In Part II of our Facilitating the Renewable Transition blog series, Phius Associate Director Lisa White examines how passive buildings interact with the grid and how that relationship is evolving.
In Part I of this blog series, I provided some background information on passive building and the grid, so now it is time to answer the questions: how do they interact, how is this changing, and why is this important?
The grid is changing on many fronts. Most notably for the decarbonization movement is that dispatchable fossil-fuel based resources are being replaced and out-bid in the market by renewable resources. The renewable resources have variable, non-dispatchable generation profiles and therefore are challenging to utilize to meet demand-side loads. They are also more distributed (often referred to as distributed energy resources or DER) and may be behind-the-meter, meaning grid operators have no visibility to or control over them, which presents a further challenge. Historically, grid operators have relied on visibility of available resources and have been able to orchestrate dispatching resources as needed to meet the load.
In our existing centralized utility markets, available generation resources bid into the market at the price at which they’re able to deliver power, which is generally a combination of operational and fuel costs. Luckily for our push toward decarbonization, wind and solar have no fuel cost and are able to bid in at very low prices. Therefore, those are utilized first when possible. As the load increases on the grid, the operators must dispatch more and more expensive resources to meet that load. And often, this is not linear; as the grid load approaches a peak, resource prices may double or triple, which can cause significant spikes in the cost to deliver and purchase electricity during those peak times.
Similarly to how the cost to provide electricity is variable, so are the carbon emissions associated with each unit of delivered electricity, and they depend on the mix of generation resources that are utilized to meet the grid load at that given time. Typically, in times of low grid stress, the emissions are lower, and during high stress, emissions are higher. As more emission-free resources are integrated into the grid mix, there will be a greater disparity between low-emission hours and high-emission hours.
Image 1: Image of Hourly Marginal Carbon Emissions on the grid at a node in Chicago, IL in 2019. The months of the year are displayed across the horizontal axis, while hours in the day are on the vertical axis. Hours filled in red have higher marginal emissions associated with electricity production relative to hours filled in green. This means, conserving energy during the red hours actually reduces carbon emissions more than conserving during the green. But remember, this is a snapshot at a point in time and will continue to change as more renewable resources come online.
We must also keep in mind that saving a unit of energy at different times displaces the marginal emissions on the grid at that time, i.e. the emissions from the last dispatched resource called upon to meet that load.
There are also significant new loads coming onto the grid from electrification of heating, hot water and cooking in buildings on top of electric vehicle charging. In areas with substantial heating loads that are currently served by natural gas, the electrification of space heating now places that new load on the grid. This alone will shift the grid peak from the summer to the winter. The load (and opportunity) presented by electric vehicle charging is a topic for its own article.
The grid’s generation capacity installed is based on the grid peak – sized to meet the time where the load on the grid is the highest. Right now, that peak is in the summer in almost all regions of the US due to air conditioning loads, but as mentioned above, will shift to the winter in many regions. To meet this peak, there’s significant overinvestment in generation capacity for redundancy and reliability. Building designers confront this type of planned redundancy at a smaller scale, such as when the engineer calculates a building’s heating load at a “peak” or worst-case design condition, and sizes heating equipment to meet that load and then an extra percentage over, just for good measure. That type of over-sizing and redundancy has been implemented at a much larger scale in the planning and design of the electric grid.
Some grid-regions of the United States are changing more quickly than others, such as California, where renewable energy integration has been accelerated. Areas of higher renewable penetration are experiencing ramping challenges (i.e. the “duck curve”) due to renewable resource output steeply entering and exiting the grid mix. They also experience renewable energy curtailment often due to excess production during certain hours (visible through negative energy prices) and due to congestion on the transmission lines (the infrastructure wasn’t sized to carry that load).
To state it simply, we are intentionally integrating renewable generation resources (supply side) that have generation profiles that do not align identically with our building loads (demand side). In order to fully utilize and continue to rely more on renewable resources we must gain more control of our building load and rely on energy storage to re-shape the profiles into alignment.
With that information about the grid in mind, let’s get back to passive building and net zero.
Passive building yields low-load, low emissions buildings. This is already a huge first step for grid friendliness. Remember, the generation resources on the grid are sized to meet the peak load. Passive buildings can dramatically reduce the peak building load, specifically the heating load, often by a factor of two to three compared to a code-compliant counterpart. This translates to two to three times less resource capacity required to match that load. If we consider that fossil-fueled resource capacity is being swapped for renewable capacity, this opens an opportunity to reduce required new capacity.
Passive building load profiles are also flatter, dampening the ramping challenges experienced in areas of high renewable penetration (often referred to as the “duck curve”).
Pairing passive with renewable energy to offset annual energy consumption brings us closer to true decarbonization. This conservation-first approach to net zero is absolutely critical. This is most evident when you consider the resources required on the supply side to meet the demand side. Saving 50% on annual energy use in a building results in the same 50% reduction in the renewable capacity required to offset it, and often this reduction is enough that renewables can now fit on the building’s available roof area. But, this ‘net’ zero concept on its own cannot achieve the ultimate goal of zero emissions.
This is where timing comes into play and enabling building loads to align with clean energy supply becomes paramount. Once a building has reached passive levels of reduction in energy consumption, adjusting the timing of energy use may be the next best way to further reduce operational emissions. Shifting the load from an hour with high emissions to low emissions could actually reduce the building’s emissions more than continuing to conserve energy or add more renewable energy, depending on when that saved or produced kWh occurred. Aligning building loads with renewable energy availability can also reduce curtailment of excess energy, and if the renewable resource is on or near the building site it can also reduce the stress on the transmission and distribution network.
The importance of timing was well illustrated by Peninsula Clean Energy, a community choice aggregator (CCA) in California, in a recent report it released on its path to provide 24/7 clean energy to its customers by 2025. The CCA already procures 100% renewable energy resources for its customers, but its goal is to deliver 100% renewable energy on a 24/7 basis. The CCA differentiated between these two targets. The “100% clean energy” goal requires purchasing enough renewable energy to cover the customer load over the course of the year, similar to “net zero.” The “24/7 clean energy” means that the CCA must meet the customer load every hour of the year with clean energy, which is a whole different ball game and requires significant coordination and planning between supply and demand.
Image 2: Shows the supply stack required, seasonally, for Peninsula Clean Energy to reach 100% clean energy goal on an annual basis. Notice the seasonal variability in renewable resource output,the minor variability of the grid load (given the mild climate) and the mismatch between supply availability and load during the night which makes achieving 24/7 clean energy incredibly difficult.
Image Source: Peninsula Clean Energy
In the 100% clean energy scenario, renewable energy can be procured that doesn’t align with demand or during times of high renewable output that could be curtailed or otherwise considered less useful, while in the 24/7 clean energy scenario, the procured energy must align with demand.
The reality is, with net zero building, the renewable energy produced or procured isn’t required to align with when the building is using energy. Over the course of the year, it nets out to zero. But over the course of a day, or even seasonally, not so much. Rather than aiming for just “net zero”, I suggest we strive toward “24/7 zero,” which could theoretically be met with a combination of passive levels of efficiency, (super) flexible building loads, renewable energy production and energy storage.
Stay tuned for the third and final installment of the Facilitating the Renewable Transition blog series as we examine Grid-interactive technologies and Grid-Interactive Efficient Buildings (GEB).
