A Back of the Panel Boost for Solar Power

Chinese photovoltaic giant Suntech looks to electronics to help squeeze more power out of solar arrays.

Electronic power boost: This chip set is the heart of National Semiconductor’s power-optimization device for solar arrays. Attached behind every solar panel in an array, the electronics could correct for a drop in the array’s power output due to shading or debris, increasing the final output by 25 percent or more.
Credit: Courtesy of National Semiconductor

As manufacturers work to drive down the cost of solar power, refining solar cells and panels to make them more efficient is only half the story. Another option is to incorporate newer electronics into the panels that could boost the power output of photovoltaic systems and make them easier to design and install.

Suntech Power, the world's largest maker of crystalline-silicon solar modules, based in Wuxi, China, has announced partnerships with Santa Clara, California-based National Semiconductor and other solar electronics makers to develop "smart" panels that would give the most power possible even if other panels are underperforming due to damage or to sunlight being blocked by shade or debris. This kind of system is useful because in conventional photovoltaic systems, one panel's performance affects the output of the whole system. "We think smart module technology is a clear path for the future," says Andrew Beebe, Suntech's chief commercial officer.

Solar manufacturers are finding it difficult to eke out additional increases in how efficiently crystalline-silicon solar panels convert sunlight into electricity--so solar innovation has shifted to back-of-the-panel electronics. "Every incremental power advantage brings down cost per watt, and electronics are where the improvements are going to be," says Matthew Feinstein, a research associate at Lux Research.

National Semiconductor's power-optimizing device is already on the market. Tests on customer installations have shown that it can squeeze 25 percent more energy from a photovoltaic system, says Kevin Kayser, a marketing manager at the company. Independent tests by the National Renewable Energy Laboratory and Photon International have demonstrated power gains from arrays as high as 39 percent.

Solar modules operate at various current and voltage levels. Panels are traditionally strung together in a series, and their combined DC power is sent to a large inverter. The inverter does two things: it converts the power into grid-ready AC electricity, and its control circuit constantly searches for and sets the operating voltage and current levels for all the panels based on the total power output of the array. But if one panel's current drops because of shade or debris, the inverter lowers the current of all the other panels, bringing down the array's power output. "Ten percent shade on the array means a 50 percent power loss," Kayser says.

National Semiconductor's power optimizer does away with the central control circuit in the inverter, instead placing a separate control circuit behind each panel. This allows the optimizer to wring the most power from each panel. In addition, Kayser says, while some power-optimization products either increase both current and voltage or decrease current and voltage, theirs can increase and decrease both current and voltage, squeezing out even more power.

The device adds about 12 cents per watt to the installation cost of a photovoltaic system but pays for itself within two years for most installations. In addition, installers don't have to worry about, say, the shifting shadow of a chimney or the precise tilt angle of each panel. "It can simplify design time and reduce installation time so their profit margin goes up," Kayser says.

Suntech hasn't put all its eggs in one basket. The company is also looking at microinverters, another electronic technology expected to boost photovoltaic power. Microinverters adjust the voltage-current levels of each panel, and then go one step further: they convert the panel's DC power to AC.

The two approaches have their pros and cons. Microinverters make it simpler to wire panels together, so new photovoltaic systems are easier to install, and it's also easier to add panels to an array later. But it's easier to retrofit existing systems with power optimizers--and Kayser says they should also offer better overall system efficiency. That's because converting DC to AC at each panel, as microinverters do, requires stepping up each panel's low operating voltage of around 30 volts to the grid-standard 120 volts, leading to some power loss.

Suntech has teamed up with half a dozen companies that make microinverters and power optimizers. These include the startups Enphase Energy in Petaluma, California; Tigo Energy in Los Gatos, California; and Azuray Technologies in Portland, Oregon. Tigo makes a DC power optimizer that adjusts panel current levels and can increase power output by up to 20 percent. Enphase claims that its microinverters can help solar systems harvest up to 25 percent more energy. Azuray, meanwhile, is making both power optimizers and microinverters.

While both technologies have been around for two decades, they have only recently been implemented in low-cost, reliable products, says Eric Wesoff, a solar analyst at Greentech Media. "Panel manufacturers have finally been convinced that this is something that can last," he says. And as engineers max out other means of increasing the efficiency of photovoltaic arrays, they're more willing to try different electronics. At least 20 different solar-electronics startups showed off their products at the Solar Power International conference in Los Angeles this week.

Wesoff adds that Suntech is taking the smart, cautious approach by partnering with multiple microinverter and power-optimizer vendors. "Clearly they're not picking a winner or an architecture," he says.

Source:   Technology Review (published by MIT)