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Solar Expansion

Technologies are scaling up quickly to meet industry needs.

Fortnightly Magazine - December 2009

the value chain. You can measure changes on a quarterly basis. But the customers know that. We tell them, ‘Here’s where the cell efficiency will be a year from now.’”

Utility Grade Solar

Over the next five years, SCE expects to blanket some 65 million square feet of unused Southern California commercial rooftops with 250 MW of PV technology. Two facilities have gone commercial so far—a 1-MW system in Chino, and a 2-MW facility in Fontana. First Solar supplied the panels for both. Among the many takeaways of these projects is the ability to measure each system’s impact on the California ISO grid operations.

“In the last year, renewable power has come to represent 16 percent of our total power delivery,” says SCE spokesman Gil Alexander. “As our renewable resources increase, it’s obviously going to be a challenge to keep the grid in balance. These two plants will help us determine how to best integrate a variable, intermittent power supply with conventional, dispatchable resources. We intend to share those findings with the industry.”

The key to such a balancing act is the inverter technology that transforms the direct current (DC) produced by PV panels to alternating current (AC) and sends that current to the distribution grid. Technology advances at this interface are making PV power more grid-friendly. Boston, Mass.-based Satcon, which supplied the inverters to the Fontana installation, announced in September a third-generation product called Satcon Solstice, a utility-scale inverter for large solar farms. With Solstice, both the plant and the interconnection can be monitored and controlled remotely.

Individual circuits continually will monitor the operations of each array, giving the operator the ability to isolate or even shut down individual panel threads that are experiencing technical problems and undercutting the array’s performance. The ability to control each individual thread optimizes the amount of electricity harvested from the PV facility.

At the same time, the AC side of the inverter system is configured to allow the utility to monitor the facility’s output in real time. If a change in the weather is predicted—perhaps thunderstorms are expected in the afternoon—the utility can monitor the output to closely synchronize the time it dispatches other generation to replace lost solar capacity.

“The inverter is the brain and the muscle of the PV system,” says Michael Levi, Satcon’s senior director of marketing. “With a 1-MW system or larger, the inverter gives the operator a window into the PV operations and a control device that gives the utility 100ths of a second reaction capability. Most utilities are reluctant about solar power because they view it as unstable and disruptive. They need reliability and performance, along with an interconnect that lets them on-board the power in a comfortable manner. That’s what this system provides.”

Indeed, with solar plants becoming vastly larger than they once were, utilities require much greater ability to manage and control their output. Not long ago, a 1-MW PV facility was considered a major technological achievement. Now Chicago-based Exelon is building an 10-MW facility on the city’s south side; FP&L owns and operates the 25 MW