Case Study: NRG San Francisco Energy Center

NRG’s San Francisco Energy Center is a district steam plant that provides steam to roughly 172 buildings in San Francisco. When there were grid outages, the plant was limited in its ability to produce steam which is its obvious primary revenue source. Therefore NRG decided to install a CHP (combined heat & power) system to provide on-site electric and thermal generation.

NRG wanted a system that could operate in an island mode from PG&E. An island system needs to have a synchronous generator that is self- exciting and does not require grid provided electricity in order to produce power.
Because co-generation is the simultaneous generation of both electric and thermal energy from one fuel source, you have to size the system so that in producing X amount of electricity, you have to be able to utilize the X amount of thermal energy that is simultaneously produced. This is how a system is efficient, by wasting as little of the thermal energy produced as possible.

SF Energy Center could probably utilize the heat produced by 5 MW of co-generation. But the facility has an average electrical load of roughly 212 kW, very small in comparison to the thermal load. Additionally, the utility requires the plant to take at least 5% of the co-generation producing capacity at all times. In anticipation of the addition of a water treatment plant in the next year, coupled with the fact that during cold periods there are spikes that are in excess of 350 kW, NRG chose to deploy 2 Lightfoot Energy 250 kW CHP systems. With a 22 Liter MAN V12 internal combustion engine as the main driver, each of these are capable of producing 250 continuous kW of electric generation and 1,325,000 BTUs of thermal energy an hour. The system is designed to load follow with one unit will running all the time and when the facility load gets to 320 kW, the 2nd unit will start and they will share the load equally. The thermal produced is tied into the NRG hot water loop before the boiler, giving the water from the DA (deaerator) tank an injection of 120 degree water from the co-gen loop.

While this CHP plant is somewhat of an anomaly because of the deviation of normal co- generation efficiency, it gives NRG the reliability necessary to continue to generate steam for its customers and revenue at all times.

*Actual installation image

*Actual installation image

Case Study: Chocolate factory

1,250 kWh combined heating, chilling, and power project
Base cost for cogeneration plant installed- $4,366,690
Annual savings of $767,205 which equates to 44% of current utility costs of $1,738,727
Simple payback = 5.7 years
Simple payback with Federal Grant and SGIP rebate = 4.1 years

Other Lightfoot Energy Solutions Customers

*Actual installation image