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

Table 6

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 Stockholm (latitude +59°17′N; longitude +18°03′E). The monthly mean of the daily global solar radiation was not acquired in the periods relative to the solar declinations 𝑑₁, 𝑑₁₁, and 𝑑₁₂.

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	n.c.		n.c.		n.c.		n.c.		n.c.	n.c.
𝑑2 = −13.289	67.1	5.18	73.2	6.99	69.5	5.65	73.8	8.79	1.37	0.70
𝑑3 = −2.819	54.7	10.25	63.1	13.77	57.9	11.15	63.8	12.56	1.88	0.68
𝑑4 = 9.415	43.1	18.64	51.3	24.32	46.4	20.37	51.8	18.32	1.80	1.19
𝑑5 = 18.792	33.0	21.99	41.8	29.10	36.2	23.88	40.7	19.95	1.77	1.70
𝑑6 = 23.314	29.5	25.39	37.3	32.92	32.4	27.54	35.9	22.19	1.52	1.95
𝑑7 = 21.517	29.8	21.84	39.0	29.12	32.9	23.59	37.0	19.68	1.78	1.75
𝑑8 = 13.784	33.8	14.17	46.5	20.12	37.2	15.15	43.4	13.98	2.50	1.25
𝑑9 = 2.217	46.3	10.25	58.0	14.45	49.8	11.02	56.9	11.52	2.44	0.79
𝑑10 = −9.599	60.5	5.65	69.5	7.93	63.5	6.09	69.3	8.25	1.92	0.56
𝑑11 = −19.148	n.c.		n.c.		n.c.		n.c.		n.c.	n.c.
𝑑12 = −23.335	n.c.		n.c.		n.c.		n.c.		n.c.	n.c.