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

Table 5

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 London (latitude +51°32′N; longitude 0°05′W).

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	61.8	2.24	73.8	3.10	64.7	2.32	70.6	4.00	2.36	0.36
𝑑2 = −13.289	52.1	4.39	66.1	5.95	55.5	4.56	63	6.26	2.80	0.41
𝑑3 = −2.819	41.4	7.79	55.9	10.46	44.9	8.14	52.6	9.26	2.90	0.52
𝑑4 = 9.415	32	13.31	44	17.36	35.3	14.02	40.8	13.70	2.33	0.80
𝑑5 = 18.792	25.8	18.88	34.6	23.65	28.6	19.96	31.7	17.86	1.45	1.09
𝑑6 = 23.314	20.7	17.87	29.9	22.55	23.1	18.71	25.2	16.84	1.69	1.07
𝑑7 = 21.517	21.7	16.61	31.7	21.20	24.2	17.37	26.7	15.83	1.84	1.03
𝑑8 = 13.784	28.2	14.54	39.6	18.85	31.2	15.29	35.8	14.44	2.17	0.90
𝑑9 = 2.217	39.1	11.02	51.1	14.37	42.6	11.63	49.3	12.24	2.43	1.13
𝑑10 = −9.599	54.9	8.65	62.9	10.84	58	9.23	63.8	11.86	1.82	1.13
𝑑11 = −19.148	63.1	3.68	72.0	4.84	65.9	3.87	71.3	6.53	1.85	1.06
𝑑12 = −23.335	64.2	1.73	75.8	2.41	66.8	1.78	72.2	3.31	2.26	0.32