Grid Integration Made Easy

Darren Hammell

By reducing the cost per kilowatt-hour of solar electricity, the DRI has the potential to help overcome a major barrier to widespread deployment. But Princeton Power Systems’ Darren Hammell sees the greatest market-shifting potential in some of the DRI’s advanced grid applications.


Barely out of college and running an engineering startup in the early 2000s, Darren Hammell and his cofounders at New Jersey-based Princeton Power Systems had a vision for making intermittent renewable energy systems more valuable to utilities and their customers. They would integrate the high-power electrical circuit technology they had used to bring power conversion to naval ships into a low-cost, turn-key demand-response inverter (DRI) system incorporating energy storage and load control. No longer would commercial-scale photovoltaic (PV) and wind systems require extensive engineering and expense to deliver utilities predictable, controllable power. But Princeton Power would need serious capital to develop a prototype and the materials that would help reduce the system’s cost and size — an enterprise unlikely to attract investors. That’s where the brainchild of Sandia National Laboratories’ Ward Bower came in.

In the mid-’90s, years before the Princeton Power founders began focusing on the DRI, Distinguished Member of the Technical Staff Bower was pitching the U.S. Department of Energy (DOE) a program aimed at making PV more useful on the grid. Bower designed San- dia’s original PV inverter test facility back in the 1970s and later patented an AC PV building block concept that integrates with microinverters to deliver a complete PV system. He had long believed the industry needed to deliver communications-integrated systems that enable utilities and their customers to take advantage of power conditioning, load shifting, demand response, interactive controls and other value-added features. “We weren’t interested in evolutionary — we wanted revolutionary changes” with the SEGIS program, he said.

Industry technology and the market finally aligned in 2007, when DOE launched the Solar Energy Grid Integration Systems (SEGIS) program with funds administered through Sandia. Over the course of the three-year-program, DOE and Princeton Power will have invested more than $9 million to develop the DRI. In addition, Sandia provided technical support, reviewing SEGIS participants’ proposals and progress, providing early-stage testing and then testing prototypes for both legacy and smart-grid applications. All of the SEGIS participants partnered with electric utilities, communications and other system-related technology experts during the program.

Inside the DRI

Princeton Power System’s demand-response inverter (DRI) integrates a photovoltaic array, energy storage bank, backup generator and electric grid connection into one system — providing simultaneous control of each of these components through one programmable interface. A DRI system can provide sophisticated services, such as peak power limiting, power factor correction and demand response, automatically to the electric grid operator. It can also operate as a secure “microgrid” with no grid connection at all. The DRI provides these functions in a turnkey solution for various configurations at the commercial scale (100 kilowatts and larger), an effort that otherwise requires custom integration of multiple components.


According to Princeton Power Systems’ Darren Hammell,“What we tried to do with the DRI is make it a real turnkey, one-box solution that arrives on site and is flexible enough to allow multiple different kinds of systems and configurations, but it only requires you to change a couple of software parameters.”

By delivering predictable, controllable power output, the Dri makes renewables interchangeable with conventional energy sources. Then the solar or wind system “could almost be thought of like a peaking plant, as opposed to, frankly, as a nuisance, as some utilities see it.”

As it concludes this fall, SEGIS will have invested more than $20 million in matching funds to SEGIS participants. Along with Princeton Power, the final participants include Petra Solar, PV Powered and a collaboration of the Florida Solar Energy Center and SatCon Technology Corp. These companies are part of a coming wave of smart grid-compatible inverters that promise game-changing benefits for large-scale renewable energy. Princeton Power’s R&D 100 Award-winning DRI exemplifies the promise of these breakthroughs.

Delivering Plug-and-Play Load Control

The heart of the DRI goes back 10 years to a Princeton University dorm room, according to Hammell, Princeton Power’s executive vice president of business development. There, he and engineering classmate Mark Hoveck looked for industry applications for an electrical circuit technology developed at Princeton. When their business plan for industrial power-conversion systems won first place in the Princeton University Business Plan Contest, associated with Ed Zschau’s high-tech entrepreneur class, their senior year, Zschau helped them refine the plan and win startup financing. Zschau is now chairman of the company’s board. It didn’t take long for the growing company to see opportunities in solar and wind, Hammell said.

“The way the electric grid is set up and a lot of the ways that subsidy programs are set up, these technologies are just dumping electric power onto the grid in a way that’s not really valuable,”explained Hammell. “It’s not really allowing solar to be a replacement for more conventional energy sources.”

The first inverters Princeton Power developed enabled PV systems to operate in off-grid mode. As the price and performance of batteries have improved, the company saw an opportunity to marry the technology with a commercial-scale PV system and grid communications in a plug-and-play solution. Through bidirectional control software and communications, the electric utility can access information about and control the system as needed. Princeton Power developed advanced materials to help improve the inverter’s efficiency and significantly reduce its size and cost.

