Here’s something that’s not so smart about smart inverters: Many people assume we can’t take advantage of the voltage and frequency benefits they could offer grid operators because regulations get in the way. But, even in jurisdictions where regulations hamper autonomous operation of smart inverters, there’s still a way you could gain benefit from them. Just hook them up to a DER-management platform like Symphony by Enbala.
What could be could be
For those who don’t know much about smart inverters, here’s a quick look at what they are and what they can do.
Like traditional inverters, smart inverters convert direct-current voltage into alternating-current voltage, which is what flows through the power grid to energize all the electric devices and appliances in our lives. Solar PV systems have inverters because they generate electricity in DC current. Batteries need inverters, too, because they’re all DC-based, as well. The difference between a regular inverter and a smart one is that smart inverters have computing power and communications capability that accommodates bi-directional flow.
Because of their computing power, smart inverters can collect data about voltage, frequency and volt amperes reactive – or VARS – at their terminals. But, here’s what makes them powerful. They can operate autonomously once programmed to dial down output from PV panels when system frequency starts to rise.
In addition, smart inverters can produce reactive power, which is AC electricity with a current wave that leads or lags the voltage wave on the grid. So, when voltage rises because of PV generation, the smart inverter can inject a lagging current that will pull voltage back down. If voltage drops suddenly – which can happen if cloud cover impedes PV generation – the inverter can inject VARS with leading current to bring voltage back up.
Inverters could take these actions autonomously if regulations allowed it. In the U.S., most states don’t.
Getting around 1547
Most state regulators and the utilities they supervise use IEEE 1547 as their interconnection standard, and it mandates that DERs disconnect quickly in the event of abnormal voltage and frequency.
How quickly? Below is a chart showing the standard states at which DERs must cease to energize. The clearing time includes both relay time and breaker time, so DERs must trip even before the specified time is reached.
Right now, 1547 is being updated, and voting on the new criteria and requirements for interconnection of DERs with electric power systems will begin in 2017. It’s going to be a while before most areas get the kind of voltage and frequency ride-through that would enable smart inverters to autonomously provide grid support.
Even when that happens, there may be concerns. After all, the mandatory disconnection rules protect utility line workers from unexpected current. And, with both smart inverters and utility capacitors working on voltage corrections, some worry the devices might fight with each other. That’s one reason why some industry participants are concerned about letting customer-sited equipment address voltage and frequency excursions.
Fortunately, the technology exists now for utilities to leverage smart inverters themselves. Inverters can be networked into a system like Symphony by Enbala easily. With it, grid operators know the state of grid-connected devices continuously, as Symphony tracks capacity, ramp rate, output and consumption every two seconds. It also brings back data on voltage, VARs and frequency, so grid operators can program the platform to respond within their own requirements.
Through Symphony by Enbala, smart inverters – and any other DERs connected to the network – come under a grid operator’s control. This functionality exists today, and it doesn’t violate regulations built on IEEE 1547.
If you'd like even more information about this topic, you are invited to download the more in-depth white paper.
And take a second to sign up to receive notifications as new blogs are published. Simply fill in the "subscribe' information in the top right column of this page.