Photovoltaics Flashcards
Energy
[J] Capacity for Work
Work
[J] Macroscopic Motion of a System due to the action of a force
Power
[W = J/s] Energy Flow
Irradiance
[W/m^2] Power of electromagnetic radiation per area
Spectral Irradiance
[W/m^2nm] Considers each freq. in the Spectrum
Insolation
[kWh/m^2] Irradiance on a given surface in a given time interval
Solar potential
[kWh/m^2] average daily insolation during the year
Photovoltaic potential
[kWh/kW] average yearly energy production per 1 kW of installed PV Power
Energy of Photon
characterised by eiterh wavelength in lambda or energy in eV
Spectral Irradiance F
[W/m^2nm] Power density at a particular wavelength
Power density of a blackbody M
M = sig*T^4 T= Surface Temp. sig = Boltzmann constant
Solar Constant
Io 1350 W/m^2
depends on applied spectrum
Extraterrestrial Irradiance
Changes due to eccentricity in earths orbit
+- 3%
Terrestrial Irradiance
Changes due to:
Atmosphere
Sun trajectories relative to Horizon ( due to axial tilt)
Atmospheric Effects for PV Applications
- reduction of Irradiance due to absorption, scattering, reflection
- change in spectral content
- local variations in the atmosphere
Air mass
represents the proportion of atmosphere that the light must pass trough
Global Irradiance
I_hg = I_hb + I_hd + I_hr (Beam, Diffuse, Reflected)
usually measured hourly (Pyranometer)
Atmospheric Influence
Considered by clearness indices K_g and K_d
Solar Measurements
- typical mean year data for a location
- avg. daily, monthly or yearly solar insolation
- sunshine hours data
Solar Time
LocalSolarTime (LST) and Local Time (LT) Noon LST is defined as Zenith
LT varies from LST due to timezones, eccentricity
Local Standard Time Meridian
LSTM reference meridian for a particular timezone 15° * deltaT_gmt
Equation of Time
EoT empirical equation that corrects for eccentricity and axial tilt
Time correction Factor
Accounts for the variation of the LST within a given timezone due to longitude variations and incorporates EoT
TC = 4(Long-LSTM) + EoT
Declination Angle
angular position of the sun at solar noon with respect to the plane of the equator. varies seasonally
Utilization of terrestrial irradiance
- Maximize irradiance on surface of PV Module
- > single or two axis tracking system - Maximization of energy conversion process
- > MPPT / efficient dc/dc and dc/ac converters
Rated Power
Maximum power the system is capable of delivering. This is also called the nominal power
Peak Power
This is the power a module delivers if subjected to a standard radiation (25 0C, AM-1.5) of 1kW/m².
Cell Efficiency
Rate at which the semiconductor cell converts energy from radiation into electricity.
Module Efficiency
As several cells are connected to form a module, there are additional losses stemming from the wiring. Note that there is no difference between cells and modules in thin-film technology.
Capacity Factor
With respect to a specific installation, the capacity factor is the average power delivered over a year compared to the rated power.
