The digital grid: technology to make the grid smart
Portland General Electric lithium ion battery system
The digital grid, also known as the smart grid, has created quite a buzz in recent years.
No one designed the current grid. It is a patchwork of different parts that merged together as electrical service became more widespread. After nearly everyone had electrical service, regulators and the industry attempted to impose some order on it.
It has served us well, but it is vulnerable to massive disruption. It is vulnerable to large-scale blackouts and a tempting target for terrorists. The rise of renewable energy has subjected it to new strains.
New battery technology is beginning to store electricity to help integrate renewables with the grid. The idea of microgrids allows local areas to operate independently of each other. That way, they can insulate themselves from power failures that occur elsewhere.
Digital grid technology promises to combine these and other innovations to create a system more responsive and resilient than we have ever known.
The grid as it exists now
A transmission substation on the electrical grid.
The electric grid in the US and Canada comprises all generation, transmission, and distribution of electricity. It amounts to the biggest single machine in the world.
Physically and administratively, it is divided into three “interconnects.” The Eastern interconnect serves the eastern two thirds of the two countries and the Western interconnect serves most of the rest of them. The exception, Texas, has its own interconnect.
They all operate at 60 Hz, but they’re not in phase with each other. Each one is joined to both neighbors with direct current links in order to convert from one phase to another.
Before the 1990s, all electric service was delivered by regulated monopolies that performed all three major functions. They had little need for long-range connections but could use them to guard against sudden power loss.
Deregulation
The 1990s saw a wave of deregulation, or at least a new regulatory philosophy. The Energy Policy Act of 1992 allowed, and in practice sometimes compelled the separation of power generation from transmission and distribution. Generating companies sold to multiple transmission/distribution companies, and transmission/distribution companies bought from multiple generating companies.
As a result, long-range connections became more important. The physics of power transmission means that these longer distances require more complexity. Industry officials and other experts warned that the new regulatory conditions increased the likelihood of blackouts. The new rules ignored the physics of operating this large machine. It became more difficult to operate and control.
Electricity became a commodity that companies could trade. Enron and others cheated. They created artificial shortages and drove prices up. Too much of the grid operated too close to its capacity.
As a result, blackouts increased. Most spectacularly, a blackout started in Ohio in August 2003. It became a multi-state power outage from Michigan to Massachusetts, including parts of Ontario in little more than two hours.
An abundance of energy we cannot yet use effectively
Internal view of a solar inverter. Note the many large capacitors (blue cylinders), used to store energy briefly and improve the output waveform.
As the grid now exists, everyone must focus on how to use less energy at the same time development of technology demands consumption of more energy.
Power companies respond with strategies such as time-of-use pricing, which requires considerable administrative overhead. Both power companies and large-scale customers must devote excessive effort to keeping track of costs.
This situation can only get worse as long as we rely on fossil fuels and other consumables to produce electricity. Meanwhile, the sun and wind produce more power than the entire human race could ever capture or use.
Solar and wind technology continue to become both more efficient and less expensive. As energy storage technology improves, it will become possible for renewable energy to supply all the world’s energy needs even as we consume more and more of it.
As it is now, however, the grid cannot maintain stability if the penetration of renewable energy exceeds 30%. In many locations, grid capacity is saturated. Only by building new transmission lines can these areas keep up with the demands placed on the grid. This construction comes at great monetary and environmental cost, but it can provide only temporary relief.
Companies like Amazon can pay for renewable energy equal to the amount of energy they use. Renewable energy certificates provide a complicated and controversial way for them to claim to use green energy. But there is no way to trace where that energy goes. No one knows who actually gets to use it.
Digital grid technology
This is a basic representation of campus microgrids on an Air Force installation. Each campus has separate energy resources and both campuses are controlled by a master controller to island them and direct power within or between them.
Energy flows according to the laws of physics. It doesn’t go in a straight line or by the most efficient route. Current topography inefficiently makes electricity flow around mountains and lakes. The grid as it exists doesn’t allow tracing of the actual flow of energy. It enters and leaves the grid at millions of different points.
In principle, the digital grid routes electrical power analogous to the way the Internet routes data. Like the Internet, it uses addressable nodes and interconnectivity. The smart grid enables power to be traced and guards the grid against failure by making it more robust.
Where the existing grid relies on one-way network management, digital grid technology will allow two-way system operation.
For example, when owners plug their electric cars into a charging station, the digital grid can charge the battery or feed electricity from the cars to the grid as needed. A vehicle-to-grid communication standard already exists for that purpose.
Digital grid technology will segment the three large interconnects into smaller, independent units. As in the days before deregulation, energy transfers between these cells will be necessary occasionally, but not regularly. Constructing these new cells will not require construction of new infrastructure. It can happen gradually using existing transmission lines.
It will be possible to generate electricity closer to where it is consumed. ConEd has experimented with a “virtual power plant” in New York City. Along with its partners, it connected rooftop solar installations on 300 homes in Brooklyn and Queens and used cloud-based technology to allow energy to flow either to or from the grid as needed. Without this application of smart grid technology, it would have had to spend $1.2 billion to build a new substation.
ConEd has since created the position of vice president of distributed resource integration to follow up on this successful pilot. It’s not the digital grid yet, but it demonstrates the possibilities. The solar panels on those homes continue to operate in event of any kind of power failure.
Smart inverters
Example of a smart meter based on Open smart grid protocol (OSGP) in use in Europe that has the ability to reduce load, disconnect-reconnect remotely, and interface to gas and water meters
Besides microgrids and storage, the digital grid will need newly designed equipment, such as smart inverters.
Solar panels generate direct current. Our electrical gadgets require alternating current. To convert direct current to alternating current requires an inverter.
With conventional inverters, an entire installation of solar panels feeds into a central inverter. The panels are connected to each other in series.
Therefore, the entire array can produce only as much power as the weakest panel. If one has a manufacturing defect, is in the shade, or is dirty, it reduces the output performance of the entire system. Even if all the others are operating at peak capacity.
Conventional inverters also are available in few different power ratings. The panels’ rating must match the inverter’s. If the inverter has a higher rating than the panels, the system wastes inverter capacity. The system can only add more panels up to the rating of the central inverter unless it, too, is upgraded. Large central inverters require built-in cooling fans. The noise may be a problem for installations not in remote locations.
Smart inverters, on the other hand, are much smaller. Each panel has its own inverter, although sometimes two panels can share an inverter.
The panels are connected in parallel, not in series. If something adversely affects the performance of one panel, it doesn’t affect the others. It is possible to add more panels, even if they have a different power rating from existing panels. A smart inverter can match grid power at the level of a single panel. Being much smaller, it is not prone to overheat.
Smart inverters cost more than a conventional centralized inverter, but the price difference continues to shrink.
The digital grid will not appear overnight, but some jurisdictions have already started to require smart inverters. Other components of digital grid technology are also moving into place.
Sources:
2018: the year of the digital grid / Jennifer Delony, Renewable Energy World. December 27, 2017.
The future of solar system: the era of smart inverter technology is coming / Steve Huang, Medium. October 24, 2017
Pushed by REV, ConEd tests new utility business models in New York / Robert Walton, Utility Dive. April 3, 2017
What’s wrong with the electric grid? / Eric Lerner, Physics Today. August 14, 2014
What is the digital grid? / Digital Grid Consortium. [2010]
Photo credits:
Lithium battery system. Some rights reserved by Portland General Electric
Transmission substation. Public domain from Wikimedia Commons
Solar inverter. Public domain from Wikimedia Commons
Microgrid diagram. US Air Force photo illustration by Jeff Pendleton
Smart meter. Public domain from Wikimedia Commons
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