After treating extraterrestrial and terrestrial solar radiations in the previous chapters, the use of this information in treating an important question regarding the installation of fixed solar systems, namely the tilt and orientation of the solar receivers, becomes possible. There are several rules that guide designers in this field. These rules are called the rules of thumb. There are two rules that are directly related to the subject of this chapter. One of these two rules says that a solar collector should be orientated towards Equator. The other one says that solar collector should have a latitude tilt value. Are these two rules valid all over the world? The present chapter focuses on presenting an algorithm for determining the optimum tilt angle all over the world and for any collector azimuth angle. The Earth surface, located between latitudes 66.45oS and 66.45oN, is divided into 3 characteristic zones. The first zone is the tropical between latitudes 23.45oS and 23.45oN. The second zone is the mid-latitude zone between 23.45oN and 43.45oN and between 23.45oS and 43.45oS. The third zone is the high-latitude zone between 43.45oN and 66.45oN and between 43.45oS and 66.45oS. For each of these zones an adequate method is proposed for calculating the solar collector optimum tilt. Moreover, four simple equations are proposed for predicting daily optimum tilt angle and optimum tilt angle for any number of consecutive days. It is found that the above mentioned rules of thumb are not applicable in the tropical zone while they could be applied with a sufficient accuracy when dealing with fixed installations all over the year in the mid- and high latitude zones.
TopIntroduction
Due to pollution problems related to fossil fuels, such as being non-renewable, their impact on environment and increasing their price due to uncertainties in future, the global investment to utilize renewable energy sources is rapidly growing. The total global investment in renewable energy from $220 billion in 2010 reached to $257 billion in 2011. Also by the end of 2011 the total renewable energy capacity reached to 1,360 GW with the most contribution belong to hydro power and wind power summing up to 970 GW and 238 GW, respectively.
Most countries in the world have realized the need for reduction of gases emission to contrast the adverse global climatic change, encouraging the use of renewable and sustainable sources of energy. Indeed, large quantities of carbon dioxide, nitrogen, and sulfur oxides are emitted in the world by conventional energy sources, which are released to the earth’s atmosphere contributing to climate change. Furthermore, the world will soon run out of its conventional energy resources because of the rapid depletion of fossil fuel reserves. This future scenario and the risks associated with CO2 emissions and global warming have increased the interest in renewable energy.
The major renewable energy systems include solar photovoltaic (PVs), solar thermal, wind, biomass, hydroelectric, and geothermal. However, among various renewable energy sources, the photovoltaic technology for power generation is considered well-suited technology, particularly for distributed power generation. Solar panel is the energy conversion fundamental component of PV systems or solar collectors. Solar panels use light energy from the sun to generate electricity through the photovoltaic effect, whereas solar thermal systems generate heat. The amount of electrical power produced from PV systems is related to the amount of solar irradiation projecting on the modules. Hence, the global solar irradiation on tilted surfaces facing in different directions should be considered to estimate thermal and electrical power obtained in architectural planning.
Renewable energy obtained from the sun is very important because of the fact that it is free and environment-friendly. The importance of detailed knowledge of solar radiation received from the sun at a site in the design and selection of solar devices cannot be overstated. Solar energy is the most important clean, free and unending renewable energy source which can be utilized in many parts of the world. The limitation and shortage of fossil fuels and the issues resulted from changes of world environmental and weather conditions have created a good opportunity for solar energy to compete with fossil based fuels. This is more important, in countries with high potential of solar radiation to be benefited from green and clean energy. Utilization of different kinds of solar energy technologies such as solar photovoltaic, concentrating solar thermal power, solar hot water/space heating systems, solar dryers, solar stills and solar ovens are becoming rapidly widespread. Aligned with recent augmented deployment of these technologies, many studies have been undertaken to enhance the performance of such technologies (Khorasanizadeh, Aghaei, Ehteram, Dehghani Yazdeli and Hataminasar, 2014). In order to optimize solar isolation on solar collectors, appropriate method to determine solar tilt angles at any given time is essential to increase the efficiencies of the collectors and that of the devices connected to them (Gunerhan and Hepbasli, 2007). The position of the earth relative to the sun changes with time; the change must be monitored adequately in order to increase the amount of energy being received by solar devices (Gavin, 2007). The magnitude of solar radiation received by a collector is a function of many factors such as location latitude, the declination angle (the angular position of the sun at solar noon with respect to the plane of the equator), tilt angle, the sunrise hour angle and the azimuth angle (Kumarasamy, Tulika, Guddy and Manicam, 2013).