What Makes a Building Product Green
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.
While a heat-pump water heater will save significant energy on a year-round basis, be aware that in a cold climate the net performance (water heating plus space heating) will drop in the winter.
Why we opted for electric water heating over a solar water heater
As we build more energy-efficient houses, particularly when we go to extremes with insulation and air tightness, as with Passive House...