In order to reach “24/7 zero,” one of the goals outlined in Part II of our Facilitating the Renewable Transition blog series, the way we view “net zero” energy use must evolve to an accounting method that more accurately reflects the timing of use, and technology to enable this must evolve alongside.
Grid-Interactive technologies are responsible for addressing the timing of energy use and buildings that harness these are referred to as “Grid-Interactive Efficient Buildings” (GEB). Two key GEB technologies are “load shifting” and “load shedding,” also more generally referred to as “demand response”.
Demand response is defined as a building’s change in load based on a grid signal. Historically this has been thought of as reducing load but can also refer to an increase in load.
Demand response programs have been around for a while, often targeted at large consumers, such as manufacturing plants. In these programs, consumers are paid to reduce their energy consumption during peak times; it is less expensive for a utility to pay the consumer to use less than it would be for the utility to ramp up more generation. Similar, but less direct, programs are targeted at smaller buildings – sometimes in the form of notifying customers to reduce energy use to avoid spiking prices or in the form of “time-of-use” rates that are generally simplified to “on-peak” and “off-peak” (and my favorite, I recently saw “super off-peak”) pricing.
Load shifting can occur with loads that must be met but the timing can be adjusted. This is most commonly preheating or pre-cooling a space, preheating water or adjusting temperature levels in water heaters, or timing when large appliances are run.
Consider a typical fossil-fueled grid versus a grid with high solar penetration. In a fossil-fueled grid, the grid emissions are high in the middle of the day when the grid stress is higher. A building connected to that grid would best avoid/shift energy use away from those hours, into the cleaner hours, when possible.
Consider a twin building that has the same load as the building described above, connected to the same fossil-fueled grid but has rooftop solar. Now, the energy resource available in the middle of the day is cleaner than other hours because it is coming directly from the rooftop solar output. That building should be programmed to shift energy use toward the middle of the day, when possible, to align with the cleaner hours.
Hypothetical scenario for adjusted building load profiles based on the same building with varying grid signals (fossil-fuel based (left) vs. high solar penetration (right))
Load shedding can occur for loads that may be defined as non-critical and can be shed, which most often are space-conditioning loads. When you set your heating setpoint back from 74 to 70, the load shed is the difference between the required output to maintain the higher versus the lower setpoint. This is generally for a short period of time and may be called upon on short notice.
I’ve also recently heard of the “load shimmy,” which refers to quick responses that act as ancillary services for the grid.
Buildings that have significant potential for demand response–load shifting and shedding–are often referred to as those with “load flexibility”.
Passive buildings inherently have the potential for load flexibility with space-conditioning loads. Through outage and resilience studies, it has become clear that passive buildings can completely cut space-conditioning system output for significant periods of time (in many cases for multiple hours, depending on the desired indoor condition and the setpoint before f any pre-conditioning was used) with little to no impact on the interior temperatures. Their envelopes create a thermal storage system that can be tapped into easily and deeply.
At PhiusCon 2022, Graham Irwin spoke in a lunch keynote about bringing passive building to mainstream market audiences. He joked about how excited he was that “the time constant of passive buildings might be the most untapped resource” (but that wasn’t how or why his clients want to build passive). Anyway, that statement alone was so accurate and simply put that it stuck with me. Just as electrical energy storage paired with renewable resources can make that resource dispatchable and more reliable, thermal storage, made possible through the enhanced thermal enclosure in our buildings, can do the same. And, unlike a battery, we’re already building the building, so why not stretch the benefit?
This load flexibility and shedding capacity can be aggregated between many buildings and called upon in the same way (and at the same price) that traditional generation capacity is dispatched. The ability for a group of buildings to shed load and sell that as supply-side capacity to meet the load can become increasingly valuable — especially if bid in at a high price to be dispatched during peak hours when competing with the most costly resources. Some aggregators do just this, but the volume of participants in demand response programs is low, and the concept still foreign or unsettling to many.
None of this is possible without the appropriate technology and communication protocols between the grid and the building or occupant. These have come a long way over the past decade, with some technology available that can attach directly to existing equipment while other equipment is being sold with grid-enabled technology integrated, allowing that equipment to be programmed to respond to grid signals. In terms of market share, there’s still a way to go. And, there are still challenges with defining the appropriate signals, as well as a lack of access to real-time emissions on the local grid. Occupant participation to configure the appropriate response system for the user is also a hurdle, but it also presents an exciting opportunity for everyone to be part of the renewable energy system transition. On top of this, demand response program managers have reported psychological hurdles of the user not feeling in control. Again, there is a long way to go, but in my opinion, there’s a whole bunch of potential.
Peninsula Clean Energy, the California CCA, is aiming to deliver 24/7 clean energy by 2025. Based on the CCA’s modeling, they could achieve 24/7 clean energy for 99% of the hours in the year with a 2% increase in cost relative to their existing portfolio. But, reaching that last 1% of the hours during cold, winter nights was predicted to increase the required generation procurement capacity by 50%! This is how variable the renewable generation versus demand profiles can be, even in a mild region in California. This suggests we have a real challenge ahead of us.
The next decade is sure to bring innovation and novel solutions to further progress toward a decarbonized economy. I’m incredibly optimistic about the potential of not only passive building, but also grid-interactive efficient building technologies to drive the transformation needed to achieve a fully decarbonized grid and bring a surge of other benefits alongside it.