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| Harvesting Maximum Solar Power | |
| Writer : 관리자 Date : 2010.11.23 Views : 2,328 | |
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Harvesting Maximum Solar Power The photovoltaic industry is striving to become competitive with traditional energy production. Distributed solar power harvesting systems accelerate achievement of this goal. In traditional systems, the inverter performs Maximum Power Point Tracking (MPPT) for all modules, therefore, working at an average point compatible for all, leading to lower energy production. Other mismatch contributors increase the losses. In distributed systems, MPPT is performed at module level. This, together with a fixed string voltage, has multiple benefits: maximum module power output regardless of other modules‘ performance; design simplicity and flexibility; module-level monitoring and advanced safety and anti-theft features.
SEOUL, SOUTH KOREA (November 22, 2010) – In 1763, at the beginning of the industrial revolution, James Watt, the famous inventor, was asked to review the only working steam engine available during those times of mounting energy demands. He modified it to provide rotary motion. The new innovation used dramatically less coal, was cheaper to run and was more suitable for driving factory machinery, accelerating the revolution.
The main challenge faced by the solar Photovoltaic (PV) industry today is becoming truly competitive with traditional forms of energy production, independently of government incentives. To reach this goal, the industry will need to leap in efficiency while reducing the overall cost of energy.
Small PV installations are composed of dozens to a few hundred solar modules. An installation is typically divided into parallel strings, each consisting of several modules (typically 10-15) in a series, and connected to an inverter. The inverter performs two tasks: first, it converts the harvested energy from Direct Current (DC) into Alternating Current (AC), the prevailing type of current in the electrical grid. Second, it performs Maximum Power Point Tracking (MPPT) for all the modules. MPPT is a continuous process in which the current that would yield the maximum power is sought—delicate fine-tuning task.
It remains questionable whether a single device can effectively handle the MPP tracking of multiple modules. In fact, power derating of roughly 25% in comparison with the modules‘ name-plate capacity is commonly assumed.
The Missing 25%
Panels in today‘s market are not completely uniform, and they vary in their output power and electric characteristics by an accepted standard of about 3%. This phenomenon is called panel mismatch and its causes are built in the module manufacturing process. As a result, each module requires a slightly different MPP current to provide its maximum power. But inverters cannot set the optimal current for every module individually, since the same current has to flow through all of them. The inverter is bound to select an average current, typically leading to sub-optimal performance of the stronger panels.
Take the mismatch problem a step further. What happens if shadows are cast over a panel by a nearby tree, chimney or clouds? Such real-life conditions amplify the mismatch scenario. Shaded panels can produce less energy and therefore require lower currents. When a partially shaded module is connected to non-shaded modules, the inverter has to lower the overall current to a value suitable for the most shaded module, or to bypass that module altogether. Due to the modules interdependency, in both cases, the energy loss is disproportionate to the shaded area.
Distributed Power Harvesting: The Quiet Revolution
As the industry becomes more aware of traditional system drawbacks, a new technological approach is emerging in an effort to retrieve lost energy. Distributed power harvesting systems address the inherent limitations of traditional PV systems. As the name implies, distributed systems remove the MPPT function from the inverter and transfer it to each module. The benefit of the individual MPP trackers, also called Power Optimizers, is that modules become self-governing entities, able to locate and manage their own maximum power point. Each panel is able to deliver its maximal energy output at all times independently of other panels in the string. The chain is no longer as strong as its weakest link. If a panel is shaded, it is still contributing to the array‘s output instead of lowering it.
[Text by By Hannah Mann and Amit Rosner. Hanna Mann is a marketing associate and Amit Rosner is Director of Marketing at SolarEdge Technologies
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