Renewable Energies


Photovoltaic Systems

 

Photovoltaic (PV) systems use active semiconductor cells, typically silicon based, to directly convert the sun's energy into electricity. This conversion of sunlight to electricity occurs without moving parts, is silent and pollution free in its operation. The solar electricity fed through electronic equipment is converted to utility grade electricity for use directly in the home. The solar electricity can be used to offset the need for purchased utility electricity or, if the PV electricity exceeds the home's requirements, the excess electricity can be sent back to the utility, typically for credit.

High concentration photovoltaic (CPV) systems have concentrating optics consisting of dish reflectors or fresnel lenses that concentrate sunlight to intensities of 200 suns or more. Multijunction solar cells can then be used to convert sunlight into electricity. Multijunction cells typically have much higher efficiency than silicon ones and work with high current density in CPV (typically 8 A/cm2 at 500 suns). Though the cost of multijunction solar cells is roughly 100x that of a comparable silicon cell, the cell cost remains a small fraction of the cost of the overall concentrating PV system, so the system economics favor the CPV technology.


Geothermal Heat Pumps

 

Geothermal heat pumps use the relatively constant temperature of the earth to heat and cool homes and businesses with 40% to 70% less energy than conventional systems. While conventional furnaces and boilers burn a fuel to generate heat, geothermal heat pumps use electricity to simply move heat from the earth into buildings, allowing much higher efficiencies. The most efficient fuel-burning heater can reach efficiencies around 95%, but a geothermal heat pump can move up to 4 units of heat for every unit of electricity needed to power the system, resulting in a practical equivalence of over 400% efficiency.


System Integration

   




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