Influence of angle and dirt on solar panel output

< Index Influence of angle and dirt on solar panel output

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My daughter Jennifer helped me one afternoon in Katatu to hold a group of solar panels at different angles to the sun. I measured the voltage and current to see how many Watts were sent to the battery.

From these values and some trigonometry one can calculate the possible amount of energy one can get in one day. (From 3p. 51 W panels which are fixed at the midday (12 o'clock) sun: 758 Wh or 63 Ah at 12 Volt. An ordinary car battery holds about 60 Ah)

Solar Panels (3x"51W")
Angle	U[Volt]	I[Amp]	P[Watt]
0 (=only indirect sunlight)	12,36	0,86	11
10	12,39	1,89	23
20	12,51	2,91	36
30	12,59	4,32	54
40	12,62	5,72	72
50	12,74	6,40	82
60	12,87	7,15	92
70	12,89	7,66	99
80	12,91	8,05	104
90	12,93	8,34	108

placement of solar panels on different roof angles summar & winter.

        Usually one doesn't track the sun with solar panels. But it can be worthwhile to move them semiannually. The sun is 0-23,5 degress North during April to September and 0-23,5 grader South from Sept to April.
        A rather common roof angle is 18-20 degrees from horizontal. If the roof ridge goes East to West, one can easily move the panels in April and Sept to "follow the sun" pretty well.
        A 20 degree misalignment (at 12 midday) gives about 6% energy loss. For 40 degrees off the loss increases to about 29%! So a horizontal panel would give within 6% (at midday, lower at other times) of maximum during the whole year without moving. (A horizontal panel might be more prone to collecting surface dust.) A panel that was fixed so it points at midday sun in June would give only 71% (at midday) of max in December. (I haven't taken into consideration that solar intensity per perpendicular square meter can be less when entering the atmosphere at an angle. MsWorks Spreadsheet that was used )
        Another measurement I made (in Kibosho) was to measure the midday power output before and after whiping off surface dust on a panel (that looked moderately dirty). I saw no significant (noticeable) difference.

Measurements made in Tanzania 1994-95

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How to measure possible solar exposure before choosing a place for a collector or panel.

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