With energy-consuming equipment, such as water heaters and refrigerators, we have good data on energy consumption and can set clear standards accordingly. In some product categories—clothes washers, for example—Energy Star standards were adopted because those standards provide a high enough threshold to represent just the very top segment of the product market (less than 10%). In other product categories—e.g., refrigerators and dishwashers—we set a higher threshold than ENERGY STAR: for example, exceeding those standards by 10% or 20%. With lighting and lighting control equipment, certain generic products qualify, such as compact fluorescent lamps and occupancy/daylighting controls, while in other categories only a subset of products qualify. In some cases, products that meet the energy efficiency requirements are excluded, because of evidence of poor performance or durability. Microturbines are included here because of the potential for cogeneration (combined heat and power) that they offer.
Clean Cycle
GE's Clean Cycle system produces 125 kW of high-quality electricity from waste heat as low as 250°F, from sources such as biomass boilers and reciprocating engines. Captured heat boils a non–ozone depleting refrigerant (R245fa) in an evaporator, and the resulting vapor spins a turbine to generate electricity. Cooled vapor is then returned to the evaporator to continue the cycle.
Combined heat and power (CHP) or cogeneration units, microturbines and reciprocating engine generators without heat recovery, and fuel cells all support distributed electricity generation.
Microturbines and reciprocating engine generators use natural gas, propane, or other fuels to generate electricity onsite. The same principle is used for microturbines as for large gas turbines at power plants, but the units are much smaller and thus are suited for distributed power production—producing power where it is needed).
When combined with cogeneration equipment—heat exchangers that make use of thermal energy that is usually wasted—the overall efficiency of these units can be increased to over 60%. These units have a number of applications, including off-grid generation, utility peak-shaving, emergency back-up power, and combined heat and power (CHP) at restaurants, commercial laundries, hospitals, manufacturing plants, office buildings with dehumidification or absorption cooling systems, and even homes.
Fuel cells offer exciting opportunities for clean, efficient, distributed generation of electricity. Very simply, fuel cells generate power by reversing the common high school chemistry experiment in which electric current is used to split water into hydrogen and oxygen.
Fuel cells have been used for decades in space. In buildings, fuel cells can be especially useful for back-up power needs. For lack of a readily available supply of hydrogen, most fuel cells in common use today run on natural gas or some other fossil fuel, which is converted to separate the hydrogen from the other elements, so they are not actually a renewable energy source, but they do support alternatively fueled power production.
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