By Samir Ahmad
OWING TO the unprecedented level of power shortage being faced throughout the major cities and villages of Pakistan, a substantial demand of quick and reliable power solutions for household and industrial application has been observed. People have now started understanding that quick fixes in the form of UPS (Uninterrupted power supplies) and petrol/diesel generators are not a long term and sustainable solution to the impending power crisis, which is here to stay.
In scenarios such as these solar PV systems have shown great acceptability amongst the masses, not only because solar PV systems can be quickly installed on demand but can also be designed to be a dependable source of power. Pakistan is amongst the few countries which are blessed with tremendous solar resource potential year out, and thus solar PV systems can be a commercially viable alternative for a number of applications. However, unfortunately seeing this exponential growth in the off grid solar PV market a significant number of “easy money” oriented opportunists and make shift companies have started to sell these solar PV systems without taking into account the numerous engineering design factors and design practices that have to be brought under consideration before such an installation is actually made. The current situation is pretty clear; traders are selling solar PV system equipment like vegetables. The lack of knowledge and awareness amongst the customers result in bad deals (system failures or equipment failures) which in turn damage a prospective solar market and the possibility of wide spread applicability of solar energy.
This articles objective is to educate solar PV customers of the factors that have to be brought into perspective before any solar PV system is bought. Overlooking these factors would otherwise make the PV system vulnerable to performance failures and which could also possibly lead to the damage of system components. The major components of an off grid solar PV system includes the photovoltaic module, charge controller, inverter and the batteries.
A solar PV module is the most sophisticated component of the complete system, designing a solar system energized by PV modules requires the thorough study of the performance behavior of a solar module in outdoor conditions. PV module manufacturers rate their panels at standard testing conditions based on the IEC 61215 (Crystalline) and IEC 61646 (Thin Films). PV Module performance or output in outdoor conditions is strongly linked with three important factors which are irradiance, cell temperature, air mass. Other factors which also influence PV module outputs are wind speed, shading, dust accumulation, module inclination and humidity, all of these factors contribute to the net wattage produced by the module.
With so many varying conditions worldwide a generalization was essential to compare different PV panel manufacturers, and this is where the standard testing conditions (STC) were introduced. STC specifies the irradiance to be 1000W/m2, cell temperature to be 25C and air mass to be 1.5. This means that when STC prevails the panel will produce its rated output; however, in actuality such conditions are rarely ever reached. Pakistan is a country where there are generally high ambient temperatures which result in higher cell temperatures and thus resulting in a reduced output. The solar irradiance also generally varies from 100W/m2 to 1000W/m2 throughout the day. Thus knowing the actual output of the PV panel under all the stated conditions is crucial for designing a reliable solar PV system. Amateur designers of solar PV systems tend to make a lot of generalization while designing, like for e.g. assuming the amount of sunshine hours in which STC conditions are assumed. This leads to the systems which are likely to fail under the deviating conditions. All contingencies like the variability of environmental conditions and their influence on all the components must be taken into account.
Batteries are another component which requires a careful study and understanding before it can be deployed with any system. The batteries which should be used should have the capacity of undergoing deep cycle discharges that is the depth of discharge is higher compared to conventional car batteries. There are a range of different batteries which can be used each having its own advantages and disadvantages and must be selected while keeping the application in perspective. Ambient temperature and the time of discharge also determine the batteries charge holding capacity and must be considered in the design of a reliable solar PV system. The number of cycles (i.e. life of battery) that the battery is capable of withstanding under the anticipated environmental conditions and also based on the applications must be communicated with the customer. The life of the battery must be accurately determined as this is one component which has to be replaced at least 3 to 4 times within the life of the PV system thus represents a recurring cost. Mediocre PV system designers fail to understand that cutting corners while selecting batteries is detrimental to the economics of a Solar PV system.
The charge controller and inverters is considered as the heart and brain of the solar PV system, sizing both components adequately based on a number of factors is crucial for the long reliable life of the PV system. The charge controller can only be sized once the max and min current/voltage output from the PV array is determined and the inverter can only be sized once the load wattage dynamics are understood. Detailed understanding of the PV performance is necessary to size the right charge controller.
Companies in Pakistan currently selling solar PV systems are designing these systems without any regard to the technicalities associated with executing such a task, most are primarily traders willing to get the most out of the sustainable energy hype. The end result is that people end up accusing the technology for not being able to cater their power demands. This makes the renewable energy market even more challenging to work in. Thus people should be aware whether the solar solution provider they go to is capable of providing a solution which incorporates all the above factors. The government should also take appropriate steps to ensure people get the necessary training and awareness.