More yield and easier to install – micro inverters at residential PV systems

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Micro inverter technology is widely regarded as one of the most promising ways to attract residential investors to solar power.

The technology generates more yield, reduces installation costs and lasts longer than string inverters.

One of the largest manufacturers of micro inverter technology recently announced that it sold more than three million units in just five years. But the company is one of just a handful of companies that produce micro inverters. So why does the number remain surprisingly low?

A major reason is the reluctance of the industry’s established string inverter companies to enter the field of micro inverters, which might be by individual market strategies and related R&D budgets. The knock-on effect is that the market potential as well as the technical superiority of micro inverter products is being overlooked.

Another key reason is the lack of education. Many companies are unsure about the differences between the two technologies and the benefits they give to customers.

The main difference between micro inverters and string inverters is that one micro inverter is used per PV module whereas one string inverter is used per system. This makes for a number of differences between the two technologies, from their installation and maintenance to lifetime and performance.

“It’s all about reducing costs for the life of the PV system, not just for the system owner but for the installation company as well,” explains Florian Dieckmann, marketing manager at ReneSola. “The costs are comparable to string inverters and yet the benefits are so much greater. A micro inverter system will generate more revenue and last longer. So it’s a no-brainer and we need to educate people to that fact.”

ReneSola aims to be the world’s leading supplier of solar inverters by 2015. The company’s Micro Replus micro inverters will contribute significantly to this ambition. Launched in 2012 as the leading product of its comprehensive Replus inverter family, Micro Replus was designed from scratch by two teams, one in Silicon Valley and the other in Chicago. The teams included veterans from GE Corporate R&D and Motorola who set out to develop an innovative new micro inverter. The result is a product that increases yield by up to 16% and is guaranteed to operate for 25 years.

Easier and safer to install

Rather than visiting the site, surveying the rooftop, creating a design and returning to install it, a micro inverter PV system offers installers the flexibility to visit the site, and then design and install the system on the same day. This helps the sales process and enables smaller installation companies or local electrical contractors with little experience to install a system quickly and easily. A micro inverter also holds less risk for installers and owners as it runs on a far lower DC input, so the risk of injury caused by electrocution is reduced.

ReneSola’s Micro Replus is designed as a one-box solution that contains a standardized cable harness and all connectors needed for installation. There is also an anti-islanding and automated grid connection device already built in, as required in markets such as Germany.

“There is no need for time-consuming planning, configuration and logistics. Electrical wiring gets a lot safer and easier, and almost anyone can install it,” states Güven Altun, sales engineer at ReneSola’s European technical support squad. “And the system is fully prepared and certified to work with any grid code around the world.”

The decentralised concept also gives owners far more flexibility, as they can add new PV modules with ease.

More yield

ReneSola’s Micro Replus system is proven to generate up to 16% more yield when compared to a string inverter, and operate at an overall efficiency of more than 96.5%. This increase in yield, which means increased revenue, is mostly thanks to reduced shading problems. A common issue with many rooftops, shading can dramatically reduce a PV system’s power production due to overhanging trees or nearby buildings, which are often impossible to avoid. In fact, just 9% shade can influence up to 54% of the total system’s output. Micro Replus inverters significantly reduce this power loss by managing each PV module individually, so if one module performs poorly it has a far less dramatic effect on the overall system. This also helps to prevent expensive breakdowns.

The use of one inverter per module also aids system management. Micro Replus can be connected to a web management interface through an inexpensive communication gateway that allows owners to monitor individual modules, allowing any weakness to be easily spotted and fixed.

To further protect both the PV module and inverter, each Micro Replus unit has an in-built fire detection system that recognises hot spot issues or overheating and can cut off the individual module, allowing the rest of the system to continue generating electricity without risk. But if an inverter were to fail, the owner need only replace a single unit rather than an entire string inverter.

Longer lifetime

Micro Replus inverters are guaranteed for 25 years, far more than the average 10 years for a string inverter and the same length of time as most good PV modules. “It’s a fit-and-forget concept where a one-off investment is followed by decades of revenue,” says Dieckmann.

This impressive longevity is partly due to the use of epoxy resin, which seals the device from moisture, dust, water and any ingress of dirt that could potentially cause a component to fail. It is also down to the use of generic components that are found in many electrical devices around the world, which keeps costs down and ensures their reliability, as all components have a proven track record of long service.

“Keeping costs down is key,” Dieckmann says. “The R&D behind Micro Replus is similar to that used to create smartphones: innovative U.S. design mixed with high-quality Chinese production to give the required economies of scale.”

Compared to string inverters, the electrical components used in Micro Replus share similarities, such as the DSP, MOSFETs, SCR and transformers, but the topology is different and the devices are scaled down. It also includes features like an isolation transformer, which most string inverters, particularly in Europe, do not have.

Where some inverters produce a loud buzzing noise from the electrical current, Micro Replus is virtually silent. As a result of its design, the entire device is IP68 rated, which guarantees integrity even in extreme climates. During testing, Micro Replus inverters continued to function in temperatures down to -40˚C and up to 65˚C.

“While string inverters will remain a popular choice for large-scale and industrial PV systems, the huge benefits that micro inverters bring to residential systems cannot be ignored,” says Dieckmann. “Giving installation companies the tools to build a more efficient PV system faster will allow them to sell more systems. It is a slow process, but the more we can do to promote and educate on the benefits that micro inverters bring, the better.”