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Combined Heat and Power and Grid Resiliency


Making the grid more resilient to natural disasters is critical to protecting customers and significantly reducing the magnitude of outages as well as the economic costs associated with them. The Electric Power Research Institute (EPRI) provides a useful three-pronged approach for improving grid resiliency that consists of: hardening (infrastructure), recovery (restoring power), and survivability (equipping customers).1 Distributed generation (DG) directly supports two of EPRI’s focus areas. First, DG resources can harden the grid by providing uninterrupted power onsite for critical facilities and by generating power near high-density load centers. Second, DG can improve recovery efforts after a disaster by increasing the speed of power restoration.

Hardening and DG

One of the most obvious means to harden the grid is to bury power lines to prevent outages from fallen trees and broken poles; however, doing this for the whole system can be prohibitively expensive. The most cost-effective way to ensure uninterruptible power for critical infrastructure, such as hospitals and communication centers, is to generate it onsite. For most facilities with the need to maintain power throughout every type of grid disruption, combined heat and power (CHP) is the most efficient DG solution. Additionally, DG can strengthen the grid by placing power generating assets within the distribution network. When power generating assets are sited near demand centers, they help maintain power to critical portions of the grid even when transmission lines or larger centralized power plants are down.

Hardening Facilities

CHP, also commonly referred to as cogeneration, is a highly efficient method of generating electricity and useful thermal energy from a single fuel source. This simultaneous generation is a distinctive and valuable characteristic of CHP and often results in 80 percent overall fuel efficiency. There are primarily three technologies used in CHP applications—gas turbines, gas reciprocating engines, and boilers used with steam turbines. In CHP systems using any of these technologies, waste heat from the combustion process is captured to provide useful thermal energy to a variety of applications: hot water for an apartment complex, steam for an industrial facility, cooling for a data center, or heating for a hospital. This is in addition to the electricity provided directly to the facility and, in some instances, exported back to the grid.

Installing CHP has many advantages. Emergency preparedness is the most prominent advantage. Apartment buildings, hospitals, airports, and other facilities stayed online during Superstorm Sandy while their surrounding communities plunged into darkness. CHP was more reliable in these situations because the power generation equipment was used continuously leading up to the disaster, and thus, was regularly serviced and connected to an uninterrupted fuel supply through the natural gas grid. This contrasts to diesel backup generators that are rarely used, rely on a limited/expensive source of fuel, and experienced serious failures during Sandy.2 Not only can CHP keep critical infrastructure online in an emergency, but it is dispatchable, meaning that it can be called on to provided heat and power at a moment’s notice, which is not true of onsite wind and solar technologies.

There are non-disaster benefits of installing CHP systems as well. Due to the utilization of waste heat, these systems often achieve efficiencies of 70 to 80 percent, significantly higher than producing the heat and electricity separately, which has average levels of efficiency of 40–50 percent in the U.S.3 Higher total efficiencies result in lower fuel usage, decreased energy costs, and reduced emissions. Additionally, CHP systems utilize low-priced, domestically abundant natural gas. This makes CHP a valuable asset to reduce a facility’s energy costs, even without considering the benefits it will provide when a facility is weathering a disaster.

While Sandy severed power to millions across the eastern U.S., CHP kept the lights on at a number of facilities. In New Jersey where more than 2.6 million lost power—more than 65 percent of total utility customers4 —the CHP plant at Princeton University provided steam and electricity to the university community of around 12,000 people throughout the storm while the surrounding community remained without power. The plant, which runs on natural gas, uses an aeroderivative gas turbine (a modified jet engine) and provides one of the highest levels of reliability.

