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How solar plants should keep an eye on glint and glare

With more solar farms likely to be constructed near towns and settlements, developers will have to carefully consider the impact of glint and glare from photovoltaic (PV) panels before they proceed.

Global experience shows that sunlight reflecting off solar panels can cause annoying visual discomfort and even hazardous glare to surrounding receptors such as residents, motorists or pilots. Sunlight reflecting off solar panels can be experienced in two forms: glint which is a momentary flash of bright light; and glare – a continuous source of bright light. Both glint and glare can result in an after-image, which is a visual illusion where an image persists after exposure to the original image has ceased.

Motorists passing by may be affected, for instance, posing a potential traffic hazard – while nearby communities could be disturbed by sunlight reflections. Recent changes to the licensing regulations for Independent Power Producers have opened the door for private renewable energy projects up to 100MW. While most commercial solar projects to date have been located in remote areas, these developments may now be increasingly located closer to urban areas, according to Chris Dalgliesh, partner and principal consultant at SRK Consulting.

“We have seen a few solar projects being established fairly close to towns, and there will be more of these to come,” says Dalgliesh. “This increases the likelihood of glint and glare impacting more often on human settlements and other receptors.”

Sue Reuther, partner and principal consultant at SRK Consulting, highlights that while there was generally a high level of public support for renewable energy projects, the growth of solar farms had shown that glint and glare could be significant visual impacts. As such, these aspects have become an essential component of Visual Impact Assessments (VIAs) that SRK Consulting conducts for Environmental Impact Assessments (EIAs).

Kelly Armstrong, environmental consultant at SRK Consulting and a specialist in modelling visual impacts, says that developers need accurate, science-based predictions on how their solar installations might affect the local environment.

“A range of parameters are loaded into glint and glare modelling software to assess whether the glint or glare from solar panels will impair vision or cause discomfort,” says Armstrong. “This includes the project’s precise location, local topography and the height of the mounted panels – as well as the axes and aspect of PV arrays.”

The exact longitude and latitude determine the position of the sun across the seasons, allowing the model to account for the aspect of the sun on each day of the year. This is significant in measuring not just the occurrence of glint or glare, but to quantify exposure (minutes per day) to this impact.

Photovoltaic panels in a solar energy installation can be fixed or can rotate on a single- or double-axis, she notes. The model requires specific parameters of the proposed PV array inter alia the panels’ maximum tracking angle, resting angle and whether backtracking technology is used.

The position of the receptors relative to the solar energy installation is also critical. Typical receptors could include buildings, homes, roads and flight paths, with dozens of different points around the project all having to be assessed to understand the potential impact. Topography is important, as elevated areas around a solar farm could be more exposed to glint and glare. Dalgliesh notes that a viewshed is typically a vital component of visual impact assessments, and shows those areas (receptors) from which the solar farm would be visible.

“This spatial map guides our understanding of who or what will be visually affected by a development,” he said. “We can then identify those receptors which are likely to be most sensitive to visual impacts – including glint and glare.”

Both glint and glare can result in an after-image, which is a visual illusion where an image persists after exposure to the original image has ceased (Image: SRK Consulting)

The outcome of the modelling, explains Armstrong, is to accurately predict the exposure and duration of glint and glare impacts down to the minute each day – for each key receptor.

“The accuracy of these models allows us to report very detailed glare results,” she says. “For example, we can predict that a particular receptor would experience glare for a maximum of 15 minutes between 4.30 and 6.30 pm during the summer months.”

This provides the basis for strategic decisions, either on the precise location or orientation of the solar farm, or on appropriate mitigation measures. While there are currently no legally specified thresholds for glint and glare, she pointed out that there are international best practice guidelines to follow.

“These guidelines incorporate tolerable exposure thresholds, viz.  maximum 60 minutes per day, for more than three months of the year, above which mitigation measures must be implemented” she explains. “Our reports include mitigation measures, aiming to avoid any glare affecting receptors.”

Reuther highlighted that, as a leader in the field of EIAs, SRK is among only a few consultancies with advanced in-house expertise in glint and glare modelling – a niche likely to be in growing demand.