Why we need a "Partly Cloudy Grid" to integrate renewables

Editor's note: We've been talking for years about moving computing into the cloud. What about moving electric power generation into a cloud configuration? We might be able to get there partway, suggests Telvent's Jeffrey Meyers, a concept he dubs "the Partly Cloudy Grid." We asked him to explain his thinking in the piece below. -- Jesse Berst

By Jeffrey Meyers, P.E.

Reducing society's dependence on fossil fuels is a core value proposition of a smarter grid. Thus, one of the key drivers for grid modernization is the desire to use distributed renewable generation. Sourcing renewable energy nearer to its use creates both a smaller carbon footprint and much greater energy efficiency.

We might imagine a new grid configured along the lines of cloud computing, with varied generation resources (many of them renewable) connected throughout the grid, many at unknown locations. In this "Generation in the Cloud" concept, distributed energy resources (DERs) would be transitory. Plug-and-play, grid-independent control schemes would enable them to connect and disconnect from the grid at will. They could easily be attached to the distribution system at medium or low voltage. They might even be mobile.

Roadblocks to "Generation in the Cloud"

Alas, as with many visions, the Cloudy Grid configuration faces some insurmountable engineering and operations obstacles.

First, deployment of completely control-independent DERs would de-stabilize the network. Managing real and reactive power and frequency of interconnected generators can be challenging at times. Voltage set points and reactive power requirements are not static, but vary with the changing conditions of the system. Given the intermittent nature of many renewables (solar, wind), an every-DER-for-itself scheme could be potentially disastrous.

Beyond that, there are times when it makes sense to monitor and control the grid in a holistic, centralized fashion. A bigger picture view is helpful to optimize voltage and VARs, for example, and to dynamically reconfigure the network for various operating constraints. Yet exclusively centralized control cannot be the answer either. It is highly unlikely that the communications infrastructure to connect all DERs throughout the distribution system will even exist, much less with the bandwidth and latency needed for a single point of control.

But what about "Partly Cloudy" instead?

If the Cloudy Grid won't work, what about a Partly Cloudy version? Operators would know the location and characteristics of all generators. But they would only interact directly with distributed generators under certain limited conditions. This configuration would employ a hybrid or hierarchical control scheme with multiple levels. DERs would operate in completely distributed mode at times. Under other conditions -- such as fault restoration -- they would be subject to coordinated control at the substation or feeder level.

When the system was in steady state, control would roll-up to the centralized control-room for holistic optimal operations. Such a hierarchical control scheme could provide the best of all worlds, allowing for the safe, reliable and efficient use of DERs. 

Next page: Benefits of a Partly Cloudy Grid >>