The calculation of solar thermal in nPro is based on the standard DIN EN 12975-2. Here, the global horizontal radiation and diffuse horizontal radiation are first used to calculate the radiation on the inclined module surface as a function of the elevation and azimuth. In a second step, the thermal collector output power is determined. In addition to the incident angle modifier, the air temperature, mean collector temperature, and the three standardized loss coefficients \(\eta_\mathrm{0}\), \(a_\mathrm{1}\), and \(a_\mathrm{2}\) are taken into account. The loss coefficients were taken from data sheets of a typical flat plate collector and evacuated tube collector.

The nPro tool calculates for arbitrary orientations and inclinations the heat generation profile of solar thermal collectors in hourly resolution.

How have the solar thermal profiles been validated?

The profiles generated with nPro were compared with the generation profiles of the ScenoCalc tool from the SP Technical Research Institute of Sweden for a variety of different locations and orientations. The ScenoCalc tool is an open Excel program that is recognized by all institutions for energy yield prediction when certifying collectors according to the Solar Keymark procedure. The tool is limited to the consideration of a single collector. However, it is ideally suited as a basis for almost any type of solar thermal collector. An excerpt of the validation is shown in the tables below.

Table 1: Comparison of the thermal yield of a flat-plate collector calculated with nPro and with the tool ScenoCalc for the location Frankfurt (Germany) for different orientations and a mean collector temperature of 25 °C.

Orientation	nPro	ScenoCalc	Deviation
Horizontal	611 kWh/m²	603 kWh/m²	1 %
30° / South	738 kWh/m²	714 kWh/m²	3 %
90° / East	307 kWh/m²	296 kWh/m²	3 %
90° / West	320 kWh/m²	309 kWh/m²	4 %
30° / North	378 kWh/m²	384 kWh/m²	2 %

Table 2: Comparison of the thermal yield of a flat-plate collector calculated with nPro and with the tool ScenoCalc for the location Frankfurt (Germany) for different mean collector temperatures and an orientation 30° / South.

Collector temperature	nPro	ScenoCalc	Deviation
25 °C	738 kWh/m²	714 kWh/m²	3 %
50 °C	484 kWh/m²	461 kWh/m²	5 %
75 °C	289 kWh/m²	272 kWh/m²	6 %

Table 3: Comparison of the thermal yield of a evacuated tube collector calculated with nPro and with the tool ScenoCalc for the location Frankfurt (Germany) for different orientations and a mean collector temperature of 75 °C.

Orientation	nPro	ScenoCalc	Deviation
Horizontal	379 kWh/m²	378 kWh/m²	1 %
30° / South	463 kWh/m²	453 kWh/m²	2 %
90° / East	162 kWh/m²	155 kWh/m²	5 %
90° / West	172 kWh/m²	164 kWh/m²	5 %
30° / North	220 kWh/m²	221 kWh/m²	1 %

Table 4: Comparison of the thermal yield of a flat-plate collector calculated with nPro and with the tool ScenoCalc for different locations, a horizontal orientation and a mean collector temperature of 50 °C.

Location	nPro	ScenoCalc	Deviation
Frankfurt (Germany)	365 kWh/m²	358 kWh/m²	2 %
Stockholm (Sweden)	285 kWh/m²	278 kWh/m²	3 %
Geneva (Switzerland)	446 kWh/m²	438 kWh/m²	2 %
Athens (Greece)	813 kWh/m²	798 kWh/m²	2 %