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Energy Island Integration Study

Executive Summary

Throughout the world, countries are seeking pragmatic solutions to increase the efficiency of their energy systems through the use of smarter energy distribution and the advancement of technology. The drivers for change vary from mandates to economics to environmental conditions. Within the United States, utilities are being required to integrate more renewables and increase the efficiency of the demand-side user.

Demand-side reductions and renewables are important investments for the overall system, but often times these foci result in a missed opportunity. Each day, millions of Btus1 of thermal and electric energy potential are lost through wasted heat or stranded energy. Waste heat occurs when a process creates thermal energy as a by-product that must be disposed of using cooling water from rivers or other bodies of water, through cooling towers or otherwise exhausted to the atmosphere. Most often this heat is produced by industrial processes or electricity generation. Stranded energy includes waste heat and the excess capacity of existing production assets that are currently under-utilized due to the isolation of production facilities or limitations of existing systems.

According to the United States Department of Energy (DOE), “the U.S. industrial sector accounts for about one-third of the total energy consumed in the United States and is responsible for about one-third of fossil-fuel-related greenhouse gas emissions.” Of these industrial energy inputs, 20-50% are lost as waste heat.2 In addition to waste heat from the industrial sector, most electricity generation facilities lose an average of 50-70% of their fuel inputs to waste heat each year. Combined-cycle and combined heat and power (CHP) facilities greatly reduce these losses by increasing electricity production through additional turbine cycles or through the re-use of waste heat for heating and cooling applications, such as district energy. District energy is a thermal delivery system that connects energy users with a central (or shared) production facility.

The waste heat left behind by these facilities rep­resents a clear opportunity to make better use of available fuel resources. In addition, this waste heat carries a value that can be placed in the market to displace fossil fuels and create financial opportunities for the producer and increase rate stability for the users. In order to maximize these opportunities, systems must be looked at with a new perspective that integrates the capabilities and needs of energy islands.

Energy islands are the existing production facilities and aggregates of users operating independent of each other within a close proximity. Operating as islands, these systems could more effectively use their own resources. More importantly, these islands hold vast potential as integrated energy systems, with facilities possessing excess or waste energy resources that could connect users with matching demands for energy.

An integrated energy system is one that combines aspects of multiple systems and technologies to achieve greater efficiencies than any single system could ever achieve on its own. Integrated energy systems can help solve the challenges that prevent a renewable energy technology from reaching its full potential, thereby making it more viable and cost-effective. Consider the promising technology of solar thermal in which the sun’s energy is used to heat water, which can then be used to heat buildings. Or, using a CHP plant to generate electricity and capture the excess steam to heat the water used to heat downtown buildings. Better yet, distributing the excess heat from local industrial processes and using the otherwise wasted heat to provide opportunities for neighboring businesses and jobs.

To substantiate the benefits of energy island integration, District Energy St. Paul (District Energy) partnered with its affiliate Ever-Green Energy, as well as the Department of Energy and Barr Engineering to evaluate the existing production facilities surrounding the Central Corridor Light Rail Transit (LRT) Project, referenced in this report as the Green Line or Green Line corridor. The Green Line corridor stretches between the downtown areas of Saint Paul and Minneapolis in Minnesota. Along this corridor are several existing fossil fuel energy production facilities of varying sizes and efficiencies, including campuses, hospitals, and industrial facilities. Each of those facilities operates independent of the other and most utilize fossil fuels as their primary source of energy, with the exception of District Energy St. Paul, which utilizes waste heat from a biomass-fired CHP plant and the Hennepin Country Energy Recovery Center, a waste-to-energy facility.

In addition, some of these facilities have excess capacity or generate waste heat from their processes that could be recovered and used to meet the heating needs of the surrounding community instead of being dumped to the atmosphere.

Although the study area features unique facilities and user groups, the core components of integration are similar to those in most towns, cities, and campuses throughout North America. By examining the types of producers and consumer loads that can be found in a snapshot of a metropolitan area, this study aims to provide a methodology for other regions to create an energy inventory and examine the potential for the region to integrate existing assets and energy sources into symbiotic systems.

The first phase of this project created an inventory of the energy islands/energy production facilities along the Green Line corridor that are reasonably contiguous to areas with a concentration of heating loads. The inventory assessed business districts, health care complexes, business parks, large places of assembly, government buildings, colleges and universities, and commercial and industrial facilities. The second phase examined the proximity of each of the district energy systems, load concentrations, and waste heat generators; assessed the potential of converting systems from fossil fuels to renewable energy; identified potential locations where solar thermal could be utilized; and studied the potential of developing an interconnecting network throughout the study area.

This study examines specific opportunities for integration of assets and also shares the approach to the evaluation. Components of a system were evaluated based on major development factors and then ranked by the complexity of these factors. Major components were defined as production assets, distribution systems, consumer load, renewable potential, and system integration. With integration as a priority, systems were also evaluated based on their potential to expand the reach and potentially connect with other major systems.


  1. For the purposes of this report, multiple energy units were utilized to estimate thermal energy potential depending on information sources and the type of energy measured. This includes Btu (British thermal units), mmBtu (one million Btu), watt (3.41214 Btu/ h), kW (one thousand watts or one kilowatt), kWh (kilowatt/hour), kWt (kilowatt thermal), MW (megawatt or one million watts), 6MWh (megawatt/hour), MWt (megawatt thermal). Unless otherwise noted, all units are thermal equivalents.
  2. BCS Incorporated, Department of Energy, Waste Heat Recovery: Technology and Opportunities in U.S. Industry, (March 2008)