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Case studies

Improving yield estimates in bifacial photovoltaics

NPL helped develop uncertainty calculation tools for assessing the risks associated with solar farm sites

Case study

photovoltaics-case

The need

The global market for building new solar energy systems is worth more than £100 billion a year. Bifacial photovoltaics (BFPV) are a new type of solar panel that can harvest light on both sides of the panel, making the use of light reflected from the ground. They can generate 5 % – 15 % more energy than conventional panels. The increased energy production of bifacial photovoltaics could reduce costs of electricity and bring a step change in this multi-billion pound market. It is estimated that up to 40 % of new installations will be bifacial by 2025.

However, being a new technology, accurately predicting how much extra energy will be generated remains a challenge. This uncertainty adds financial risk to new BFPV systems and can deter investment. The principal energy gain when using BFPV modules depends on ground albedo, which is the fraction of light that is reflected by the ground. Calculations for modelling bifacial energy gain are tightly connected with the measurement or estimation of the ground albedo value for a given site and its spectral profile (colour).

The solution

photovoltaics-case2.jpg

NPL partnered with RINA Tech UK through the Analysis for Innovators (A4I) programme [1]. NPL completed analysis on ground and satellite data which enabled an accurate source of albedo data to be identified. During this collaboration, NPL introduced the concept of effective albedo, for which the spectral profile of albedo and the spectral response of the bifacial PV modules are considered as well as the influence of the position of the Sun and cloud cover.

RINA and NPL worked together to install measurement systems on a number of sites. NPL’s expertise in BFPV technology and uncertainty analysis, along with measurements from these monitoring stations, fed into the development of new uncertainty calculation tools which RINA used to assess the financial risks associated with different albedo measurement methods.

The work on establishing these on-site measurement systems paved the way for a new methodology for forecasting future albedo at BFPV systems, in a major advancement for the solar energy sector. The effective albedo data analysis methodologies developed were formalised and standardised so that any site globally can be analysed with the same process.

The impact

The collaboration has delivered a significant step-change in RINA’s technical capability for bifacial PV system assessment, greatly enhancing their expertise in the BFPV systems sector. NPL has communicated the insights gained from this project into the working group for the improvement of the IEC 61724-1 standard, which is focused on the monitoring of system performance. The developed methodology demonstrated that the use of BFPV technology can reduce levelised costs of BFPV systems by almost £1 per MWh. This corresponds to approximately £100,000 per year for a medium sized 50 MWp solar farm. It has been estimated by RINA that the work on this project is likely to facilitate around £0.3-1 billion of new PV investments in BFPV systems.

The adoption of effective albedo studies will become more commonplace within the industry leading to the requirement of an international standard requirement over time, with the results of this project playing a central role in their development. Industry-wide standards will lead to more accurate BFPV system energy yield quantification, resulting in higher confidence in the finances of such systems and a reduction in project costs globally. This will be key in accelerating the greater adoption of BFPV over the next few years, underpinning the potential of solar power as cheap and clean energy source for decarbonising economies.  

References

[1] https://www.a4i.info/a4i_case_studies/rina/?bpage=

[2] J. C. Blakesley et al., “EEffective Spectral Albedo from Satellite Data for Bifacial Gain Calculations of PV Systems,” in EUPVSEC Conference Proceedings, 2020, no. October, pp. 6–11, doi: 10.4229/EUPVSEC20202020-5CO.9.3.

[3] J. Blakesley, J. Holder, G. Koutsourakis, S. Douglas, R. Abrams, and F. Mukadam, “Effective spectral albedo and uncertainties from ground based and satellite ground reflectance data for bifacial PV systems modelling,” in bifi PV Workshop, 2019, no. September.

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