PVGIS

Compare Solcast historical and TMY products to PVGIS

Solcast’s historical solar irradiance database was released in 2019, with a mission to provide highly accurate, validated data to the solar development community.

Using a proprietary cloud detection and identification model, utilising the new fleet of third-generation geostationary satellites and refined over a four-year period, we’ve been able to produce the best performing solar database available. We’ve always thought developers should focus on planning and assessment, with fast and easy access to bankable, high quality, low uncertainty data.

The Photovoltaic Geographical Information System (PVGIS) has been developed for more than 10 years at the European Commission Joint Research Centre, most visibly through the online PVGIS web application. PVGIS make a number of datasets freely available but has limited coverage and a higher uncertainty when compared side-by-side with Solcast data.

Summary

  Solcast PVGIS
Free trial with instant access and data download?
Price point $$ Free
Download wait time 1-9 minutes 1 minute
Mean Bias Error (GHI) 0.0% 0.7%
Bias Deviation (GHI) ± 2.0% ± 3.2%
90% of sites have bias (GHI) smaller than ± 2.5% ± 4.1%
Mean RMSE (GHI) 16.5% Not published
Comprehensive, global, independent validation
Validation Sites 46 22
Satellite based estimation
Global Coverage
Resolution of satellite data used 1-2 km 2-5 km
10+ years of satellite data at full temporal resolution
Ignores older, less reliable satellites

Source: A New Database of Global and Direct Solar Radiation Using the Eastern Meteosat Satellite, Models and Validation

Accuracy & Validation

Solcast’s model has been independently validated at multiple locations globally using hourly ground measurements. Solcast’s model has been compared with BSRN ground station measurements, available in the public domain. You can request a copy of our validation data, see accuracy and validation.

PVGIS offers data from several databases, with differing levels of coverage, and spatial and temporal resolution. These data sets have been independently validated, but most studies focus on daily means of solar resource data over hourly data. This makes a side-by-side comparison difficult.

This page will focus on the PVGIS-SARAH database, a collaboration between PVGIS and CM SAF. The SARAH dataset has the broadest coverage of PVGIS data sets and has had hourly data validated with BSRN stations. For America’s data, PVGIS uses the NSRDB database.

  Solcast PVGIS
Comprehensive, global, independent validation
Validation Sites 48 22

As there is a low number of validation sites it is difficult to objectively evaluate the two data sets. That being said, we have presented a summary of Solcast’s and PVGIS’s hourly mean GHI validation results below.

  Solcast PVGIS
Mean Bias Error 0.0% 0.7%
Bias Error Standard Deviation ± 2.0% ± 3.2%
90% of sites have bias smaller than ± 2.5% ± 4.1%
Mean RMSE 16.5% Not published

Solcast v PVGIS Bias Distribution

PVGIS _Bias_Artv2.PNG

Understanding bias helps to understand a possible error of the long-term estimate. Bias variability and RMSE are important for estimating the accuracy of energy simulations and operational calculations. The Solcast model is symmetrically centred with an average bias error of 0.0%. PVGIS-SARAH has a positive bias of 0.7%.

Solcast data shows significantly less variability than PVGIS. A lower bias deviation of ±2.0% v ±3.2% means our data is represented by a narrower probability distribution.

RMSE, a measure of the differences between the values predicted by the Solcast model and the values actually observed, shows strong model performance. No RMSE data was available for PVGIS-SARAH. With much less variability in our dataset, developers can trust the accuracy of their energy simulations and operational calculations.

You can find more details on the Solcast dataset on the accuracy and validation page.

Model Inputs

The Solcast methodology is semi-empirical and satellite-derived. We begin using validated, published models that offer excellent performance to build clear sky models. We combine this with the ‘secret sauce’, our in-house methods for detecting and tracking clouds. This lets us model the amount and type of solar radiation reaching any particular 1-2 km2 grid cell. For more details see inputs and algorithms.

