Utilities deliver both active (or real) power and reactive (or imaginary) power along their distribution lines. Real power does the actual work when you flip on a light switch. Certain energy loads, such as motors and refrigerators, include energy storage elements that periodically need to reverse the direction of energy flow. This electric power from stored electromagnetic energy, which returns to the source in each cycle, is known as reactive power.
Utilities care about reactive power because, even though it does no work at the point of consumption, it is needed to maintain voltage to deliver active power. Do you remember the largest blackout in U.S. history that surged through the Northeast in 2003? The cause for this, and several other major blackouts, can largely be attributed to a severe shortage of reactive power, which failed to maintain voltage along major power routes.
Utilities can produce any combination of kilowatts and VARs (Volt-Ampere-Reactive units measure reactive power) but they must constantly focus on maintaining the right balance. Motors and other reactive power requirements impact that balance, meaning that any imbalances are generally located near the motors. Because VAR support comes from utility generators that are located far from load, distributed generation (DG) provides the potential for a new way to provide VAR support – by using the inverters on solar arrays connected to distribution circuits to help create a more balanced and reliable grid.
In a similar vein, this also means that inverters with reactive power capability may be able help utilities accommodate higher penetrations of photovoltaics (PV) on the distribution grid with fewer grid upgrades.
It seems like a win-win situation, no?
Interestingly however, the ability of DG systems to provide VAR support has largely been ignored in the U.S., generally because any policy action has been too complex to implement. That may be starting to change, with three recent and somewhat noteworthy policy developments.
- Last October, the Federal Energy Regulatory Commission (FERC) made a move toward formally recognizing the benefits of reactive power. On October 17, FERC issued an order that requires jurisdictional entities providing reactive power to formally file reactive power rates with the commission, even though the rate schedule would provide no compensation for such a service.
- In California, this issue recently came up in a Smart Inverter Working Group that IREC has been participating in over the past several months. The group put forth their recommendations for inverter capabilities regarding reactive power in a highly technical report, starting on page 32, section 2.4.5. California is proactively addressing some of these technical matters in order to lay out the technical steps needed to accommodate high solar penetration and to optimize DG resources.
- And in January, the Planning Committee for PJM, the regional transmission operator serving the mid-Atlantic states, gave near unanimous approval to a problem statement and issue charge to explore whether to require renewables such as solar PV to install enhanced or “smart” inverters that can produce and absorb reactive power in addition to inverting DC power to AC. However, any smart inverter requirement is not likely to come about until PJM goes through the approval process to revise IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems.
This topic is certainly nothing new, however. Germany and other European countries have been relying on reactive support from DG systems for quite a while. And FERC has long espoused the host of ancillary benefits, including reactive power, that DG can provide to create a more stable and reliable grid.
In a 2007 report, FERC noted that, “on a local basis there are opportunities for electric utilities to use DG to reduce peak loads, to provide ancillary services such as reactive power and voltage support, and to improve power quality.”
While implementing ancillary services and VAR support at the distribution level will still require significant technical and regulatory changes, these recent actions are promising. At the least, they’re a signal from the powers-that-be that we will need to shift how we approach utility services, from a technical standpoint, in order to safely accommodate the rapid growth of distributed resources.