Rensys Help & Documentation
Learn how to use the free Rensys solar PV calculator to set up a photovoltaic (PV) yield estimate, understand each simulator input, and interpret the results. This guide describes the current Rensys v1.1 browser-based calculator.
1. Quick start
You can run a first estimate in a few steps. For a more meaningful result, set the location and review the system assumptions before running the calculation.
2. Location and solar data
City or address
Enter a recognizable place name. Rensys uses the Open-Meteo geocoding service to find a matching location, then requests long-term average solar irradiance from NASA POWER for those coordinates. The first geocoding match is used, so check the displayed location status and search again if the result is not the intended site.
Use my location
This option asks the browser for your device’s location. Allow the request if you want to use it; otherwise, enter a city or address manually. Location services and solar-data requests require an internet connection.
Global horizontal irradiance (GHI)
GHI is the solar energy received on a horizontal surface over a period. In Rensys, it is entered as an annual value in kWh/m²/year. A location search populates this input from NASA POWER’s climatological daily data, aggregated to an annual estimate and rounded to the nearest 25 kWh/m²/year.
3. Parameters explained
The table below lists the controls currently available in the Rensys simulator, their units, supported ranges, and default values.
| Parameter | Unit / range | Default | How to use it |
|---|---|---|---|
| City or address | Text search | None | Search for the project location to load coordinates and solar climatology. Confirm the matching place is correct. |
| System peak power (Pnom) | 1–100 kWp; 0.5 kWp steps | 10 kWp | Enter the nominal DC capacity of the PV array. For example, 10 kWp is 10,000 Wp of rated module capacity. |
| Module technology | Monocrystalline silicon (PERC), polycrystalline silicon, or CdTe | Monocrystalline silicon (PERC) | Choose the technology closest to the planned modules. The current model applies a simplified technology factor; it does not model a specific manufacturer’s datasheet. |
| Array tilt angle | 0°–90°; 1° steps | 30° | The angle between the panel plane and horizontal. Use the planned mounting angle. After a location search, Rensys suggests a latitude-based starting angle. |
| Array azimuth | −90° to +90°; 5° steps | 0° | Rensys defines 0° as facing the equator (south in the Northern Hemisphere, north in the Southern Hemisphere). In the current simplified calculation, the loss uses the absolute value, so east/west direction is not distinguished. |
| Inverter efficiency | 90%–99%; 0.5 percentage-point steps | 97.5% | Use the inverter’s rated or representative conversion efficiency if known. This is a simplified input, not a detailed inverter efficiency curve. |
| Global horizontal irradiance (GHI) | 500–2,800 kWh/m²/year; 25-unit steps | 1,750 kWh/m²/year | Use the annual solar resource for the site. A location search fills this value automatically; a user-entered value can replace it if supported by better local data. |
System peak power
Capacity scales the annual yield estimate. If all other inputs remain unchanged, doubling Pnom doubles the calculated annual energy.
Module technology
The current model uses a factor of 1.03 for monocrystalline PERC, 1.00 for polycrystalline silicon, and 0.98 for CdTe. Treat this as a simplified assumption, not a universal ranking of module performance.
Tilt and azimuth
The model applies a simplified orientation adjustment relative to its latitude-based tilt estimate. It does not perform a full plane-of-array irradiance calculation, so use these controls for screening rather than detailed optimization.
Inverter efficiency
Efficiency adjusts the simplified performance-ratio estimate. Real inverter performance varies with load, temperature, voltage, and operating conditions, which are not separately simulated here.
4. Understanding the results
Annual Yield (kWh/year)
The estimated total electrical energy produced over a year. It depends on system capacity, annual GHI, the orientation adjustment, and the simplified performance ratio.
Average Daily Yield (kWh/day)
Annual yield divided by 365. It is a yearly average, not a promise that the system will produce the same amount every day. Seasonal weather and daylight vary.
Performance Ratio (%)
A simplified model indicator representing the assumed share of solar resource converted into useful system output after modeled losses. It is not a measured value from an installed system.
Monthly Energy Production Profile
A bar chart allocating the annual estimate across months. After a location search, the distribution is based on the location’s NASA POWER climatology; without a selected location, a generic default profile is used.
How to read the terminal log
The log records the simulation event and reports the system size, selected module technology, and calculated annual yield. It is a simple activity log, not a detailed engineering report or an error audit.
5. How the estimate works
Rensys v1.1 uses a compact, deterministic screening calculation. Understanding the simplified method helps you judge when it is appropriate.
Orientation factormax(0.70, 1 − |tilt − estimated optimum tilt| × 0.002 − |azimuth| × 0.0008)
Performance ratioclamp(0.80 × technology factor × (inverter efficiency / 0.975), 0.65, 0.90)
Estimated specific yieldannual GHI × orientation factor × performance ratio
Estimated annual yieldsystem peak power (kWp) × specific yield (kWh/kWp/year)
The estimated optimum tilt is calculated from latitude using a rule of thumb, capped at 60°. After a location search, monthly shares are derived from NASA POWER’s climatological monthly irradiance; otherwise, Rensys uses a generic preset distribution.
6. Troubleshooting
Location search does not find my site
Try a nearby city, include the region or country, and confirm you have an internet connection. The geocoder uses the first returned match, so a more specific search may help.
Solar data fails to load
Retry after checking your connection. The solar-data service may be temporarily unavailable. You can enter a known annual GHI value manually, within the control’s supported range.
The result seems unexpectedly high or low
Check the location, annual GHI, system capacity, tilt, azimuth, module technology, and inverter efficiency. Make sure the GHI value is annual kWh/m²/year—not a daily value or monthly total. Remember that this model is simplified and does not represent every site-specific loss.
The monthly chart looks generic
If no location has been loaded, Rensys uses a default monthly distribution. Search for a location to replace it with the solar climatology returned for that point.
7. Frequently asked questions
Is Rensys free to use?
Yes. Rensys is a free, browser-based PV yield estimator.
Does Rensys save my inputs?
The current calculator does not implement saving a project or exporting a report. Location searches send the search query to Open-Meteo and solar-data requests to NASA POWER.
Can I use the result as a guaranteed energy forecast?
No. Treat it as an early estimate. A detailed design should use project-specific weather data, shading analysis, equipment specifications, and a more complete loss model.
Why does a location search change the tilt?
Rensys calculates a starting tilt from the latitude of the selected location. You can then adjust it to reflect the planned installation.
What does 0° azimuth mean?
In Rensys, 0° means the array faces the equator: generally south in the Northern Hemisphere and north in the Southern Hemisphere. The current simplified model only uses the magnitude of azimuth, not east/west direction.