National Physical Laboratory

NPL hosts cross-industry workshop on developing new standards for photovoltaics

A one-day workshop bringing together energy consultants, developers of photovoltaic systems, test labs and the R&D community was held at NPL on 22 November 2016.

The workshop introduced an improved framework for rating the performance of photovoltaic (PV) modules in real-world conditions. It overviewed the need for a new approach, introduced the concept of an 'energy rating' and discussed how it can provide a fairer comparison between different PV technologies to benefit both manufacturers and customers.

Structured around three sessions of talks and panel discussions, the workshop investigated the drivers for accuracy and comparability, the process of developing an energy-rating, and the future landscape for PV performance standards.

In addition, a survey was open to delegates to determine community needs and help define future research programmes. This survey is still open and we welcome input from stakeholders in the PV community.


Traditionally, PV modules are sold based on the power they produce under standard test conditions (STC). However, this artificial metric does not reflect real-world conditions; temperature, irradiance, angle-of-incidence, spectrum and wind-speed all cause deviations in annually-averaged module efficiencies of up to 20 %. The result is that modules are optimised and selected for STC, not the conditions under which they will actually operate. It also impedes the uptake of emerging and innovative technologies, such as modules optimised for moderate light levels or high temperatures.

An alternative method is to rate the output of solar modules based on a metric that takes into account these real world factors.

A new set of standards, IEC 61853, provides a framework for energy rating of PV, including measurement, modelling and reference meteorological data. These have been developed through the large European research project, PhotoClass, which aims to:

  • Enhance capability across Europe for the accurate and traceable characterisation of PV modules under different conditions, including developing new techniques to reduce costs
  • Provide open-access meteorological data and models for evaluating energy rating and uncertainty
  • Complete the formulation of energy rating standards IEC 61853 and promote of their uptake across the value chain

Uptake of the energy-based metric over traditional power rating will better align the interests of the manufacturer and customer. By encouraging the collection of more data on module performance under different conditions, it enables a fairer comparison between different PV technologies, and improves the accuracy of energy-yield estimates and financial models.

The agenda and slides of each talk are available for download below:

Contact: James Blakesley

Last Updated: 26 Apr 2017
Created: 9 Dec 2016


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