Interview with Thomas S. Basso
In this interview, Thomas Basso sorts out the subtle but important differences between renewable energy resources and distributed generation. He also gives his perspective on the trend toward renewable energy generation, the challenges and value it has for utilities, and the related topics of microgrids and islanding – all terms that need some explaining.
Question: We hear a lot about distributed generation in the media these days. It appears to be a topic that means different things to different people. But before we get into that, could you tell us why, in your opinion, the idea of distributed generation has become so popular?
There are various reasons. Perhaps the tipping point is that it is becoming increasingly more cost-effective. Some distributed generation technologies are more efficient than some central station generators supplying electricity via transmission and distribution delivery systems. Distributed generation also tends to offer cleaner solutions – less carbon emissions, for example – while also offering customers a choice other than solely relying on central station electricity. And with distributed generation sited close to loads, it can improve availability for those loads.
What precisely is distributed generation?
The technical community uses a definition of distributed generation that is not perfectly aligned with the one used in the wider community. Many people use the term as if it were almost synonymous with renewable energy sources such as solar and wind. This may be because renewables have a very high public profile but they are only a subset of distributed generation. The more accurate definition of distributed generation is much broader: Distributed generation is any electric generation facility connected to electric utility delivery systems that are not traditional central station generation systems such as fossil fuel and nuclear power plants.
What are the synergies between Smart Grid and the general topics of distributed generation, microgrids and islanding?
Smart Grid – being the integration of power, communications, and information technologies -- is a complex system made up of interrelated systems. Those systems, encompassing a data network overlay, provide capabilities that enable greater performance and flexibility, more highly effective communications, and advanced operations not just for utilities but also for customers and third parties. And for distributed generation and microgrids, those applications require common capabilities that Smart Grid provides. The corresponding common capabilities are synergistic to accelerating Smart Grid realization as well as for increasing the implementation of distributed generation, microgrids, and renewable energy resources.
Why are renewable energy resources – primarily photovoltaic and wind – a cause of concern for utilities and what challenges do they pose?
There are two basic challenges for utilities and they are pretty well known. First, power produced by photovoltaic and wind renewable energy resources depends on environmental conditions – the amount of sun or wind at the moment, for example. Second, the power quality can vary considerably more than we would see in conventional central station power plants. However, these challenges are all addressable and are resolved from an engineering perspective.
Before we look more closely at the challenges, could you give us some idea of how much photovoltaic and wind generation there is the now and how much is expected to come online in the future?
I can give you some estimates that I personally believe are on the very conservative side. Looking at only photovoltaic and wind and assuming the investment tax credits are extended through 2035, the federal Energy Information Agency has estimated that in the U.S. there would be between 5.4 GW to 10.4 GW in the next 10 years and 12.3 GW to 44.7 GW in the next 20 years.
We’ve already noted that renewables have the implication of being weather related. Could you comment in more detail on the challenges that a large amount of distributed renewable generation has the potential to create?
To begin, I have to talk about two concepts that are tightly coupled: Penetration and electric delivery infrastructure capacity. Penetration relates to how much distributed generation exists in a utility circuit over a fairly small geographic area relative to overall capacity of the circuit. This is important because renewable generation can vary tremendously from time to time – it is not dispatchable. So how to mitigate what one might call “excessive” penetration becomes a very site-specific challenge. Viewed from the perspective of renewables, infrastructure capacity is an interesting “legacy” issue. What do I mean by that? Decades ago, the electric grid was typically overbuilt. Utilities did not build to tight margins so they oversized the conductors and transformers and other infrastructure equipment. Now fast-forward a couple of decades or so. As our use of electricity grew significantly, and we also began to address deregulation based on finer technical details, we cut the margins on those overbuilt assets. But now we are looking at a modern integrated electricity infrastructure that is based on renewable being a formidable contributor. Ironically, once again we need either those extra margins or the real-time certainty of the amount of distributed generation to account for the variability of the renewable resource. This brings us to a third concept: Variable and uncertain generation.
What kinds of solutions are being considered for renewables and their “variable and uncertain” generation capacity?
For the most part, the issues have been resolved or are being addressed. There are no show-stoppers, in other words. We can find solutions in advanced operations and spatial diversity of the distributed generation resources – that is, through studies and planning to mitigate the variability and uncertainty that compounds the issues of high penetration of photovoltaics, and wind –– that might cause instability the infrastructure can’t handle. Sometimes spatial diversity will be enough. But when it is not, we can employ advanced operations and “balancing technology” solutions such as flexible conventional generation and properly-scaled energy storage. Effective advanced operations offers a powerful set of solutions such as establishing more fine-scale control areas, the use of load management, and perhaps providing for limited curtailment for extreme events.
What are some positive aspects of distributed generation and renewable generation for utilities?
By accommodating distributed generation within their infrastructure near customer loads, utilities can reduce the loading on assets and this, for example, would allow them to defer upgrades or additions to delivery infrastructure and conventional generating capacity. As well, distributed generation could increase the reliability and availability for customers and lead to less downtime for certain utility maintenance.
So far, we’ve talked fairly generally about the challenges distributed generation might cause and the possible solutions. Can you give us a concrete example?
One of the problems that can be caused by high penetration of photovoltaic generation is creating high voltage on the utility’s distribution system. An example would be in a suburban solar subdivision, mid-day when the sun is brightly shining with little household loads since almost everybody has gone to work. What do you do with the solar power being generated? A scenario would be to charge batteries. Today, system integrators are installing battery banks as community energy storage systems and, when being charged, that offsets the higher voltage that otherwise would result from the high penetration solar supplying electricity to the grid. In the future, electric car batteries could similarly be charged. And when Smart Grid is a widespread reality, smart appliances could be turned on by home energy management systems. A hot water heater and a washing machine or electric dryer are examples and that is only somewhat futuristic.
That example brings us to two other topics: Microgrids and islanding. How do microgrids fit into what we’ve been discussing?
The term microgrid is basically synonymous with “planned islanding.” They include a portion of the grid, loads and distributed generating facilities. Microgrids are engineered, designed, and implemented to achieve stated goals, such as reliability or availability improvement, carbon emission reduction, diversification of electricity supply, and cost reduction. And when “smart technology” is used in microgrids, then that enables improved integration of distributed generation including renewable resources in the grid. Examples might be a campus or hospital facility with distributed generators that supply some or all of the loads in the microgrid. Additionally, some utilities plan and use temporary islands to decrease or eliminate outage time to affected customers allowing the utility to perform some maintenance that otherwise would have required longer outage of those affected customers.
What is the relationship between microgrids and islanding?
Unfortunately the term “islanding” alone leads to confusion - it is generally taken by utilities that “islanding” is an “unplanned and unintentional” grid condition and that if unintentional then it is inherently risky if not unsafe. However, “planned islanding” being synonymous with “microgrid” is transparent in that it is indeed planned as an intentional grid condition. Planned islanding includes disconnecting and reconnecting to the utility grid. That is accomplished under pre-determined conditions and operations. The goal is – and this is what we’ve established in IEEE Std 1547.4™ -- connecting and disconnecting islands from the utility main grid pretty much seamlessly with all the safety and protection equipment in place. Monitoring and control equipment are key to success for island operation and for the transitions from normal grid mode to planned island mode and return to normal grid mode. Depending on the degree of monitoring and control features needed, this controller may need to be very sophisticated.
Thomas Basso is the Vice-Chair of IEEE Standards Coordinating Committee 21 that includes sponsoring the IEEE 2030™ Smart Grid interoperability, IEEE 1547™ interconnection series of standards, and IEEE photovoltaic standards.