The calculation of PV generation profiles in nPro is based on the well-known and validated calculation tool PVWatts of the National Renewable Energy Laboratory (USA). Here, the radiation on the tilted module surface is calculated from weather profiles with the global horizontal radiation and diffuse horizontal radiation and as a function of elevation and azimuth. In a second step, various loss coefficients are taken into account, which represent, for example, aging or ohmic losses. The calculation model used in nPro assumes that the direct current of the PV system is converted to alternating current. The inverter model also uses a calculation approach from the PVWatts tool, which is based on analyses of inverter performance data from the California Energy Commission. For the inverter, partial load efficiencies in the low-light phases are modeled in detail, among other factors. The calculation approach is documented in the technical description of the PVWatts tool. In nPro, a cell temperature coefficient of -0.47 %/K is assumed. This describes the decrease in cell efficiency with an increase in cell temperature.

The nPro tool calculates for arbitrary orientations and inclinations the PV generation profile in hourly resolution.

How were the photovoltaic generation profiles validated?

The profiles generated with nPro were compared to PVWatts generation profiles for a variety of different locations and orientations. An excerpt of the validation is shown in the tables below.

Table 1: Comparison of PV generation profiles from nPro with those from the PVWatts tool for Berlin (Germany) for different orientations and a plant capacity of 1000 kWp.

Orientation	nPro	PVWatts	Deviation
Horizontal	789 MWh	790 MWh	0.2 %
30° / South	893 MWh	900 MWh	1 %
90° / South	633 MWh	614 MWh	3 %
45° / West	672 MWh	671 MWh	0.2 %
45° / East	684 MWh	684 MWh	0 %
90° / West	457 MWh	445 MWh	3 %
90° / East	466 MWh	455 MWh	2 %
45° / North	446 MWh	431 MWh	3 %

Table 2: Comparison of PV generation profiles for different locations for a module orientation of 30° / South and a system power of 1000 kWp.

Location	nPro	PVWatts	Deviation
Berlin (Germany)	893 MWh	900.2 MWh	1 %
Riyadh (Saudi Arabia)	1725 MWh	1740 MWh	1 %
Moscow (Russia)	906 MWh	907 MWh	0.1 %
Kiruna (Sweden)	768 MWh	771 MWh	0.4 %
Bangkok (Thailand)	1324 MWh	1334 MWh	0.7 %
Barcelona (Spain)	1309 MWh	1341 MWh	2 %
Cairo (Egypt)	1547 MWh	1562 MWh	1 %

Table 3: Comparison of monthly PV yields calculated with nPro and PVWatts for Munich (Germany) with 30° inclination and south orientation and a plant capacity of 1000 kWp.

Month	nPro	PVWatts
January	33.3 MWh	34.3 MWh
February	58.0 MWh	58.8 MWh
March	78.7 MWh	79.8 MWh
April	109.8 MWh	110.9 MWh
May	138.5 MWh	139.1 MWh
June	116.8 MWh	117.0 MWh
July	136.5 MWh	137.5 MWh
August	122.4 MWh	123.3 MWh
September	88.7 MWh	88.8 MWh
October	71.0 MWh	70.3 MWh
November	35.2 MWh	35.1 MWh
December	25.8 MWh	26.0 MWh

Table 4: Comparison of monthly PV yields calculated with nPro and PVWatts for Cairo (Egypt) with 30° inclination and south orientation and a plant capacity of 1000 kWp.

Month	nPro	PVWatts
January	96.8 MWh	97.9 MWh
February	111.4 MWh	112.2 MWh
March	134.5 MWh	135.3 MWh
April	139 MWh	140.1 MWh
May	150.2 MWh	151.8 MWh
June	149 MWh	150.5 MWh
July	153.4 MWh	154.8 MWh
August	149.1 MWh	151.0 MWh
September	145.3 MWh	146.7 MWh
October	117.3 MWh	118.2 MWh
November	101 MWh	101.7 MWh
December	99.8 MWh	101.2 MWh

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