What RatedPower learned after running 1,000 bifacial solar project simulations last month

bifacial solar tests ratedpower

RatedPower, a young company focused on the design and engineering of solar plants via pvDesign software, recently launched its own bifacial energy yield model. This model enables pvDesign users to experience first-hand the gain they might obtain using bifacial technology. Since the introduction of the bifacial energy yield model on May 19, pvDesign clients have run over 1,000 simulations (155.59 GW) in more than 100 countries in 5 different continents. This represents more than 36% of total GW simulated in pvDesign during this period.

Before jumping into any conclusions…

7 key parameters that affect the energy yield must be considered when developing solar plants with bifacial modules: the irradiance factors, the module efficiency, the ground albedo, the tilt angle, the elevated height to the ground of the structure, the ground cover ratio (GCR) and the array shading.

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Bifacial modules take advantage of the light reflected from the ground and received by the rear side. The proportion of that light reflected off the ground is known as albedo and it is directly related to the type of soil. The higher the albedo factor, the higher the power gain.

Following the albedo, the height of the structure to the ground is another of the key parameters when simulating with bifacial technology. Increasing the height improves the backside irradiance uniformity, therefore increasing bifacial power gain due to improved perception of ground-reflected light on the rear side.

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Additionally, a third parameter to be considered is the GCR , the ratio between the area occupied by PV modules and the total available area. This ratio is directly related to the pitch distance, the inter-row spacing between tables of PV modules. Decreasing the GCR implies a greater pitch distance, thus increased specific energy production.

Industry experts believe that typical project energy production gains are, on average, 3-10% and up to 30% on optimal scenarios. The report “Modelling of Single-Axis Tracking Gain for Bifacial PV Systems ” predicts that for a low ground albedo factor of 0.25 corresponding to vegetation/soil, ground-mounted bifacial solar modules can only achieve bifacial gain up to 10% relative to their monofacial counterpart across the entire world. On the other hand, on “Optimization and performance of bifacial solar modules,” the gains in terms of specific production (kWh/kWp) can be estimated to be between 5% and 15% for “normal” ground albedos (0.2-0.5) in the case of fixed-tilt structures, and between 3% and 11% for 1 axis trackers in comparison to standard PV plants.

To confirm the above market assumptions…

… and the bifacial gain ratios obtained by the different technological reports, RatedPower simulated its own analysis within pvDesign using the following parameters:

● Commercial module 425 W STC, 1500V, and a 75% of bifaciality factor.
● GCR of 50%
● Ground Clearance (elevated height to the ground) of 1.10m
● Fixed structures and trackers
● Different locations (California and Iceland) and albedo factors (normal satellital albedo 0.21, optimal desert conditions 0.36 and snow satellital conditions in Iceland of 0.68).

When comparing fixed structures with trackers, RatedPower’s analysis found out that fixed structures obtain a 6% higher bifacial gain compared to trackers (4.45% to 4.17% respectively) in realistic satellital albedo of 0.21. These ratios would increase to 7.3% and 6.83% respectively in optimal conditions in California with sand albedos of 0.36.

On the other hand, in scenarios with higher albedos (0.68) and latitudes such as Iceland, the percentage of bifacial gains ascended to 16.55% in the case of fixed structures and 12.65% for trackers. In terms of specific production kWh/kWp, trackers outperform fixed structures resulting in 12.5% and 16.2% higher specific production kWh/kWp in albedos of 0.21 and 0.68 respectively.

In conclusion, pvDesign´s simulation numbers are a great worldwide snapshot of what is really happening concerning the adoption of bifacials and the industry preferences: pvDesign simulations obtained bifacial gains up to 10%, with better results in high-albedo scenarios (up to 16%). Furthermore, fixed structures were found to obtain higher bifacial gains than single-axis trackers (using the same GCR), but still lower yield specific production than trackers.

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