Dominican Rebublic — Way back at the dawn of the “Electrical Age,” Westinghouse – based on discoveries made and technology invented by Nikola Tesla – famously won the fiercely fought competition with the Edison Electric Co. that resulted in the use of alternating current (AC) to transmit and distribute electricity to homes, businesses and public facilities, as well as other types of infrastructure. Tesla’s discovery of AC and invention of the first AC electricity generators were keystones that paved the way to building out our current centralized system of massive, fossil fuel-fired power plants and regional electricity grids. Now, with so much changing in the electricity industry, we are beginning to loop back and come around full circle.
Today, installation of distributed generation capacity fueled by the wind, sun and other clean, renewable energy resources continues to grow at an unprecedented pace. The electricity generated by wind and solar farms, fields and rooftops is DC electricity, which is often generated much nearer to where it’s used, if not right on-site. So why not use DC rather than AC electricity to the extent feasible?
Developing cost-effective all-DC microgrid technology installed “behind the meter” on customer sites is just what Robert Bosch LLC, a U.S. arm of Germany’s multinational engineering and electronics company Bosch, has been working on since 2012. Earlier this year, the California Energy Commission (CEC) awarded a Bosch-led project team a $2.8 million grant to install and “demonstrate a high-penetration, renewable-based microgrid” that relies entirely on DC electricity.”
Evaluating an All-DC Renewable Microgrid in California
Linking rooftop solar PV arrays to energy-efficient DC lighting, DC ventilation and DC energy storage systems on a 380-volt DC bus, Bosch’s Direct-Current Building-Scale Microgrid Platform “allows commercial buildings to become zero-net-energy users in a cost-effective manner,” according to the Bosch news release. “Once the project is installed and commissioned, performance data will be collected to validate the cost savings, energy efficiency gains and the capabilities of the advanced microgrid energy management system.”
“The project will directly enhance the technical understanding of how to integrate and optimize distributed renewable energy generation into the California distribution infrastructure, pave the way for introduction and large-scale adoption of cost-effective and energy-efficient DC power distribution architectures, and establish a complete supply chain for system integration through various partnerships,” the company said.
Added Oliver Steinig, VP of business development at Robert Bosch LLC: “We are confident the Bosch DC microgrid system will contribute to California’s carbon reduction and energy efficiency by increasing the reliability and utilization of distributed renewable energy and improving the energy efficiency of state-of-the-art technologies – such as LED lighting paired with advanced lighting controls, motors with variable frequency drives and energy storage systems – by operating them on DC power. This will reduce installation costs and lower operating costs, while increasing reliability and quality of the power provided to building loads.”
Along with innovative energy technologies from Imergy Power Systems and Maxwell Technologies, Bosch’s Direct-Current Building-Scale Microgrid Platform will be installed, demonstrated and evaluated over a nearly three-year period at an American Honda Motor Co. parts distribution center. The DC grid “will cover approximately 250 kW of loads,” according to Bosch’s Director of Business Development Sharmila Ravula, who declined to give any more details about the project specifics.
Pitching in to cover the costs of installing and assessing the DC renewable microgrid, CEC project partners are contributing an additional $1.8 million, mostly in the form of in-kind contributions of equipment, expertise and labor.
Shifting to DC microgrids could save significant amounts of electrical energy lost to heat in inverting DC to AC electricity. That translates into significant cost savings and/or returns on investment (ROI) for facilities across the private and public sectors. Retrofitting a facility with an all-DC microgrid could improve PV output by 7-10 percent and slash facilities’ energy bills by much more, it’s estimated. And that’s not all.
An Idea Whose Time Has Come?
Retrofitting facilities with all-DC microgrids could shave peak demand on utility grids, as well as enhance the resiliency of power supplies to failures and outages. It would also accelerate integration of distributed, local renewable energy generation assets, thereby reducing overall electricity consumption and generation. That would be a big step forward in U.S. and global efforts to reduce greenhouse gas (GHG) emissions, climate change and environmental degradation.
Deployment of all-DC microgrids coupled with local solar and renewable energy generation assets would also speed up development and commercialization of emerging demand response, smart grid and advanced energy storage solutions.
Though advances are coming quickly, commercially viable all-DC renewable microgrids are still in their infancy, Sharmila Ravula, a Robert Bosch LLC director of business development, explained.
“It depends on the facility, but if you look at some of the loads, electricity is quite a significant percentage of operating expenses,” Ravula pointed out. Retrofitting such facilities with DC renewable microgrids “could make a significant impact on [utility] customers’ electricity bills.”
It turns out it doesn’t take much to retrofit a commercial or industrial facility to take advantage of DC microrgrids, Ravula noted. “If you’re looking at any load at a commercial site, they’re typically using a standard 208-277-volt AC bus. All that can be very easily ported to operate on our 380-volt DC bus.”
Integrating On-site PV and Advanced Energy Storage in a DC Microgrid
Replacing AC with DC renewable microgrids offers environmental and social, as well as economic, advantages and benefits to electric utilities, as well as their customers and society, CEC DC microgrid project partners say.
At the American Honda parts distribution center in California, Bosch’s DC microgrid platform will manage and enhance solar electricity generation and power supplies by making use of Imergy Power Systems’ vanadium-flow batteries and Maxwell Technologies’ ultracapacitors. “The fluctuations in PV output power generally occur on a time-scale of seconds,” Maxwell Technologies’ Director of Business Development Dr. Kimberly McGrath said.
“In order to firm power output with energy storage, the energy storage source must be able to instantaneously respond to the fluctuation and then ride through the intermittency. Further, the energy storage source should have low- to zero-maintenance and have a lifetime that is at least as long as the PV system’s lifetime.”
Imergy points out that its vanadium-flow batteries likewise will imbue American Honda’s DC renewable microgrid demo with the ability to smooth out variability and intermittency of on-site solar power generation, as well as serve as a more efficient and cost-effective back-up power supply in the event of grid outages.
Just this week, SunEdison announced it is purchasing and will install more than 1,000 Imergy vanadium-flow batteries as it works to achieve a recently announced goal of deploying renewable microgrids a goal to bring power to 20 million people in rural India by 2020.
Like Maxwell’s ultracapacitors, Imergy’s vanadium-flow batteries are capable of responding rapidly to short-term fluctuations in power supply, voltage and frequency. They’re also inherently scalable, and they also have a lifetime of 20 years or more, with no need to replace the batteries’ electrolytes, Imergy COO Tim Hennessy said.
“If you shave peak demand from 4 to say 3 megawatts (MWs), you free up grid capacity,” and that, among other substantial benefits, is what combining on-site solar PV generation with Imergy’s vanadium-flow batteries affords utilities and their customers, Hennessy said.
“When you throw in DC bus-based highly efficient lighting, heating, cooling and ventilation, you can end up with some extremely attractive returns, especially in highly constrained markets such as those in California and New York.”
Lead image: Electricity. Credit: Shutterstock.