar geometrical factors
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Rahul Bhattacharjee, Subhadeep Bhattacharjee
Figures 11, 12 show the cosine efficiency and field optical efficiency distribution over the designed heliostat solar field over the days of an equinox, summer solstice, and winter solstice. The characteristics show that the higher cosine efficiency and field optical efficiency zone moves from north-west side to the north-east side of the heliostat solar field from sunrise to sunset, which means the high-efficiency zone of the solar field that travels from the western part of the field (8 am) to the eastern edge (4 pm). At 12 noon, the maximum power is obtained, because the sun stands highest in the sky at this time. The heliostat mirrors which are situated at the shorter distance from the receiver have better collective performance because they have less azimuthal angles. Comparatively, the heliostats situated far away from the receiver have a larger azimuthal angle and lower cosine efficiency, as well as less energy concentrated. The curves show that the cosine efficiency is highest at 12 o’clock for all of these days. The average cosine efficiency at solar noon is highest at winter solstice with 92% followed by equinox (86%) and summer solstice (77%). On the other hand, the average field efficiency is obtained as 76%, 73%, and 68% corresponding to equinox, winter solstice, and summer solstice days. The obtained results may be compared with the study made by Rinaldi et al. (2014). Where field optical efficiency of PS-10 and Gemsolar plant were found to be 74.78% and 66.34%, respectively, at the solar noon of the equinox.
Solar Energy Fundamental Methodologies and its Economics: A Review
Published in IETE Journal of Research, 2023
The time based on the perceptible angular motion of the sun across the sky with solar noon denoting the time the sun crosses the meridian [40] of the observer. The disparity in minutes between solar time and standard time is solar Time or simply Standard Time: The equation representing the solar time standard is given as follows: Lst is the standard meridian for the local time zone (for India the value is (81°54´), Lloc is the longitude of the location [41] and E is the equation of time (in minutes) that can be demonstrated as follows:
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).