A solar PV plant often has vegetation/weeds growing , which are the unwanted plants grown on the plant premises. Vegetation management is a practical task that needs to be taken care of in O&M and on an average, can contribute upto 4% to the total O&M cost. Increased vegetation can cause
- Shading- Results in shading losses
- Hot spot creation- if a part of the solar cell is shaded, the cell can heat up to such extreme temperatures that a module can burn out causing permanent damage, leading to reduced output, in turn affecting plant performance
- Infestation- of some insects or snakes, which in turn can cause a threat to the people working at the site
- Growth of various disease- causing pathogens resulting in irritation of skin or allergies
- An accidental fire in the plant
Methods of Vegetation control in a PV plant:
There are quite a few methods being deployed to avoid vegetation growth in solar plants across the globe. Below are some of the most prevalent methods used:
- Hired labourers:
Pulling the weeds by hand or hand weeding with the help of weeding hook is the oldest and most effective methods for control of weeds. Weeds can be easily uprooted after a good rain. But this method includes involvement of a lot of manpower hence leading to additional cost. Ensuring safety of the labourers at site is also essential.
- Herbivorous animals:
Herbivorous animals can also help to some extent. This practice softens the industrial image of a large-scale solar system. However, to ensure safety at site, a supervisor is required to continuously observe the animals.
This method too has some shortcomings, like there might be some weeds that even these animals don’t eat and if the plant is left unattended and is only remotely monitored then these could lead to false alarms.
This is a chemical method and is a bit easier to deploy, less costly as well as less time-consuming than weeding by hired labourers or by herbivorous animals.
However, there are a lot more disadvantages of using chemicals e.g. falling health conditions of labourers using them or the site manpower, several harmful consequences to ecosystems, as it can lead to deterioration of soil nutrients, resulting in loss of soil productivity.
While these are some of the conventional means being used for vegetation removal, advancements in technology has led to the emergence of new techniques. These technologies are either being used or are being tested in PV plants around the world. Some of them are as discussed below:
- Weed cutter machines:
Weed cutter machines are tractor based machines with large blades. These can significantly reduce the time taken to remove weeds, however they need to be designed to work in small pitch within modules. Also, there’s a huge initial investment required. The merits need to be evaluated vis a vis the cost required to be spent in designing these.
- Self-propelled mower:
The self-propelled mower can also go under the module tables and clear weeds from there. This includes efficient trimming of large area (500 m² to 300,000 m²) and can trim under modules edges from a 450mm distance to the ground. This resolves the issue of clearing weeds under the modules. However, high initial investment is required for this alternative too.
- Weed-controlling PV sheets:
These PV sheets are especially useful at very narrow or steep slopes where lawn-mowing/weed-cutter machines are particularly difficult to use. Unlike regular systems, there is no need to develop mounting systems, just placing it on the surface would be sufficient. These sheets must be properly placed and covered using a good quality of adhesive tape to prevent the wind from picking them up. This alternative also requires high initial investment, however operating costs are low. This can control weed for almost three years in solar plants.
In addition, below are some methods for small/medium size weeds in a small area:
- Use of boiling water:
It kills weeds in a very easy, quick and safe way with just a scalding jet of hot water on the weeds. It leaves no toxic residue and is nearly 100% effective treating small to medium sized weeds.
- Use of Propane Torch:
This is the quickest method for the small weeds removal. There is a turbo gas trigger and flow valve to adjust the flame and heat with a steel nozzle which is to be connected to a 20-pound propane tank and then gas is sprayed over the green weeds.
In summary, a lot of alternatives are available for weed control- strategic decisions are to be taken to evaluate the efficacy of the alternative for a particular solar plant vis a vis the cost involved.