Said Hammell, “What we tried to do with the DRI is make it a real turnkey, one-box solution that arrives on site and is flexible enough to allow multiple different kinds of systems and configurations, but it only requires you to change a couple of software parameters.” The system can operate in modes for distributed generation (basic operations), demand response, power factor correction or stand-alone/emergency. (See “Inside the DRI.”)

By reducing the cost per kilowatt-hour of solar electricity, the DRI has the potential to help overcome a major barrier to widespread deployment. But Hammell sees the greatest market- shifting potential in some of the DRI’s advanced grid applications.

The device has tremendous promise to help utilities better integrate renewable energy on the grid. As electric vehicles draw greater amounts of grid power, Hammell believes utilities will see value in the DRI’s ability to deploy point-of-use storage to enable PV system sizing that better matches the local load, thereby minimizing infrastructure upgrades. In addition, utilities are interested in the DRI’s advanced grid services that, by delivering predictable power output, make solar and wind interchangeable with conventional energy sources. For the utility, Hammell said, the system “could almost be thought of like a peaking plant, like a natural gas generator, as opposed to, frankly, as a nuisance, as some utilities see it.” Princeton Power is working with utility Public Service Electric and Gas (PSE&G) and other utilities on this type of arrangement.

Ward Bower“We weren’t interested in evolutionary — we wanted revolutionary changes.”
— Ward Bower, technical lead for the DOE’s SEGIS program, which helped fund the DRI concept

Yet another application is for cities and off-grid locations to install microgrids that will help them avoid the use of fossil fuel generators and the cost of extending distribution lines. The company is working on a microgrid with Alcatraz Island, in the San Francisco Bay, and has seen interest from the Caribbean, China, Asia and Africa.

Noting the prevailing business model for standard commercial-scale PV systems installed by power purchase agreement (PPA), Hammell sees an emerging demand for the DRI’s advanced functionality. “We’ve begun carving out a niche for ourselves for those rare customers that need something different, like, say, an Alcatraz Island — and we see that being the trend, that customers will start asking for that more and more,” he said. As this niche grows and large solar integrator/financers become interested, he added, Princeton Power may be a natural partner as the system designer and inverter manufacturer. With its expertise in balance of systems and experience in designing and installing full PV systems for several clients, the company is poised to take advantage of a range of market opportunities.

Working with Sandia and PSE&G, Princeton Power will demonstrate the DRI with a 200-kilowatt (kW) PV array it’s installing in Princeton this fall. It will include MX Solar USA panels, a 200-kW lithium ion battery bank from International Battery and grid-interface software from Viridity Energy. Princeton Power will finance and own the project.

“That system will have communications with PJM, our grid operator, so we’ll be able to provide services back to the utility,” Hammell said. “We’ll also be able to demonstrate for our customers and for the utilities some of the advanced features of batteries with solar systems combined, which is actually, at that size, that power level, pretty rare.” Delegates from Sandia and the New Jersey utilities will be on hand for some of the field-testing. After completing compliance testing early next year, the company plans to start manufacturing the DRI at its new facility in Princeton.

Changing the Way Utilities View PV

As Princeton Power and the other final SEGIS participants have progressed through the program, all four have experienced strong business growth. Princeton Power has doubled in facilities space and employees in the past few years, now at about 30,000 square feet (2,800 square meters) and 50 staff. It’s profitable, with revenues doubling every year for the past four, according to Hammell.

Like Princeton, the other participants will demonstrate their technologies with Sandia this fall. But SEGIS doesn’t end there. DOE has launched SEGIS Advanced Concepts (SEGIS- AC), with $10 million in funding to be awarded over three years. The SEGIS-AC request for proposals closed this spring. DOE expects to make awards by the end of 2011. Said Bower, “It will be the next exciting stage of SEGIS with increased focus on demonstrations of the advanced concepts.”

The new SEGIS funding is welcome news, according to Bower, because the development of grid-integration innovations like the DRI is crucial. As more utilities gain experience with systems having advanced communications and control, he sees utilities beginning to demand them. “In the last year and a half, they are now saying, ‘we want it, we demand that a PV system provide [intentional islanding support], low-voltage ride-through,’ this kind of thing,” Bower said. “So it’s been a real game-changer in terms of the way utilities are looking at connecting photovoltaic systems [and] possibly even other kinds of distributed generation — so that it’s a dispatchable source rather than an uncontrolled negative load.”

Access more information about Princeton Power and the DOE’s SEGIS program.

Gina R. Johnson is the editor/associate publisher at SOLAR TODAY.

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