12th November 2017
The solar PV market in India has seen a meteoric rise. The year 2016-17 has seen a double capacity addition (see Figure 1) and it is expected that India would add close to 10 GW in 2017-18 an approximate of 130% year on year rise. India is spread in huge lengths and breadths with varied weather conditionsat different places making it difficult to chooseideal spots (apart from few states) for solar PV plant installation. Additionally with the unprecedented growth of PV market the number of module, inverter, and Balance of System (BoS) suppliers have risen to huge numbers. While there is standardization and certification at (almost) each and every vertical, the solar PV power plant still encounters many problems on daily basis. This article aims to educate its reader on the common problems encountered at (both rooftop and utility scale) PV power plant.
Figure 1: Y-o-Y cumulative capacity addition of Solar PV technology in India (Source: MNRE Annual report and Mercom capitals)
This part of the article shall deal with the initial problems of PV power plant i.e. site selection, design and planning and physical installation of component.
Problem in site selection
Site selection includes selection of parameters such as orientation, inclination, simulating nearby shading effects to name a few. The utility scale power plant (as they are installed on huge open land) has fewer problems as compared to Rooftop power plants. As we mentioned in our previous article "Orientation & Positioning of solar module" about the optimum tilt angle and orientation of solar module. However not all the roof have adequate space to install the power plant at the south orientation (for sites in northern hemisphere) and inclination equal to tilt angle. Sometimes in order to squeeze in more modules (resulting in increased capacity and cost of power plant) the system installation may be compromised. Additionally there may be times when few minor obstaclesare overlooked (or grow in size such as small trees)or adequate considerations for new constructions are not given causing shadowing at PV modules leading to reduced generation (Figure 2). With reference to utility scale power plants it (sometimes) becomes important to consider the environmental impacts and impact on biodiversity while erecting a power plant.
Figure 2: Partial shadowing of PV module (Source: Google images)
Problems in design considerations
The designing of the solar PV plant is worked out in a way that it simulates the real field conditions. While there has been a lot of development and improvement in the design of power plant, there still seems to be few problems associated with it. The primary problem is yield estimation of power plant. Attributed to varying climatic conditions and unexpected losses in the plant, the expected energy output from plants (after it has operated few years) cannot be simulated with 100% accuracy.
Figure 3: Estimated energy generation (Source: PVsyst)
The next most important consideration is of Module Mounting Structure (MMS). There are ample designs based on different technology and/or material available in the market. It hence becomes important to select the particular MMS based on detailed calculations, ground/ roof type, etc. However there are evident examples that due to improper considerations or inadequate design/material usage (to make more money) the plant eradicates from ground/roof causing irreversible damage to the plant (Figure 4).
Figure 4: Inadequate module holding capacity of MMS (Source: Google images)
One of the most important design considerations is safety of the system. This is because the solar PV plant houses equipment's which are usually conductive in nature. Thus this metallic conductor forms the least conductive path to lightening strike causing heavy damage to the entire solar PV plant. This justifies the importance of Lightening Arrestor (L.A) and a separate grounding pit for it. While it is mandatory now to install a separate L.A for solar system, there are few plants where there is no L.A increasing the chances of damage (Figure 5). Additionally a Surge Protection Device (SPD) (which stops the reverse current to flow due to heavy surge) is also seen missing in few small installations.
Figure 5: Module damaged due to lightening
Physical installation of solar PV plant
This is the important step and physical installation needs special care as many problems occur during installation. Few common problems occurring during or just immediately after physical installations are mentioned here. One of the most important and highly ignored common problems while installing the power plant is the difference in tilt angle and/or orientation of solar modules. While this may/may not be evident is new power plants, few aged power plants is the place where we can find such defect. This is because the MMS due to various reasons such as wind loads, module load may have bent. This causes a change in tilt and some times orientation of the modules (in comparison to its adjacent module). Such change would lead to difference in power production between module and/or shading of surrounding (other) module leading to generation of hotspot and reduced power output after some times.
Figure 6: Difference in tilt angle and orientation of solar module
Installing a rooftop PV power plant requires drilling holes and/or grouting of MMS in the roof. While not immediately evident leakage in the rooftop is a problem in the long run. This may be attributed to low quality and/or inadequate sealing of rooftop while installing power plant. Additionally using wrong type of MMS of a roof (say heavy bolted roof for weak roof) may lead to weakening the roof causing such leakage as well.
Figure 7: Leakage in roof due to faulty installation
The next most common problem is heating of cables (conductors) which carry current. There are various factors which contribute to this problem. Inadequate wire designing leading to increased resistance, poor heat dissipation from the insulation of wire, loose or tight cable connection causing rise in temperature, faulty system wiring may be few of the contributing factors (Figure 8). Such increased temperature would lead to significant loss of power and hence reduces the monetary output from the plant. Additionally such increase in temperature (if not rectified) may also damage other parts/equipment worsening the damage.
Figure 8: Increase in temperature of wire due to faulty installation
We would continue this article in the next post where equipment specific problems shall be discussed. Keep looking this space for our next article.
Let us all pledge to make solar energy the primary source of energy in the near future.
RAHE ROSHAN HAMARA NATION