Editing Managing a complex energy system: Appendix A: Examples of Alternative Energy Systems
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District energy is an underground energy distribution system that delivers thermal energy to buildings from a central plant. Although not strictly an “alternative energy” system, single district energy installations heat or cool several buildings or homes and so are generally more efficient and produce lower emissions than traditional heating and cooling systems.
District energy is often associated with combined heat and power (cogeneration), which produces both electricity and heat (as steam) from a single fuel. Cogeneration systems recover heat that would normally be wasted in an electricity generator, and save fuel that would otherwise be used to produce heat or steam in a separate unit.
Geoexchange technology uses the relatively constant temperature beneath the surface of the earth (between 4°C and 10°C yearround) to heat and cool buildings. Geoexchange systems require either a circuit of underground piping (closed loop) or water from a well (open loop), as well as a heat pump and a distribution system within the building. In the winter months, heat is pumped from the ground into the building; in summer months, this is reversed and heat is pumped from indoors into the ground, which acts as a heat sink. Although some electricity is required to operate the heat pump, practitioners estimate three to four equivalent units of free thermal energy is produced from every one unit of electricity used.
Traditionally, the term geothermal energy described geologically deeper and higher temperature resources used for electricity generation in residential and commercial applications, which recover waste heat from their operations. However in recent years, the term has been used to describe a broader spectrum of geothermal energy resources including geoexchange systems.
Passive solar refers to a system that collects, stores, and redistributes solar energy without the use of fans, pumps, or complex controllers. Passive solar makes use of the sun’s energy, usually as it enters through south-facing windows, by storing heat in a “thermal mass” such as walls or floors made of stone or steel. This heat can significantly reduce the amount of additional mechanically-produced heat required. Passive solar design can be used in combination with any type of conventional or alternative space heating system. Despite Ontario’s cold winters, passive solar has proven to be successful at greatly reducing residential space heating load.
Since access to adequate sunlight is required for successful passive solar design, street orientation and spacing between houses are key factors in passive solar efficiency. Streets running east to west, where houses have large south-facing facades with windows unobstructed by neighbouring buildings, are ideal for maximum access to winter sun and lower levels of heat from sun in the summer.
Solar photovoltaic (PV) cells transform the sun’s energy into electricity, which is then used as an energy source. Unlike other technologies described above, this high-grade electricity can be used, in addition to heating needs, to power appliances and lights.
'Solar thermal is a type of active solar technology used for space or water heating that collects solar energy in the form of heat and transfers the heat directly to air or a heat-transfer fluid. The use of fans or pumps is required to move the heat for direct use or for storage. All buildings need to bring in outside air for health reasons, and in winter if this air is preheated using solar thermal technology before moving indoors, significant amounts of energy can be saved.
Solar thermal is a type of active solar technology used for space or water heating that collects solar energy in the form of heat and transfers the heat directly to air or a heat-transfer fluid. The use of fans or pumps is required to move the heat for direct use or for storage. All buildings need to bring in outside air for health reasons, and in winter if this air is preheated using solar thermal technology before moving indoors, significant amounts of energy can be saved.
Citing This Article:
Environmental Commissioner of Ontario. 2010. Annual Energy Conservation Progress Report, 2010 (Volume One): Managing a Complex Energy System. Toronto, ON : Environmental Commissioner of Ontario. pp. 59-72
