The geographical position of India is in the tropics. The sun shines brightly throughout the year, except for some days during the monsoon season. As per estimates, India gets around 3000 hours of sunshine annually. In terms of energy production, this amounts to 5,000 trillion kWh of energy that can be generated yearly from solar radiation.
These are, of course, approximate calculations. But it confirms that the sun is an energy source we should tap into. Given the degradation of the environment, replacing electricity generated by fossil fuels with solar energy is seen as a clean and renewable option.
If one examines the process of solar energy production, starting with the manufacturing of solar cells to its installation and final use, it is rather difficult to wholly agree that it will arrest environmental degradation or that it is a ‘green’ energy entirely.
However, keeping these doubts aside, let me address this question – what does a solar-generated energy system mean for a common person?
As a person who has, after a lot of thought, decided to install a rooftop solar energy system to generate electricity for my household use, let me share my thoughts and experiences about this system and the processes involved.
We had been mulling over moving from the electric grid to solar for years. But the high cost made us hesitate. From 2010 to now, the cost of setting them up has come down, although the subsidy available earlier has been taken away. More about the subsidy a little later.
What finally tipped the scale for us was the nature of the electricity supply from the grid. It was erratic, with surges and low voltage, either damaging expensive electrical appliances or reducing electricity-dependent equipment’s efficiency. Power outages and low voltage during summer became more frequent. These factors were the primary reason for turning to the sun.
There is no dearth of information regarding setting up solar energy systems. But the details are many and somewhat technical. How does one decide and choose? We wanted to move all our electricity needs to the solar system. We also knew that the solar panels were the ones that captured the sun’s energy and, through an inverter, converted it to electrical energy for our use. The first step, therefore, was to calculate the monthly electricity consumption. It helped us determine the quantum of energy to generate and the number of solar panels we need. The next step was the choice of solar panels.
Several Options For Solar PV
There are different types of photovoltaic (PV) solar panels. All panels are silicon-based but may contain other molecules such as phosphorus and boron. The efficiency lies in the alignment of silicon molecules. In the market, different solar cells are available. They include monocrystalline or polycrystalline solar cells; thin film solar cells; amorphous silicon solar cells, and biohybrid solar cells.
The most efficient is the monocrystalline photovoltaic solar cells. Technological advancements have found ways to make these monocrystalline PV panels even more effective in capturing solar energy. The one we have installed is the half-cut mono PERC solar cell. Why monocrystalline panels, and what do these terms half-cut and PERC signify?
Monocrystalline cells are cut from a single silicon source, while polycrystalline ones are blended from different sources of silicon. So, the former is more efficient but also costlier.
The monocrystalline solar cells are cut in half to improve the module’s performance efficiency and durability. As they are smaller, they are supposed to be more resistant to cracking as they need less space. The labour, wiring, and racking costs for setting them up are lower. At the same time, it generates more power in the same given space.
PERC stands for ‘passivation emitter rear contact cell’ and is applied to improve the current flow. A standard monocrystalline cell has a uniform black surface field (BSF). In contrast, a mono PERC has the BSF over an aluminium oxide (Al2O3) and hydrogenated silicon nitride (SiNx: H) stack as the rear passivation layer. It improves the optical reflectivity of the rear surface, thereby increasing the absorption of infrared light in the solar cell due to improved light trapping, which improves the capture of light and electrons.
After finalising the solar cells, our next consideration was whether the energy generated from the sun is to be shared with the grid or stored in batteries or a system where both these processes can be used together.
On-Grid, Off-Grid Or Hybrid
The quantum of electricity generated by PV cells on bright sunny days is more than what one is likely to consume. If the excess electricity generated is passed on to the general grid — the system that supplies electricity to our homes – then you have opted for the on-grid solar system. It is an off-grid system if you choose not to connect to the grid but store the excess electricity generated in batteries. If you decide to have both systems operating together, you have a hybrid system. Each of these options has its advantages and shortcomings.
An on-grid system is cheaper to install as one does not have to invest in batteries. The difference in cost could be anywhere between Rs. one to one and a half lakh. It does not include the cost of installing a net meter. The electrical energy generated is sent to the general grid. In turn, one can import energy from the grid for use. It is especially useful to run heavy consumption appliances such as the AC or heaters and for any other use at night. In an off-grid system, running ACs and heaters require more batteries, increasing the cost.
A bi-directional meter, commonly called a net meter, is installed for on-grid consumers. It calculates the units of electricity exported and imported from the grid. When the export exceeds the import, the electricity department will pay you for the excess units supplied to the grid. If the export is less than the import (i.e., what you draw from the grid is more than what you have given), then you are charged for the same. Except during monsoons or winters, the energy generated by the system often exceeds your needs. So, you can earn some money and retrieve the cost incurred for installation within a few years. But here is a catch.
