Off-grid solar inverters have a stereotype of being for homeowners who prefer living in the mountains away from the grid. In reality, off-grid inverters are an established market. As power outages become more common and last longer, consumers are looking for homes with seamless back-up power. Off-grid inverters can fulfill this need of converting stored energy for common use.
With their ability to provide grid-forming voltage and manage battery storage, Derek Pettingale, global product line manager of off-grid inverters at Schneider Electric, says off-grid inverters and chargers play key roles in forming essentially private microgrids.
“Photovoltaic inverters, previously used only in grid-tie applications, are also being used in off-grid systems to reduce the use of diesel generators,” Pettingale says. “The integration of PV and diesel-energy generation is an essential partnership driving the development of large off-grid systems.”
Off-grid inverters may serve as an example for future generations of grid-tied inverters. Grid-tied inverters will begin to have the battery backup, multiple modes and functions seen in today’s off-grid inverters.
The biggest change in off-grid solar, according to Gary Baxter, VP of sales and marketing for Magnum Energy, is a fairly new concept called AC coupling. This allows a new or existing grid-tie installation to add battery backup, which adds demand for off-grid inverters and batteries. The same concept used in AC coupling is also used in microgrid design, with microgrids typically being larger installations.
“Energy storage is a huge part of the smart grid, and AC coupling is a small step in energy storage,” Baxter says.
Today’s off-grid inverters have also become multitasking rather than single-application inverters.
“It’s not as easy to segregate inverters into two classes of now that so-called “off-grid” inverters go beyond off-grid operations,” says Mark Cerasuolo, senior marketing manager at OutBack Power. “These next-generation smarter inverters will offer generator and battery-bank management, grid or generator support, energy-offset functionality, load management and can create a renewable energy microgrid to ensure greater stability for existing grids.”
But off-grid inverters face challenges. For instance, Pettingale says poor system design and installation are ongoing issues for larger systems. Too many systems are over- or underdesigned for the intended application.
“Standardization of large systems will lead to greater satisfaction with off-grid performance, lower implementation costs and, eventually, even make financing easier to obtain,” Pettingale says.
Training installers and homeowners on best practices for off-grid inverters is important.
“While the installers are qualified in AC grid-tie systems, they typically do not have the experience in designing and installing DC systems,” Baxter says. “Homeowners must also be trained on off-grid living.”
The United States should take a lesson from developing nations that prepare for natural disasters and extended power outages using microgrids powered by renewable energy, Cerasuolo says. “Last year’s Hurricane Sandy, for instance, left some homeowners without power for a week or more,” he says.
Cerasuolo believes that eventually, the mainstream choice will be hybrid inverters that offer off-grid independence with grid-tied savings. Only niche applications and cost-driven installations will deploy single-purpose off-grid or grid-tied inverters.
“Advances in retrofit technologies such as AC coupling will result in more grid-tied system owners adding off-grid features and performance to existing systems to get the best of both worlds,” Cerasuolo says. SPW
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