Traditional silicon photovoltaics collect energy for electricity production from wavelengths <1100 nm. e V = 1234.5 n m ⋅ e V λ ( n m )įor more information on how we get to this equation, see the Key Equations page in the Resources box. eV (just count to five and use the right decimal point).Because the error is negligible for us in the field, we can even use 1234.5 nm eV by the wavelengths that you found in nanometers to find their respective energies in electron volts (eV).To convert energy values as electron volts from nanometer wavelengths: divide 1239.8 nm Photometry is not used for solar resource assessment. Photometry: measure of optically perceived light (illuminance, illumination ).Irradiation: solar field convention, metric for energy ( Wh/m 2 Watt-hours per area or Joules per area).Irradiance: metric for flux of light received on a surface ( W/m 2).Electron volt: energy unit for light/photon wavelengths ( 1 e V = 1.60217646 × 10 − 19 J ).Nanometer: wavelength units for light/photons (sometimes micrometer).Shortwave: solar band of interest in measurement for the applied solar field.If we group irradiance over a block of time, say an hour, we call the measure irradiation, in units of Wh/m 2 (Watt-hours per area, similar units to electrical energy measure). Within the solar field, we measure the shortwave band in terms of irradiance, as W/m 2(Watts per square meter, a flux of light per receiving area). Solar energy is comprised of the shortwave band of light found between 250-2500 nanometer wavelengths of light ( 1 n m = 10 − 9 m, or one billionth of a meter). Why not measure the irradiance/irradiation along with the temperature? What if we, as a solar culture, were to learn what 1200 W/m 2 meant versus 500 W/m 2 for an average hourly or minute irradiation upon an exposed surface (vertical wall or sloped rooftop)? Radiometryįor solar resource assessment, radiometry (the measure of electromagnetic or radiant energy) is more valuable than thermometry (the measure of temperature). Think of how you “know” what 80 ☏ versus 65 ☏ means. Our historical affinity for burning fuels has been paired with an affinity and strong awareness of temperature, but we lack an awareness for measures of light, found through radiometry. While reading, pay attention to the basic rules of light measurement. Brownson, Solar Energy Conversion Systems (SECS), Chapter 3: Laws of Light.
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