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What If You Could Store Electricity Without A Battery?

What If You Could Store Electricity Without A Battery?

Energy storage. It’s the ultimate flexible resource for utilities, as it holds the potential to reduce peak load, ease the duck curve, assist with frequency regulation, and defer transmission and distribution capital expenditures.

For consumers, the main economic driver exists for those who are on time varying rates - when using batteries on a daily basis can help offset peak pricing. But even for those customers, today’s electrical batteries cost too much to justify the upfront investment, limiting widespread adoption.

However, what if I told you there is another way for both utilities and consumers to access the value of energy storage - regardless of the utility’s rate plan and without the need of electrochemical batteries?

It’s not a hypothetical: batteryless electricity storage is possible right now. When sophisticated energy analytics are applied, homes can become predictable and dispatchable energy storage resources for utilities. And the only thing homeowners their homes.

Homes can act as their own energy storage mechanisms thanks to their thermal mass. Thermal mass is the ability of a material (wood, concrete, stone, etc.) to absorb and retain heat. The denser and heavier the material, the higher its thermal mass. The thermal mass is insulated from the outside environment by the walls, floor, and roof of the building, sometimes called the thermal envelope. When people enter or exit the house, the thermal envelope is opened and the thermal mass is exposed to outside temperature and humidity.

A house with great insulation and low thermal mass will change temperature quickly when the HVAC system is running. This can help save energy. However when someone enters or leaves the house the temperature also changes quickly, causing the HVAC system to run again in order to maintain a comfortable temperature. But a house with high thermal mass resists change in temperature more easily, due to stored thermal energy inside of the home. A typical home can store 2-4 hours of thermal energy, every single day.

The thermal mass of a home depends on the convergence of many different factors, from the size of home, to the amount of furniture within it, to the building materials. To calculate a home’s thermal mass, we use Tendril’s TrueHome Simulation model. We aggregate data inputs on everything from thermostat readings, to materials used in the home’s construction, to insulation type, to demographic data on residents to create a thermal model of the home. Once we measure the thermal mass of a home, we can put that thermal mass to work saving energy.

Thermal Mass and Continuous Demand Management

Continuous Demand Management (CDM) optimizes thermal mass by harnessing its power in concert with homes’ HVAC systems. CDM orchestrates this relationship between thermal mass and HVAC with refined, technology-driven communication between devices and thermostats within the home. When the technology knows the thermal mass of the house, and that thermal mass’s susceptibility to outside weather fluctuations, it can then program the HVAC system to cool or heat a home in the most effective and efficient way. Residents maintain their desired in-home comfort levels and lower their energy costs at the same time.

This past summer, we piloted the use of thermal mass as energy storage in the home to reduce peak load while maintaining customer comfort. The chart below shows the temperature inside of a pilot home (upper graph) and the operation of its cooling system (lower graph) from a hot summer day in August. With our measurement of thermal mass, knowledge of outdoor conditions, and our optimization technology called Orchestrated Energy, we were able to cool the house early in the morning when the outdoor temperatures were cooler, making the cooling system operate more efficiently. In fact, Orchestrated Energy saved about 20% of the energy that the house would have normally used to keep it at a comfortable temperature. In the afternoon, the temperature inside of the house stayed comfortable even though the cooling system did not operate until after 6:00 pm.

Being able to schedule cooling loads because of the thermal mass inside the house is equivalent to charging a battery when electricity is cheap and discharging that battery later, when the electricity is more valuable. When CDM is employed every day, a homeowner can save up to $40 a month during the cooling season.

 Figure 1.

Utilities also benefit from investing in CDM to leverage thermal mass for their customers. In response to Utility Dive’s 2016 State of the Electric Utility survey, 65 percent of participating energy executives said storage was an area in which they should invest more. But, electric battery storage is still an expensive prospect for both utilities and their customers. When utilities put thermal mass to work, they make a more feasible, immediately rewarding investment in storage: one that uses a resource that’s already there, helps meet regulatory demands, and simultaneously improves customer satisfaction by ensuring comfort at a lower cost.

Interested in learning more about how thermal mass and CDM can work for you? Check out Tendril’s Orchestrated Energy to learn more. 




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