The PVGIS methodology is similar. It is semi-empirical and satellite-derived, relying on validated, published models to build a clear sky model, and for cloud detection. The PVGIS-SARAH cloud model has a lower resolution than the Solcast model, based around a 5 km2 grid. The cloud detection algorithm only processes one image per hour, instead of the native satellite time step. This large time step between satellite images can provide misleading information on cloud formation, tracking, and opacity.

Solcast only uses data from recent generation geostationary meteorological satellites (GMS). For this reason, we do not use data prior to 2007. Prior to this time, we find that too many of the GMS satellites have significant data quality problems including geolocation, poor temporal sampling frequency, and unreliable, bad or drifting data signatures. This ensures our entire database is based on data of the highest possible resolution, whilst still containing 12+ years of data history from which to understand the interannual variability. Users can be sure our accuracy and validation statistics apply to all our data, not just the most recent half of it.

We don’t believe in using data from older satellites. With longer refresh rates and larger spatial resolutions, it’s just not possible to produce bankable solar radiation assessments with the certainty demanded by the solar community. We’re firm of the opinion that bad data in, bad data out.

PVGIS has an extensive database, compiled using high-resolution new satellites, and lower-resolution, pre-21st century satellites.

  Solcast PVGIS
Resolution of satellite data used 1-2 km 2-5 km
Use of 10+ years of satellite data at full temporal resolution
Ignores older, less reliable satellites

Data Availability

Solcast offers near-global coverage (latitudes higher than 60-70 degrees are not effectively covered by geostationary satellite images). PVGIS’s database coverage is limited to Africa, Europe, the Middle East, South Asia and parts of South America. Coverage of the Americas is provided by NSRDB. We have included the high-latitude coverage from other PVGIS datasets ERA5 and COSMO in the image below.

PVGIS Coverage

PVGIS_Coverage.png

Solcast Coverage

Solcast_Coverage-453a99.png

Solcast offers data from as recent as the last week. NSRDB data is available only until 2016. Without the provision of recent data, developers are not able to make one-to-one comparisons with ground observations to better understand the accuracy of data. Further, it is not possible to improve the accuracy of a long-term estimate by quantifying systematic deviations between modeled data and high-quality ground observations or use regular updates of recent data to monitor the operational performance of PV power plants. Data parameters available are shown below.

Data parameters available

  Solcast PVGIS
Most recent data available 7 days ago 2016
Global Horizontal Irradiance (GHI)
Direct Normal Irradiance (DNI)
Diffuse Horizontal Irradiance (DHI)
Air Temperature (TEMP)
Wind Speed (WS)
Wind Direction (WD)
Relative Humidity (RH)
Atmospheric Pressure (AP)
Precipitable Water (PWAT)
Dew Point (DWPT)
Snow Depth (SWDE)
Cloud Opacity

Solcast strives to make our data easy to use, immediately. Our data is available within 1 to 9 minutes of ordering. Our data is available in the following ready-to-import formats:

  Solcast PVGIS
Download Wait Time 1-9 minutes 1 minute
TMY3
CSV
PVsyst (CSV)
SAM (CSV)
EnergyPlus (EPW)

Pricing

Being a free-to-access database, PVGIS can appear to be cheaper from the first viewpoint. However, the proven bankability of Solcast’s database offers better value by lowering risk for developers, investors, and operators of solar power plants. When decisions on development or operation of high-value solar assets are to be made, higher risk associated with the use of high-uncertainty data can be very expensive. View Solcast prices

In addition to commercial pricing, Solcast offers free access to data for researchers. Solcast also provides every account registered with some initial credit, so users can get the feel of how our system works, and get your hands on some data quickly - Try it now.

  Solcast PVGIS
Free data to researchers
Free credit to every new account

Test now, free

Get free historical data credits when you sign up, so you can try our data for yourself. You can download data automatically within around 1 to 9 minutes of submitting your request.