The efficiency of solar panels depends on many factors. The same panel could therefore perform better in one place than at a different place. This provides a problem for the industry, how to specify the amount of power a solar panel can deliver? The solution has been sought in the unit peak watt (Wp). The power of solar panels is almost always expressed in that unit, the amount of power the solar panel can deliver under ideal conditions (25 ° C in 1000W/m2 intensity). In practice, unfortunately these circumstances will  never be made, at least not in the  Netherlands sunny country. However, you can really do too in the Netherlands to get the maximum possible from your solar panels. Here we discuss various factors affecting the yield of the panels. Keep this in mind at the purchase of solar panels!

The intensity of the Sun
The first one is probably obvious. The brighter the sun shines, the better a solar panel can do its work. It is for this reason that a particular solar panel in the spring and summer months are entitled to come. As the sun in autumn and winter is less powerful, there are fewer free electrons and holes created (see solar cells and semiconductors), so the current in the circuit decreases. With a properly installed solar cell with little discomfort to resistance (see next section), the voltage remains at about the same level, so the decrease in power is relatively limited.

The resistance of the circuit
If your PV system is used as a separate system (ie not linked to the network), it is important that the resistance of the circuit as low as possible. Since the resistance through Ohm’s law directly affects the voltage and current, these two factors with co-resistance others. The downside of this is that the current-voltage solar cells on a point to work that deviates from the ideal maximum power point. With further increasing resistance, the solar cell is actually more like a worn Ohmic resistance (see chart). In Dutch clear: the total yield of a solar cell decreases with increasing the resistance of the circuit.
g1This graph is clearly visible the effect of increasing resistance on the IV curve of a solar cell is. The stress associated with a given induced current decreases, making the total yield (P = V * I or P = V ^ 2 / R) is also lower.

Shade
Also for solar panels is that the proverbial chain is as strong as the weakest link. Especially when both solar cells and solar panels in series, this proposition. Because serial switched on the solar current of the lowest cell work, it may be that a single shaded cell yield of the whole system gets down. The alternative, in parallel, in such a situation is often impossible because the converter is calculated at a certain voltage. Fortunately, most of the solar PV systems for a large part in parallel, because solar panels often itself 12V or 24V supply. Keep in placement of solar panels also consider how such buildings, trees, chimneys and balconies.

The material of the solar cell

Not every solar cell is the same; cells can be made of different materials, each with its advantages and disadvantages. Most current solar panels are based on mono-crystalline, Be it polycrystalline silicon. Cells based on monocrystalline silicon are expensive, but offer a higher return than polycrystalline solar cells. Thin-film solar cells based on amorphous silicon, heavy metals and / or organic components for the commercial market is not interesting enough. In recent years however, major advances made in research into the use of organic polymers. The expectation is that the thin-film solar panel the street, slowly but surely dominate.

Temperature
Many people think that a solar panel performs better at high temperatures. The opposite is true. Because the conductivity of semiconductors increases with increasing temperature (the electrons are more mobile), it is easier for electrons to holes elsewhere in the material back to fill. Being the electrical balance in the cell increases, the electric field falls away to the boundary, so the load can no longer remain well separated. The result is a decreasing tension between the two layers. This effect is illustrated in the figure below.
g2The effect of temperature on the IV curve of a solar cell. From this graph we can infer that the proceeds of a solar cell decreases with increasing temperature. The current rises or by increasing the mobility of the electrons, but the increase is so small that it is hardly noticeable.

The yield of solar panels (in watts peak) is determined at a temperature of 25 ° C. On a hot summer day, a comfortable 65 degrees however, solar panel hot, a temperature at which you hand in about 20% yield (roughly 0.5% per degree Celsius above 25 ° C). It is therefore important to keep solar panels as cool as possible. While this is obviously not always possible, it is important in any case, the passive in order to have good cooling. Install the solar panels are not too close together and make sure the wind, between the panels by addition, even under the panels can blow through. A solar panel actually performs at its best during a sunny summer day with a cool breeze to keep the panels cool.

Especially in warmer countries it is important to choose a solar panel with a low temperatuurcoefficient. This value indicates the sensitivity to temperature variations of the solar panel again, the lower the better. In the Netherlands, hardly, but a solar panel based on monocrystalline silicon performs with -0.4% / ° C slightly better than a solar panel based on polycrystalline silicon (-0.5% / ° C). What the future will make out, is that solar cells based on amorphous silicon have a sensitivity of only -0.15 to -0.25% / ° C.