Photovoltaics: Calculation and validation
nPro helps to generate hourly resolved power profiles for photovoltaic systems. On this page you learn how these are calculated and validated.
How are photovoltaic profiles calculated?
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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