A group of scientists led by the Zurich University of Applied Science (ZHAW) in Switzerland performed simulations and measurements aiming to maximize power yield in east-west oriented PV arrays installed on flat roofs.
One of the experimental setups included horizontal single-axis tracking (HSAT) with PV panels arrayed in an east-west orientation with an atypically high area utilization – a ground coverage ratio (GCR) of over 90%. The HSAT angles were set at -5°, 0° and 5°.
The researchers noted that the setup differs from HSAT systems which are typically installed in ground-mounted projects and have much lower GCRs to suppress self-shading of neighboured module rows. “In our study, the aim is to maximize the energy yield per area on a flat roof and not the specific energy yield. For this reason, low GCRs are not a sensible option,” the researchers said.
The reference PV system was a rotating rooftop bifacial module system with tilt angles of 10° and also oriented in east-west direction with a GCR of 0.9. The power measurements were completed as a function of tilt angles.
The simulations were done in PVSyst 7.4, combined with physical measurements, including a special measuring setup with a miniaturized test rig that is available from Germany-based Solarc Innovative Solarprodukte GmbH.
“Surprisingly, it has been shown that horizontal tracking within only a small angle range, in combination with high area utilization rates, can lead to additional yields in the range of 5%,” Hartmut Nussbaumer, head of the ZHAW photovoltaic research group told pv magazine.
The simulations and measurements showed that, compared to the reference system, the proposed HSAT setup may achieve a 5% higher energy production. Furthermore, the group said that the approach could eventually rely on very simple trackers that could be manufactured at a low cost. For example, it said all rows of modules on a roof could be moved with just one drive, noting that future research could involve installing an HSAT system on a roof for outdoor testing.
Another experimental setup involved near-vertically installed reflectors at the edge of the photovoltaic system. Motor driven reflectors were used to be retracted or extended depending on the irradiation and weather conditions.
Initial results showed the use of reflectors enabled area-specific yield increases of 30% on the days measured. Energy yield in the morning or evening was enhanced “significantly.” The researchers also noted that additional reflectors, either dynamic or static, could enhance the irradiance on the collector field and therefore increase the energy yield.
“The main challenges in the research were to simulate and measure relatively small increases in yield, which when combined end up having a major impact on the profitability of system adaptations,” said Nussbaumer.
Noting that both HSAT systems and reflectors on flat roofs are effective, the researchers said that the chance of the variants becoming more widely used “depends on the cost-effectiveness.”
In the future, the researchers will investigate time-dependent controllable reflectors to enhance energy yield with temporal adjustments based on specific energy demand or time-varying electricity prices, in addition to cost studies on both initial investment and tracking system maintenance costs.
Their findings are available in the study “Highest Energy Yields per Area for PV Systems on Flat Roofs,” published in European Photovoltaic Solar Energy Conference & Exhibition 2024 Proceedings.
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