Pared-down MLPE: How Empower Micro Systems does residential solar with two SKUs

empower-genesys-8k-powerbridge-1In its early days, the U.S. residential solar market was dominated by high-volume buyers like Sunrun, Solar City and Vivint, which means they bought most of the equipment, with the remaining market being served through distribution channels. But big-time growth going forward in the residential solar segment will be driven by the local installer, and the growth of that local installer market will come through greater simplicity, in both process and systems. That’s how we see it at least, and that’s the thesis driving a new PV electronics platform from Empower Micro Systems, a technology company that is currently licensing its new patented solar platform to larger established brands.

“With more financing options available, there is just not a huge advantage in being larger,” says Mika Nuotio, CEO of Empower Micro Systems. “The system is collapsing. Hyper regionalized deployment is coming. The vast majority is from installers, sold through distribution.”

So, if smaller companies gravitating toward simple solutions is the operating assumption, Nuotio says SKU consolidation is one of the most important goals to shoot for — reducing inventory costs and inventory turns makes an installer’s job easier and more profitable.

“In particular in solar, if you sit on inventory for a month or two, you are eroding your profit margin and reselling that equipment. Fast inventory turns make things much easier,” Nuotio says. “Installers are in the service business. They need transactional efficiency. When we designed our technology, we looked at the whole value chain from manufacturers through distributors to homeowners. What’s the technology that streamlines everything?”

SKU consolidation

Installers like stocking products in a van or keeping confined stock at a distributor. Select the wrong size or put the wrong one in the van and another trip is needed.

Simplicity is far from a new concept, as pretty much all manufacturers are trying to simplify their products and an installer’s workflow, but Empower’s Genesys 8K modular technology platform is maybe the simplest out there, cutting the SKU count to two: just a PowerBridge and a PoweHub. With those two, Nuotio says you can build any system from 2.4 to 11.4 kW, which could cover about 99 percent of U.S. residential installs. Comparable module-level power electronic solutions will likely have eight to 15 different SKUs.

Introducing ‘fractal inversion’

Empower Genesys So, how is Empower able to say “just buy two components and then that’s it?” Nuotio explains it is part technology and part design. The Empower technology uses a combination of microinverters and DC optimizers, an architecture that Nuotio is calling fractal inversion.

Here’s how it was described to us: The PowerBridge is a microinverter, one installed per module; the input is DC, and the output is low voltage AC (operating between 0 and 40 volts). Multiple units are then connected in series to create an AC string and aggregated together to hit grid voltage.

The PoweHub is the smart energy combiner. It combines multiple output circuits into one circuit that goes into the service panel and can support up to three strings. Each string is 16 amps, and the aggregate output max is 48 amps. The power rating of the system scales with the number of PowerBridges.

“Because we are connecting the PowerBridges serially in the string, we have an all AC system that doesn’t need a proprietary trunk cable,” Nuotio says. “Installers we talk to say they don’t like trunk cables; they are complicated to deal with, you need three different versions in stock, slicing connectors, sealing caps. That whole thing goes away.”

Overall, the system concept reminds us of Enphase, except for the commitment to pared down SKUs and the move away from trunk cables. It is similar to SolarEdge in that the DC to AC ratios aren’t rigid, which is a trend you can expect to continue in residential solutions. It differs from SolarEdge by being all AC voltage, which means less thermal stretch compared to an oversized DC string.

“Thermal stretch on an individual PowerBridge actually goes down when you oversize in our system,” Nuotio says. “Each PowerBridge is operating at a lower power output, and the string current is limited to a max level of 16 amps. If you keep loading more and more DC power, the total power is max 3.8-kW AC, so each unit actually processes less power and therefore puts less thermal stretch on the electronics.”

Lastly, as solar + storage systems start to take off, Nuotio says the PowerBridge simply couples to a lithium ion battery pack in the way it would a PV module, to help keep those SKU counts low and install solar today but be ready with the infrastructure for storage down the road.


The rigid modularity of the system might not work for every single home on the market because a single string of at least 8 PV modules is needed to make the system and economics payoff. But that is a fairly small volume of projects.

“If you look at the cost of customer acquisition, permitting, installation and truck rolls to do anything, an eight-module system is just not economical. It is washed out by soft costs, so we don’t see that as a major limitation from an overall market perspective.”

