In parallel, the cosine factor for each hour of each day has to be determined. (5.8) and including the corresponding limitations.

In any case, the incidence angle for tracking surfaces can be calculated from Eq.

The alternatives are the two-axis tracking, following the Sun path both in altitude and azimuth, and the single axis tracking, which opts by one of the tracking alternatives. This would be the desired situation at any time, but the operation of the different solar systems does not always allow such tracking. When the solar panels are tilted so that the sun's rays are hitting them at a 90°angle, the amount of direct radiation that they receive is maximum. 5.3.2.2 Incidence angle for tracking surfaces įinally, high-temperature solar concentration technologies as the central tower and the Stirling Dishes present two-axis tracking, therefore the high temperatures reached inside the receptor. In fact, slopes lower than 3% are demanded for the area when the solar field is constructed. Although the possibility of mounting the collectors with a constant tilt on their rotation axis has been studied and prototypes have been erected, this option is not commercially suitable. Medium-temperature solar concentration systems (parabolic trough collectors and Fresnel lines) are mounted on flat land and north-south or east-west tracking, that is, linear tracking. PV production may be multiplied by 1.3 with this alternative. Two-axis tracking incorporates both azimuthal (along the day) and altitude movement (it changes each day as the solar path on the sky does, but it is the same along every single day). One-axis tracking if only one movement has to be chosen, the azimuth axis (east-west movement along the day) is the usual option, since it may increase the electricity production of about a 20% in South Europe locations. A detailed study is usually performed attending to maximize year production (if it is a grid-connected system) or the demand coverage (the worst month method, if it is an isolated PV system). It is the most common option in mid- and North Europe, where the extra cost of the tracking systems is not justified. Photovoltaics systems admit any option: (a)įixed structure with features (slope and orientation) maximizing the production. (Reprinted from Utzinger and Klein (1979), with permission from Elsevier.)ĭepending on the considered solar technology, a fixed or mobile structure for the solar system will be proposed.

The values with an overhang are given in Table 6.1, where e is the relative extension of the overhang from the sides of the window, g is the relative gap between the top of the window and the overhang, w is the relative width of the window, and p is the relative projection of the overhang, obtained by dividing the actual dimensions with the window height ( Utzinger and Klein, 1979). It should be noted that, for a window with no overhang, the value of F w − s is equal to /2, which is equal to 0.5 because half of the sky is hidden from the window surface. (6.57) accounts for the diffuse radiation from the sky, and the view factor of the window, F w − s, includes the effect of overhang. (6.57) accounts for the ground-reflected radiation and, by ignoring the reflections from the underside of the overhang, is equal to /2, which is equal to 0.5.

(6.53) by finding the average of F for all sunshine hours. (6.57) accounts for the shading of the beam radiation and can be estimated from Eq. All the above data are for oh Greenwich civil time in the year 1950 the variations of these data from year to year are negligible for solar engineering purposes the largest variation occurs through the four-year leap-year cycle. * US Naval Observatory, The American Ephemeris and Nautical Almanac for the Year 1950, Washington, 1948.

Efine altitude geometry