Power Factor and Panel Size: New issues to consider for the fully electrified home

Shutterstock / Petovarga
Shutterstock / Petovarga
Published On
Nov 15, 2021

It’s not a secret that local electrical distribution systems must evolve quickly, and utilities are thinking about residential customers in new ways. For example, while homeowners were once simply electricity buyers, now they might also be selling power back to the grid from their rooftop solar panels.

How owners and renters use electricity has also changed, with LED lighting, variable-drive furnace fans and other energy-saving equipment causing shifts in residential power profiles. Two reports document the need for increased attention to two specific residential issues—power factor correction and panel capacity—that utilities and their customers have overlooked in the past.

The reports were produced by Austin, Texas-based Pecan Street, which has developed a real-world testbed of more than 1,000 homeowners who volunteered to have their energy and water use monitored in real time—electricity use for every circuit is tracked on a second-by-second basis.

In “Course Correction: Residential Power Factor,” the group found many residences are presenting very poor power factor profiles to the grid. Correcting this issue could add 12%–16% more capacity to an existing system’s carrying capacity without needing a single new wire, transformer or substation.

Power factor is a measure of how much of the electricity delivered to a customer is actually being used by lights, appliances and other equipment. A perfect power factor is 1, meaning 100% of delivered electricity is actually being used by on-site devices. Commercial and industrial customers can start facing utility penalties if their power factor falls below 0.9. This is because the local utility is essentially wasting capacity in continuing to serve these facilities.

Residential customers, however, generally pay flat, per-kilowatt-hour rates, with no adjustment for poor power factor. And, ironically, these homeowners could be making problems worse as they opt for more energy-efficient appliances. Switch-load devices such as LED lighting and variable-speed motors such as those in high-efficiency furnace and air conditioning systems all create a need for “reactive” power, which is the voltage needed to turn on an AC load. Utilities still must support that reactive power, even though it does very little actual work.

Pecan Street also found that rooftop solar panels only increase the need for reactive power, even though they have no direct impact on a home’s power factor. The panels produce “active” power, the power needed to drive actual work, and might cancel out a customer’s active power needs on a sunny day. However, the grid still needs to support reactive power use. So, as the report notes, a house with a 0.8 power factor will still be drawing 20% of the electricity it uses from the grid, even if it appears to be supporting itself with solar.

“We could reduce the amount of current needed at every house by correcting this,” said Cavan Merski, a Pecan Street data analyst and contributor to the report.

While it could be possible to address the issue with a whole-house solution at the panel, he supports a more localized approach. “I would like to see the individual devices take care of it,” he said, referring to the appliances and lighting fixtures now contributing to the problem.

In “Addressing an Electrification Roadblock: Residential Electric Panel Capacity,” the Pecan Street team looked at improvements builders and owners need to consider to get homes ready for full electrification—including vehicles and heating, cooling and cooking appliances. Today’s standard 100A panel simply won’t cut it, according to the study, once future loads are added into a residence’s total demand.

Most homes today use a mix of energy sources, including natural gas for such heavy loads as water heaters and cooking ranges. Switching all appliances to electricity can be cleaner for the environment (depending on the generating source), but it can push a 100A panel to its limits. California regulators are already proposing to boost minimum panel size up to 200A as they seek to electrify all homes. Adding an electric vehicle (EV) charger, which could range between 32A and 50A or higher, also could easily max out a home’s panel capacity.

Scott Hinson, Pecan Street’s chief technology officer and contributor to both reports, noted that ECs have a role to play in ensuring homeowners have adequate capacity moving forward, especially in renovation or new construction projects.

“If you are already doing a renovation, the incremental cost for the higher-capacity panel is nothing,” he said, adding a message to share with those customers, “don’t modernize and not go without the full 200A.”

Adding a second EV could mean incorporating a load-management system rather than another panel upgrade. Some chargers already include this capability to throttle back power being delivered to a vehicle, while still ensuring it’s fully charged by the time the morning commute rolls around.

“Electric vehicles, as much as they could be a problem, they also could be a very valuable resource, in terms of shiftable load,” Hinson said.

About the Author

Chuck Ross

Freelance Writer

Chuck Ross has covered building and energy technologies and electric-utility business issues for a range of industry publications and websites for more than 25 years. Contact him at chuck@chuck-ross.com.

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