Palo Alto Utilities in California, working with EDF Innovation Lab, has used a grant from the American Public Power Association’s Demonstration of Energy & Efficiency Developments program to produce studies and develop tools for testing thermal microgrids.
The aim of the grant was to provide information and tools to support public power utilities in evaluating the feasibility of deploying thermal microgrids.
Palo Alto Utilities used the $54,000 grant to have EDF Innovation Lab produce several resources including a case study report on a thermal microgrid at Stanford University. The paper studied the Stanford Energy System Innovations project, which replaced a 50 MW combined heat and power plant that was installed in 1987 with a more efficient thermal microgrid.
The new thermal microgrid system was able to reduce greenhouse gas emissions by 68% and water use by 18% and is expected to save hundreds of millions of dollars for the university over the next three decades compared to cogeneration, according to the report. The report notes that shifting from gas cogeneration to grid electricity may be opposite of current trends, but said that for Stanford heat recovery and renewable power are the path to sustainability.
The key to the Stanford Energy System Innovations project is that it recovers waste heat from the campus district chilled water system to meet building heating and hot water needs.
Originally it was thought that with cooling occurring primarily in summer and heating in the winter, the opportunity for heat recovery was assumed to be modest. But Stanford engineers compared the simultaneous delivery of heating and cooling from the cogeneration plant all year long and found a 71% overlap in the heating and cooling produced by the cogeneration plant and that pointed to an opportunity to improve efficiency and reap cost savings.
The heating-cooling overlap occurs because of two factors; the size of the campus – about 800 buildings – and the fact that there are many laboratories and other facilities that have equipment that needs to be cooled around the clock.
In addition to the case study on the Stanford thermal microgrid, the DEED grant provided funding for a white paper that described the technology and the market for the technology, a suite of tools and guidance for assessing technical and economic feasibility, and two case studies on applying the tools to carry out feasibility assessments.
The white paper on the technology and market aspects of the Stanford project concluded that public power is “uniquely positioned” to lead thermal microgrid exploration and development because public power utilities have the ability to standardize interconnection procedures and because local energy system design choices often result in tradeoffs and synergies because municipalities often provide multiple services such as water service, as well as electric power.
The two feasibility case studies that came out of the DEED grant were both conducted in Palo Alto, one for the downtown area of the city and the other for a corporate research park.
The feasibility studies found that the use of a thermal microgrid could reduce the end cost of energy by about 50% and emissions by 42% in the downtown area and reduce natural gas use by 48% at the corporate campus, reducing both costs and emissions, Robert Spragg, microgrid assessment analyst at Palo Alto Utilities, said. On average, the corporate campus could save about $600,000 a year using a thermal microgrid, he said.
The key is the heat recovery system, which is more efficient even than a cogeneration plant, Spragg said.
“It is fair to say that a thermal microgrid could be put in a variety of places,” Spragg said. A corporate campus could have advantages in siting because of its unified ownership structure, but a downtown area is well suited for the technology because of its more diverse load, he added.
For additional information about the DEED program, click here.