Tigo with Amazon AlexaTigo Skill connects a PV system to Amazon’s Alexa

Tigo is now offering its customers the benefits of Amazon Alexa technology via the new Tigo Skill, available on Alexa-enabled products. Using the Tigo Skill, residential and commercial customers with monitored PV systems can request tailored information from Alexa, the cloud-based voice service by Amazon. For example, simply saying “Alexa, ask Tigo how much power my PV system generated today,” will report a day’s worth of power without the need to log in to Tigo’s SMART website.

“Within seconds, you can know how well your PV system is producing — without logging on to a computer or climbing on the roof,” says Maxym Makhota, Tigo’s VP of Software Development. “Tigo Skill is the first to bridge the gap between solar, artificial intelligence and the Smart Home mentality in which information is always available.”

— Solar Builder magazine

PV Pointer: Minimize truck rolls by using smart software


We’ve all heard the expression “work smarter, not harder,” but you would be surprised how often solar installers get in a truck and roll out to a jobsite to adjust or repair something that probably could have been fixed remotely back at HQ. Many software-savvy solar installers are boning up on best practices to better utilize the systems and information already available to them — most of it right at their fingertips — to save both time and money.

For solar arrays, the most critical software typically lies within the power conversion devices, gateways and interconnected online monitoring platform provided by the inverter manufacturer. The online platform not only monitors the performance of the system, but also tracks a profusion of data points simultaneously and stores that information in the cloud. By checking certain performance specs, settings, activity and historical data, installers can quickly troubleshoot and fix common hitches or, at worst, narrow down the problem.

Every inverter monitoring interface is a little different, but much of the information and tools available are typically the same. With an MLPE system like microinverters, you’re able to drill down to the PV panel level to see what each module is producing at any given time. When troubleshooting a system issue, or when you see a panel reporting low or zero watts, first try rebooting the system remotely if your monitoring platform offers that capability. With some systems, a reboot may help the interface identify the issue, or it might reset the array to its default parameters in case an unusual grid event threw a monkey wrench at it. It could also spur the system to begin downloading recent updates that may have stalled when the system encountered the issue. You may even consider rebooting more than once.

If you’re still troubleshooting the issue, check the DC side of the system. For a microinverter system, be sure each inverter is reporting at its minimal operating range (such as 16 V) incoming from the panel. Next, check your AC output. If your system shows it registering zero or 120 V, the inverter may not be sensing the grid or enough volts from the grid to register as a 240 V grid connection. Without an identified grid connection, the inverter will not convert energy, so if you see this as an issue with multiple sequential inverters, it could be a cable or connector problem. If it applies to the entire string or array, the problem could be a loose wire in the junction box or a tripped breaker.

2017 Solar Inverter Buyer’s Guide

With a low wattage problem, you can drill down to the panel level online and check the voltage. If it’s registering under its minimal operating range, it’s likely a panel problem and not the inverter. You may still have to visit the site, but at least you know what you’re replacing and exactly where it is on the array. At the site, unplug the suspect panel from the inverter and take a live load DC voltage and current reading. If your panel is reading below its minimum startup voltage and 0 current, then the panel is the culprit and needs replacing.

Don’t underestimate the value of historical data. Looking back over a system’s history — especially that of a single panel — may help identify recurring issues affecting that particular panel. Perhaps a chimney shadow hits the panel at the same time each day. You can look back through the production history to see if it occurs often, or if you have multiple installations in a particular area, you can check each of those to see how unusual grid activity may be affecting your other sites.

Understanding what the site metrics are telling you will give you better insight into what’s happening at a jobsite. Learning what you can do to troubleshoot an issue online can not only save you a truck roll but also significantly reduce your time identifying the problem if you do have to drive to the site.

Larry Busby is a technical services manager at APsystems.

— Solar Builder magazine

All Fronius Primo, Symo inverters are now Rule 21 compliant

Fronius summer promotionFronius USA received UL certification for the Fronius Primo 10-15 kW and Fronius Symo 208-V inverters to comply with California’s Rule 21 inverter requirements. With that, all Fronius Primo and Symo inverters are now Rule 21 compliant.

What this means

Rule 21 refers to the generator interconnection requirements of each California Investor-Owned Utility (IOU). A years-long process has been underway to update Rule 21 with “smart inverter” requirements. Rule 21 requires inverters to have new grid support functions and a new certification under UL 1741 SA. Each new inverter also gets a new nameplate label that identifies it as a “Grid Support Utility Interactive Inverter.”

