Marc Hoffman, CEO of startup Innovus Power, believes that the synchronous generator, the workhorse of the power grid for the past century, needs a makeover for the green-powered future.

Sure, power turbines that run at a fixed speed -- 60 hertz, or cycles per second, in the U.S. -- have served the grid well to date. But the increase in wind and solar power, which rise and fall with the weather, and uses inverters to turn direct current into grid-ready alternating current, presents them with a serious set of challenges.

These include low efficiency when they’re forced to ramp up and down to match fluctuations in renewable energy, with some strict limits on how low they can go before they need to be shut off entirely. Beyond that, fixed-speed generators have problems maintaining stable frequency under those circumstances, Hoffman said during a presentation at last month’s Grid Edge Live conference in San Diego.

For microgrids that run diesel generators to back up renewable energy, these problems can add up to rocketing fuel costs, excessive wear and tear, and the need to significantly oversize generators to cover relatively rare moments of fluctuating load, he said. For the grid at large, it could place strict limitations on how much renewable energy can be integrated before the need arises for excessive amounts of fossil-fuel-fired power plants, or expensive batteries, to back it up.

Innovus Power’s variable speed genset could solve those problems in one neat package, Hoffman believes. Developed over a decade of work in the marine engine and off-grid power space, the 600-kilowatt units combine a high-efficiency engine from Rolls Royce-owned manufacturer MTU, a permanent magnet-based generator from Finnish company Axco, and an AC-DC-AC power converter from wind turbine maker Northern Power Systems.

“We start by taking a generator and allowing it to run proportional to the load,” Hoffman said during his Grid Edge Live presentation. The unit’s engine has more flexibility than a traditional fixed-speed generator, he said. Then, that flexibility is expanded by the power conversion system, which provides a clean and stable source of alternating current.

The result, Hoffman told me in an interview, is a system that should cost less and work better than diesel-backed generators or lots of battery storage for the microgrid market, which GTM Research has estimated will grow to a cumulative $3.5 billion in the United States by decade's end. In the longer run, it could also serve the needs of utilities seeking a flexible, yet scalable, solution to integrating an ever-growing share of renewables on their grids.

“You may look at our platform on the surface and say that it’s more complex at the micro level -- and yes, it is,” he said. “But by solving what we think are the most important issues at the micro level, it then makes everything beyond it much simpler.”

Building a variable-speed generator where others have failed

Variable-speed generators have been out there for decades, but they’ve struggled with key technical and engineering challenges. “There are a lot of companies that have tried to do what we’re doing and have failed," said Hoffman.

But in the last decade or so, consistent advances in power electronics have allowed the kind of combination system that Innovus is building to start to approach commercial viability, he said.

Innovus’ technology comes from Glacier Bay, a maker of diesel-electric marine propulsion systems, which Hoffman led as CEO. About two dozen ships now run on Glacier Bay systems, but the company couldn’t make the business work due to the relatively small market opportunity.

Innovus has raised from $4 to $6 million from three unnamed investors, Hoffman said. They include two individuals he knew from his years working at General Electric and aircraft engine maker Allied Signal, as well as a third angel investor.

The company's executive team includes CTO Mark Preston, a veteran of Vestas, United Technologies and Northern Power Systems. It also includes Steve Levy, the VP of sales and business development, who previously held similar positions at aerospace giant Northrop Grumman and inverter maker Advanced Energy.

Innovus is looking to maintain high fuel efficiency and the constant delivery of clean and stable power while running at varying speeds. That allows the Innovus generator to run at lower than 30 percent capacity, a range that can only be accomplished with a steep sacrifice of efficiency by fixed-speed gensets.

“I don’t want to give too much away, but that’s in the know-how, that’s a big part of the secret sauce,” said Hoffman.

Innovus’ 600-kilowatt units are built to be stacked up to the megawatt scale, and come with a master control system that senses load. “That’s part of our IP, being able to detect load changes in a way that’s far more advanced than the way a synchronous generator would operate,” he said.

That should allow the system to integrate multiple power sources, whether they’re inverter-based renewable energy or battery storage systems or traditional spinning generators. With the benefit of the Northern Power Systems’ power converter, “the frequency coming out of it is perfectly stable, high-quality power -- whether I have 10 of them or 10,000 of them, I have positive contribution to my grid.”

At the same time, “I am balancing out the unevenness of my renewables -- and instead of transmitting these huge load changes from the clouds overhead, with all these big solar farms and everything else, I’m leveling everything out, and filling in the voids with a highly dispatchable system,” he said.

Testing against traditional battery-based options

All of these claims need to be backed up by real-world deployments, of course. Right now, Innovus is close to completing its first orders with one Alaska utility and another Australian project developer.

The Alaska customer is TDX Power, which has built a 1-megawatt wind farm and backup diesel generator array for the Aleutian Islands town of Sand Point, which has a 700-kilowatt peak demand. That’s forced TDX to curtail its wind production to as low as 20 percent of capacity at times.

According to an analysis using modeling tools from microgrid consulting firm Homer Energy, Innovus should be able to allow that wind capacity to be used for both electricity and additional uses like heating (noted as "dump power" on the chart below), while saving about 450,000 liters of fuel per year -- a significant cost reduction for an island that must import all of its fuel

In Australia, off-grid project development company EMC is looking at using the Innovus system to back up truck stops, mining operations and other remote locations where grid electricity is either very costly or simply unavailable. Unlike remote islands, diesel costs in mainland Australia are low enough to make a renewables-plus-batteries microgrid uneconomical --- but not so low that the advantages of a flexible generator wouldn’t pay off, said Jamie Ally, director at EMC.

“There’s a lot of work happening off the grid in Australia, most of it diesel-fired,” he said. Mining companies pay roughly 70 cents per liter of diesel fuel, but often have to over-size their fixed-speed generator fleets to meet rare peaks in demand, which leaves much of that fleet sitting idle most of the time. Bringing in solar and wind power could offset those costs, but not without a certain amount of energy storage in the form of expensive lithium-ion batteries.

“The Innovus genset is going to allow us to achieve a very high renewable penetration without a very large battery,” he said. According to his analysis, the levelized cost of energy of a Western Australian microgrid system using an Innovus genset comes to 25 cents per kilowatt-hour, compared to 29 cents per kilowatt-hour for one using fixed-speed generators.

Beyond that, Innovus has a “technology pathway that looks at coupling renewables into their system in the future,” he said. “Because they have a DC bus in their genset, you could connect PV arrays and batteries on the DC bus.” That, in turn, “would allow you to eliminate all those inverters, and just use the inverter that comes with the Innovus generator, because it’s the same size as the system anyway. That’s a pretty attractive technology pathway and R&D pathway.” 

Hoffman noted that this capability to link multiple DC generation sources into a single Innovus DC bus could lend an additional level of simplification to microgrid operators seeking the flexibility to grow with the times. The call isn’t just coming from off-grid realms, he added.

“We have one very large utility in Asia that’s now very interested in running some pilot systems,” said Ally. “What they’re concerned about is load defection -- industrial and commercial customers seeing rising costs, and creating their own generation.” 

One might argue that combining batteries with green power is a more environmentally friendly alternative, since it doesn’t imply any burning of fossil fuels. But pure battery systems still have a hard time penciling out in all but the most expensive fossil fuel markets. 

Even if batteries get to the point where the round trip is more cost-effective than burning fossil fuel, “that’s great” for Innovus, Hoffman said. “We’d still say, dispatch it when it’s there. But it’s in storage’s best interest to have fossil fuel, or a fuel cell, or some dispatchable power source beyond your storage.”