Buildings as Batteries: A Flexible Load for a Modernized Grid


This article is the first in a series referencing a paper Sue Coakley and I authored for the Electricity Journal. This special edition of the Electricity Journal titled “Energy Optimization is the Key to Affordable, Reliable Decarbonization” was coordinated by the Regulatory Assistance Project. NEEP’s contribution, Transforming our Buildings for a Low-Carbon Era: Five Key Strategies, discusses the most promising areas to advance building decarbonization and presents initial strategies to begin the transition to a low-carbon built environment.

The following extract from NEEP’s paper focuses on the first of five strategies presented and is augmented by additional discussion of some key points. For the complete strategy and associated references, please see the full article.

Strategy one – buildings as batteries: a flexible load for a modernized grid

How building electrification is implemented can make all the difference in electric grid usage and customer rate impacts. Adding advanced heat pumps to electric grid loads offers an opportunity as well as challenge. The opportunity is to improve the economics of our electricity system and reduce GHG emissions by using underutilized off-peak grid capacity to deliver renewable electricity for space and water heating, displacing the direct use of fossil fuels. The challenge is that, at the same time, building electrification can add to peak period demand, drive the need for costly new grid capacity, and increase the need for peak period fossil-based generation.

Efficient buildings with smart controls can minimize increases in electricity demand and shift demand to off-peak periods (DOE, 2019). For example, low-load homes and buildings using passive house design minimize grid requirements in all periods. Thermally efficient, air-sealed buildings with low emissivity windows can respond via smart thermostats to grid signals to reduce the demand for heating (or cooling) during peak periods while maintaining comfortable indoor temperatures. Similarly, water heaters and electric vehicle (EV) charging can further defer the call for electricity to meet grid reliability needs. Currently, 80% of EV charging is done at home and most of the remaining charging is completed at work, which makes EV charging effectively a “buildings” load.

Adding thermal storage within buildings (e.g., ice storage, hot water tanks) can be part of electrification strategies. Additional electric storage within buildings has been piloted and may have value for resiliency and reliability as well as load shifting. EV battery systems can also become part of a building’s resiliency with modifications to controls. While most building-sited renewable systems to date do not include electricity storage, grid scale and community scale systems sometimes do include storage. As building-integrated batteries become more common (Jin et al., 2017), adding storage either to a building directly or within a community of buildings may become more common to smooth distribution loads.

Additional Discussion

A lot of attention has been paid to making sure that the EV charging system is broad enough and spread far enough to enable longer distance traveling and to address range anxiety associated with limited battery capacity of many early generation EVs. One key point from the “buildings as batteries” discussion is that the vast majority of EV charging occurs, and will likely continue to occur, at either homes or workplaces. EVs will essentially be a building load for smaller residential and commercial buildings, but for larger buildings will probably be built and operated separately.

Charging EVs at home in later evening and early morning hours will help better utilize existing grid and generation capacity. Charging at the work place (or at home, for non-commuters) during mid-day can match well with solar PV generation, possibly on-site or community scale. Fully charged EVs can be configured to provide power to serve building loads, but currently this potential capability is not being exploited. This capability could be important for resiliency and load management.

The primary storage capabilities that most homes currently have is storage water heaters. Increasing the storage capacity of replacement water heaters can be an inexpensive way to shift the water heater loads throughout the entire 24 hour day to improve grid system utilization.   

Meeting winter heating loads in cold climates is an issue that is not completely solved by current generation advanced air source heat pumps (ASHPs) and provides challenges to the grid. Advanced ASHP performance in colder temperatures is improved over prior systems, but both ASHP capacity and temperature limitations can come into play. There are multiple possible solutions, and how cold climate heating can be completely addressed has no well-defined long-term solution. Thermal or electricity storage options could be an option along with other types of heat pumps (e.g. ground and water source), supplemental heating systems (potentially including renewable generated hydrogen) and continued advancements in ASHP systems cold weather performance.  Multiple building or community-scale systems, such as ground loops that serve several buildings, may have better economics than individual systems. If additional energy storage systems can resolve cold weather performance at either the building or community scale, these systems could also have other benefits for the electric system.

Even with (or perhaps especially with) all of these advanced systems and sophisticated controls, better building efficiency is still fundamental to overall costs and performance. When considering “buildings as batteries” as part of the electricity system, reducing loads reduces overall system costs as well as providing improved comfort and security to building occupants. The depth of the efficiency may ultimately be determined by the costs of new renewable generation, but ensuring the reliability of providing that power to all customers during very cold weather is a significant challenge that must be considered in electric system planning and by the programs and policies that support building efficiency and electrification. Reliability and resilience continue to be critical factors to ensure the safety of consumers as low carbon solutions grow in the market.

This blog is part of Building Decarb Central, a series of blogs and other resources aimed at providing a constant flow of information on building decarbonization. Be sure to check out our web portal for more stories, resources, and information.

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