How California’s Rule 21 inverter requirements expand grid capacity, limit energy (revenue) generation

New smart functions, such as voltage and frequency ride-through or soft start ramp rate, will pave the way for further solar penetration into the California grid and help to better manage the fluctuations caused by distributed energy resources (DER). These new functions have a stabilizing effect on the grid as more DER is added to it. Fronius has always been a driving force when it comes to inverters’ Grid Support Functions and has years of experience from highly solar-penetrated markets such as Germany or Italy.

Fronius is currently shipping Rule 21 compliant residential inverters (the Fronius Primo 3.8-8.2 kW) and commercial inverters (the Fronius Symo 10.0 – 24.0 480V). Beginning November 6, 2017, the Fronius Primo 10-15 kW and the Fronius Symo 208V models will also ship with Rule 21 compliance. For more information on ordering your Rule 21 compliant smart inverter, please contact your local Fronius distributor.

— Solar Builder magazine

On the Scene: We went to the Eaton Experience Center to see the grid’s future

Eaton Xperience center

Eaton is one of those companies that does everything without you realizing it, with innovations for industries as diverse as aviation, data centers, food and beverage, rail and, of course, utilities, just to name a few. The company recently expanded its Experience Center in Pittsburgh to show the latest advances in electrical power quality, energy management and safety in a real-world, hands-on setting for interested customers, electrical contractors, consultants and builders in need of training.

In other words, it is a playground for engineers. Everything around the building, except maybe the coffee maker, is labeled, which isn’t just useful for novices like me.

eaton experience center“We’ve had engineers come in here and we’ve asked them to identify a transformer, and they couldn’t do it. They could easily point to the symbol on a design, but they don’t always see them in real life,” noted Dan Carnovale, Power Systems Experience Center manager for Eaton, which again shows the practicality and importance of the Experience Center.

The Solar Builder team stopped by to take it all in, and believe me, it was a lot to take in. Full disclosure: I was showed a lot of stuff and took a lot of notes as fast as I could. That notepad contains in-depth info on super capacitors that aid in solar smoothing, substation vs. pad-mounted transformers, balancing voltage regulation on a larger scale, aggregating string inverters in larger applications and more. The formula for cold fusion might be in there somewhere, but we will never know because they are illegible and incoherent. But that’s OK because the Experience Center isn’t about relaying those details, it’s about the experience, duh.

chris crowell at eatonExperiencing the Experience

The facility includes a functioning microgrid demonstration. There is a 24-kW solar canopy in the parking lot, 86 panels on the roof, 30 kWh in battery storage and a 100-kW generator, all of which are controlled by Eaton’s Power Xpert Energy Optimizer controller. The intersection of all those assets and optimizing their usage is at the core of advancing energy resiliency, so that Eaton’s Experience Center can operate even when the local utility grid may be impacted by an outage.

The standout display plays out two fault scenarios on a small grid that involves three local controllers and one master controller: You enter into an artificial neighborhood, complete with fake squirrels in fake trees. Suddenly, the room gets dark, a thunder rumble is heard and lightning strikes a tree that topples into an electric pole.

Scenario one plays out with no automation. The fault is triggered and the recloser fires and keeps closing, but power won’t be restored until a truck is rolled. Scenario two plays out with automation and is able to isolate the fault and restore power to the critical loads on the microgrid downstream.

Trust me, it was cool.

Animatronic show aside, it feels like we are looking at the future of the grid, not just in terms of the technology, but the mindset needed for deploying and managing distributed energy resources in ways that are much more efficient and economical than how things are done today.

— Solar Builder magazine

How OMRON reduces solar module PID potential through its inverter topology

omron inverter PID reduction

Potential induced degradation (PID) of a solar module — you know it, and you hate it. We met with string inverter manufacturer OMRON at Solar Power International, which claimed its inverter can actually prevent PV degradation from PID.

They explained it like this: Grounding module frames causes a voltage difference between the frames and the cells, which causes mobile ions to migrate to and from cells. Positive sodium ions contained in the module glass can then migrate toward the cells and crystalline defects known as stacking faults permit the ingression of these sodium atoms in the PV cells. This results in short circuits that are symptomatic of PID. There are PID reduction boxes that can reverse this effect, but OMRON wants to simplify that and eliminate problems caused by module duds.

The answer is in its ZCC inverter topology, which introduces a DC virtual link that allows transformerless string inverters to connect the negative pole to the AC neutral. Ta-da.

The Ultimate SPI Showcase: Here’s what to see at Solar Power International 2017

— Solar Builder magazine