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

Table 3

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 Rome (latitude +41°54′N; longitude +12°27′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	57.5	6.93	64.6	7.93	60.4	7.21	65.8	11.47	1.66	0.91
𝑑2 = −13.289	49.5	10.56	56.9	12.04	52.7	11.02	58.1	14.38	1.71	0.74
𝑑3 = −2.819	40.1	16.05	46.7	18.15	43.1	16.82	47.4	18.12	1.47	0.44
𝑑4 = 9.415	28	20.02	34.3	22.67	30.7	20.95	33.3	19.77	1.22	0.56
𝑑5 = 18.792	20.2	24.07	24.6	26.66	22.2	25.07	23	22.46	0.79	0.76
𝑑6 = 23.314	16.8	27.14	20	29.45	18.4	28.17	18.5	24.90	0.57	0.83
𝑑7 = 21.517	19	28.82	21.9	31.08	20.7	29.98	20.9	26.21	0.52	0.90
𝑑8 = 13.784	26.5	26.82	30.1	29.19	28.6	28.07	29.7	24.99	0.70	0.78
𝑑9 = 2.217	36.5	19.81	41.8	22.06	39.2	20.80	42.3	20.75	1.15	0.40
𝑑10 = −9.599	49	15.29	53.6	16.83	51.6	16.04	55.3	19.35	1.17	0.76
𝑑11 = −19.148	55.7	8.01	62.6	9.13	58.6	8.35	63.9	12.56	1.63	0.90
𝑑12 = −23.335	61.5	7.05	66.7	7.94	64	7.38	68.4	12.76	1.31	1.15