Low-Energy Friday: Winter Relight
As they say in Westeros, “Winter is coming.” Whatever this El Niño cycle brings in rain and snow, winter represents two system level shifts and one household shift for the United States. First, the use of electricity with the bulk electric system changes from a single daily peak because of afternoon cooling to a dual-peaking system. Why? Because people will use more heat in the morning and then in the evening as the sun goes down. Second, our natural gas storage systems stop injecting gas underground and start withdrawing to balance systems both on pipelines and within local natural gas utilities. On a more local level, homeowners and renters across the colder regions are going to their thermostats and turning on the heat for the first time in months.
To understand why the change in when the electric system peaks is relevant to our daily experience, it’s important to understand how household behavior changes with the seasons. In much of the country, our air conditioners kick on and primarily run during the afternoon into the evening. If you own an electric vehicle, it’s not unusual to plug it in after your commute, but it adds to the already large load from air conditioners. To some degree, the deployment of utility and residential solar has helped to mitigate the air conditioning load because when the sun is creating heat, it’s also generating energy on solar panels. When electric vehicles are incentivized through time-of-use tariffs, real-time pricing, or demand response programs to start charging after the cooling load has shut off, the summer peak can be mostly mitigated.
The winter dynamic is completely different. As of the most recent American Community Survey, electric heating represents 42% of homes nationwide, while natural gas is 47%. The remaining 11% is made up of propane, fuel oil, wood, or no heating fuel. But it’s important to remember that even if a household has natural gas or propane heating, the fan that moves that heat throughout the house runs on electricity. Add the fact that temperatures typically bottom out just before dawn, when solar produces nothing, you have an electric system under tremendous load.
You can solve that through natural gas peaker plants, 4-hour batteries, or demand response/real-time pricing to incentivize customers to adjust their behavior to not turn on at the same time as every other electric vehicle and heat pump on the system. Once the grid gets through that morning warm-up, the solar comes online and can recharge the batteries, pumped hydro, and run the system through the day to prepare to do it all over again. Solving for these two seasons, summer and winter, is a major driver of capital costs which ultimately end up in your utility bills, whether through cost of service regulation or market solutions.
As mentioned above, local natural gas utilities that have on system storage typically stop injecting into their storage and start removing when the cold weather sets in. Besides this seasonal swing, the utility needs to manage the daily pipeline draw so they don’t exceed their contractual limits. This is primarily driven by the natural gas heating in furnaces, which can represent between 60 and 80% of annual household natural gas use. Combine that with a morning warmup as folks get ready for school and work, and an evening repeat as the solar heat gain dissipates, and you stress a natural gas system that is predicated on stable flow throughout the day.
Once you’ve solved the greater societal problems of supply and demand for electricity and natural gas, then you have the problem of your personal heating system. It’s a system that lies dormant for about half the year, and when you go to start it up, you hope you’re not calling an HVAC contractor because of a weird smell or no heat being delivered to your cold house. If the verdict is full replacement, it’s usually an emergency one. The HVAC industry estimates that at least 85% of replacements are emergency. Which is a problem for an appliance that typically has a 15- to 20-year lifespan and costs a lot to replace, regardless of which fuel you choose. If you care about emissions, consider that a baseline furnace is 80% efficient while variable capacity heat pumps can achieve between 200% and 500% efficiency depending on outdoor air temperature (colder is lower efficiency).
Said another way, for each unit of energy you put in, the furnace only delivers 80% to your house and exhausts the other 20% to the atmosphere, while the heat pump can deliver at least two units of heating. And while I’ll spare you the complex math, a standard efficiency furnace replaced with a high-efficiency heat pump, powered by a combined cycle gas turbine on the electric grid, could result in a 44% reduction in CO2 emissions. High-efficiency heat pumps do increase electrical load, but they use dramatically less than older single-speed heat pumps that rely on electric heat strips at low temperatures.
So as you turn on the heat and settle in for the winter, figure out who your local high-efficiency heat pump contractor is and tuck that number away. If you’re a renter, make sure your landlord understands split incentives and any utility rebates that might reduce the cost of a higher-efficiency heat pump. Until then, consider adjusting when you charge your electric vehicle in the winter away from 4:00 am to 8:00 am to daylight hours when solar production is greatest. Winter is coming.