Lowering emissions in the Northeast: Key strategy for a New, Sustainable Grid

The trend to decarbonize is transforming the U.S. power grid. The grid increasingly depends less upon fossil fuels and more upon distributed energy resources or technologies such as solar photovoltaic and offshore wind alongside new energy efficiency, demand response, energy storage and other customer-based technologies[i].

Thermal energy storage technology is a key enabler of this transition because of the flexibility it provides to building operators. It is widely viewed as a key way to reduce carbon emissions as more wind and solar, come online: by allowing renewable energy to be available when it is needed the most. The solution stores excess renewable energy for later use and discharges the stored energy when renewable energy is not available.

This trend is evident in the Northeast United States (U.S.) where power grid is undergoing a rapid modernization to decarbonize the electric supply through beneficial electrification. With the fuel mix changing, transmission grid operators in New York and New England – New York Independent System Operator (ISO) and ISO New England, respectively – have looked to all forms of energy storage, from batteries to thermal energy storage are energy storage resources to improve grid operations and reach clean energy goals[ii].           

However, new data suggests that thermal energy storage does more than accommodate renewables: it can also lower greenhouse gas (GHG) emissions across the Northeast by storing[iii] less expensive, lower emission energy overnight and make that energy available during peak daytime periods when emissions are higher. With thermal energy storage, buildings and campuses can swap out high-GHG on-peak power with much less carbon-intensive electricity at night[iv]

New York: Achieving Clean Energy Goals

New York’s Clean Energy Standard (CES), the most comprehensive and ambitious clean energy goal in the state's history, represents one of the drivers behind the state’s decarbonization[v].

Previously, in New York, the downstate region’s fuel mix contained some of the Eastern Seaboard’s dirtiest, most carbon-emitting plants:[vi] Implementation of distributed energy resources has helped enable New York to transform to cleaner energy while maintaining grid reliability. The New York grid is now powered mainly by clean hydro and nuclear with the state’s “peaker” power plants turned off at night.

At night, those peaker plants are off, and the grid is powered mainly by clean hydro and nuclear. The thermal energy storage tanks then discharge – using stored energy to offset chiller consumption – during the heat of the day, when statewide demand is highest, and peaking units must be called to contribute. Therefore, thermal energy storage enables the NY grid to cut back its use of the dirtiest, most smog-producing peaking plants in the state.

Figure 2. Marginal Emissions by Month of Year, and Hour of Day. Columns 1 to 12 on the y-axis equate to Midnight through Noon; columns 3-24 are the PM hours. Source: NYSERDA, NY DPS 2016.

New England: Reducing Emissions

In New England, off-peak marginal emissions were shown to be significantly lower –0.7 percent less than during on-peak hours.[vii] On-peak emissions are at their highest when the temperature is highest.

“In New England, high electric demand days (HEDDs) are typically characterized by high temperatures leading to elevated cooling (energy) demand. During peak energy demand periods, such as HEDDs, the ISO relies on peaking units, which are less utilized during the rest of the year but respond quickly to meet system demand. These peaking units are often jet (aero-derivative) or combustion turbines with higher emission rates.[viii] - ISO-NE. April 2019.

Research showed that marginal emissions for hot, “high electric demand days” in 2017, were a full 34 percent higher than during off-peak hours.[ix] So by relying on energy stored at night to cool the building during the day, thermal energy storage can have a big effect on greenhouse-gas emissions in New England.

This impact is only expected to grow as more wind power comes online across the region.[x]

From Ice to Heat: Thermal Energy Storage in the Age of Electrification

In recent years, regulators and policy-makers across the Northeast have embraced the electrification of heating as a means of reducing the region’s greenhouse gas emissions: by shifting heat from natural gas-powered boilers to electric heat pumps, consumers and businesses can reduce their carbon footprint by relying on an ever-cleaner grid rather than a fossil fuel.

Thermal energy storage will soon be playing a role in this transformation. Trane has developed a thermal energy storage solution for both heating and cooling, the Thermal Battery™ Storage Source Heat Pump System (SSHP).

In this system, each standard thermal energy storage tank (7.5’ diameter, 8.5’ height) can hold approximately 2,000,000 BTUs for each charge and discharge cycle. Thermal Battery SSHP’s can recovery energy for heating during the coldest days of the year and can help utilities and grid manage their winter peak more effectively.

Thermal energy storage: in today’s grid, more sustainable than ever

Thermal energy storage, like all forms of energy storage, have long been considered a necessary component of a sustainable grid[xi]. Experts and regulators consider energy storage as a key way to balance the supply and demand of variable, intermittent resources like wind and solar, which only provide power when the sun shines or the wind blows. As the Northeast’s fuel mix changes, thermal energy storage can accomplish even more: not only do they prepare us for the renewable grid of tomorrow; they also reduce greenhouse gas emissions today.

In many respects, thermal energy storage systems are an ideal asset for reducing greenhouse gas emissions across the Northeast: they can discharge cost-effectively over a long duration; they make their biggest impact during hot summer days, when the fuel mix is most carbon-intensive; and they are frequently located in population centers like New York City, whose generation fleet is the dirtiest in the region. As the Northeastern U.S. power grid’s transformation continues at breakneck pace, thermal energy storage will continue to play a key role in shaping and balancing our energy system.

[i] See for example, NYISO Power Trends 2019. P. 29. Also, ISO New England 2017 Air Emissions Report. P. 29, and  A New World, The Geopolitics of Energy Transformation, https://geopoliticsofrenewables.org/report/the-global-energy-transformation

[ii] Energy Storage, New York State, a program of NYSERDA, https://www.nyserda.ny.gov/All-Programs/Programs/Energy-Storage and See for example, NYISO Power Trends 2019. P. 29. Also, ISO New England 2017 Air Emissions Report. P. 29

[iii] See for example, NYISO Power Trends 2019. P. 29. Also, ISO New England 2017 Air Emissions Report. P. 29.

[iv] ibid

[v] CES Resources, New York State, a program of NYSERDA, https://www.nyserda.ny.gov/All-Programs/Programs/Clean-Energy-Standard/Important-Orders-Reports-and-Filings

[vi] See for example, “Governor Cuomo Announces Proposed Regulations to Improve Air Quality and Reduce Harmful Ozone Caused by Power Plant Emissions.” NYSERDA Press Release, 28 February 2019.

[vii] ISO New England 2017 Air Emissions Report. P. 29

[viii] ibid. P. 18.

[ix] ibid

[x] ibid. P. 7

[xi] See for example: U.S. Department of Energy. “U.S. Department of Energy Launches Energy Storage Grand Challenge.” Press Release, 8 January 2020.