Further upstate, a CHP plant employing a different technology (reciprocating gas engines) at Rochester International Airport was also able to maintain power among widespread outages in the region as Sandy moved further inland.5 There are numerous other examples of CHP keeping the lights on during Sandy for tens of thousands in just New York City alone, from apartment and university facilities in Manhattan to large residential complexes in the outer boroughs.6

Hardening Distribution Grids

Strategically placing power generation assets within a distribution grid is an effective way to ensure uninterrupted power for many customers who are unable to build their own CHP plants. A recent example is the case of New York Power Authority’s (NYPA) Power-Now sites. In early 2000, NYPA implemented six widely distributed power generation sites throughout the city near major load centers. Equipped with ten aeroderivative gas turbines, they can provide more than 450 megawatts of power. The plants kept running through Superstorm Sandy and delivered critical voltage stability to the New York City grid. Prior to Sandy, these units proved their worth in the wake of the September 11, 2001, terrorist attacks. The New York Independent System Operator, which runs the state’s transmission system, limited deliveries of electricity into the area from upstate plants. On another occasion—during the Northeast blackout in August 2003—the plants helped return power to New York City while stabilizing the downstate transmission system.

Recovery and DG

After a natural disaster hits, the priority for the electric grid is to restore power to parts of the system that were damaged, severed, or otherwise left powerless. Typically, this takes the form of repairing damaged lines and bringing power plants back online that were shut down as a result of the disaster. However, there are circumstances where plants cannot be brought back online easily or transmission lines are damaged beyond simple/rapid repairs. This can result in leaving large swaths of customers in the dark for days or require forced energy reductions that can last for weeks or even months after the disaster occurs.

In these situations, a very effective solution is to have a fleet of mobile, trailer-mounted power plants that can be rapidly deployed to areas with the largest or most critical power needs. This type of solution uses proven technology, such as gas turbines and reciprocating engines, which can quickly connect to and provide power for an existing grid. For example, after the Fukushima earthquake and tsunami damaged transmission lines and brought numerous power plants offline in Japan, trailer-mounted gas turbines were a critical part of the strategy that helped prevent widespread blackouts in the summer of 2011.

The advantages of an energy-dense fleet with a small footprint that has natural gas or dual fuel capabilities is that it:

  • can be connected to the buried and undisturbed natural gas grid, and
  • can avoid liquid fuel supply issues that arise after a disaster (e.g., fuel shortages in New Jersey and New York after Sandy).

Additionally, utilities can improve recovery for residential, commercial, and industrial areas by rapidly bringing in power-generating fleets, which bypass more drawn out transmission restoration efforts.

Takeaways and Next Steps

DG is a critical component of grid resiliency investments because of its ability to harden the power system and improve recovery efforts after disasters.

  • Hardening of a facility: CHP should be used to provide uninterrupted power because it is dispatchable, does not rely on liquid fuels, and has non-disaster related benefits including lowering energy costs and reducing emissions. Additional funding and policy incentives are needed to spur private sector investments.
  • Strategic locations: DG assets should be placed in strategic locations within distribution networks, specifically, near high density load centers.
  • Recovering from a disaster: To prevent long-term power outages, mobile DG technologies (e.g., trailer mounted gas turbines and reciprocating engines) need to be deployed to help get power to customers quickly by providing emergency/bridge power before the grid is fully restored.
  • Government involvement: Government leaders at the federal, state, and local levels should focus resources on infrastructure that includes DG applications as part of a larger strategy for a more resilient grid.

Next | Key to Staying Connected is Disconnecting

 


1 www.intelligentutility.com/article/12/11/epri-sandy-exposes-smart-grid-limits-and-maturity?quicktabs_6=1&quicktabs_11=1

2 www.businessweek.com/news/2012-10-30/new-york-hospital-evacuates-patients-as-sandy-hits-power

3 www.epa.gov/chp/basic/efficiency.html

4 www.dailyfinance.com/2012/11/16/power-outages-after-hurricane-sandy-werent-unusually-long-after/

5 nrg-concepts.com/rochester-international-airport/

6 nrg-concepts.com/cogeneration-chp-plants-keep-the-lights-on-for-thousands-during-sandy/