Microinverters Aim to Improve Solar Efficiency

Enphase Energy recently launched what it says is its most efficient and powerful technology to date, the 215-Series Microinverter and the accompanying Engage System, designed to streamline solar installations.

The third generation microinverter series was developed to maximize the performance of 60-cell photovoltaic modules, and can achieve a weighted power conversion efficiency of 96 percent.
The system has a 13 percent higher output than previous generations that enables compatibility with the 60-cell modules, according to officials from the company.
With the goal of addressing a growing global solar market, the ACM’s design simplifies installation by eliminating rack mounting, a separate system ground wire and DC cable management.
The microinverter comes with the “plug and play” Engage System, featuring a size-to-fit cable and built-in connectors to support a 4-kilowatt system on a single branch.
“Providing installers ultimate flexibility and requiring no special equipment or training, the Engage Cable can be cut to length and also comes with additional cable termination and splice kits to further reduce balance of systems requirements,” company officials said.
Enphase’s system features one inverter per panel. The system is less prone to performance degradation from shading or module mismatch and produces more energy for the overall system, company officials said.
The fundamental challenge of inverters has been preventing the entire system dropping to match the lowest performing module, said Bill Rossi, chief marketing officer at Enphase. Because each solar panel performs independently, if one microinverter fails, it does not bring the entire system down, which makes it inherently more reliable, he said.
“We generally produce more energy because we’re doing it on a per-panel basis versus a central inverter, which converts energy for the entire string,” Rossi said. “The panels are connected in a series, with each panel connected to the next panel in the string — if there were one panel in the string that was shaded, that wasn’t producing any energy, the whole string can be impacted by that.”
Enphase microinverters can result in energy gains of anywhere 10 to 25 percent.
The digital device technology leads to reliability, high volume and built-in intelligence that enables an extensive energy communication network within buildings, company officials said.

One of the challenges with inverters is operating efficiently despite the loss of energy in the conversion process, Rossi said.

Currently, inverters operate at 96 percent efficiency or higher, but because they have such high voltages of 600 to 1000 volts, a 4 percent loss is a small percentage but a large number, he said.
“Enphase has been able to match the efficiency of central inverters so they’re now at 96 percent efficiency for the microinverters which means when you take that DC voltage in from the panel, if we take one watt in, by the time we get thru the other end of the microinverter and out the AC cable you’re producing 0.96 watts, which is a very efficient device,” Rossi said.
The Engaged cable runs along the rack as a cable to connect each microinverter into the AC bus, and eventually connects to the grid.
The set-up enables flexibility because it is a cable that can be sized to custom-fit the facility, and can be easily terminated with the accessories.
AC connectors lock the system into place, which Rossi said is critical since the system is designed to last 25 to 30 years and be waterproof. A tool can be used to disconnect the microinverter from the connector.
The system works to converts energy, then provides overall monitoring and analysis of the energy being produced.
The system’s monitoring capability alerts users of a problem — the first time this kind of level of granularity of system monitoring has been built in fundamentally to the microinverter system, he said.
An additional advantage of the system is that it enables easier installation because unlike high voltage central inverters that require special training to work with, it is an entirely AC-based system that can be handled and installed by normal electrical contractors, general contractors and anyone who understands AC wiring, Rossi said.
This has resulted in very rapid growth for the company since more installers are able to do the work, he said.
Installation ease is also due to the Engage System, a balance of system improvement that entails all key equipment related to the solar panel system aside from the modules and inverters, and connects the microinverter to the grid with its various components.
Due to debut in 2012 is an Engage Port designed for further simplicity that will attach directly on the module and connect to the port, replacing any DC cables and allowing Enphase microinverters to be directly attached to the module.
“The nice thing is, from an installer’s standpoint, it’s really all … one system — 
one Engage cabling scheme, same enlightened software, so it’s very much an evolution that further reduces the balance of system costs and further simplifies installation,” he said. 
The system delivers a higher power than previous generations at 215Wac as opposed to 190Wac, aimed to meet the “sweet spot” of residential solar business ­– the best performing modules at the lowest cost per watt, which is 60 cell module rated at 225 to 230 watts.
The company designed the inverters to support newer modules in the future, which are expected to reach 260 watts of DC.
Average installation time on a 25-panel system is one hour and 20 minutes.
If a unit fails, the user receives a notification through the Enlighten monitoring system. The installer can then contact Enphase to ship an advanced replacement unit, which they will do within 30 days and reimburse the system owner for any energy loss during the failure to guarantee 100 percent uptime.
The company’s warranty has extended from 10 years on the first generation to 15 years on the second, and now, to 25 years.
“Installers are applauding this because when they pitch a system to a customer a single system warrantee, it just makes the whole pitch to the consumer that much easier and pretty much guarantees a payback for the system,” he said. “That’s a very important thing, especially as system owners are laying out $25,000 to $30,000, they want to guarantee 1.5 to 2 times payback, which is what this system guarantees.”
The new system also includes the Enlighten system as part of the system, eliminating the $2 per inverter monitoring cost.
The M215-Series Microinverter and Engage System are now shipping in North America, with the European model available for purchase in the second half of 2011. Enphase-enabled AC modules from leading module manufacturers are expected to ship in the first half of 2012.
Enphase was founded in 2006, with their first product released in 2008.
“Pretty much every year to 15 months, we’re innovating on our next platform of higher power, better efficiency and lower costs, those are the three main areas (we look at) with each new generation.”
The company has seen very rapid growth with 11,000 units in 2008, 126,000 in 2009, and 414,000 in 2010. For the first three months of 2011, Enphase has shipped 123,000 units, or almost the same as it shipped for the entire year of 2009.
“It really speaks to the microinverter being a key innovation in the industry that typically doesn’t adopt new technology very easily,” he said. “The value proposition is so strong that like any new technology and any risk that anyone would take, it’d have to be kind of worth it.”
Officials said that while some critics feel there isn’t enough data about solutions like the microinverter, the company released field data aimed at demonstrating the reliability of its microinverter technology.
“The data, collected separately and independently by Westinghouse Solar and SunEdison over a two-year period from 2008 to 2010, show the reliability of microinverters is 45 to 70 times greater than traditional central inverters,” officials said. “This level of field-proven reliability allows installers and system owners to benefit from the exceptional system uptime that the Enphase Microinverter System provides.”

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