There are various ways to estimate how much energy a solar panel or solar system generates. 
Depending on how precisely you want to know, a rule of thumb is often sufficient. We’d like to explain these here. We’ll also introduce two tools that can be used to determine solar yield and solar radiation very accurately at
.

Basically, it’s important to know that the sun is higher in the sky north and south of the equator in the summer and lower in the winter. The following graph illustrates this.
Furthermore, the installed panel area and the type of cells are, of course, decisive factors for the system’s power output and yield. The power output per unit area varies slightly depending on the cells used. It ranges between 190 and 200 Wp/m².
Furthermore, the orientation of the panels is critical to the yield. The following graph illustrates this.

If the solar system is operated as a portable unit, it becomes clear that an exact calculation makes little sense, as conditions are constantly changing.
However, the rule of thumb provides an idea of what to expect.

Rule of Thumb

Generally speaking, the more hours of sunshine, the more energy. The closer to the equator and the longer the summer, the closer the system is to the sun, and accordingly, more radiation hits the solar panel, which increases the yield.

In the summer, we can use the following rule of thumb:

- In Central European latitudes, you can expect 3–4 times the installed capacity if the panel is not shaded and is mounted at a 45° angle facing south.

- In Southern Europe, you can expect 4–5 times the installed capacity if the panel is not shaded and is mounted at a 45° angle facing south.

- As you get closer to the equator, you can expect up to 5–5.5 times the installed capacity if the panel is not shaded and is mounted at a 45° angle facing south.

For example:

2 × 175 Wp (350Wp) of installed capacity yields a daily output of approximately 1–1.2 kWh in Central Europe during the summer (x 3.5), or 80–96 Ah in a 12V system


Here’s a visual overview:

Rule of thumb

Victron Energy offers a tool on its website for sizing solar controllers. There, you can also easily view the annual solar yield as a graph, broken down by location and based on the desired power output.

Here are three examples:

350 Wp in Oslo, Norway		350 Wp in Split, Croatia		350 Wp in Agadir, Morocco

Victron Energy MPPT Solar Calculator

Precise Calculation

For example, the EU’s PVGIS (Geographic Photovoltaic Information System) provides information on solar radiation and the output of photovoltaic (PV) systems for any location in Europe and Africa, as well as in large parts of Asia and the Americas.

The portal offers free and open access to:

- Electricity generation potential for various PV technologies and configurations
- Solar radiation and temperature, as monthly averages or daily profiles.
- Complete time series of hourly values for solar radiation and PV power output.
- TMY data for nine climate variables, formatted for building energy calculation programs
- Application programming interface (API) for fast, automated data retrieval
- Maps of solar resources and PV potential, by country or region, in print-ready files.
- PVMAPS, a software suite that allows users to create custom maps

PVGIS uses high-quality, spatially and temporally high-resolution data on solar irradiance derived from satellite imagery, as well as ambient temperature and wind speed from climate analysis models.

The PVGIS energy yield model is validated using measurements taken on commercial modules at the GFS European Solar Test Facility (ESTI). The ESTI is an ISO 17025-accredited photovoltaic calibration laboratory for all photovoltaic materials.


Disclaimer

The designations used and the presentation of the material on the maps do not imply that the European Union expresses any opinion whatsoever regarding the legal status of any country, territory, city, or area, or its authorities, or regarding the delimitation of its borders.


Original Link:EU Science Hub