ASSESSMENT OF THE SOLAR ENERGY INTENSITY ...

ASSESSMENT OF THE SOLAR ENERGY INTENSITY IN SOUTHEAST SULAWESI BASED ON THE RELATIVE POSITION OF THE SUN Budiman Sudia Aditya Rachman Kadir Published in Journal of Metropilar Haluoleo University ISSN 1693-6205 (Vol 9 No 4) ABSTRAK Mesin konversi energi berbasis matahari adalah salah satu teknologi yang memiliki sifat bersih, lokal dan terbarukan. Dalam mendesain mesin ini, salah satu data yang dibutuhkan adalah keadaan lingkungan dimana mesin akan ditempatkan. Salah satu data keadaan lingkungan tersebut adalah intensitas energi matahari. Studi ini bertujuan untuk mengkaji karakteristik dari intensitas energi matahari di Sulawesi Tenggara. Metodologi yang digunakan adalah model matematika untuk menghitung sudut datang matahari berdasarkan posisi relatif dari matahari dan garis lintang suatu daerah. Sudut datang ini akan digunakan untuk menentukan komponen intensitas matahari yang tegak lurus bidang datar. Dalam studi ini aktivitas perbandingan intesitas energi matahari di Sulawesi Tenggara dan daerah yang memiliki perbedaan garis lintang juga dilakukan. Hasil dari kajian ini menunjukan bahwa rata rata intensitas energi matahri di Sulwesi Tenggara adalah 1985 KWH/m2/tahun. Jumlah ini lebih besar jika dibandingkan intensitas energi matahari di deerah yang memiliki garis lintang yang besar ( jauh dari garis katulistiwa ). Hal ini tejadi karena Sulwesi Tenggara terletak disekitar garis katulistiwa yang memiliki keuntungan mendapatkan intensitas tegak lurus matahari yang lebih banyak dibandingkan dengan daerah yang jauh dari garis katulistiwa. Dari hasil dari kajian ini dapat disimpulkan bahwa letak geografis merupakan salah satu faktor yang menyebabkan Sulawesi Tenggara memiliki potensi untuk pengembangan energi terbarukan berbasis matahari. Keyword : kajian energi matahari, intensitas, posisi relatif matahari, karakteristik, Sulawesi Tenggara, perbandingan ABSTRACT Solar energy conversion device is one of promising clean decentralized renewable technologies. In designing the device, it requires deriving the environment condition at which the solar technology is situated. One of the conditions comes from the local solar energy intensity. This study assesses the behaviour of the solar energy intensity in Southeast Sulawesi. The method utilized is derived from a mathematical model for calculating the incidence angle in a plane area based on the relative angle of the sun and the latitude angle of the corresponding location. A comparison of the region which has a different latitude angle is also conducted. The result shows that over a year, the solar energy intensity in Southeast Sulawesi is approximately 1985 KWH/m2 which is higher than that of the region which has higher altitude angle (far from the equator). This is because that Southeast Sulawesi is situated around equator line; thus deriving benefit in term of receiving more perpendicular solar radiation than the region that is far from the line. Based on this assessment, the geographical position enables Southeast Sulawesi to be potential for the development of the renewable energy based solar. Keyword: assessment, solar energy, intensity, the sun relative angle, behaviour, Southeast Sulawesi, comparison BACKGROUND Introduction Energy plays an important role in the socioeconomic development of a country. Economic growth and improvement of people’s living standard are all directly or indirectly related to the increasing utilization of energy (Khan & Nguyen, 2006) Unfortunately, many Indonesia’s regions are still inaccessible with the electricity. A data of ESDM

(2009) shows that the national electricity ratio is 65%. In this percentage, more than 18 provinces have the ratio below 60%. It is believed that the geography and topography of areas in Indonesia is one of the factors hindering the national electrification program (Dasuki et al, 2001).

Decentralized renewable energy technologies have several advantages over grid extension. They can be located closer to the demands so distribution and transmission cost and consequently energy and capacity loss are reduced. They do not require fuel, as their operation is independent from fuel supply availability. In environmental terms, they are relatively clean. Thus, the use of renewable energy will potentially provides the benefits of reducing emissions of air pollutants, including greenhouse gas (GHG) (Khan & Nguyen , 2006 ) The renewable energy technology based solar is a one of the decentralised renewable energy which can be a feasible option in providing an alternative source of energy in areas where conventional grid electrification is a major issue. As the most of Indonesian archipelagos lie in equator line, this enables the nation to receive high energy intensity of the sunlight. In a report of DESDM (2002), the potential solar based energy sources in Indonesia is more than 1 billion MW ( Marpaung et al 2007) Southeast Sulawesi is one of the regions in Indonesia in which some places are still inaccessible to the electricity. According to ESDM (2009), the electricity ratio of this region is below 50%. This province lies at latitude around – 3 ͦ to 6 ͦ (PEMPROV Sultra, 2009). This means that this region is situated around the equator line. This condition is believed to enable this province to harness abundantly the sunlight to assist this region in fulfilling its electricity requirement with the renewable energy based solar.

