Intelligence to the Rescue!

Rules and regulations may try to hold them back, but smart inverters will soon be an integral piece of the solar puzzle.

Inverters are an important — albeit boring — part of a solar power system. They convert the DC power produced by the solar array into AC power ready to use by the masses. Over and over and over again.

And that’s all. No bells, no whistles. The traditional electric grid really won’t let them do much more than that basic conversion. But smarter inverters can do more with a smarter grid.

The “smart grid” is a modern version of the traditional electrical grid, using information and communications technology to improve on efficiency and reliability. Using constant communication and monitoring, a smart grid would improve fault detection and allow for self-healing because problems could be found before they attack. But until the smart grid is finished (efficiencies are still evolving), smart inverters can pick up the slack.

An inverter with smart capabilities transforms the unit from a simple power converter to a piece of equipment necessary for grid durability.

“Inverters were designed to feed as much active power available from the solar array to the grid,” says Thomas Enzendorfer, director of sales and marketing for Fronius USA, an inverter manufacturer. “Recently, utilities have shown enormous interest in inverter capability to absorb and provide reactive power from and to the grid.”

Most PV inverters run below their rated power output because they’re sized to convert the maximum available energy from the solar array. But the weather, panel orientation and seasons affect the actual power being converted. A smart inverter can take that reactive power — or temporarily-stored power — and feed it on demand to help the grid recover from distant faults or momentary sags in power.

“In the past, the inverter had no interaction with the grid other than pushing energy into the grid,” says Martin Beran, head of system support for Fronius USA. “With a smart inverter, it has communication. It can be controlled from outside the PV installation by the utility or whomever. [It has] additional functionality and features, having the capability to stay on the grid when the grid is in a difficult situation.

“For a long time PV systems and inverters were seen as a threat to the grid,” Beran continues. “‘PV installations are making the grid unstable,’ some have said in the past. [But] when you use the whole capability of power electronics, then the inverters could help stabilize the grid way differently than [before].”

INTELLIGENT DESIGN
Fronius introduced a new line of smart inverters earlier this year. The Fronius IG Plus Advanced Inverters are well suited for small residential and light commercial installations. The inverter size ranges from 3 to 12 kW.

These advanced inverters are “smart” because of their extra capabilities and features. The new Fronius inverters have grounding selectable on site, are designed for indoor or outdoor installations and have integrated DC disconnect, a power plug system and field programmable AC output voltage. The Fronius IG Plus Advanced Inverter lineup is the first high-frequency PV inverter to have NEC 2011 compliant arc-fault circuit interrupter (AFCI) protection in the United States. Fronius created the IG Plus Advanced Inverter with arc-fault protection and advanced features specifically for smart grid integration.

But the U.S. grid can only benefit from some of these advanced features today.

“From a technical point of view, inverters with advanced grid features can be used in most of the typical installations we know today,” Enzendorfer says. “Activation very often would improve grid stability as well as quality immediately. However, interconnection requirements and grid codes (for example, IEEE 1547), as they are written today, are contrary to the capabilities of smart inverters. Therefore, permission from the grid operator is required to turn on an inverter with advanced grid features. We see the change of codes and standards in favor to smart grid features of distributed generators changing in the not-so-distant future and also become requirements for high PV penetration areas.”

While waiting for rules and regulations to allow the grid to catch up to the technologies out there, the Fronius IG Plus Advanced Inverters can still be used successfully in a traditional sense. The advanced inverters use Fronius Master Inverter X-Change (MIX) Technology, which allows them to achieve maximum yield, even when in the partial-load range. Fronius documents describe the system as all power modules working equally, with the “master” module allocated alternately, taking into account the operating hours worked. Loads are applied evenly to individual power modules and the operating time decreases. The new inverters also use a high-frequency (HF) transformer which provides a constant level of efficiency, resulting in higher yields as well as lightweight design.

This high-tech inverter is installed the same way as a traditional inverter.

“There are no additional requirements in order to install the inverter,” Enzendorfer says. “Because of the modern design of the inverter lineup, they make it very easy for the installer to install them as a regular inverter.”

While modern, the IG Plus Advanced Inverters were designed to be ready for smart grid evolution.

“The way we built them is to make sure they are capable of changing environments that may or may not happen over the next few years,” says Enzendorfer.

Fronius is looking ahead, designing inverters for tomorrow, not today. The new IG Plus Advanced Inverter class is ready for the smart grid before it exists, with smart functions built into the devices. The advanced inverter still functions as a successful traditional inverter when hooked up to the grid today. And once that smart grid comes into play, it’s ready to go. No extra parts will have to be installed after the fact.

Ready when you are, smart grid.

— Solar Builder magazine

[source: http://www.solarbuildermag.com/featured/fronius-usa-smart-iverters/]