The Digital Microgrid Initiative P.B.C. (DMI), is a public benefit corporation organized to provide clean, reliable and inexpensive electric power to remote areas where grid power is unreliable or non-existent. All profits are reinvested to provide more cost-effective solutions to further the company’s mission of providing clean, low-cost electric power where the need is greatest. The first Digital Microgrid products will be shipped in June and will include a highly modular family of off-grid solar energy systems with a starting price of under $5,000.
DMI’s next move is to make its residential battery management system (BMS) available to battery manufacturers and others under an MIT Open Source License. The BMS hardware is used as a building block providing safety and longevity for batteries in residential energy storage applications. DMI’s hardware is designed to handle a variety of battery chemistries. Within DMI’s solar power systems, batteries of various capacities and characteristics can be mixed to allow simple expansion and system growth to megawatt and megawatt-hour capacity.
Co-President Gene Krzywinski describes why DMI is sharing it’s technology: “Unlike other home appliances, residential grid independence is still dependent on proprietary solutions. We want replacing batteries in home energy storage to be as simple as putting an AA cell in your TV remote.”
Bill Southworth, DMI co-President, describes the market need: “All residential solar power in the future will live hand-in-hand with residential energy storage. Independent solar installers will continue and expand their role as the main retail provider of home solar. As the solar market continues to expand while net metering declines, the majority of new homes and apartments will incorporate solar independence into their construction. We all need simpler and more standardized solutions.”
Inside the system
For battery manufacturers and equipment developers interested in the Open Source program as well as other cooperation on standards, DMI will publish schematics, materials list, API specifications, PC layout and fabrication (Gerber) files. The 80×120 mm BMS is isolated for use in high voltage packs and will manage LiFePO4, lithium titanate (LTO), AGM, and NMC packs. Multiple BMS cards may be used with multiple 48 volt packs in a single high voltage battery. The BMS cards jointly report cell state-of-charge and provide cell balancing on each cell in the battery. A published API is provided describing the communication protocol. The BMS cards are programmed for maximum and minimum cell voltage, but can also be used with sophisticated learning systems for SOC optimization in a dynamic environment such as residential solar. In the DMI system, each battery has its own 8 kW charge/discharge controller and an unlimited number of batteries can be used on a 380 volt bus for megawatt level solutions.
— Solar Builder magazine