Researchers in the Netherlands have proposed extending the IEC 61853 standard to bifacial solar modules with some important corrections. In particular, they recommend amending the third and fourth parts of the standard.
“Our work provides a comprehensive approach to the calculation of the energy rating of bifacial modules and shows that to be consistent with the current standard, the climate specific energy rating (CSER) should be normalized by the frontal irradiance,” researcher Malte Vogt said. pv magazine.
Vogt noted that the IEC 61853 standard currently applies exclusively to monofacial panels. “Our paper is a step towards updating the standard to also cover bifacial modules, whose market share is growing rapidly,” said Vogt.
The scientists propose changes especially to the third part of the IEC 61853 standard, which combines module measurements and climate data with the calculation algorithm for energy yield and rating. They also recommend changes to the fourth part, which defines reference climates with information on hourly radiation, temperature, wind speed and angle of incidence.
The Dutch team said that climate data from the fourth volume could be expanded to include all irradiance values ​​of the bifacial modules. They said that in the third part, the energy yield calculation algorithm must be adjusted for bifacial panel assemblies.
The academics presented a new model for calculating backside irradiance and said that its calculation should be performed exclusively by generating energy classification climate data from the bifacial module, not by each user.
“It extends the climate data of IEC 61853-4 by providing additional back-irradiation components necessary for bifacial modules,” they said.
They share the back radiation (Gr) of the beam into direct, scattered in the sky and scattered radiation reflected on the ground.
“Note that we use a 20-degree module tilt angle in order to compare monofacial and bifacial module energy ratings because the monofacial standard fixes the angle at 20 degrees in all climates, regardless of what the optimal tilt is for the climate,” the scientists said, noting that east-west orientations and vertical installations as well as tracking devices were not considered.
The researchers said they retained the four main calculation steps of the IEC 61853 standard for single-sided panels, while correcting angular losses for the yield calculation algorithm.
“Unlike the standard, we use it twice, once for front radiation and once for back radiation,” they explained, noting that they implemented a correction for ground reflected radiation as well as a spectral correction.
The team tested the algorithm using two different approaches in real outdoor conditions for nine months. One of the two methods gives the same CSER value for bifaciality zero as monofacial modulus. The second always gives a lower CSER.
The researchers said their work consists of extending the backside angle correction to ground-reflected radiation and combining the overall and effective radiation in the temperature and power calculation steps.
“Thus, only relatively simple calculation steps and no measurements that are not yet used for the front face will be added when the standard is extended to bifacial modules,” they said. They presented their findings in the paper “Developing an energy rating for bifacial photovoltaic modules”, which was published recently Advances in solar power.
