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The results obtained by GS and NR for various panel of KD245GX, U5-80, and Shell SP70 under STC are given in Tables 1.2 and 1.3, respectively. It is inferred that under STC, the results obtained from the GS and NR technique are reliable; however, the NR method is accurate with minimum convergence error compared to GS method. Similarly, the results obtained under varying irradiance and temperature conditions for PV panel such as KD245GX and Shell SP70 using GS and NR techniques are given in Tables 1.4 and 1.5, respectively. It is seen that the parameters such as A, R_se, I_LG, I_sat increases as there is increase in operating temperature of PV panel. On the flipside, the shunt resistance R_sh decreases with increasing in temperature. Similar observation is found in both the techniques, however the maximum power obtained from NR technique is higher than the GS method.

Table 1.2 Estimated values of five parameters using GS method at STC [15].

PV module	Estimated parameters at STC
A	Rse (Ω)	Rsh (Ω)	Ilg (A)	Isat (A)
KD245GX	1.43	0.156	623.23	8.91	4.71E-07
U5-80	1.606	0.009	68.1	5.21	2.79E-06
Shell SP70	1.553	0.324	321.22	4.7	1.56E-06

Table 1.3 Estimated values of five parameters using NR method at STC.

PV module	Estimated parameters at STC
A	Rse (Ω)	Rsh (Ω)	Ilg (A)	Isat (A)
KD245GX	1.429	0.1562	623.235	8.9122	4.67E-07
U5-80	1.6043	0.0086	66.6312	5.2107	2.76E-06
Shell SP70	1.5536	0.3242	321.2234	4.2543	1.42E-06

Table 1.4 Estimation of PV module parameters under change in irradiance and temperature using GS method [15].

PV Modules	G (W/m2)	T(°C)	A	Rse (Ω)	Rsh (Ω)	Ilg (A)	Isat (A)	Vmpp (V)	Impp (A)	Pmpp (W)
KD245GX	1000	30	1.432	0.157	621.37	8.94	8.39E-07	29.11	8.23	239.61
1000	50	1.45	0.159	614.02	9.05	7.04E-06	26.38	8.21	216.64
1000	70	1.483	0.16	606.84	9.15	4.62E-05	23.68	8.16	193.14
800	25	1.449	0.125	779.04	7.13	5.89E-07	29.69	6.58	195.47
600	25	1.47	0.094	103.87	5.35	7.89E-07	29.34	4.93	144.72
Shell SP70	1000	25	1.553	0.324	321.22	4.7	1.56E-06	16.51	4.25	70.16
800	25	1.577	0.259	401.53	3.76	1.57E-06	16.59	3.41	56.52
600	25	1.609	0.195	535.37	2.82	1.58E-06	16.49	2.55	42.11
400	25	1.657	0.13	803.06	1.88	1.60E-06	16.12	1.7	27.35
200	25	1.748	0.065	1606.1	0.94	1.65E-06	15.18	0.84	12.77

Table 1.5 Estimation of PV module parameters under change in irradiance and temperature using NR method.

PV Modules	G (W/m2)	T(°C)	A	Rse (Ω)	Rsh (Ω)	Ilg (A)	Isat (A)	Vmpp (V)	Impp (A)	Pmpp (W)
KD245GX	1000	70	1.3184	0.1562	623	8.9123	4.68E-07	29.7962	8.2304	245.2376
1000	50	1.3184	0.1562	623.2256	8.9123	4.68E-07	29.799	8.2304	245.2596
1000	30	1.3184	0.1562	623.2331	8.9122	5.85E-07	29.8017	8.2304	240.538
800	25	1.4485	0.125	779.0438	7.1291	5.84E-07	29.6937	6.5839	195.496
600	25	1.4758	0.0937	1040	5.3465	7.84E-07	29.3463	4.9321	144.7091
Shell SP70	1000	25	1.5536	0.3242	321.2234	4.7047	1.57E-06	16.4975	4.2498	70.1122
800	25	1.577	0.2594	401.5293	3.7624	1.96E-06	16.5814	3.4061	56.4832
600	25	1.6082	0.1945	535.3723	2.821	2.59E-06	16.4755	2.5542	42.0926
400	25	1.6588	0.1297	803	1.8803	3.89E-06	16.0935	1.6979	27.3231
200	25	1.7483	0.0648	1610	0.94	7.27E-06	15.1603	0.8415	12.7591

Figures 1.4 and 1.5 represent the P-V and I-V characteristics of solar PV panels such as KD245GX and SHELL SP70 under varying irradiance from 200 to 1000 W/m² and temperature of 25 to 50^°C, repectively. The results have shown that the decrease in the solar irradiance reduces the maximum power output from the PV panel and increases the power loss due to increase in the shunt resistance. However, the increase in temperature has minimum effect on shunt resistance and almost maintains the output power from the panel. On comparing the results obtained from both N-R and G-S methods, the maximum power exhibits excellent agreement with good accuracy by the NR approach under varying irradiance and temperature.