Solar CHP—Combined Heat and Power Using the Infinia Concentrated Solar Power System
David Townley | Infinia Corporation
Objectives of the Demonstration
The objective of this demonstration was to assess the capabilities of the Infinia PowerDish™ Combined Heat and Power (CHP) technology to generate clean solar electricity as well as thermal energy for domestic hot water and space heat requirements. When applied to Department of Defense facilities, at both domestic facilities and forward operating bases, the PowerDish CHP technology could reduce the consumption of utility electricity and fossil fuels, thus reducing air and carbon emission pollution as well as stabilizing or even reducing total energy costs for the application site. An alternative to the PowerDish CHP technology for providing non-fossil fuel electric generation and thermal energy for end-use application would be to install two systems: a photovoltaic system for electricity and a solar thermal system for water and space heating applications. Specific performance objectives addressed in the demonstration included monitoring estimated facility energy usage, maximizing renewable energy usage, maximizing savings for systems economics, minimizing direct greenhouse gas emissions, monitoring facility metering, monitoring system maintenance, and monitoring system integration. Overall, the demonstration confirmed that the PowerDish CHP technology can provide clean solar electricity as well as thermal energy for water and space heating applications. However, while the amount of electric production was somewhat less than expected, the quantity of thermal energy delivered to the facility for end-use applications was significantly lower than expected.
The PowerDish CHP system is a modified Infinia PowerDish solar system. The Infinia PowerDish solar system uses Infinia’s free-piston Stirling generator placed at the focal point of a concentrator dish. The solar energy falling on the mirrored concentrator dish is focused on the hot end of the Stirling generator. Through the Stirling energy cycle and a linear alternator, that solar energy is converted into electricity that can be injected into the utility electric grid. The excess energy from the Stirling cycle is rejected to the air through a closed loop cooling system (much like the cooling loop in a car). To capture the rejected energy from the Stirling cycle and make it available for water and air heating in a nearby facility, a heat exchanger was added to the Infinia PowerDish cooling loop system: the PowerDish CHP. The liquid-to-liquid heat exchanger, mounted on the PowerDish heat drive, was also connected to a closed loop system that carried the heat transferred across the cooling loop heat exchanger to a nearby building where the thermal energy was used for space and water heating. In this way, some of the thermal energy that was “thrown away” by the Infinia PowerDish was captured by the heat exchanger in the PowerDish CHP and injected into the building heat loop for use in heating water and air in the demonstration facility, Building #9246 at Fort Carson, Colorado.
Over the test period of January 17, 2012 through December 31, 2012, the PowerDish CHP produced 4315 kilowatt hours (kWh) of electricity (kWhe) and 11,109.7 kWh of thermal energy (kWhth) measured at the engine heat exchanger. The demonstration confirmed that the PowerDish CHP can deliver both electric and thermal energy to a facility from a single solar system. Due to PowerDish CHP forced outages and Infinia control system changes, this measured output was about 22% lower than the predicted output of 5500 kWhe for electricity and about 30% lower than the predicted output of 16,000 kWhth for thermal energy production at the Fort Carson site. In total, the PowerDish CHP provided 54% of the actual electricity and 6% of the actual thermal energy used by the Fort Carson facility.
Very shortly after startup, Infinia identified a potential problem with the high cooling loop temperatures needed for the CHP applications. Infinia ordered the lowering of the cooling loop temperature from the planned 70ΕC to 60ΕC maximum and made control system changes that effectively lowered the output of the system by about 10%. This resulted in lower heat transfer to the building heat loop than planned.
During the first winter months of the demonstration, the heat energy transferred to the building and used for space heating was well below expectations. Infinia redesigned and implemented changes to the building heat loop system before the winter season 2012-2013 which resulted in an approximately 350% improvement in heat delivered for space heating.
Implementation issues encountered in this demonstration project included initial grid interconnection software incompatibility with utility interconnection process, low thermal energy delivery to in-building applications (space heating and water heating), and unexpected PowerDish failures due to design implications from the CHP application.
Some lessons learned for improving the application of the PowerDish CHP technology to future projects include: (1) a low-temperature heat exchanger (more surface area) should be utilized to provide more heat to the building; (2) the solar CHP system should be kept close to the building and point-of-use (POU) applications to minimize losses; (3) thermal heat should be taken directly to the POU applications first and then to storage to maximize the utilization of available thermal energy; and (4) an improved design PowerDish that enables 70ΕC generator cooling loop temperature should be used to improve efficiency of heat transfer to building and POU applications.