Solar Radiation Measurements for Solar Energy Applications Precision Monitoring of Solar Radiation for Photovoltaic and Thermal Concentrating Solar Energy Systems technology research • quality control • optimise locations • select system type • inform investment decisions • maximise operating eciency • schedule maintenance • monitor performance • output forecasting

Why is Accurate Solar Radiation Measurement Critical for Solar Energy? Good quality, reliable radiation data is extremely important for all activities in the solar energy sector. Photovoltaic (PV) and concentrating solar power (CSP) thermal systems may have slightly diering requirements, but they need accurate solar radiation information for the same reasons. and the scale is too large, to provide a reliable basis on which to make technology and investment decisions. Due to micro-climate and topographical dierences, changes in location of a few hundred kilometers can result in a change of hundreds...

Having selected potential sites based on resource maps and other criteria (access, distance to grid, climate, etc.), these locations need to be evaluated by making high quality on-site measurements of the solar radiation (energy) over at least a full year. The temporal resolution must be sucient to understand real-time variations on a daily basis (for example, a particular location may have a lot of sun, but if there is too much pollution or dust at certain times, the site may still be unsuitable). Select system type The on-site measurements need to be independent of the power generation technology...

Introduction to Solar Radiation The sun provides 99.98 % of the energy for our planet (the rest is geothermal) and it is responsible, directly or indirectly, for the existence of life on Earth. The sun is a star that consists of 71 % Hydrogen, 27 % Helium and 2 % solid matter. Near the sun’s core the temperature is approximately 16 million degrees and at its outer layer (the Photosphere) it is about 5,770 Kelvin. The energy emitted by the sun is approximately 63 MW for every m² of its surface, about 3.72 x 10²⁰ MW in total. The SI unit for the measure of irradiance (radiative ux) is Watts per...

When passing through the atmosphere some solar radiation reaches the Earth’s surface undisturbed and some is scattered or absorbed by air molecules, aerosol particles, water droplets or ice crystals in clouds and ice in aircraft contrails. Gaseous molecules and aerosols cause most of the absorption. Scattering of solar radiation by water droplets and ice crystals takes place over the whole spectral range, whereas molecules predominantly scatter short wavelengths and aerosol particles mainly scatter longer wavelengths. Response [arbitrary units] figure 2: the wavelength bands of radiation, where...

The solar radiation reaching the Earth’s surface is partly reected and partly absorbed, depending on the reectivity (albedo) of the surface. Snow and ice are good reectors (high albedo), dark and/or rough surfaces in general reect less eciently (except rad i clou ated t ds a o spa nd atm ce from osp her e For observations of radiation at the Earth’s surface, two wavelength regions are dened; short-wave radiation, of wavelengths from 300 nm to 4,000 nm, and long-wave radiation from 4,500 nm (4.5 µm) to more than 40 µm. The short-wave radiation includes the ultraviolet, visible and near infrared...

How is Solar Radiation Measured? High quality ground-based measurements of solar radiation are always made using radiometers with a at spectral response over a wide spectral bandwidth. This is usually achieved using a ‘thermopile’ detector with a black coating that absorbs the incoming radiation, heats up, and converts the temperature rise into a small electrical signal. The global horizontal irradiance (GHI) falling on to the Earth’s surface consists of the diuse horizontal irradiance (DHI) from the sky and the direct normal irradiance (DNI) from the sun. This is all short-wave radiation (UV,...

This combination of instruments, for GHI, DNI and DHI makes a ‘solar monitoring station’, to which a horizontally mounted pyrgeometer may be added to measure the FIR long-wave radiation to WMO specications. A pyrgeometer is similar in principle to a pyranometer but the spectral response, shown by the pink line in gure 2, is determined by a silicon window (or dome) that transmits far infrared radiation and has a special internal coating to block the short-wave radiation. The low level millivolt analogue outputs from the radiometers are normally connected to a data logger that records and stores...

What Instruments are Needed for Research or Prospecting? As previously described, measurements from WMO/ISO type pyranometers and WMO compliant pyrgeometers can be compared directly across sites anywhere in the world, with data from meteorological networks, with satellite information, and with solar radiation prediction algorithms. They are technology independent and can be used for any type of solar thermal energy or PV system and are therefore the ideal solution for solar energy research and site prospecting. The basic requirement is always a horizontally mounted pyranometer to measure global...

Traditional photovoltaic (PV) semi-conductor materials are mainly sensitive in the visible and near-infrared parts of the spectrum, from approximately 400 to 1100 nm with a peak just beyond the visible radiation, as shown by the green line in gure 2. However, depending upon the sky conditions, there can be signicant energy available from the ultraviolet radiation below 400 nm and also from near infrared radiation beyond 1100 nm. Therefore, materials development is pushing to make use of this resource. Increasingly, in PV research, a Kipp & Zonen CUV 5 ‘total UV’ radiometer is being included to...

What Instruments are Needed for Particular Solar Energy Plants? Several types of solar radiation measurement instruments may be required within a single plant, depending upon the power generation technology in use and the purpose of the measurement within the plant operation and process ow. One requirement is for ‘reference’ instruments that are used to quantify the solar energy available at the location. These are high quality, high accuracy instruments that can provide the data for comparison with other sites and other measurement sources, such as satellite data, and to build-up a historical,...