An Algorithm to Determine the Optimum Tilt Angle of a Solar Panel from Global Horizontal Solar Radiation

Table 1

Optimum tilt angle values and monthly mean of the daily global solar radiation values computed by means of the algorithm proposed in Section 2 applied to the monthly averages of the daily global horizontal solar irradiation data acquired from 1985 to 1989 at the site of Tripoli (latitude +32°57′N; longitude +13°12′E).

Solar declin. (deg)	Isotropic model		Le Quere’s model		Hay and Davies’ model		Klucher’s model		SEM values
	𝛽 (deg)	𝐸 (MJ/m^2)	𝛽 (deg)	𝐸 (MJ/m^2)	𝛽 (deg)	𝐸 (MJ/m^2)	𝛽 (deg)	𝐸 (MJ/m^2)	𝛽 (deg)	𝐸 (MJ/m^2)
𝑑1 = −21.269	50.7	12.44	55.3	13.05	53.3	12.73	57.0	18.54	1.17	1.26
𝑑2 = −13.289	43.6	17.13	47.5	17.96	46.0	17.59	48.7	21.56	0.95	0.87
𝑑3 = −2.819	33.7	22.54	37.0	23.61	35.8	23.18	37.4	24.06	0.72	0.28
𝑑4 = 9.415	21.9	27.08	24.3	28.24	23.5	27.79	23.8	26.01	0.45	0.42
𝑑5 = 18.792	12.9	29.26	14.3	30.16	13.8	29.83	13.6	27.56	0.25	0.50
𝑑6 = 23.314	8.6	30.92	9.5	31.53	9.2	31.34	8.9	29.31	0.17	0.44
𝑑7 = 21.517	10.6	31.92	11.4	32.55	11.2	32.39	10.9	30.00	0.15	0.50
𝑑8 = 13.784	18.4	30.71	19.8	31.58	19.4	31.35	19.4	28.77	0.25	0.55
𝑑9 = 2.217	29.5	25.74	31.9	26.77	31.2	26.43	32.0	25.90	0.50	0.22
𝑑10 = −9.599	40.9	20.16	44.0	20.99	43.0	20.69	44.9	23.73	0.75	0.69
𝑑11 = −19.148	48.5	13.26	53.2	13.94	51.1	13.58	54.8	18.79	1.18	1.13
𝑑12 = −23.335	51.8	10.64	57.2	11.21	54.5	10.87	58.9	16.54	1.35	1.23