By Francisco Flores-Espino, NREL
Distributed energy resource (DER) deployment levels in the distribution grid are increasing in many parts of the United States. As the profitability of installing DERs increases, the upward trend in DER deployment will continue, and be further helped by regulations and policies that have the goals of increasing clean generation capacity, empowering utility customers, and diversifying local energy portfolios. The National Renewable Energy Laboratory (NREL), in collaboration with utilities, vendors, and researchers, is studying the effects of increasing levels of DERs to find the most cost-efficient integration approaches while maintaining or enhancing reliable grid operations.
In this article we briefly describe the technical and financial assessment performed so far on different technologies and our plans in the near future.
Technical Assessment
Emerging technologies and traditional upgrades can be and have been used, individually or in coordination, to increase the amount of DERs that can be integrated into a specific part of the grid without violating acceptable voltage and thermal operating ranges. And although it sometimes viewed as an inherent fixed quantity, the hosting capacity can be increased through traditional upgrades such as reconductoring; upgrading or adding new transformers, voltage regulators, load tap changers, and capacitor banks; changing equipment settings; and others.
As an alternative to traditional upgrades, emerging technologies—e.g., remote inverter control (via a DER management system, for example), volt-volt ampere reactive (VAR) optimization, autonomous inverter settings, net-load control, etc.—can also be used. NREL is studying the capabilities of emerging technologies to increase the hosting capacity in distribution networks and is assessing the financial costs and benefits associated with the use of such technologies.
We are partnering with utilities, vendors, and industry experts to understand which technologies are being used most widely and which technologies are the most promising for cost-effectively integrating distributed generation into the electric grid. NREL is also trying to understand under what circumstances emerging technologies can be more effective, technically and financially, in increasing hosting capacity.
To fairly compare diverse technologies, we have developed new tools, metrics and methods that compare impacts across weeks or months of operations. Looking at operations throughout the year helps evaluating technical and financial costs and benefits more accurately. This improves over the usual method of looking at worst-case time periods.
Is There a Way to Compare?
A major question we have been working through with our partners is whether it is possible to compare technologies against each other in absolute terms of the net cost in dollars per watt of integrated photovoltaics (PV). In other words, is it possible to rank emerging integration technologies by their cost-effectiveness to integrate PV and other DERs into the grid without diving into location-based specifics?
Our collaborations and analysis indicate that it is not feasible to use a single metric to justly compare one DER integration strategy to another given the complexity of modern distribution grids and the multiple way in which emerging technologies interact with each other. A key part of the problem is that results heavily depend on the conditions and idiosyncrasies of each feeder, making it hard to generalize conclusions.
However, several other factors conspire to make cost and benefit assessment difficult and uncertain — the market is not yet mature, which translates into costs that vary widely from one project to another. Current DER integration technologies are evolving rapidly, which makes cost analyses obsolete rather quickly. Distribution integration technology is almost always part of a bigger solution (e.g., an advanced distribution management system), which makes it difficult to assess costs and benefits specifically associated with hosting capacity expansion.
However, NREL and its partners see a positive way of moving forward. By working with our partners, we have come to realize that the advanced models and approaches we have developed, coupled with real-world industry expertise, can help utilities and other stakeholders identify which technologies have the most potential in both technical and financial terms.
Although generalized cost-benefit assessments might not be possible, NREL’s ongoing research can provide the industry with important guidance regarding the technical capabilities and cost-effectiveness of different technologies. And we look forward to continuing to work with the industry, regulators, and developers to provide actionable and objective information and to help address questions around the most effective way of integrating DERs.
Francisco Flores-Espino is energy analyst for Markets and Policy at National Renewable Energy Laboratory.
