Atmospheric optical calibration system

The method of converting actual outdoor photovoltaic device test performance to standard atmospheric optical condition results on a real-time basis concurrent with the test, comprising the steps of:

• measuring ambient pressure, direct normal irradiance at about 0.368 .mu.m, direct normal irradiance at about 0.500 .mu.m, and direct normal irradiance at about 0.862 .mu.m at the test site concurrently with the photovoltaic device test;
• feeding said ambient pressure P, direct normal irradiance V at 0.368 .mu.m, 0.500 .mu.m, and 0.862 .mu.m wavelengths measurements as data input to a microprocessor on a continuous basis, which microprocessor has stored therein data for Rayleigh optical depth .tau..sub.R, standard sea level pressure P.sub.o, ozone optical depth .tau..sub.o, relative air mass m.sub.r, earth orbit eccentricity correction factor .epsilon., and extraterrestrial direct normal irradiance V.sub.o for 0.368 .mu.m, 0.500 .mu.m, and 0.862 .mu.m wavelengths and is programmed to calculate aerosol optical depth .tau..sub.a for each 0.368 .mu.m, 0.500 .mu.m, and 0.862 .mu.m wavelength according to the formula ##EQU11## measuring direct normal photon flux density for the wave band of about 0.4 to 0.7 .mu.m, global horizontal photon flux density for the wave band in the range of about 0.4 to 0.7 .mu.m, direct normal irradiance for the wave band in the range of about 0.3 to 1.1 .mu.m, and global horizontal irradiance in the wave band of about 0.3 to 1.1 .mu.m at the test site concurrently with the photovoltaic device test;
• continuously feeding said measurements of direct normal and global horizontal photon flux density over about 0.4 to 0.7 .mu.m and of said direct normal and global horizontal irradiance over about 0.3 to 1.1 .mu.m on a continuous basis into a microprocessor that is programmed to calculate the ratio of diffuse horizontal skylight to global horizontal photon flux density by subtracting photon flux density by subtracting direct normal photon flux density over 0.4 to 0.7 .mu.m and dividing the difference by the global horizontal photon flux density over 0.4 to 0.7 .mu.m and to calculate the ratio of diffuse irradiance to global horizontal photon flux density over 0.4 to 0.7 .mu.m and to calculate the ratio for diffuse irradidance to global horizontal irradiance by subtracting the direct normal irradiance over 0.3 to 1.1 .mu.m from the global horizontal irradiance over 0.3 to 1.1 .mu.m and dividing the difference by the global horizontal irradiance over 0.3 to 1.1 .mu.m;
• measuring the direct normal irradiance at about 0.940 .mu.m wavelength at the test site concurrently with the photovoltaic device test;
• continuously feeding said measured direct normal irradiance V.sub.940 at about 0.940 .mu.m wavelength along with said measured direct normal irradiance V.sub.862 at about 0.862 .mu.m in to a microprocessor that has stored therein the relative air mass m.sub.r, ambient pressure P, standard sea level pressure P.sub.o, and constants k.sub.i, K.sub.3, K.sub.5 and N.sub.3, which microprocessor is programmed to calculate precipitable water vapor PWV according to the formula ##EQU12## continuously feeding said aerosol optical depths for the wavelengths of about 0.378, 0.500, and 0.862 .mu.m, said diffuse horizontal skylight to global horizontal photon flux ratio for about 0.4 to 0.7 .mu.m wave band, said diffuse irradiance to global horizontal irradiance ratio for about 0.3 to 1.1 .mu.m wave band, and said precipitable water vapor as input data into a microprocessor programmed to generate a computer spectral model of solar irradiance from said input data at the test site over the spectrum from about 0.3 to 4.0 .mu.m;
• converting said computer spectral model to a model of irradiation on a tilted surface at the test site having an angular orientation the same as the angular orientation of the photovoltaic device being tested;
• continuously calculating the spectral mismatch of the photovoltaic device being tested.

A method of determining the character and quantity of skylight solar irradiance available at a particular location on a real-time basis where outdoor testing of a solar device is being conducted, comprising the steps of:

• measuring environmental outdoor optical skylight conditions including molecular scattering, aerosol scattering and absorption, the ratio of diffuse horizontal skylight to global horizontal photon flux density, and water vapor absorption;
• generating a signal from said measured optical conditions indicative of the spectral solar irradiance available at the location of the solar device;
• and
• generating a spectral-mismatch correction factor for correcting actual performance results of the solar device in response to actual outdoor irradiation at the test location to standard atmospheric optical condition performance results for the solar device being tested.

Apparatus for comparing actual atmospheric optical conditions at an outdoor location for testing a photovoltaic device with standard atmospheric optical conditions, comprising:

• means for measuring and determining aerosol optical depth at said testing locations;
• means for measuring and determining the ratio of diffuse horizontal skylight to global horizontal photon flux density at the testing location;
• and
• means for comparing a plot of the product of the actual aerosol optical depth times relative air mass versus the diffuse horizontal skylight to global horizontal photon flux ratio at the testing location with a plot of the product of aerosol optical depth times relative air mass versus the diffuse horizontal skylight to global horizontal photon flux ratio for standard atmospheric optical conditions.

Apparatus for correcting actual outdoor test performance output of a photovoltaic device to standard atmospheric optical condition output values on a real-time basis concurrently with the testing, comprising:

• pressure measuring means for measuring ambient pressure at the test site;
• first sunphotometer means to be located at the test site and pointed at the sun for measuring direct normal irradiation at a first wavelength;
• second sunphotometer means to be located at the test site and pointed at the sun for measuring direct normal irradiation at a second wavelength;
• third sunphotometer means to be located at the test site and pointed at the sun for measuring direct normal irradiation at a third wavelength;
• fourth sunphotometer means to be located at the test site and pointed at the sun for measuring direct normal irradiation at a fourth wavelength;
• first quantum sensor means to be located at the test site and pointed at the sun for measuring direct normal photon flux density in a first wave band;
• second quantum sensor means to be located at the test site and oriented horizontally for measuring global horizontal photon flux density in said first wave band;
• first pyranometer means to be located at the test site and pointed at the sun for measuring the direct normal irradiance in a second wave band;
• second pyranometer means to be located at the test site and oriented horizontally for measuring the global horizontal irradiance in said second wave band;
• first microprocessor means connected to said first, second, and third sunphotometer means and programmed for calculating aerosol optical depth for said first, second, and third wavelengths utilizing irradiance measurements for said first, second, and third wavelengths from said first, second, and third sunphotometer means, respectively;
• second microprocessor means connected to said first and second quantum sensor means and to said first and second pyranometer means and programmed for calculating the ratio of diffuse horizontal skylight to global horizontal photon flux density from measurements by said first and second quantum sensor means and for calculating the ratio of diffuse irradiance to global horizontal irradiance form measurements by said first and second pyranometer means;
• third microprocessor means connected to said third and fourth sunphotometer means and to said pressure measuring means and programmed for calculating precipitable water vapor utilizing measurements from said third and forth sunphotometer means and from said pressure measuring means;
• fourth microprocessor means connected to said first, second, and third microprocessor means and programmed for generating a computer model of the solar spectrum;
• fifth microprocessor means connected to said fourth microprocessor means for converting the computer solar spectrum model to a conversion model of irradiance on a surface tilted at an angular orientation to match the angular orientation of the photovoltaic device under test;
• sixth microprocessor means connected to said fifth microprocessor means and to said photovoltaic device under test and programmed to generate a spectral-mismatch factor and for correcting actual performance responses of the photovoltaic device being tested to standard atmospheric optical condition performance responses.