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Effects of Lightning Strike on Solar PV system: A solar PV installation is vulnerable to the effects of lightning stroke. The potenti...

Friday, 5 May 2017

Necessary Tools for Solar PV installation

One, as a solar PV installer, requires several tools and equipments for the safe and successful installation. Solar PV systems are installed on flat-roofs, pitched roofs and on ground. Each location has its own unique requirements and therefore needs specific tools. Yes of course, some tools are common.

Personal Protective Equipment (PPE):

Safety must be the foremost issue and hence the tools for personnel safety are of prime importance. The tools for personnel safety are helmet, safety belt or rope, hand gloves, boots, safety glasses, ladder etc. Each installer must have these tools, also called Personal Protective Equipment (PPE), and should be familiar with their use.

Tools for Array Layout Design:

Installation of Solar PV system starts with the array layout. The necessary tools required for array layout and installation are magnetic compass, measuring tape, chalk or marking pen, angle finder, torpedo level etc. Figure 1 shows a magnetic compass, measuring tape and marking pen.

Fig.1: A magnetic compass, measuring tape and marking pen.

A solar pathfinder is also needed for more precise design incorporating the shadow effects. It evaluates the solar energy potential at that particular location. A compass is not needed when you are using solar pathfinder. A careful and accurate layout helps to avoid any unwanted delay or shifting of solar array in future.

Installation of solar PV on pitched roof requires the exact location of roof rafters or trusses. That’s why installations on flat-roof are the easiest one, only the shade free surface area has to be kept in mind.

Hand-tools for structural support and module installation:

The hand tool required for installation of solar structure and modules are drill machine with assorted bits, cutter machine, spanner set, hammer, cutting plier, slip joint plier, nose plier, screw drivers of different sizes, utility knife, wire stripper, crimping tool, neon tester, hole punch etc. It’s better either to carry an extension board with you or all the power machines should be battery operated. Figure 2 shows a spanner set of assorted size, cutting plier, wire stripper, screw driver, neon tester, nose plier and hammer used for solar PV installation.

Fig. 2: A spanner set of assorted size, cutting plier, wire stripper, screw driver, neon tester, nose plier and hammer used for solar PV installation.

Ground mounted solar PV installations require pit digging for preparing the concrete base. Tools such as shovel etc are required. A spirit level and string line is required to install the solar PV modules in straight line and plumb.

After the correct installation of support structures, solar PV modules are placed and secured to the structure with the help of nuts and bolts. Usually spanners or sockets of two or three sizes, depending on the used nuts and bolts, are sufficient. Some installers use torque wrench also.

Tools and Equipments for Wiring:

Before wiring the PV modules, you have to check them for proper open circuit voltage. For this a digital multi-meter or digital clamp meter can be used. 

After ensuring that all the modules are OK and will properly work, they are connected in series, or parallel or series-parallel combination as per the approved or decided design.

For wiring of modules, sometimes lugs are required. Thus, one has to keep with himself a wire stripper and a crimping tool. Usually MC-4 connectors are used to interconnect PV modules, and for that you have to keep wire stripper and a crimping tool. Several crimping tool kits with interchangeable die sets are available in the market. 

After connecting all the modules, once again the voltage of the string or array should be checked for any in-correct connection. Proper checking at each stage will avoid troubles at a later stage. You may also check the PV module using a test load (may be a DC lamp capable of operating on the PV voltage). The current during the test can also be measured using the digital DC clamp meterFigure 3 shows a digital multi-meter and DC clamp meter used for PV module connections.

Fig.3: A digital multi-meter and DC clamp meter used for PV module connections.

Thursday, 4 May 2017


Efficiency of Solar PV Modules:

Photovoltaic (PV) technology uses semiconductor cells to absorb the solar irradiance and convert it into electrical energy. Commercially available solar PV modules currently have efficiency in the range 15 to 20%. Although the efficiency of the PV modules have increased over the years because of intense Research and Development efforts, there are many factors that lead to degradation of solar PV performance. As more and more MW range solar PV plants are coming up, there is an urgent need to pay attention towards issues that reduce the output of a solar PV module and hence the plant.

Factors affecting Solar PV output:

Among the various factors, the solar irradiance and cell temperature greatly affects the output energy from a solar PV module. Low irradiance and higher cell temperature significantly reduce the PV output. Cell temperature is key issue particularly in countries like India. 

In addition to these factors, the output energy from a solar PV module or solar plant also depends on the reliability and performance of the Balance of System (BoS) and environmental factors. The various losses that occur in a PV system or plant are mismatch loss, wiring loss, inverter loss, sun-tracking loss, shading loss, soiling loss and solar dimming loss.

Soiling Loss in Solar PV Plant:

This article is focused mainly on soiling loss and solar dimming loss that do happen in a solar PV plant. 
"Soiling Loss is the loss in PV output power and hence energy resulting from accumulation of dust, dirt, snow and other particles such as tree leaves and bird’s dropping, etc. over the surface of the PV module." 
Dust is a thin layer that covers the surface of the PV panels and its size depends upon the location of the PV plant and its environment. Accumulation of dust may be due to wind, human activities, vehicular movements, industrial and constructional activities etc. The amount of accumulated dust over the PV module surface reduces the daily, monthly, and annual energy yield of the solar PV plant. Study shows that Middle East and North Africa have the worst dust accumulation areas in the world. India too is prone to heavy dust deposits, particularly the states like Rajasthan. 
In one of the study carried out in Baghdad in the year 2016 showed an 18.7% decline in the efficiency of solar PV modules, when left unattended for a month. A new study, carried out under the guidance of Prof. Bergin of Duke University in one of the IIT campus, has found that dust and particulate matter (PM) are reducing the energy output of solar PV plants in Northern part of India by 17-25% annually. 

The study,  found that half the reduction comes from dust and particles deposited on the surface of solar PV modules, which forms a physical barrier to sun-light entry. Other half of the reduction came from the atmospheric pollution that reduces the sunlight reaching the ground, also known as “solar dimming”. 
Solar dimming or Global Dimming is the gradual reduction in the amount of direct irradiance at the earth’s surface. The effect varies by location and is supposed to have been caused by an increase in particulates such as sulphate aerosols in the atmosphere due to human activities. 
According to a study carried out at the Indian Institute of Tropical Meteorology, Pune, the amount of Solar radiation reaching India’s land mass is reducing by 0.86 Watts/ square metre per year. 

The output of solar PV module or panel is very much dependent on the solar irradiance on the module surface. Or in other words, the output power of the solar PV module is directly proportional to the solar irradiance. The standard solar irradiance for calculating solar PV output and performance is 1000 W/m2. At half the standard irradiance, the output power of the solar PV module is also reduced to half, as can be seen from figure 1. Lower solar irradiance also reduces the output voltage of the PV panel. Figure 1 shows the power-voltage ( P-V) curve of solar PV module at different solar irradiance level  at constant temperature of 25 oC. 

Now a days several software are available for assisting the solar PV designing which can very much predict and asses the PV module behaviour under varrying solar irradiance and other variables.
Fig1: P-V curve of solar PV module at different solar irradiance level ( at 25 oC)

A similar study carried out in Singapore found that the solar PV output has been reduced by 15-25% because of poor air quality. In the worst case the solar irradiance was recorded as low as 50%. 

This means that cleaning of solar PV panels is not enough to ensure maximum energy from a solar PV plant; environmental quality and pollution level also plays a significant role. In future solar PV plant developers will be extra cautious when signing Power Purchase Agreement (PPA) with clients having solar PV plants located in highly polluted areas.