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  •   photovoltaic solar resource level (1+ / 0-)
    Recommended by:
    Eric Nelson

    The following tutorial will cover topics related to the theory and hardware used to measure the available solar resource at a site, and methods for translating this radiation onto the inclined plane of a PV panel.
    The modern measurement of solar radiation in North America was originally aimed at better understanding the relationship between the sun and the earth's climate, and was pioneered by both the Smithsonian institution and the national geographic society, with the goal of determining the “solar constant” or the amount of energy available at the edge of our atmosphere. The first studies were performed with a device known as a Bolometer, invented by Samuel Pierpont Langley, the future secretary of the Smithsonian Institution in 1878. This was an extremely sensitive device for measuring temperatures, accurate to 0.00001C, and has the honour of supposedly able to measure the thermal radiation of a cow at a quarter mile  .
    The bolometer was used with a prism which split the light into its spectrum. The rise in temperature was measured as a current shown with a galvanometer, an extremely precise device for measuring current, which consisted of a needle made from a strand of quartz 2/25,000 inch in diameter and 15 centimeters long onto which a mirror only 1/25 inch square and 2/1000 inch thick is placed. As an electrical current is passed through this galvometer, this tiny thread will rotate on a pivot, also rotating the mirror. The mirror directs a beam of light onto a photosensitive sheet of paper, and the amount of deflection from home is proportional to the current. It is in this way that extremely sensitive measurements of the solar spectrum were originally made.
    The pyroheliometer is a device designed to measure the total energy available from the entire solar spectrum. The original pyroheliometer was designed in 1837 by Claude Pouillet which was a simple but crude instrument based on water calorimetry which eventually was proven to be inconsistent and inaccurate. Following this, an instrument was made in 1887 by Klaus Angstrom called the compensation pyroheliometer. This instrument consisted of two thin magnesium strips in thermally identical chambers. One chamber was open to the sunlight, and the other was closed by a shutter, and heated electrically by a known power. When the temperature in both chambers agreed, a measurement of the electrical power was taken. The shutter was then reversed, and another measurement was made. By comparing these two measurements, a determination of the total irradiation was made.

    This instrument was considered to be an early standard instrument, and formed the basis for the Angstrom Scale (denoted AS05), founded in 1905.

    Slightly after the development of the Angstrom compensation device, another device was developed independently at the Smithsonian institution by Charles Abbott, as they were unable to obtain an angstrom device. This device was known as the silver disk pyroheliometer, and consisted of a long tube with a shutter at one end, and a thin stip of silver painted black at the other. The silver strip is in thermal contact with a bulb thermometer. To measure the intensity of solar radiation, the shutter is closed for 100 seconds and the temperature drop is noted, the shutter is then opened again and the temperature rise after 100 seconds is noted, finally the shutter is closed a final time and the temperature drop after 100 seconds is noted.
    In order to correlate these temperature changes with the actual power being input into the system, a very complex analysis of this device would be required. Instead, this device was callibrated using another instrument, the water flow pyroheliometer. Essentially, light was admitted in the same way as the silver disc pyranometer, and the beam of light is directed onto a conical receiver, which is assumed to absorb 97% of incoming radiation. Because of the conical shape of the receiver, the reflected light is directed to the walls of the tube, which are also blackened and absorb 97% of the incident light for each time it is reflected. In this way, it is assumed that nearly all of the incoming radiation is absorbed. Water at a constant flow rate and temperature is then allowed to flow in passages in good thermal contact with the walls of the chamber. The rise in temperature at steady state can be measured and from this an exact determination of the incoming power can be determined.
    The combination of these two instruments formed the Smithsonian scale, denoted SS13 in 1913.
    •  ESRI (0+ / 0-)

      ESRI: mapping technology that allows one to organize available data about a community's health, wellness, crime, voting patterns, and develop information-based solutions. This information provides project-based learning for students, and allows them to create bottom-up solutions

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