The emergence of electric vehicles and the transition of homes to electric heating over the next decades would lead to winter peak demand that could destabilize the grid, an analysis by the American Council for an Energy-Efficient Economy (ACEEE) concluded.

But utilities could mitigate spikes and ensure reliability by improving buildings’ “thermal envelopes,” the group says.

The nation’s electric utilities would be faced either with building more generation or hastily developing “demand-side” programs and technologies to mitigate the predicted winter power demand increases, the study predicts.

ACEEE recommends that utilities in regions with the potential to become winter peaking in the future be required now to establish winter peak demand reduction goals.

A switch to electricity as a heating fuel would be herculean. Only about 40% of homes have electric heat, according to a U.S. Census Bureau survey published in 2019, while natural gas accounted for about 48%, fuel oil about 4% and LP gas about 5%.

“This transition to electrification will have major impacts on our electricity system,” said Mike Specian, ACEEE utility manager and one of the authors of the study, at webinar April 15 where the findings were presented to a panel of outside energy experts.

“Regions of the country that are currently summer peaking, meaning that they experienced their highest demand in summer, usually on the very hottest days, will become winter peaking.

“And if something like a polar vortex hits and delivers subzero temperatures for an extended period of time, you can wind up with a lot more winter electric load than there was beforehand; sometimes you will have up to three times more. And that’s a challenge that we are going to have to collectively figure out how to handle,” he said.

Strategies Examined

Strategies that ACEEE examines in the analysis include:

• upgrading existing “ground source” (geothermal) heat pumps with new higher efficiency units;
• replacing existing resistance heating (baseboard or whole-house furnace) with “cold climate” air source heat pumps able to extract some heat out of outside air at temperatures as low as 0 degrees Fahrenheit;
• developing a suite of automated demand-side management technologies;
• retrofitting existing buildings with maximum insulation upgrades, including structural changes to increase the effectiveness of their “thermal envelopes” to reduce the amount of energy needed; and
• beefing up insulation standards for new construction.

One surprising finding from the modeling of several scenarios in a postulated future four-day polar vortex outbreak in New England is that widespread use of natural gas or propane-fired heating as a backup to cold climate air source heat pumps at 0 degrees — along with a full suite of demand-side technologies — flattened peak demand the most of the several scenarios examined.

“If instead of heat pumps defaulting to electric resistance backup heating, they instead switched over to fossil backup during the very coldest periods, [we] found that the possibility of using limited natural gas propane or the like could be valuable in terms of reducing the amount of [overall] electric capacity needed to deal with the most intense winter peaks,” Specian said. The study did not address how much such backups would cost.

The study stresses that upgrading the thermal envelope of buildings is a crucial step that cannot be overlooked in favor of programs that focus on new heating technologies, smart meters or other demand-side technologies.

Specian said the study considered the possibility of a utility calling for load shedding in the form of a two-degree reduction in temperature set points during very cold weather.

“And we also look at some [other] demand response measures, including shifting when grid-interactive water heaters and electric vehicles are charging up as well as the use of behind-the-meter battery storage to strategically charge and discharge to the grid,” he said.

Using data collected during the four-day polar vortex outbreak of January 2019 in New England, the analysis presents an electrification scenario of New England in 2040, by which time the study’s authors project that winter peaking demand will be common.

“We began [by assuming] that 1.46 million residential heat pumps will be installed in New England’s 5.9 million residential buildings, and that about 8% of commercial space heating capacity will be met with cold climate heat pumps,” Specian said.

Using a record of the ambient temperatures and other data from the 2014 polar vortex, the analysts then calculated the hourly electrical load in the region as the outdoor temperatures plummeted and then stay low.

“It becomes immediately clear that space heating is the overwhelming driver of peak and that the residential contribution is larger than the commercial,” Specian said. The load profile in the analysis included all residential loads, most common commercial loads, but no industrial loads.

The objective of the modeling was to calculate now much of the spike in peak demand could be reduced given the heating technologies assumed in the several scenarios.

“We find that continuing demand-side management ‘business as usual’ could deliver peak reduction savings of between 6 and 7%,” Specian said. “And if we deploy all of our measures, we would be able to reduce peak by about 34%.

“But what measures are yielding the greatest savings? By a large margin, those [measures] that reduce heating load, and of those, residential weatherization lowered peak the most,” he said. The second most effective cost cutting measure was the cold climate air source heat pump, he added.

Other Views

For anyone doubting the realism of ACEEE’s modeling, the other three experts whose presentations rounded out the webinar made it clear that winter peak demand is a real threat that must be addressed.

“We all know that electrification is putting more burden on the grid, and grid management will become more challenging with higher renewables and less fossil generation,” said Texas-based grid expert Alison Silverstein, a former adviser to FERC Chairman Pat Wood, III, and co-chair of the international commission that investigated the 2003 Northeast blackout.

The February 2021 ERCOT deep freeze, when almost half of the fossil generation and nuclear capability inside Texas disappeared, “illustrates pretty painfully what happens when you cannot meet winter peak,” she said.

That resulted in 4.5 million customers without power — 69% of all Texans — for an average of 42 hours, said Silverstein.

More than 200 people died. “Too many people died inside their homes due to carbon monoxide poisoning or hypothermia,” she said. “That’s what happens when you screw this up, which is what makes the report from ACEEE’s team so timely.”

Silverstein added that most of the homes built in Texas in the last two decades are not insulated for severely cold weather and are heated with resistance electric equipment or heat pumps that were not designed for cold weather because Texas is a summer peaking state.

She agreed with ACEEE’s recommendation that dealing with winter peak demand starts with improving buildings’ thermal envelopes.

“I know that your study says heat pumps are the best way to reduce peak, but heat pumps fail when the grid goes off.  So simply improving a heat pump or the heating space conditioning methods [in a home in which] the building envelope is leaking isn’t going to keep people alive when your grid fails,” she said.

Calling the ACEEE research “timely,” Tom Hines, principal of Tierras Resource Consultants of Phoenix, focused his comments on a recent winter peak study his company did for Duke Energy’s North Carolina and South Carolina territories, which are transitioning to “dual peak” with winter and summer peak demand at about the same levels.

In the future, winter peak demand will become dominate, he said, and that could pose a demand-side management problem.

Summer peak demand typically occurs in the mid to late afternoon to early evening, a time when solar generation is still strong enough to help, said Hines.  But high morning demand, between 7 a.m. and 9 a.m., is demand that solar cannot meet.

“Summer peaks are not growing nearly as quickly as winter peaks are, in terms of net loads, due to the impact of solar,” Hines said.

Duke has traditionally focused its demand-side management programs to address summer peak demand, he said. His firm looked at demand-side strategies the utility could consider in dealing with anticipated higher winter peak demand.

Thermal envelope improvements quickly emerged as an area where peak demand could be reduced both in the summer and winter, he said, particularly for mobile and manufactured homes.

“We took a very holistic approach. We combined advanced rates, tariffs, things like critical peak pricing, peak time rebates … with demand side management programs. And we feel that if you can combine enabling technologies like smart thermostats and water heating controls with attractive rate designs for customers, you really drive a lot of ongoing savings,” he said.

Maggie Shober, director of utility reform at the Southern Alliance for Clean Energy, said many of the solutions that “worked in the New England example would also work in the Southeast where instead of moving into electrifying heating, we are looking to move from inefficient electric heating to a more functional option.”