As solar farms become increasingly complex, de-risking bifacial projects by reducing the uncertainty around albedo will be crucial. We sat down with Vicente Lara-Fanego
PhD, Weather and Solar Modelling Expert, and Harsh Goenka, Business Development Manager, to discuss Solargis’ new two-part report on this little understood data source, and how the solar sector can seize the opportunity to set a new standard for bifacial projects through investment into albedo data.
Hi both. To begin, could you explain what albedo is?
Vicente: In simple terms, albedo is a measure of how reflective a surface is under certain conditions. Lighter surfaces such as desert and snow will have higher albedo values than darker surfaces, such as mud or grass.
Albedo demonstrates a high spatial and temporal variability. It may change in few metres, but also varies seasonally – and even throughout the day.
Additionally, albedo depends not only on the surface characteristics, but also on other factors such as the illumination conditions. So despite its apparently simple definition, this key parameter contains inherent complexities.
Why is albedo important for the solar sector?
Harsh: Albedo is a key variable influencing bifacial solar project performance, so understanding it fully will be crucial to the continued roll-out of the technology.
The use of bifacial modules is expanding rapidly in key markets globally because the cost of producing a bifacial panel is drawing close to monofacial. This means that not only do more projects rely on bifacial technology, but the technology is also being used in more complex terrains where albedo values can vary significantly.
How exactly does it affect bifacial solar project performance?
Harsh: A higher albedo value means that more solar irradiation will be reflected onto the underside of the solar array. For bifacial modules, this leads to additional energy production.
It is therefore essential that solar developers minimise any uncertainty around albedo when estimating future project energy yields.
How well understood is albedo within the solar industry?
Vicente: There are still significant gaps in the industry’s knowledge, particularly around the practical applications of albedo for bifacial projects.
Surfaces such as snow pose challenges when looking to design an efficient bifacial solar farm, because current standards of modelling are not adequate. Even for better understood surfaces such as desert, the levels of variability are still high, raising uncertainty.
What are the risks to the market from albedo uncertainty?
Vincente: During a project simulation, Solargis calculated that for projects with typical albedo values of 0.2 to 0.3, an error of 0.1 in the albedo estimate results in differences of up to 4% in the annual energy production.
Harsh: Manufacturers of bifacial modules and trackers commonly highlight that the LCOE of bifacial systems is lower than that of monofacial systems. This may be true in general, but developers need to do their due diligence to verify this for their projects, as the decision on what technology to use is driven by many factors including land costs, civil costs, and weather. From a geographical perspective, the ratio of diffuse/global irradiation and albedo help to determine which option is more profitable.
If developers opt for bifacial technology, they also need to make design choices such as the optimal tilt angle, ground coverage ratio, mounting structure height, and so on. Not having an accurate estimation of global, direct, and reflected irradiation may result in a system design that is not optimised to be as profitable as it should be.
What are the key factors to consider when ensuring that the solar industry make full use of albedo data?
Vicente: There are three main factors which have posed challenges for the solar sector when looking to produce accurate estimations of albedo at a site. These are:
Why is not measuring albedo for long enough an issue, and what can solar developers do to mitigate this?
Vicente: Albedo values vary significantly on a seasonal basis. Even the most comprehensive measurement campaigns combining accurate ground measurements with high-quality, granular satellite data will therefore fail to provide adequate insight into the true potential of a site for a bifacial project.
To minimise uncertainty and avoid wasting time and money on ineffective measurements, solar developers need to take scientifically rigorous albedo measurements for a period spanning several months instead of couple of days – and back these with accurate satellite data.
What type of assumptions has the industry made around albedo?
Harsh: Although less common since the rapid expansion of bifacial, albedo values are sometimes given as a fixed annual value, depending on the surface type. For example, if the project is planned in the desert, project engineers may select an albedo value of 0.3 as a high-level estimate. This can result in significant deviations from the real albedo of a site, particularly with sites that have a higher albedo, such as snowy or sandy regions.
We would always recommend that solar developers refer to albedo estimates from validated, high resolution satellite-derived albedo data sources. For example, with the Solargis Prospect tool, developers can access a reliable estimate of albedo with monthly granularity even in the pre-feasibility phase, removing the guess work when estimating this key parameter. This will lead to better technology choices and design decisions.
Why is using granular albedo datasets important and how granular should they be?
Vicente: Albedo can vary significantly even across a site, due to different surface textures and shading conditions. Any element that alters the surface properties can change the albedo. Wind, humidity or the life cycle of surface vegetation are examples of natural phenomena that influence albedo.
Albedo also varies throughout the day, and by season, depending on the weather and illumination conditions. Current PV modelling tools are often unable to integrate sub-daily time series data – but higher resolutions can ensure other calculations are more accurate.
Public, freely available datasets do not have the required granularity to accurately underpin energy yield calculations. Additionally, they are ineffective for complex, challenging conditions such as snow.
As for the recommended granularity, it depends on the site in question. As starting point, we would suggest that solar developers use at least monthly temporal albedo data, and use a spatial granularity that reflects the heterogeneity of the site’s surface.
For the wider industry, there are significant gains to be made by investing in PV modelling tools that can make use of more granular datasets. Unlocking increased accuracy around albedo calculations will help ensure the continued success of bifacial projects going forward.
Thanks for speaking to us, Vicente and Harsh. Where can readers find out more about albedo best practice in the solar sector?
Vicente: Solargis has written a two-part whitepaper on albedo, breaking down the challenges that the solar industry has faced when accurately calculating albedo, and showing how a best practice approach to measurements can help reduce uncertainty. Read on below:
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