What Is Resilient Power?
We have been working with our partners Clean Energy Group and American Microgrid Solutions to analyze a variety of facilities for the potential to install resilient power. We recently participated in a CEG webinar where we discussed our real-world experience with these types of projects. So if you’ve already watched that webinar and are here to learn more, welcome!
CEG defines resilient power as follows:
Resilient power is the ability not only to provide critical power to essential facilities and services during a power outage, but also to provide economic benefits throughout the year, by reducing power bills and generating revenue through providing services to utilities and grid operators.
In other words, resilient power systems can be used all the time. Their primary purpose of course is to provide economic benefits such as utility bills savings during normal operation, that is when the utility grid is operating as it should. (And thankfully, that’s most of the time, at least here in the United States.) But in the rare cases where the grid goes down — like after a hurricane, thunderstorm, or whatever — they can operate in islanded, or microgrid, mode and provide backup power to critical systems.
This is in stark contrast to solar or solar and storage systems that are installed purely for economic or environmental reasons. We refer to these as economic systems because more of then than not, they are installed primarily for the cost savings they can produce. Of course, they provide green energy as well, but by and large, they needed to pencil out for cost savings first. And really, there’s nothing wrong with that. We just should accept that these systems are not going to help improve our resilience.
At the other end of the spectrum are backup power systems. These systems are, by definition, only designed to operate during grid outages. Historically, backup power systems have consisted of diesel generators, or some other form of fossil-based generation. You’ve probably seen these in various forms sitting behind your local hospital, grocery store, or police station. Because of the cost of operation, and often more importantly emission limitations, these systems only operate during emergencies. The rest of the time they just…. sit there. We liken them to an insurance policy — you pay an annual premium (in the form of maintenance costs) to have them around, and then hope you never have to use them.
But what if you could use a single system to save money during normal operation, and then use it to provide backup power during grid outages? That in a nutshell is the idea of resilient power. And it’s basically the holy grail of solar plus storage systems. If you can make such a system pay for itself in the form of utility bill savings, you can essentially get your resilience for free.
The key is that you have to think about the resilience that you want your system to provide during the planning and design phases.
Designing a resilient power system
In general, most solar arrays today are grid-tied. Without getting too technical, these systems employ power inverters that need to synchronize to the frequency of the utility grid. This is great because it ensures that the solar power will go into the grid with the same voltage, frequency, and phase as the rest of the big power plants. But if the grid goes down, these systems don’t have a signal to sync to, so they just disconnect. And then wait for the system to come back up. This is also useful since pumping power onto a supposedly de-energized grid introduces a safety concern for the guys that might be trying to fix downed power lines or repair equipment.
If you want your system to be able to operate independently of the grid, you need a grid-forming or islanding inverter. These are much more sophisticated devices since they can not only sync to the frequency and phase of the grid, but can also create their own stable voltage, frequency, and phase if the grid is down. That allows them to operate both ways. (Of course, if the system is operating in islanded mode, there needs to be some sort of disconnect so power isn’t inadvertently pushed back to the de-energized grid.)
Most of the commercial battery systems being installed today are put in for economics too. Behind-the-meter batteries are probably being used for peak-shaving, which can definitely reduce costs. Even utility scale batteries may be used almost exclusively for frequency regulation. But it’s unlikely that either of these batteries are configured to provide backup power during outages. For that, you need to start stacking applications, and recognizing that providing backup power is a revenue stream.
So in short, if you have a solar-only system, it’s unlikely that you are getting any added resilience at your facility. And even a solar plus storage system needs to be configured properly such that it can operate in islanded or microgrid mode.
Optimizing solar plus storage for resilience, economics, or both
The question that many of our clients is ask is whether they should design to maximize their economic return or design to maximize their resilience. In reality, there’s no wrong answer to this question. It just depends on what your primary goal for the system is. Do you want to be able to sustain a critical load for specific amount of time? If so, then you probably want to keep that objective in mind during the design phase. Or do you want to maximize your cost savings, and just take what you get when it comes to resilience? In that case, you might want to design to maximize your economics, and then add the necessary components to enable your system to operate as a microgrid. But be careful, because taking what you get when it comes to resilience might mean getting no resilience at all.
We’ve adapted our Redcloud energy optimization platform specifically to help our clients address these types of questions. Because you really need to explore the design space to really understand the cost and benefit tradeoffs that come from designing a hybrid resilient power system. Want us to help you think about enhancing the resilience of your facility? Contact us!
