National Semi plans to reduce solar energy losses due to shading

Santa Clara, Calif.-based National Semiconductor (NYSE:NSM) plans to unveil in May a distributed control system for solar systems that could reduce losses from shading and debris by 50 percent.

The company is estimating that this approach to distributing the power optimization of inverters could one day make up 25 percent of its annual revenues. Dubbed SolarMagic, the system builds on National Semiconductor’s power management devices for semiconductors, said Ralf Muenster, director of National Semiconductor’s Renewable Energy Key Market Segment.

National Semiconductor’s field trials of the technology have shown that 10 percent shading on a panel can lead to a 50 percent reduction in the amount of energy harvested, Muenster told the Cleantech Group.

The losses due to shading are one reason 54 percent of installers find any shading unacceptable, according to a recent U.S. survey by Greenberg Quinlan Rosner Research. Installers that design around vent pipes, trees to chimneys to avoid shading report that the process increases the cost of installation by about 19 percent, the survey found.

The problem is that photovoltaic systems share an inverter to optimize output. But a single inverter isn’t capable of optimizing different conditions that panels even with the same array can face, Muenster said. The result is either that the inverter picks the highest common operating point for all the panels, which can severely decrease the output of fully functional panels, or that entire strings of panels can stop contributing to the energy harvest, much like a string of Christmas lights that goes out because of one faulty bulb.

“The optimization that the inverter does can be distributed,” Muenster said. “If you can maximize the energy from every panel, then you can maximize the energy harvest.”

National Semiconductor's approach is one of many aiming to improve the efficiency, and therby lower the cost, of solar systems. Some scientists in the solar industry have concentrated on improving the efficiencies of solar cells (see Solar with 41-percent efficiency?). Others have sought to mass-produce lower-efficiency solar to achieve low costs (see Oerlikon sees 50% gains in thin-film fab, Aussie researchers develop spray-on solar and UK researchers simplify low-light solar with paint-on PV). And others, such as 3M, are developing coatings, glass, films or other materials to improve the efficiency of existing technology (3M seeks new market for tape and film in energy sector).

And just today, Pittsburgh, Penn.-based PPG Industries (NYSE:PPG) introduced Solarphire PV glass, a product designed to maximize solar energy transmission for photovoltaic modules. The high-clarity glass allows for enhanced transmittance in the ultraviolet portion of the solar spectrum, between 350 and 1100 nanometers, where crystalline photovoltaic cells are most responsive to the sun’s energy.

National Semiconductor’s SolarMagic system is being billed as an add-on to existing panels, but Muenster expects National Semiconductor to begin working with PV panel makers to incorporate the devices.

“Photovoltaic panels in the long run are going to contain more electronics, and we feel this architecture is superior to other technology,” he said.

Muenster said there are no other products that he’s aware of addressing this problem. Individual micro-inverters could be used on each panel but would be less reliable, energy efficient and cost efficient in optimizing the energy harvest, he said (see Enphase introduces micro-inverter system).

The implications for the device could be huge, Muenster said, because it betters the economics behind solar installations by extracting more electricity from each PV system.

“Before, you literally had to design around any kind of shade obstructions. Now you can live with panels that are partially shaded,” Muenster said. “It can help new roofs qualify for solar, and it could allow for an increased size for existing installations.”

SolarMagic is a self-contained, self-starting system designed with enough embedded intelligence to indirectly communicate with other power optimizers in a solar system, Muenster said. The device is the size of a junction box, with an aluminum enclosure and two inputs and outputs.

One of National Semiconductor’s field trials was conducted by Campbell, Calif.-based installer REgrid Power, which merged with Real Goods Solar in October (see Cleantech deals in garbage, lighting and batteries).

Muenster said the trial used top-of-the-line components: 14 SunPower 215-watt panels and an SMA Sunny Boy 3300U inverter on both the test and control string of panels, which were set up side-by-side. Shading ranged from nothing to 15 percent. At 13-percent shade, the system lost 44 percent power generation, but the SolarMagic recovered 50 percent of the loss. At 9-percent shading, the system lost 54 percent power generation, but SolarMagic recouped 66 percent. At 3-percent shading, the system lost 25 percent power generation, but SolarMagic recouped 40 percent.

The SolarMagic technology was able to recover 45 percent of energy lost, delivering 12 percent more energy over the entire day, Muenster said.

A similar test at National Semiconductor using Kyocera panels and a Xantrex inverter with between 8 percent and 15 percent shade led to losses of between 35 percent and 40 percent of energy harvested in the traditional solar systems. The trial using SolarMagic resulted in a recovery of 30 percent to 37 percent of the lost energy.

The results indicate that system on roofs with as much as 30 percent shade during parts of the day could now be economical, Muenster said.

“It gives you much more flexibility to install the system, whereas before you had to avoid shade at all cost,” he said.

The SolarMagic system is agnostic to the types of solar technology. It also has potential applications in the battery or energy storage sector, Muenster said (see Nat'l. Semiconductor to deliver PV "magic").

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