07-09-2014, 11:38

Step 4 - Determining the value of Rsh

As in the example presented in the study referred to in the first topic, I will also choose to calculate the value of Rsh, in order to obtain a voltage drop in Rsh with the ratio of 1 mV for each 10W / m2. So for a Solar Radiation 1300W / m2 intend to get a voltage drop of 130mV Rsh. Using Ohm's law as R = V / I, we Rsh = 0,130V / 0,075A ie Rsh = 1.7333333 Ohm.

It is important that the resistance to be used in Rsh has the maximum possible accuracy, and preferably not need to travel the world to find her. We will round the value calculated for 1.74 Ohm, as it exists in the E96 series values with precision of at least 1%. Has this value been coincidence? Continuing ...

The resistance Rsh shall be welded as possible along the positive and negative terminals of the CF, taking care to make sure that the weld is perfect. Poor welding may cause a resistance greater than the value of Rsh own contact. In each of the CF terminals, we should also weld a small piece of wire, which we will later use to read the variations of voltage drop in Rsh, which we now know will be linearly proportional to the intensity of solar radiation.

A small aside in support of rigor. We know that a photovoltaic cell, also not react at all frequencies that are part of the electromagnetic spectrum, and is practically blind those of longer wavelengths, we know also that measuring Isc we do is affected by an error has caused internal resistance of the measuring device (this mistake could be determined knowing the specifications of the device used in the measurement, but for simplicity we will ignore), but we know also that we are not dealing with the construction of a device for laboratory use, but rather a simple equipment for a fraction of the price of a real pyranometer enable readings with a margin of error that I consider acceptable taking into account the purpose for which they are intended.

Continued ... in the next topic.

As in the example presented in the study referred to in the first topic, I will also choose to calculate the value of Rsh, in order to obtain a voltage drop in Rsh with the ratio of 1 mV for each 10W / m2. So for a Solar Radiation 1300W / m2 intend to get a voltage drop of 130mV Rsh. Using Ohm's law as R = V / I, we Rsh = 0,130V / 0,075A ie Rsh = 1.7333333 Ohm.

It is important that the resistance to be used in Rsh has the maximum possible accuracy, and preferably not need to travel the world to find her. We will round the value calculated for 1.74 Ohm, as it exists in the E96 series values with precision of at least 1%. Has this value been coincidence? Continuing ...

The resistance Rsh shall be welded as possible along the positive and negative terminals of the CF, taking care to make sure that the weld is perfect. Poor welding may cause a resistance greater than the value of Rsh own contact. In each of the CF terminals, we should also weld a small piece of wire, which we will later use to read the variations of voltage drop in Rsh, which we now know will be linearly proportional to the intensity of solar radiation.

A small aside in support of rigor. We know that a photovoltaic cell, also not react at all frequencies that are part of the electromagnetic spectrum, and is practically blind those of longer wavelengths, we know also that measuring Isc we do is affected by an error has caused internal resistance of the measuring device (this mistake could be determined knowing the specifications of the device used in the measurement, but for simplicity we will ignore), but we know also that we are not dealing with the construction of a device for laboratory use, but rather a simple equipment for a fraction of the price of a real pyranometer enable readings with a margin of error that I consider acceptable taking into account the purpose for which they are intended.

Continued ... in the next topic.