The JRC’s European Solar Test Installation carries out research on reliable and accurate measurements for photovoltaic devices and supports the EU in meeting its targets for renewable energy.
The European Solar Test Installation (ESTI) is a European reference laboratory for calibration of photovoltaic (PV) devices and for the verification of their energy generation. Since its launch in the late 1970’s, it has also been at the forefront of development of international standards for the assessment of electrical performance of PV products and for their reliability. ESTI is located at the JRC Ispra site in Italy. 
ESTI has a unique range of class AAA solar simulators as well as outdoor facilities for accurate calibration, testing and long-term assessment of PV cells and modules.
To have legal validity, all measurements (including PV) are required to have an unbroken traceability chain to international primary measurement standards as well as a calculation of their uncertainty. For PV devices the most important and difficult aspect is the irradiance determination, for which ESTI is accredited for 3 methods.
The global sunlight method (1st method) and the direct sunlight method (2nd method) transfer the irradiance calibration from two cavity radiometers, which are calibrated every 5 years against the World Radiometric Reference at the International Pyrheliometer Comparison held in Davos, Switzerland. The solar simulator method (3rd method) makes reference to the international irradiance scale, as represented by a standard lamp.
ESTI maintains a laboratory management system that is compliant to the ISO/IEC 17025 and is accredited for the calibration of photovoltaic devices (Accreditation number 00465) by the Italian accreditation body ACCREDIA. The accreditation scheme includes a flexible scope that allows ESTI to develop and implement internally new measurement procedures and methods. The validation procedures applied by ESTI before introducing any variation in the methods under ‘flexible scope’ are described in our instruction Validation of Methods (PDF). We maintain a list of methods that indicates which tests and methods have been modified by ESTI under our ‘Flexible Scope of Accreditation’; the list can be consulted for reference.
For the calibrations price list or to request information on our services, please contact: JRC-ESTI-SERVICESec [dot] europa [dot] eu (JRC-ESTI-SERVICES[at]ec[dot]europa[dot]eu)
Comprehensive metrological solar resource data are essential for evaluating the results of the ESTI outdoor exposure testing on PV modules. 
The ESTI Meteo Tower, located in Ispra (Italy), monitors constantly a series of environmental VARIABLES; it measures and records minute data of the following parameters
In 1994, an amorphous silicon array was installed under ESTI supervision on the façade of the ELSA building housing the European Laboratory for Structural Assessment. At the time, it was the largest façade installation in the world using amorphous silicon technology.
The main characteristics are
Every year, ESTI organises the International Spectroradiometer Intercomparison (ISRC), a week-long event dedicated to metrology in solar radiation measurements. During the event, participating instruments measure solar radiation continuously, with the ESTI equipment serving as the standard for evaluating spectroradiometers and calibrating pyranometers and pyrheliometers. Additionally, a specialised section of the event focuses on comparing absolute cavity radiometers (ACR), where the assigned value is determined by averaging the valid WRR factors of the cavities from the latest IPC in Davos (PMOD-WRC). 
PVGIS
EU PVSEC
Follow the European Commission

source