Overcoming Forecast Uncertainties for Better DER Planning

Forecasting load growth and planning the utility investments necessary to handle changing electricity demand used to be a straightforward exercise.

Utility planners knew that customers in their service territory more or less shared the same load pattern. The only real wrinkles planners had to navigate as they considered grid upgrades were entirely new loads — like from a new subdivision — or widespread embrace of technologies like LED lighting that reduce demand.

The rapid influx of distributed energy resources (DERs) such as rooftop solar photovoltaics, energy storage and electric vehicles has introduced significant complexity to the formulation of accurate forecasts planners need to cost-effectively accommodate DERs while maintaining grid reliability. Even forecasts that accurately project the total number of new EV chargers or solar arrays that will be added to an area served by a substation can be problematic.

“A planner can assume that every x number of households has an EV charger and then space it out on the network so that every third person gets one,” said Gerhard Walker, director of product management at Opus One Solutions, a Toronto-based software engineering and solutions company that works with utilities across North America to effectively integrate DERs. “But when it comes to DERs, location is really important."

"If a Level 2 EV charger is put in at the end of a very long feeder, that additional load might cause a problem," Walker said. "Even if the forecast is correct that one new charger is added, its impacts on the grid can play out a hundred different ways depending on where it is installed.”

From worst-case to probabilistic planning

The traditional utility planning approach has been to make investments based on worst-case scenarios, usually to accommodate the highest system peak load. “We have to divorce ourselves from the old approach where we are looking at low and high load or low and high generation scenarios because those end up giving you extremes that would most likely never happen,” said Walker. “It can cause you to massively overbuild the infrastructure or under-build, both of which have problems.”  

The increasing prevalence of DERs across distribution grids demands a more flexible and accurate approach to forecasting and planning. This can be achieved by embracing forecasting based on probability studies, Walker said.

DERs come in numerous flavors and combinations. Those assets can have very different grid impacts depending on a host of factors, including where they’re located, how many other DERs are nearby, and even the time of day. Uncertainty about future DER uptake is also challenging the efforts of planners to forecast how DERs may affect the distribution grid.

Put another way, the sheer number of DER scenarios and how those many iterations could impact the grid are impossible to evaluate using traditional...

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