Wednesday, May 31, 2023

How a Single Device Helps EVs Provide Cost-Effective Backup Power to Homes

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The Smart Power Integrated Node (SPIN) delivers backup power along with cost savings and grid support in one small box

In the summer of 2020, California’s grid strained to keep up with demand for electricity during a scorching heat wave. In August of that year, rolling outages impacting hundreds of thousands of customers were initiated because not enough capacity was available to keep up with demand. The outages triggered the California Independent System Operator (CAISO), the California Public Utilities Commission (PUC), and the California Energy Commission (CEC) to issue a joint root cause analysis that found that extreme weather, market practices, and resource adequacy and planning processes combined to necessitate the power shutoffs.

At the individual household level, however, the experience of rolling blackouts and the potential for more triggered many people to investigate the potential for energy storage to provide backup power during outages. “What people are doing if they already have solar on the roof is to start to install storage,” said Sunil Chhaya, an EPRI senior technology executive who leads electric vehicle (EV) and energy system integration efforts. “Solar companies do it now, and an income tax credit incentivizes it. So, when the lights go out, you can automatically switch over to storage.”

Pairing rooftop solar with energy storage is a practical and reliable solution to deliver backup power during infrequent grid outages. But it’s also a pricey solution that is well outside of the financial reach of many. For example, a typical behind-the-meter energy storage unit that provides about 10 kilowatt-hours of capacity – enough to deliver two to three hours of backup power to the typical home – costs about $15,000 to install.

But there’s another potential backup power solution that may already be available to Californians and other Americans: the EV sitting in their driveway. “There are a lot more people who have EVs than have storage,” Chhaya said. “So, the question is this: can we use EV batteries that have 60, 80, or 100 kilowatt-hours and have already been paid for to provide backup power to the home?”

A New SPIN on Bidirectional Charging

EV batteries provide backup power

There is no lack of research and discussion today about the future potential of EV batteries to provide backup power. But there are not yet any commercially available bidirectional chargers able to take electricity out of an EV battery and use it to provide backup power directly to a building. “Today, you can find vehicle-to-grid technology that only works when the grid is on,” Chhaya said. “It doesn’t work when the grid is off, and it only sends power from the vehicle to the grid, not to the home where it’s needed.”

But there is another potential solution for both tapping EV batteries for backup power and enabling EV owners to earn revenue for providing grid services and helping utilities reduce their peak load. Since 2016, EPRI has worked with Flex Power Control on developing and testing the Smart Power Integrated Node, or SPIN. SPIN is a single device with the intelligence to automatically manage a business or household’s solar, EV, and stationary storage assets to achieve the building owner’s priorities. For example, SPIN can automatically sense a power outage, instantly provide backup power, and send power back to the grid.

Each SPIN includes multi-port bidirectional inverters that connect both to the grid and to a home or business’s solar, EV, and storage units. Each device also has a power routing matrix comprising multiple switches that connect each of the DERs and the grid in multiple configurations. Importantly, SPIN also has a brain in the form of control and coordination software that optimizes how each asset operates in grid-tied and standalone modes. Initially supported with EPRI Technology Innovation (TI) funding, SPIN has since received funding from the U.S. Department of Energy (DOE), the California Energy Commission (CEC), and the National Renewable Energy Laboratory (NREL).

For example, DOE funding supported the initial prototype development using commonly available electronic components. After demonstrating its ability to control power flow, Flex Power Control built a more sophisticated prototype that was then tested at DOE’s Oak Ridge National Laboratory. There, the device was able to perform fast EV charging, dispatch an EV battery’s electricity to the grid, and deliver backup power during an outage using rooftop solar and EV batteries.

Over the course of numerous projects with EPRI, DOE, and other researchers, SPIN has repeatedly demonstrated its functionality, including support for the grid. For example, in one study, the University of Kentucky researchers simulated a feeder with 70 houses. Each of the simulated houses included a 7-kilowatt solar system, a 10-kilowatt-hour energy storage system, an EV charger, and a SPIN to manage the DERs. SPIN was able to reduce the feeder’s peak load by 42 percent. “Our initial challenge was to develop the technology, improve it, and show that it works and delivers value,” said Greg Smith, a founder of Flex Power Control, who formerly worked as an engineer at General Motors. “We have proven the technology works and shown the potential value proposition.”

How SPIN Provides Backup Power With Minimal EV Battery Impacts

EPRI summarized the research results funded by DOE and the CEC in the report Battery Performance Assessment of Vehicle-to-Grid Capable Electric Vehicles: Testing Methodology and Experimental Results. Among other things, the report confirms SPIN’s ability to deliver backup power from an EV battery. The report also quantifies how much battery degradation would result when the battery powered an EV and was used in a home.

