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Chapter 3: Solar Energy

In this chapter, we will find out how to get the most solar energy out of the sun by considering the time, the altitude angle, the radiation and the photovoltaic (PV) materials. A simple PV model helps to understand the mechanism of energy conversion - solar to electricity. We will further use a simple equivalent circuit to represent a PV cell to investigate its current-voltage characteristics. | Chapter 3 Solar Energy I 3.1 Introduction In this chapter we will find out how to get the most solar energy out of the sun by considering the time the altitude angle the radiation and the photovoltaic PV materials. A simple PV model helps to understand the mechanism of energy conversion - solar to electricity. We will further use a simple equivalent circuit to represent a PV cell to investigate its current-voltage characteristics. 3.2 Terminology Insolation - Incident Solar radiation Ecliptic Plane - The plane swept out by the earth in its orbit Equinox - One of the two days in a year when we have equal day and night in length Summer Solstice - The day of the year when we have the most hours of daylight Winter Solstice - The day of the year when we have the fewest hours of daylight Extraterrestrial ET - Something happening existing or coming from somewhere beyond the planet Earth. 51 3. Solar Energy I 52 Figure 3.1 A fixed earth and a sun that moves up and down. Source Masters 1 . Figure 3.2 The altitude angle of the sun at solar noon. Source Masters 1 . 3.3 Altitude Angle of the Sun Fig. 3.1 shows how the positions between the sun and the earth during a year. The earth is taken as the fixed reference point. The sun makes different solar declination Ỗ to the earth between 23.45 . The declination can be expressed in terms of day in a 365-day year Ỗ 23.45 sin n - 81 3.1 365 where the sine function is measured in degrees and n 81 is the approximated spring equinox Mar 21 . With the help of Fig. 3.1 and 3.1 we may gain some insight into what might be a good tilt angle for a solar collector. In general to face the collector toward the equator and tile an angle equal to the local altitude is a good average position to receive sun ray. Altitude angle fiN as depicted in Fig. 3.2 is solar angle of the sun at solar noon. 3. Solar Energy I 53 Figure 3.3 Tilt angle making sun s rays perpendicular to the PV module. The relationship between altitude angle latitude and .