(i) For site latitude of 30 o in the northern hemisphere, calculate the optimum
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Question
(i) For site latitude of 30o in the northern hemisphere, calculate the optimum tilt angle and orientation for a PV panel to be used at noon on January 1.
(ii) If the above site is 5o west of the standard meridian in that time zone, calculate the sun’s altitude at 3:00pm on January 1.
(iii) Calculate the global radiation (R) on the tilted panel in problem (i) at 3:00pm on January 1 assuming a clear day.
(iv) Calculate the power output of a PV system composed of twenty 2mx2m 18% efficient panels on a rooftop at 3:00pm on January 1.
Explanation / Answer
(i)As a rule of thumb, if the main loads are in winter months when solar availability is reduced, tilt angles should be more vertical (approximately equal to latitude plus 15°) to maximise exposure to the low winter sun. If major loads are cooling and refrigeration the tilt angle should be reduced (approximately latitude minus 10°) to maximise output during summer. For 30 degree in the northern hemisphere, the tilt should be approx 30+15= 45 degree.
PV panels should always face true south if you are in the northern hemisphere.
(ii) altitude of the sun= 90- 30-23.5= 36.5 degree
the altitude of the Sun at solar noon can also be calculated with the following simple equation:
Altitude A = 90 - Latitude L +/- Declination D
In this equation, L is the latitude of the location in degrees and D is the declination. The equation is simplified to A = 90 - L if Sun angle determinations are being made for either equinox date. If the Sun angle determination is for a solstice date, declination (D) is added to latitude (L) if the location is experiencing summer (northern latitudes = June solstice; southern latitudes = December solstice) and subtracted from latitude (L) if the location is experiencing winter (northern latitudes = December solstice; southern latitudes = June solstice). June solstice D=23.5, December solstice D=23.5, March equinox D=0, and Septemeber equinox D=0. When using the above equation in tropical latitudes, Sun altitude values greater than 90 degrees may occur for some calculations. When this occurs, the noonday Sun is actually behind you when looking towards the equator. Under these circumstances, Sun altitude should be recalculated as follows:
Altitude A = 90 - (originally calculated Altitude A - 90)
(iii)4kWh/m2
(iv) The global formula to estimate the electricity generated in output of a photovoltaic system is :
E = A * r * H = 4 * 18* 4=288 kWh
E = Energy (kWh)
A = Total solar panel Area (m²)=2 m square
r = solar panel yield (%)
H = Annual average solar radiation on tilted panels=4(from ans iii)
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