When we see the technical sheet of a solar photovoltaic panel, they give us a series of parameters that define it electrically, we will try to explain this technical data to better understand the chips given by the manufacturers. We talk about the electrical characteristics of solar panels .
The characteristic parameters of a solar panel are measured by the manufacturers under standard conditions (STC): for an irradiance of 1000W / m2, a cell temperature of 25º and a spectral distribution of AM 1.5G.
The photovoltaic panels include a set of suitably connected cells each other, so that meet the optimum conditions for subsequent use in power generation systems, converting sunlight into electricity.
For example, the 12V panels consist of 36 cells, the 24V panels for 72 cells and the so-called «network connection» for 60 cells.
The behavior of a photovoltaic cell is defined by the Intensity-Voltage (IV) curve represented below:
Electrical characteristics of the solar panels: different parameters that are given in the technical sheet:
Short circuit current (Icc or Isc):
is that which is produced at voltage 0 volts, so it can be measured directly on terminals by an ammeter. Its value will vary depending on the atmospheric conditions of measurement.
Open circuit voltage (Vca or Voc):
is the maximum voltage of the panel, can be measured by not having any load connected, directly with a voltmeter, its value will vary depending on atmospheric conditions.
Maximum power (Pmax) ,
measure in watts peak (Wp): it is the maximum power that can supply the panel, is the point where the product intensity and tension is maximum, under standard conditions of measurement.
Current at the point of maximum power (Imp):
It is the current produced when the power is maximum, under standard conditions of measurement.
Voltage at the point of maximum power (Vmp):
is the voltage produced when the power is maximum, under standard conditions of measurement.
This parameter defines the conversion efficiency (ƞ), the amount of power radiation incident on the panel that is capable of becoming electrical power.
Performance or efficiency = Wp / Wr
Where Wr is the power of radiation incident on the solar panel.
In the manufacturing process not all solar panels are identical, they present a small dispersion. In general, manufacturers guarantee that the power of the P * module is within a band; 63%, 65, 0 + 3%.
Also ideally, look for panels with only positive tolerances, so the manufacturer guarantees at least the power of the panel declared in the data sheet.
- TONC (ºC), nominal operating temperature of the cell:
It is the temperature reached by the cells when subjected to an irradiance of 800W / m2, room temperature of 20ºC, a wind speed of 1m / s and a spectral distribution AM 1.5.
Electrical characteristics of solar panels: Other important features to consider:
- Effect of illumination intensity (Irradiance)
The current supplied by a panel is proportional to the intensity of the radiation and the cell surface of the panel. Let’s see a graph in different irradiances at constant temperature, to show how the intensity varies, to higher incident radiation greater intensity .
- The panels present losses due to an increase in the operating temperature , as a rule they oscillate by every 10ºC of increase by 4%.
Thus the tension provided by a panel varies depending on the temperature. The higher the temperature, the lower the voltage. In the graph that we show below, you can see:
So in the technical sheets we will give the variation in the maximum power (Pmax). Also open circuit voltage (Voc) and short circuit current (Isc) with temperature.