To do that, researchers at NREL tested two 17-kilowatt-hour battery packs made by LG Chem that are used in Pacifica plug-in hybrid minivans. One of the batteries was charged and discharged three times each day for over 12 months to simulate an EV used for driving and delivering energy to a home. That translated into about 11.7 kilowatt-hours for transportation and 5 kilowatt-hours to the building. To compare the degradation impact of those vehicle-to-building discharges, the second battery was cycled an equal number of times daily for the same duration of time. But its discharges only simulated what was needed for driving.

By cycling the batteries three times per day, the NREL researchers were able to collect data representing about four years of operation. The test results showed that using the EV battery for typical driving and vehicle-to-building discharge had a small impact on battery degradation. For instance, the battery that provided energy for driving and a building had about 90 percent of its original capacity at the end of the testing period; by comparison, the driving-only battery had about 95 percent of its original capacity. Using these degradation rates, the researchers concluded that over 10 years, the driving-only battery would retain 82 percent of its original capacity. In contrast, the battery pulling double duty would have 77 percent of its capacity.

Benefits Beyond Backup Power

Clearly, an EV battery won’t be called on daily to provide backup power to a home as power outages remain rare. But testing the battery as if it was being dispatched from the vehicle to a building daily also provided insights about the ability of a SPIN-managed EV to deliver additional benefits.

For example, the soon-to-be-published EPRI report includes an analysis of the potential bill savings that could come from using SPIN to shift EV charging to times when electricity rates are lowest. The potential annual bill savings for a residential customer were estimated to be almost $1200. Commercial customers using SPIN to manage charging could save over $2000 annually from lower energy costs and avoided demand charges.

The report also detailed a range of other utility, grid, and societal benefits EVs managed by SPIN can deliver. For example, 200 EVs equipped with bidirectional charging could reduce annual peak load by 750 kilowatts. By assuming an avoided cost of infrastructure of $25 per kilowatt, that would result in savings of more than $280,000 over 15 years.

Large numbers of EVs with bidirectional charging capabilities could also substantially reduce the amount of renewable energy that must be curtailed. According to EPRI, about 1500 gigawatt-hours of renewables were curtailed in 2020. But if 500,000 EVs were to charge when electricity prices are low in the late morning and late night and then discharge when demand and prices are high in the early morning and late afternoon, the curtailment would be far lower. According to EPRI’s analysis, 332 gigawatt-hours would not need to be curtailed. A bill recently introduced to the California state legislature would mandate that all EVs sold in the state be bidirectional capable by model year 2027.

For utility customers – particularly those that have already purchased an EV and solar – integrating SPIN also promises to dramatically reduce the costs associated with securing backup power. By eliminating the need to install stationary storage and an inverter, SPIN can eliminate the $15,000 needed to purchase a 10-kilowatt-hour battery. In addition, with SPIN, there is no need for either a $1750 solar PV inverter or an EV charger. According to the EPRI report, these components cost $28,000, compared to the $7000 to purchase and install SPIN. EPRI will be publishing three more SPIN-related research papers in the next year.

The Road Ahead

Sunil Chhaya has been deeply involved in helping SPIN move through the many development and testing stages over the past seven years. He believes the device is ready to begin delivering benefits to utility customers, utilities, and the grid. “This is one step away from large-scale deployment,” Chhaya said. “That’s because it’s a no-brainer. It removes a lot of hardware from the house needed for DERs. Especially for new construction, it’s a no-brainer because you would just need to put it in as part of the electric panel.”

For SPIN to move towards the large deployment Chhaya envisions, the next step is to receive Underwriters Laboratories (UL) certification. UL certification is expensive, and Flex Power Control is currently seeking funding to achieve certification. “Certification is really about starting a production line because for certification to occur, it’s done with the products you are actually going to produce,” Smith said. “It’s really a product launch.”

Flex Power Control

Flex Power Control now has two versions of SPIN to simplify and speed up the certification and production process. The initial focus will be on the SPIN-EVO, a bidirectional charger that can provide backup power to a home during outages. For homes already equipped with PV or storage backup, EVO adds the EV backup component only. Its addition is akin to a retrofit.

The second version, SPIN-MPX, is a bidirectional charger but also integrates inverters for solar, stationary storage, and the EV and manages all the assets according to a customer’s priorities. The SPIN-MPX is more suitable for new construction or new installations because it removes the need for duplicative hardware and complexity. Instead of a separate EV charger and solar and storage inverter, new installations only require a single SPIN-MPX. Once certification is secured, Smith says SPIN devices will be available to customers through a distributor able to install and service the device.

As Flex Power Control continues to pursue the funding needed to become UL certified, the company is also actively pursuing opportunities to collaborate with utilities on pilot projects. One of the main reasons to engage with utilities is to elevate awareness about how SPIN functions and what benefits it can provide. “We want to get people to experience it so that they know it is what we say it is,” Smith said. “We would first want to work with utilities in their own lab because we think it’s important for them to get comfortable with it. Then we would want to do a field pilot with a limited number of customers to help determine the best use for the device at their location.”

EPRI Technical Expert:

Sunil M. Chhaya, PhD
For more information, contact