PV Convergence

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Photovoltaic (PV) Solar Convergence occurs when multiple reflective glass panels simultaneously reflect the sun to one point with an intensity greater than that of direct sunlight. In July 2017 the City of London issued a Solar Convergence Planning Advice Note (PAN) following over-heating problems caused by the concave façade of 20 Fenchurch Street (colloquially known as the “Walkie-Talkie” building).

Causes of solar convergence:  Solar convergence is caused by concave surfaces which can be concave in the horizontal plane, vertical plane or both. Reflecting surfaces can be made of glass, mirrors or shiny metals.  Flat and convex surfaces do not cause solar convergence.

Effects of Solar Convergence:  Potential effects at locations where solar convergence can occur include:

  • Eye damage
  • Skin burn (direct or due to touching hot objects/surfaces)
  • Overheating (for example in cars)
  • Material damage (e.g. Waste bins, road surfaces, vehicles)
  • Fire(rare)
  • Predicting Solar Convergence
  • Solar Glint and Glare assessments can be undertaken to determine the likelihood of solar convergence reflections occurring. Assessments predict the times and dates of solar convergence, the impact on the retina, the duration over which the effect will occur, where the effect will occur as well as the intensity of the effect.

Intensity Recommendations:  General intensity recommendations specified in units of kilowatts per square meter (kW/m2). The recommendations are summarized in the table below:

Solar Convergence can be minimized by:

  • removing concave surfaces
  • changing surface materials
  • provision of external shading