Kent Sheldon, Power-One: Page 3 of 3

Advancing Inverter Technologies

SP: What differentiates Power-One products, and what are your expectations for increasing its US market share?
KS: I foresee Power-One’s success in Europe being repeated in the US. We will gain significant market share over the next couple of years as we introduce our full line of products and technologies into the US market and increase the PV community’s awareness of the unique features of the Aurora inverters. Our reliability is proving to be the highest in the industry. These inverters have, by far, the widest dc input range of any inverter on the market. All of the Aurora string inverters have two independent dc inputs, meaning you can have different string lengths and orientations, and shading issues are minimized. This is similar to the value proposition of a microinverter, albeit less granular, but at the price of a string inverter. All our central inverters incorporate a modular architecture built of multiple paralleled inverters. System failures can be localized to only a small portion of the inverter or PV array while allowing the rest of the system to continue operating. Repair of a central inverter can be accomplished in a matter of minutes on-site.

SP: Power-One has had a transformerless (TL) inverter available in the US market since the allowance of such inverters in the 2005 NEC cycle. To what do you attribute its general lack of acceptance? What is your projection on the deployment of transformerless inverters in the US market?
KS: Installers are more or less oblivious to the differences between TL and isolated inverters. The installation of both types is nearly identical from a wiring point of view. The 2005 NEC was poorly written and was corrected in 2008. So some of the slow adoption of TL inverters can be blamed on the NEC. More importantly, module companies did not use PV Wire on their modules in the US. NEC 2008 requires that doubleinsulated wires be used between the modules and the TL inverter, because there is no electrical ground connection on the dc side. Most module companies used less expensive single-insulated wire for their US products. The cost saving was trivial; however, this was one way of controlling product allocated to the US market. These modules could not be used with TL inverters commonly used everywhere else in the world. The first year that the majority of modules changed to PV Wire was 2009, and we are seeing a dramatic uptick in TL inverter sales as a result.

I anticipate inverters will transition from isolated to transformerless very quickly. European manufacturers have been waiting for TL inverters to be allowed in the US for many years. Isolated inverters were developed specifically for the US market, to the irritation of European inverter manufacturers. The advantages are simple: The removal of the isolation transformer achieves higher efficiency, leading to higher energy harvest.

SP: What are the benefits of the modular/scalable architecture approaches of the 250- US and 300-US Power-One inverters? And when will these models be added to the CEC’s list of eligible equipment?
KS: CEC listing for Power-One’s Aurora PVI-250 and 300 central inverter models is imminent. The Aurora PVI-250 and 300 are composed of five and six 50 kW inverters wired in parallel. They can be configured a number of ways—master/slave or multi/master or a combination of both. For instance, one 300 kW array may be connected to all six inverters. If one inverter fails, it isolates itself and the rest continue to process up to 250 kW of power from the array. You lose a maximum of 50 kW of power from the array, or a net energy loss of approximately 6%. You can also group the inverters into three sets of 100 kW blocks. Similarly, if you lose one inverter, 250 kW of production is available. If you have a problem in one of the subarrays, you still have 200 kW of production available. Spare inverters can be stored at the site for an immediate response to an inverter issue. The inverters are racked in a cage and can easily be replaced and sent back to the factory for repair rather than sending technicians to diagnose and repair on-site. I see these as important benefits to ensuring maximum system availability.

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