Recent years have seen a call for proper energy sources with PV panels taking its course as the most suitable way of generating electricity. PV panels capture the sun radiation and convert into utility electricity thru the photovoltaic system. Like any other technology, several issues affect the effectiveness of the PV panels in use, as follows: Out of these, temperature and irradiance are some of the most important variables that affects the system. This blog describes the effect of temperature and irradiance on the Rs and Rp of the PV panel and their consequences. Parallel combinations of load resistance (Rp) are also known as series resistance (Rs) of the PV Panels.
Series Resistance (Rs) in PV Panels
There is a series resistance in a PV panel which originates from the semiconductor material, metal contacts, and the connections of the cells. Actually, a higher level of series resistance will increase the levels of power loss, which decreases the efficiency rate of the panel. Another key factor which is usually incorporated in the practical design and functioning of PV panels is series resistance since it has an impact on the behavioral curve of the solar cell in terms of current-voltage.
When series resistance is high, it reduces the voltage which is available at the terminals of the solar cell. This voltage drop is most dangerous in conditions of high current which characterize the working day time or hot hours of the day. Thus, reduction of series resistance should be a critical goal for maintaining optimal PV panels over the course of a day.
With reference to the outcome above, the following factors influenced the result:
Effect of Temperature on Rs
The impacts of temperature on PV cells even though temperatures increase in the semiconductor material of the cells the resistivity is also affected. This leads to an increase in the value of the series resistance HSER. Increased temperatures can inconvenience the metal contacts to swell and damage therefore raising the resistance. Therefore, PV panels that are exposed to higher temperatures will always record low performance because of the high Rs.
The heat dependence of the series resistance is one of the several ways through which PV panels are less efficient during hot weather. To solve this problem the manufacturers uses materials, which temperature coefficient is less or in the construction of the panel the cooling is provided. However, the use of these solutions can at the same time increase the cost and complicate the working of the PV system.
Effect of irradiance on Rs
Measures like irradiance, total amount of light per area, has a great influence on the current produced by a PV panel. There is an increase in the current through the panel as the irradiance level increases. But in the case where the series resistance is considerable, the voltage drop across Rs also rises, and therefore losses occur. However, there is a relation between irradiance and current, which when exists with Rs, make existing value of Rs even more influential under high sunlight conditions.
When there is more current generation, as could be the case at midday when the sun is shining brightly, then the effects of series resistance are worsened. More generally, this relationship is important in the context of minimizing the series resistance during the design of PV panels since the panels should be able to perform under different irradiance conditions without a huge dip in the efficiency of the panels.
Parallel resistance in PV panels (Rp)
Parallel resistance, also called shunt resistance, relates to the paths of leakage across the PV cells. High parallel resistance is also desirable as this means there is little or no leakage current and hence efficiency is retained in the panel. Basically, parallel resistance in an ideal PV cell is considered to be infinite, which implies no leakage current. However, in real-life applications, there are often different factors, including manufacturing and material imperfections and mechanical damage, which creates additional parallel paths and thus decreases Rp.
Effect of Temperature on Rp
Parallel resistance is affected by temperature in such a way that as temperature increases the parallel resistance decreases. It is also noteworthy that when the temperature rises the leakage currents which are in the circuit also augment and consequently the Rp diminishes. This decrease in Rp at higher temperatures leads to higher power loss because a greater amount passes through other routes apart from the load’s path.
The reduction in Rp due to temperature is again dangerous when there is high humidity necessarily meaning that the region experiences high temperatures for an extended period. The following are some recommendations as to how engineers can reduce this issue: Engineers can choose the appropriate material to use and the design that provides small leakage currents as much as possible, and engineers should provide adequate cooling to limit the PV cells’ temperature to the optimal levels.
Impact of Irradiance on Rp
As it was explained before, irradiance does not affect Rs and, therefore, it does not affect Rp directly either. Though, at highly illuminated conditions, the enhancements of charge carriers can worsen the value of low Rp by offering more currents that can flow through the shunt paths. Consequently, the effect of Rp on the overall efficiency is more pronounced when irradiance levels are high; nonetheless, Rp does not undergo large changes with irradiance fluctuation.
However, keeping high level of parallel resistance is very desirable since all the generated current must be available to do the useful work. Sustaining in the upkeep and manufacturing control can play a part to achieve and sustain high Rp values in the PV panels.
Conclusion
It was concluded that knowledge of temperature and irradiance impacts on the amount of canonical series and parallel resistance in thermal emigrant PV plates is vital for enhancement of the calendars. High temperature makes Rs bigger and Rp smaller and both of them are not favourable for efficiency . Conversely, irradiance does not influence Rs or Rp independently, but it increases their influence on the panel’s efficiency. Hence, some of the effective interventions used in balancing thermal conditions and enhancing the effectiveness of sunlight on the PV systems are considered crucial.
For maximum output of PV panels those factors should be considered at the time of designing, installing and even in maintenance. Improvement in material science and engineering disciplines bring out suitable methodologies to decrease the effects of temperature and irradiance on the system and hence broadband solar energy systems will take continual strides.