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

Table 4

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 Paris (latitude +48°51′N; longitude +2°20′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	56.7	3.98	68.1	4.94	59.9	4.10	66.5	6.54	2.33	0.51
𝑑2 = −13.289	46.9	6.05	60.4	7.53	50.4	6.25	58	8.21	2.74	0.44
𝑑3 = −2.819	38.3	10.30	50.2	12.66	41.7	10.73	48.3	11.94	2.41	0.47
𝑑4 = 9.415	28.7	15.74	38.1	18.95	31.7	16.47	35.7	15.92	1.80	0.64
𝑑5 = 18.792	20.4	17.66	28.4	21.00	22.8	18.36	24.5	16.94	1.45	0.76
𝑑6 = 23.314	18.3	22.16	23.9	25.46	20.4	23.11	21.2	20.59	1.00	0.88
𝑑7 = 21.517	21.1	24.83	25.9	28.13	23.3	26.05	24.2	22.76	0.87	0.97
𝑑8 = 13.784	27.8	21.73	33.9	25.06	30.5	22.92	32.9	20.72	1.17	0.80
𝑑9 = 2.217	39	17.48	45.7	20.24	42	18.50	46.2	18.67	1.46	0.49
𝑑10 = −9.599	48.7	10.22	57.1	12.14	52	10.75	57.9	13.32	1.88	0.60
𝑑11 = −19.148	58.1	5.93	66.3	7.12	61.1	6.21	66.9	9.67	1.83	0.73
𝑑12 = −23.335	62.6	4.31	70.3	5.22	65.3	4.50	70.6	8.02	1.70	0.74