Generation Isn't the Center of the Universe Anymore

A revolution is underway in the world's power markets. The power industry of yesterday was centered on generation, and energy transmission simply moved power from the producer to the customer. But this equation is rapidly changing as power sources emerge that significantly differ from their predecessors.

As a result, utilities and grid operators must evolve and adapt transmission infrastructure to prepare for a major shift away from the power industry of the twentieth century.

An Energy Revolution Redefines Roles

The world's energy mix has evolved substantially over the past 20 years. According to the BP Statistical Review of World Energy, since 1997, cumulative installed solar photovoltaic (PV) and wind power has climbed from less than 8 GW to nearly 800 GW globally. Renewables were responsible for almost 165 GW of new global power capacity in 2016—nearly two-thirds of the global total, says the International Energy Agency (IEA).

Because these renewable sources of power are variable, this shift has presented challenges and opportunities for power plant and grid operators.

Historically, generators have ramped up and down following demand, but now they find themselves increasingly compensating for renewable energy variability. Therefore, modern power systems have assumed a larger balancing role, spreading over broader geographical regions. As larger and larger pools of solar energy ramp up and down in the mornings and evenings, generators have been taxed in this new role, and there has proven to be an increasing need for smarter and more flexible transmission grids.

This balancing role extends across the entirety of grid infrastructure, from low voltage through high voltage. Specifically, in many geographies today, there are periods when there's a significant mismatch between local power generation (often from renewable energy sources) and local power demand. When there's an excess of locally generated power, energy can be exported through the transmission grid over longer distances to end users who have a need. When there isn't enough local power, it must be imported into the distribution system again, using this transmission infrastructure.

Distributed Generation Spurs Smarter Distribution

As electricity systems continue to evolve, there will be different types of load profiles and new scenarios will arise. The grid must be smart enough to cope with these changes.

For example, most solar energy—with the exception of large utility-scale plants—is connected to distribution systems at low and medium voltages. While distribution substations—and the distribution networks downstream of them—have historically been used to deliver power from transmission grids to end users, these distribution systems now need to be able to handle reversals in power flow from distributed generation sources, such as solar energy.

This means that, in some distribution lines, power may flow from the end points, where the solar energy is produced, back toward the substation. In other cases, the substation may put excess energy back into the transmission grid.

Mature distribution grids like those in Europe and North America were designed for power to flow in one direction only. With power flowing in both directions, grids face challenges in two key areas.

Two-Way Energy Flows Create Complexity

The first challenge is keeping the voltage along the distribution lines within allowable limits. This issue arises because the presence of distributed generation sources can increase the voltage on the line at the point where they're connected. As the intensity of sunlight falling onto a solar panel array changes throughout the day and drops altogether at night, the voltage at the point of connection to the grid can change frequently. If the voltage exceeds its limits, the devices we use in our homes, such as TVs, can be damaged.

The second challenge is ensuring that the protection devices that disconnect portions of the distribution grid during faults, such as short circuits, continue to perform effectively. Devices that open circuit breakers most often have intelligence built into them that assumes power is flowing in one direction. When short circuits occur, distribution circuit breakers have traditionally counted on the fact that the amount of current flowing through the wire into the short circuit will greatly increase. The intelligence used to determine when to open the circuit breaker relies on this sudden increase in current to trigger the breaker opening, thus disconnecting the faulted distribution line from the energy source at the substation.

When a fault happens in a distribution system with distributed generation sources, however, ensuring that a faulted distribution line is fully de-energized becomes much more complicated. Solar arrays do not have the same characteristic of greatly increasing their current output when downstream lines suffer short circuits, and they may therefore not be able to produce enough current to trigger a traditional circuit breaker to open. In such a situation, the short circuit could be continually fed by the solar generator, presenting a problem to people and repair personnel in the area.

Smarter protection and controls are readily available to overcome both of these challenges. As distributed generation grows, the existing protection and controls in distribution systems will need to be replaced with this smarter technology.

The Future of the Grid Requires Modernization

Renewable sources of power have grown at double-digit rates for more than a decade, and will likely continue to do so. This creates new needs for flexibility to balance the grid. In the future, these needs will be met in part by more small-scale electrical systems that consist of renewables like solar PV, batteries, and perhaps EVs.

The role of the grid therefore shifts; at the transmission level, it will go from delivering bulk power over long distances to increasingly seeking to balance supply and demand with these variable resources over broader and broader areas.

At the distribution level, the grid becomes omnidirectional, not only sending power from the substation to consumers, but also allowing power to flow in the opposite direction. The future grid will even enable local transactions between members of the distribution grid.

The grid's infrastructure will need to evolve to accommodate these changes. Smarter controls at the transmission level will be important to manage the increasing complexity of energy balancing, and the interactions with evolving market structures. At the distribution level, the controls and protection that keep grids safe will need to be modernized to account for the new energy flow patterns that distributed energy resources present.

“The coordinated development of renewables and smart transmission and distribution grids is an essential ingredient for achieving a cost-effective, low carbon energy mix,” Vera Silva, Chief Technology Officer for Grid Solutions at GE Power.

New market structures that enable transactions between peers will emerge from both established players and new entrepreneurs. New technologies such as storage and electric vehicles will further accelerate this transformation, helping renewables overcome their primary disadvantage of not being controllable. As conventional generation moves from being front and center to an ensemble player in the evolving energy mix, the power play will be for all stakeholders to accept change and implement new processes now for a better tomorrow.