MEASURING INSTRUMENTS FOR SOLAR POWER SYSTEMS
While performing on numerous types of solar power systems, it’s extremely necessary to grasp the reading, regarding the radiation emitted from the sun, by its measuring devices and recording devices. The radiation of sun to the earth’s surface consists of 2 components like direct radiation and diffused radiation. Different types of solar measuring instruments, e.g., sun shine recorder, pyrheliometer, shading ring pyranometer are needed to measure these live radiations which offer the output in mV and need to be regenerate into correct units by multiplying with their calibration factors. These outputs are then recorded by numerous devices obtainable on the market.
Pyranometer is very sensitive instrument that measures the intensity of total radiation received at earth’s surface over a hemispherical field view.
Typical pyranometer, primarily it consists of a thin blackened surface, that is encircled in two concentrically hemispherical glass domes, so as to defend it from wind, rain and dirt. This surface is connected to a multi junction thermopile and is supported within a comparatively huge well polished case. The hot junctions (input) of this thermopile lie on the ring that is located along the side (upper) of the sensing element. Whereas, ‘passive’ are cold junctions which are situated in such away that they do not receive any radiations.
It is essential for the pyranometer to be mounted in the open, in such a position that there’s no obstacle to impede sun rays in all seasons between sunrise and sun set. An acceptable platform or pillar on the flat roof of the building with no tall tree or building obstructing the radiation from any part of the sky would be the most effective one.
Pyranometer are usually calibrated against standard pyrheliometers. A standard customary technique has been forth within the annals of the international geophysical year 1953. Which needs that, readings to be taken at the time of clear skies, with the pyranometer shaded and pyranometer unshaded at an equivalent or constant time, once readings are taken with pyrheliometer. Shading is suggested to be accomplished by means of disc held at 1m from the pyranometer, with the disc simply large enough to shade the glass envelope. The calibration constant is the ratio of the difference within the output of the shaded and unshaded pyranometer to the output of pyrheliometer and cosθz, the angle of incidence of beam radiation on the horizontal pyranometer. Care and precision / exactitude are needed in these calibrations. It’s potential to calibrate the pyranometer against a secondary standard pyranometer. The direct comparison of the measuring device (secondary) and field instrument (primary) is additionally created to effort the calibration constant of the spherical instrument.
2. SUNSHINE RECORDER
The hours of bright sunshine, (i.e. through that the solar disc is visible) which is used to estimate the long term run of average solar radiation. The instrument accustomed to collect such data is termed as sunshine recorder.
It consists of glass sphere mounted in a brass bowl with a groove for holding the recorder cards. The spherical glass once exposed to the sun produces its image on the alternative facet / side that burns a trace on the cardboard, which are mounted concentrically with the sphere. As the sun moves across the sky, so as the position of the spot across the card. Once the sun is obscured, because of clouds etc., the trace is interrupted. Within the end of the day the overall length of the traceless gaps provide the duration of bright sunshine. The instrument is commonly mounted on a marble base, the bowl being supported within a semi circular brass bar. The sphere is controlled at 2 ends by brass screws that match into cups fixed on the sphere. The bowl has 3 sets of grooves for taking 3 sets of cards, long spline for summer, short spline for winter and straight cards at equinoxes.
As just in case of pyranometer, the sunshine recorder ought to be installed at an area wherever there’s no obstruction to the sun.
Once the instrument has been setup and properly adjusted, it needs very little attention beyond changing the cards everyday. While inserting the cards, care should be taken to make sure that midday line on the card coincides precisely with the noon mark on the bowl.
Anemometer may be a van-type digital instrument used to measure the air speed & air velocity in meter per second. Its variation of range is 0-15 m/sec. The operation of vane-type gauge is as follows.
DIGITAL TEMPERATURE INDICATOR:
The most common electrical method of temperature measurement uses the thermo-electric sensing element, which also referred as the thermocouple junction. The construction of the thermocouple junction consists of two wires of various metals twisted and brazed or welded in conjunction with every wire coated with insulation. The variation of range is of 0-16000C.