Why We Are Moving to a Transformerless Future

By Scott Kolek, Senior Product Manager of TX Inverters & Solutions, AE Solar Energy

Up until 2005, U.S. regulations dictated that all electrical systems be grounded. For PV arrays, this required the use of transformer-based inverters to create galvanic isolation between the direct current (DC) and alternating current (AC) sides of the system. When the code was updated to allow for ungrounded systems, building transformerless solar arrays became a possibility for the first time.

Photo courtesy of solarenergy.advanced-energy.com

Eliminating the grounding requirement for solar arrays provides many benefits for project developers: greater energy harvest; lower operations & maintenance (O&M) and BOS costs; and a smaller overall footprint of the inverter system. Although the benefits are clear, adoption has been slow as the market adjusts to the updated code. Inverter manufacturers are now focused on providing transformerless solutions for the U.S. market, and system designers, installers and code enforcement officials are becoming more knowledgeable about ungrounded systems.

Other technological advances — such as higher voltage input capabilities and improved DC monitoring tools — are notable drivers in the transition to transformerless inverters.

Previously, when max DC input was limited to 600 volts, reaching a desirable AC output required a boost provided by the transformer. With the market now moving toward a standard DC input of 1,000 volts or more, there is a reduced need for a transformer because the higher DC voltage also brings up the native AC output.

Project developers have historically been hesitant to switch to transformerless systems because of insufficient monitoring capabilities of the DC side. Without a transformer, problems such as ground fault and arc fault that occur on the DC side aren’t isolated and can therefore affect the AC system. While fault detection tools are still new, the technology is expected to advance significantly, which will provide developers and utilities with greater assurance in transformerless arrays.

Even though advances in transformerless inverters are quickly negating existing pitfalls, utilities often favor transformer-based inverters because it’s easier to integrate AC output into power models when it’s completely isolated from the DC side. There is also the argument that although fault detection is improving, total galvanic isolation is the only way to ensure that issues on the DC side don’t transfer to the AC side.

Although widespread acceptance of transformerless inverters is still in flux, the industry can expect to see greater adoption in the coming years. Combined, the benefits of eliminating transformers, advancements in monitoring technology and a favorable regulatory environment will speed the transition to a transformerless future.

— Solar Builder magazine

[source: http://www.solarbuildermag.com/featured/transformerless-future-ae-solar-energy/]