The results of this assessment can be utilised as a consideration aspect in designing and implementing the renewable energy based solar in Southeast Sulawesi. METHODOLOGY In assessing the behaviour of solar radiation intensity in Southeast Sulawesi, the characteristic of the solar intensity in one year in the determined location is evaluated. In this study, the evaluation of solar intensity is purely based on the beam radiation (direct normal irradiance, the amount of solar radiation from the direction of the sun). One of the factors determining the intensity of the solar radiation is the amount of perpendicular element of the beam on a plane surface. The more perpendicular the direction of the sunlight relative to the plane, the more intense the energy is. To find the perpendicular element of the beam radiation, it requires projecting the radiation into the line perpendicular to the plain surface. To do this it requires multiplying the beam radiation with the cosine of the incidence angle of the sun in a plain surface. As the position of the sun relative to a corresponding location is always changing, this do results in the change of the incidence angle the perpendicular element of the beam radiation changes. Thus to evaluate the solar radiation intensity over a year, it requires summing the perpendicular element of the beam radiation for every elemental time, such as seconds, minutes , hours , days , weeks or months ).

Problem Definition In effort to develop the renewable energy based solar in fulfilling the electricity requirement in Southeast Sulawesi, an assessment on the environment condition in this region is required. This is because that the environment condition can be an important consideration in determining the size of a design. Thus, if a certain size solar device design is proposed, the performance can be predicted. As the performance is figured, the economic consideration can be proposed to assess whether the proposed design is feasible or not.

Mathematical model To find the incidence angle, the mathematical model in Duffie & Beckman (1991) is utilised. The reason is that the model is able to calculate the relative angle of the sunlight to a perpendicular line to the plain surface, based on the relative solar position and the latitude angle. Referring to Figure1, ω is the hour angle which is the angular displacement of the sun east or west of the local meridian due to rotation of the earth on its axis at 15° per hour. φ is the latitude which is the angular location north or south of the equator. δ is the declination the angular position of the sun at solar noon with respect to the plane of the equator (-23.45° ≤ δ ≤ 23.45°). The declination can be found from

Aims of the study The purpose of this study is to assess the behaviour of the available solar radiation intensity in Southeast Sulawesi based on the relative position of the sun. An additional activity in comparing the annual solar energy intensity with the region far from the equator will be also conducted.

δ = 23.45 sin 360

284 +n 365

(1)

where, n is day of the year. Klien (1977), made a simplification to find the declination as a function of month, Month January February March April May June July August September October November December

Declination ( δ) - 20.9 - 13.0 - 2.4 9.4 18.8 23.1 21.2 13.5 2.2 - 9.6 - 18.9 - 23.0

Table 1. The declination in month variation ( Klein ,1977) Sources : Solar engineering of thermal processes', second edition, J. A. Duffie, W. A. Beckman, Wiley, 1991

Figure2 The relative angle of the sun J. A. Duffie, W. A. Beckman, Wiley, 1991.

Referring to Figure2, γs is the solar azimuth, which is the direction of the beam radiation relative to South. To find the angle, it can used the equation developed by Tarboton D (1965)

cos γs =

sin δ−cos Ѳz sin ω sin Ѳz cos ω

(2)

β is the slope between the plane surface in question and the horizontal. γ is surface azimuth angle, that is, the deviation of the projection on a horizontal plane of the normal to the surface. The incidence angle is determined by following equation cos Ѳ = sin δ sin Φ cos β − sin δ cos Φ sin β cos γ + cos δ cos Φ cos β cos ω + cos δ sin Φ sin β cos γ cos ω +

(3)

cos δ sin β sin γ sin ω

For plain horizontal surface, this equation can be simplified as cos Ѳ = cos Φ cos δ cos ω + sin Φ sin δ

(4)

Thus, the daily solar energy intensity can be found

Ed = Figure1 Latitude, hour angle, and sun declination Sources McQuiston et al (2004)

24 E cos Ѳ 0

dh

(5)

Where, h is hour and E is the global solar radiation intensity. In this study, this intensity is represented by the bean solar radiation. The annual solar energy intensity can be found Ea =

365 0

Ed dd

(6)

Where, d is day. Beam Solar radiation Outside the earth's atmosphere, solar radiation has an intensity of approximately 1370 watts/m2. This is the value at mean earth-sun distance at the top of the atmosphere and is referred to as the Solar Constant. On the surface of the earth on a clear

CALCULATION The following graph is the calculated hourly solar radiation in Southeast Sulawesi over a year.

