Developers of solar photovoltaic projects within the UK and internationally will be familiar with the potential constraints posed by solar glint and glare. The issue is also prevalent in other industries including the construction of tall buildings.
For those unfamiliar with the topic, solar glint and glare can occur when sunlight is reflected by a smooth surface towards an observer where it can cause a nuisance and/or a safety hazard.
Figure 1: Solar Farm. 
The most common receptor types, in no particular order, that require consideration in terms of such impacts are:
- Road users on surrounding roads.
- Residents in surrounding dwellings.
- Pilots and air traffic controllers at nearby aerodromes.
- Railway drivers and other infrastructure along surrounding railway lines.
The above is applicable in countries all around the world, although the perceived level of importance varies in different states. This article is mostly focussed on the current situation in the United Kingdom, with some commentary as to how this ties in internationally.
There is practically no legislation in the UK that is prescriptive or detailed in terms of how a developer needs to quantify, manage or mitigate glint and glare concerns. Any aspects of actual legislation that could encompass this topic tend to be very generalised and/or vague. This is broadly true internationally, with some exceptions. The United States of America which was ahead of the curve in terms of setting rules for glare from solar panels at airports, for good reason, we will come back to this. Germany also has a federal regulation pertaining to the issue.
Guidance and Policy
Guidance and policy documents are sometimes slightly bolder in terms of content on the issue of glint and glare. For example, Future Wales, The National Plan 2040  has two policies (17 and 18) that are applicable to solar glint and glare, the most direct of which is in Policy 18 which states in part 7 the following criterion (emphasis added for clarity):
“There are no unacceptable adverse impacts by way of shadow flicker, noise, reflected light, air quality or electromagnetic disturbance”.
Another source of great interest to UK developers is the Draft National Policy Statements for energy infrastructure (EN-3), which was issued in September of 2021 by the UK government’s Department for Business, Energy & Industrial Strategy (BEIS).
The BEIS itself was formed in 2016 by merging two previous departments, and then split once again into three subsequent ones in 2023 in keeping with overall theme of British politics during that period, but back to the topic at hand…
As government guidance goes, the 2021 draft issue of EN-3 was unusually detailed regarding the topic of glare insofar as it provides extensive and reasonable definitions of what the phenomenon is and why it’s a concern.
The 2021 document did, however, cause a stir with its inclusion of the infamous section 2.52.5 which stated:
“There is no evidence that glint and glare from solar farms interferes in any way with aviation navigation or pilot and aircraft visibility or safety. Therefore, the Secretary of State is unlikely to have to give any weight to claims of aviation interference as a result of glint and glare from solar farms.”
The above was contentious because it is counter to the view of the aviation industry in general in the UK and abroad.
Factually, the statement is incorrect, but perhaps only just. As noted in the ‘Legislation’ section earlier, the USA took the lead on developing policies around the issue of solar glare for aviation. This is not a coincidence, as the development of a large solar panel array in 2012 at an airport in New Hampshire did impact air traffic controllers, and prompted the Federal Aviation Administration there to review the reflectivity section of the technical guidance issued two years prior.
This means that it is not true to say that there is ‘no evidence’ of a problem, however the example above is perhaps the only case of a glare impact that was significant enough to be widely reported. It was also exacerbated by the fact that panels at that time were not typically fitted with anti-reflective coating, which is now very standard. We must remain open to the possibility that:
- Other impacts have occurred that are not widely known.
- The reason impacts are not widespread is that aviation interests are now safeguarded, preventing issues from manifesting in the first place.
There is also plenty of theory and indeed basic logic supporting the idea that glare towards pilots or air traffic controllers is hazardous. Nevertheless, real-world cases of significant glare impacts from solar panels or similar are few and far between, so the statement in the 2021 draft issue of EN-3 may not be far off the mark depending on how we interpret the word ‘evidence’.
To be clear, the stance of Pager Power (and this author) has been, and remains, that aviation safety does need to be safeguarded in the context of glare and that the language of the 2021 draft issue of EN-3 was inappropriate.
More recently, the UK government has issued its consultation response on the draft issue of EN-3. The topic of glare is raised extensively and therefore not this content is not reproduced here in full. One aspect of interest is the inclusion of:
“We acknowledge that there is some evidence that glint and glare from solar farms can be experienced by pilots and air traffic controllers in certain conditions, although this does not in our view suggest that this results in significant impairment on aircraft safety. We have updated the NPS to clarify that when determining applications, the Secretary of State should consider the impacts of glint and glare on aviation infrastructure (including aircraft departure and arrival flight paths) as well as the impacts on other receptors.”
In general, the consultation response goes quite some way in referencing that the issue is more complex than presented in the draft issue and that this will be captured in the final version.
The solar industry has expanded rapidly in the UK and elsewhere, and has therefore in many ways outpaced the provision of guidance for some planning issues, including glint and glare.
Pager Power has taken a lead on attempts to establish an industry standard that helps all sides navigate the issue appropriately. To that end, we undertook a literature review and industry consultation exercise ahead of producing our own guidance document in 2017. The latest issue was released in 2022 and is freely downloadable here. This is something of a living document because it is continually shaped by new data and experience. This document represents the basis for our methodology.
The most widely known source of guidance on the topic worldwide may be the USA’s Federal Aviation Authority guidance, which itself has evolved over the years. This guidance and the associated methodology first devised by Sandia Laboratories is incorporated in a significant proportion of detailed aviation glint and glare assessments, including those undertaken by Pager Power.
The Final Word
The definitive ‘correct’ way to manage almost any planning constraint is usually up for debate to some extent. This is amplified for issues that:
- Are new.
- Are rare.
- Are highly specialised.
Glint and glare concerns tick all of the boxes above, much to the chagrin of those tasked with navigating the topic.
The case of EN-3 highlights, to a degree, the reason that authorities may be reluctant to issue very specific comment on complex planning issues. It is easier, for someone producing a policy, to hide behind ambiguity rather than invoke the wrath of those that may know better. This author applauds any attempt to establish clear rules that are helpful to developers who are trying to build new things, even if it means butting heads in the early stages.
About Pager Power
Pager Power has been helping developers overcome constraints for over 20 years. Glint and glare concerns are comparatively recent as a problem, as a company Pager Power remains committed to providing the highest quality advice to ensure that new projects can coexist safely with their environment. To that end, we:
- Continue to regularly update our own guidance document, which is freely available and will remain that way.
- Routinely review all formal written legislation and guidance on the topic.
- Actively engage with the wider industry and contribute to the knowledge bank, for example via our membership of the Combined Aerodrome Safeguarding Team (CAST), a group under the UK Civil Aviation Authority which provides guidance and into to new policy and legislation across a range of disciplines.
If you think we might be able to assist you in any way, please do get in contact.
 Available via gov.wales
 Solar Panel Farm by Benoît Deschasaux (March 2023) on Unsplash.com. Last accessed on 13th April 2023. Available at: https://unsplash.com/photos/l050F6hA9xY