No one ever said changing the world is simple. Below are some terms and questions that we frequently encounter when discussing microgrids and GridLink, our innovative technology.
The Department of Energy (DOE) defines a microgrid as: "A group of interconnected loads and distributed energy resources (DER) with clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid [and can] connect and disconnect from the grid to enable it to operate in both grid- connected or island mode."
The DOE also considers a microgrid to have four key attributes:1. Grouping of interconnected loads and distributed energy resources
We concur with the DOE's description of a microgrid. In fact, we go one step further in regards to attribute #2: we believe that an effective microgrid cannot require a blackstart, which is one of the disadvantages of a synchronous interconnection with the grid. GridLink, on the other hand, uses a non-synchronous approach to seamlessly interconnect with the grid. No blackstart required.
GridLink is a patented technology for connecting distributed energy resources (generation that is on-site) with a larger grid (i.e. a utility's distribution grid). The common application of GridLink is as the heart and brains of a microgrid. GridLink is an innovative configuration of off-the-shelf, commercially-available power electronics equipment that is packaged into an eHouse. Its core consists of large inverters commonly used in the wind power industry to bring each power source in individually, combine these sources onto a single DC bus, and convert the combined power flows into a single AC current. GridLink also utilizes an active rectifier front-end. Unlike traditional “synchronous” interconnection approaches, GridLink integrates power flows “non-synchronously” and completely separates the voltage, frequency, and phase angle of each power source, including that of the utility grid. As such, generators never synchronize to the grid, and the grid remains completely isolated from other generation sources—it never “sees” the generators running behind GridLink. This eliminates the “interconnection issue” that has been the largest technical barrier to large-scale distributed generation development.
The power grid was built to facilitate one-way power flows from large power producers to end-users. In 1978, groundbreaking legislation was enacted that required utility companies to purchase energy from small-scale generators. Since then, utilities have increasingly added more generation going the other way, from the end users to the rest of the grid. To connect on-site generators to the grid, power systems engineers have typically “synchronized” the generators to the utility grid. When the generators are large and at a weaker part of the grid, synchronization can create grid instabilities (namely voltage instabilities and fault current contributions) that are dangerous to line workers and expensive to support through substation upgrades. These issues have been costly to remedy, requiring substantial investments of time and capital, making potential microgrid projects a good, but economically unfeasible idea. We believe GridLink can change this economic and operational paradigm. GridLink technology resolves longstanding grid connectivity issues. GridLink enables utilities and grid operators to seamlessly “island” and safely and affordably comingle on-site distributed power with the central grid. We believe GridLink can become the national standard for connecting local, on-site micro power systems to the grid. Consolidated Edison (New York), PEPCO (DC, Maryland, Delaware, New Jersey) and Northeast Utilities (Connecticut, Massachusetts) have all determined that the GridLink approach separates on-site generation from the grid to such an extent that the generators will not cause these problems for the utility.
Example I: A large university campus in the northeast US has high power costs, power outages that too frequently leaves their students in the dark and endanger valuable research, and a commitment to lower its carbon footprint. They have rooftop solar panels on two buildings on opposite sides of the campus, and they would like to develop new research opportunities in their electrical engineering program. They have old boiler systems that were installed when the baby boom generation went to college and now have to replace the old boilers (deferred maintenance). Their utility company is apprehensive about continuously adding new on-site generation to an aging system that was not built to accommodate power flows from the end-user to the grid. They decide to build a Pareto Energy non-synchronous microgrid. We can integrate all the existing distributed energy resources (DER) using GridLink. We install a 10MW combined heat and power (CHP) system in a vacant lot on-campus. Solar stays on the roof of the student center, their existing wind spires at the edge of campus continue to generate power, and their backup diesel generators remain in the parking lot behind the gymnasium. We strategically position three GridLink eHouses near these generators, and integrate them with grid power and the new CHP plant. Because the grid is integrated 24/7, they have no reliability issues (one blackout every 5 years). They can add more DER to meet their carbon footprint goals without the high costs because they don’t have to interconnect to the grid.
Unlike synchronous interconnection technologies that take years to permit with utility companies and cost thousands of dollars per KW to implement, GridLink has gained utility approvals within several months at costs of less than $1 per watt.
Each microgrid can be custom designed for the generators, load, and incoming utility as required. As a result, the substation now simply sees a reduced load, not the connected generators. Consequently, the voltage, frequency, and phase angle of the utility grid and the customer-owned distributed generation are completely isolated from one another. This allows for distributed generation to plug-and-play anywhere in the grid without the complications of a synchronous generator interconnection. Additionally, the distributed generators run more efficiently at variable speeds, which they cannot do if they have to be synchronized to the utility grid.
Electricity is passed around the grid in the form of alternating current (AC). AC has a sinusoidal waveform. In the past, the waveform of the distributed generation source had to be synchronized with the waveform of the utility grid. The rotation of a synchronized generator creates an output with the grid’s frequency. In essence, a synchronous interconnection creates a tightly coupled relationship between DG and the central grid. Utility approvals and custom engineering and controls to synchronize can be very expensive and take several years to complete. Furthermore, the dependencies created by synchronization sub-optimizes the operation of distributed generators. We developed GridLink as a non-synchronous interconnection technology to address the specific challenges presented by a synchronous approach. Instead of making waveforms play nicely, we use AC-to-DC-to-AC power converters and an active rectifier front-end. The voltage, frequency, and phase angle of the distributed generator and the utility grid never touch. Onsite operators can throttle the distributed generator for local demand, equipment longevity, and financial considerations without limitation by the distribution grid. By creating a layer of abstraction between the utility grid and the distributed generator, GridLink provides both parties essential design flexibility and the autonomy to optimize their assets. We believe that an effective microgrid cannot require a blackstart, which is one of the disadvantages of a synchronous interconnection with the grid. By contrast, GridLink uses a non-synchronous approach to seamlessly connect or disconnect from the grid. No blackstart required.
An “Electric House”, or “Energy House”, or “eHouse” is a standard term for a shipping container-sized unit that stores the microgrid control equipment (GridLink). They are used for systems that are non-microgrid related and are assembled in the U.S. mostly in Houston. They measure approximately 8’ X 8’ X 14’ feet. eHouses are used as exterior housing unit for the power electronics on military bases, ship yards, oil rigs, etc.
A black start is the process of restoring a power station to operation without relying on external power sources. Black starts can involve significant risks both to the electrical grid and the business (such as operational downtime), and as such, must be carefully managed and executed.
A microgrid or distributed generator operating in island mode means it is operating in isolation from the distribution grid.
Distributed generation (DG) refers to power generation at the point of consumption (i.e. on-site power).