Solar radiation ( Watt)

800 600 400 Nov

200

Sep

0

Jul

3

May

7

Mar

11

15

Hour

Month

Jan

19

23

Figure3 the calculated hourly solar radiation in Southeast Sulawesi over a year

By utilising Equation (6), the total annual solar radiation in Southeast Sulawesi is 1985 KWH/m2. The following graph is the calculated solar hourly radiation in Wollongong – Australia in a year. Using Equation (6), the total annual solar radiation is 1646 KWH/m2.

Solar radiation (Watt)

day, at noon, the direct beam radiation will be approximately 1000 watts/m2 for many locations. (Discovery Solar Energy, 2010). In determining the beam radiation with more representation fact, the data of the beam radiation measured in Sudia (2009) is utilised, instead of the general approximation of 1000 watt/m2 in the previous reference. This radiation is derived from location of South Sulawesi, a region which is also around the equator (latitude of -5.8). The data was taken by pyranometer of POLTEK Makassar in October 2009. The beam radiation at 12.00 noon is used as the base reference. The reason is that the radiation at the corresponding time more represents the intensity at a perpendicular position of the sun relative to horizontal surface compared to the other hours. As the data was taken at October, it actually gains advantage in deriving more precision data. This is because that in the month, the solar declination is almost at zero (Equator) (see table1). It can say that at 12.00 noon, at the corresponding region (latitude of -5), in October, the beam radiation is almost perpendicular to the horizontal surface. In Sudia (2009), the radiation in the corresponding to the above constraint is about 765 watt/m2. Thus in this study, it utilises this number for determining the beam solar radiation. In comparing the intensity of solar radiation in region far from equator, Wollongong in Australia is chosen. This is because that this region is relatively has a wide gap to the equator line as it lies at latitude of -34ͦ ͦ25 (Time and Date, 2011).

800 600 400 Nov

200 0

Sep Jul

3

May

7

Hours

Mar

11

15

Mounth

Jan

19

23

Figure4 the calculated hourly solar radiation in Wollongong over a year

DISCUSSION From the Figure3, it is shown that over a year, the radiation in Southeast Sulawesi is relative constant. A slight deviation exists at the middle of the year. The reason may come as the in these events, the

declination angle is at around +20, while the latitude of Southeast Sulawesi is at around -5. This means there is a wide gap in radial direction of the location and the sun path (see Figure5). The gap can decrease the perpendicular element of the radiation. From the Figure3, it is shown that over a year, the radiation is considerably varying in Wollongong. The minimum intensity exists at the mid of the year. The reason may be similar with that in Southeast Sulawesi case, that in the corresponding month, the position of the sun path is at 23.34 ͦ , while Wollongong is at -34. This means that there is a wide gap between them, reducing the perpendicular element of the beam radiation (see Figure6). Compared to that in Southeast Sulawesi, almost over the year, the solar radiation in Wollongong is smaller. The reason may come as the radial gap of the sun path and the latitude of Wollongong is much wider than that of the Southeast Sulawesi (see Figure5).

CONCLUSION The assessment the behaviour of the available solar intensity in Southeast Sulawesi has been demonstrated. The annual solar radiation based on the utilised model in a horizontal surface is 1985 KWH/m2 (or 5.57 KWH/m2/day). This value is higher than that in Wollongong-Australia. The reason could come as Southwest Sulawesi lies around equator line; it derives advantage in receiving more solar radiation intensity than that of the region far from the equator line. The results show that as Southeast Sulawesi is situated nearly the equator line, it is very potential to be developed for the renewable energy based solar.

REFERENCES

Fifure5 The solar path and the corresponding region assessed in variation of latitude

Limitation The following presents some limitations of this study. The assessment in this study is purely based on the perpendicular element of the beam radiation based on relative angle of the sun. The effect of diffuse radiation, cloud, weather, rain or other metrological condition is not considered in calculation the solar intensity. Indeed, in calculating the declination, it is based on the monthly approximation by Klein (1977). Actually, the angle is affected by the day on a year (see Equation (1)). All these facts are highly possible affecting in the precision on the assessment of the solar radiation intensity.

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