The following matrix provides an overview of key energy production technologies, classified by ultimate energy source.

Ideally, these technologies should be weighed in the context of local conditions and an overall municipal strategy that ensures maximum community benefits at the lowest possible cost.

• Biomass combustion or gasification involves using organic waste from landscaping, demolition and land clearing, forestry, and agriculture and households to produce heat, electricity or combined heat and power, either directly through combustion or indirectly through gasification. These uses must be weighed against other disposal or recycling alternatives for some forms of organic waste such as composting; combustion also requires consideration of potential air quality impacts.
• Geo-exchange is a set of technologies that rely on energy stored in the earth (and in some cases surface waters) to heat and cool individual homes, multi-unit residences, commercial spaces, or industrial facilities. 
• Sewer or wastewater heat recovery utilizes heat recovered from wastewater to provide space or hot water heating nearby residential and commercial buildings, or for industrial facilities and processes. The heat recovery can be done at the building scale (e.g., GFX); from sewer mains (e.g., Rabtherm technology from Switzerland); or from sewer pump stations (e.g., Oslo, Tokyo, and Vancouver applications). The City of Vancouver, British Columbia will heat homes for over 4,000 people from heat extracted from one wastewater pumping station.
• Wastewater biosolids digestion utilizes methane produced from wastewater treatment plant biosolids (sludge or residuals) to produce heat and/or power.
• Solar technologies may be passive, active thermal, or photovoltaic (PV). Passive solar is covered in the Buildings section. Active solar involves collecting solar energy to heat water, which can augment domestic hot water heating, or heat outdoor swimming pools (where heating is seasonal and coincides with the periods of most sunshine). PV utilizes panels to produce electricity. Panels are most commonly placed on roofs, but they can be freestanding or integrated with exterior finish materials or set upon freestanding supports.
• Landfill gas capture involves capturing methane from landfills to produce heat and/or power.  Methane from many landfills is either not currently collected or is burned off in flares, rather than used for energy production. 
• Micro-hydro is a form of hydropower involving very small turbines.  For example, in a municipal water supply system, it is sometimes possible to replace pressure release valves in gravity-fed systems with hydroelectric turbines. The turbines reduce pressure and produce electricity.
• Wind power involves the conversion of wind energy into more useful forms, such as electricity, using wind turbines. There are many different sizes of turbine available and applications may involve a single turbine or many turbines grouped into a wind farm.  Wind farms composed of many very large turbines still tends to be the most common and cost-effective application.
• Tidal energy is a form of hydropower production that exploits the rise and fall in sea levels due to tides or the movement of water caused by tidal currents.  Tidal power is not yet widely used.   

District Energy Systems

• District energy systems centralize the production of heating or cooling for a neighborhood or community. Most plants produce steam, hot water, or chilled water, but some do double duty (providing electricity as well as heating) or even have triple products (heating, cooling and electricity).
• District energy offers the potential for economies of integration (load diversification), economies of scale, longer amortization of equipment and lower financing costs. District energy schemes can enable more efficient and/or renewable energy supplies to reduce GHG emissions and support other community objectives.
• District energy systems can save energy and money. They offer economies of scale, longer amortization of equipment and lower financing costs. With a diversity of users, they also offer economies of integration through flattening of peak demand and sharing of heating and cooling flows. And district energy plants can enable the use of more efficient alternative and/or renewable energy supplies, adding even further to their ability to reduce greenhouse gas emissions and support other community objectives.
  • For example, as part of the largest hot water district heating system in North America, District Energy Saint Paul, in Minnesota, provides an estimated annual savings of 280,000 tons of carbon dioxide.
• The economics of district energy are very site-specific. As a rough rule of thumb, a neighborhood will be a good candidate if it has some of the following characteristics:
  • Several large buildings or building complexes (such as hospitals, hotels or colleges).
  • A mix of uses (such as a town or village center). 
  • Moderate residential densities (such as multi-family units or apartments).
  • Relatively small spacing between buildings and a grid street layout.
  • A source of relatively cheap energy (such as waste heat from an existing boiler or sewage treatment facility). \
  • Few electric resistance heating systems in existing buildings. (These cannot be easily retrofitted.)

Combined Heat and Power, or Co-Generation

• Combined Heat and Power, co-generation, is the simultaneous production of power and usable heat. These systems may be fueled by natural gas or biofuels (e.g., wood waste).  Applications can range in size from individual buildings to district energy systems.  Larger applications tend to be more economical. 
• In conventional power plants, a large amount of heat is produced but not used. By designing systems that can use the heat, the efficiency of power production can be increased to 80 percent. Without that, efficiency ranges between 35 and 55 percent.

Tri-generation

• Tri-generation means the combined production of electricity, heating and cooling. It involves connecting cogeneration units to absorption cooling units (cooling produced from heat).

Energy Net Metering

• Net metering supports the production of electricity on-site by enabling the selling or trading of excess power to the local electric utility.   
• A single, conventional meter is allowed to spin backward when the customer’s system produces excess power; it spins forward when the grid supplies supplemental power. Customers pay for their net consumption.  
• Local governments that own their electric utility can develop net metering programs for their customers.  Other cities and counties can work with the local electric utility to ensure they offer net metering. 
• Municipalities can take advantage of net metering to implement electricity production within their own facilities.