There is no uniform billing procedure among the states in India when it comes to paying you for the electricity you have exported to the grid. For example, it is a straightforward billing procedure for solar users in Kerala and Karnataka. They get the same rate per unit of electricity they supply to the grid as charged to regular consumers. But in Tamil Nadu, the billing system is slightly different. There are several payment slabs in place for per-unit consumption. Up to the first 200 units, it is Rs 2.20 per unit. But above this, the rate of payment per unit increases. Such consumers also have to pay a network service charge of around Rs 450 per month. The benefits for households in Tamil Nadu are not the same as it is available in Kerala and Karnataka.
In an off-grid system, the electricity generated is consumed directly, and the excess is stored in batteries. From late evening to early morning, when there is no power generation from the sun, energy stored in the batteries is consumed. The number of batteries needed to store and run the system is decided based on the units of electricity consumed and the power requirement for the equipment used.
The advantage of the off-grid system is that one can get uninterrupted energy without any problem with surges or low voltage. The disadvantage is that if you want to run ACs and heaters, the number of batteries and panels increases, increasing your cost. More space is required to set up the panels. The batteries should also be placed not far from the solar cells to avoid transmission loss. Batteries are best placed within a distance of 20 feet from the cell. The off-grid system has a recurring cost too. The battery lasts only 12 years, at the end of which they have to be replaced. Hence many prefer the on-grid system.
In an on-grid system, if there is a power outage, shutdowns for maintenance, transmission failures, etc., power will not be available for use, despite solar energy being generated. At such times, the energy generated by solar cells will be blocked from supplying to the grid to protect those working on the grid. The second disadvantage of the on-grid system is that your electrical equipment is not protected from the vagaries of the electricity supplied by the grid. You will have to suffer surges or low voltage. It does not happen with the off-grid system.
To overcome the disadvantages of both systems, some opt for a hybrid system or what I would like to refer to as a mixed system. In a hybrid system, a special type of inverter is used, whereas in a mixed system, two separate inverters – one for on-grid and another for off-grid connections. Such a system ensures that the consumer can draw power from the grid at night or when the batteries cannot supply the required power. Similarly, excess power generated can be exported to the grid, and income generated.
I have installed a three Kilo-Volt-Amperes (kVA) inverter connected to six 450 watts solar panels. The six panels together generate 2.7 kilowatts (KW) or 10.8 units of electricity. The three kVA inverter can support an input of 3.5 KW. Due to the paucity of space, we had to limit the number of panels to six, limiting the generation to 2.7 KW. The rule of thumb is that a one KW solar panel would be able to generate between 4-5 units of electricity per day.
In an on-grid scenario, we would have all the 10.8 units generated for use. Being an off-grid system, some electricity is utilised in converting the direct (DC) current to alternating (AC) current in the batteries. Hence, I get 7-8 units of electricity per day. On rainy days, this decreases to 5-6 units per day. Despite the increase in cost, we preferred an off-grid system to have an uninterrupted power supply without any change in the quality of electricity we get.
Maintenance And Usage
The solar panels have to be cleaned once a month at least to remove the layer of dust that settles on them. The consumer needs to replenish the battery with distilled water, another cost to be considered periodically. The battery life is dependent on how well it is taken care of.
In terms of usage, we must be particularly careful in operating our electrical equipment. We must ensure that we do not use equipment that simultaneously needs high energy. A water heater and an oven cannot be used together. Similarly, when I have to run a motor pump, I do not run any other equipment other than the fridge.
The display panel on the inverter and an internet-connected Wi-Fi installed on the inverter let me know how many units are being generated and what percentage is stored in the batteries at any given time. So, we generally run our motor, washing machine, or oven when the generation is at its peak. This is normally between 9 am to 12 noon. The power generation comes down mid-day when the sun is at its peak because the solar panels get heated due to harsh sunlight.
The system I have opted for does not support running an AC. The reason was that we did not have space to install additional panels to generate more energy. It is instead connected to the power supply from the grid, which is separate from my rooftop solar system. I must add here that on days when only limited sunshine is available, the system draws electricity from the grid to charge the batteries. If I do not use AC, my monthly bill from the grid is nil or minimal (around Rs 50 or less per month). It is only when I use AC that my bill rises. Even then, it stays put at around Rs. 150 per month. It is quite minimal, considering my monthly bill was in the thousands.
I have mentioned so far, the use of rooftop solar energy systems for household use. It is a different matter when it comes to commercial establishments. The system in our house generates energy that can meet the needs of a small family of three members. If an on-grid system is installed for the same specification, it could meet the needs of a family of four. For us, it was important to have an electric supply that did not damage our equipment and was available at all times of the day and night. To that end, we are happy with the solar-generated power system, although we are also aware that it is not completely green energy as proclaimed by all.
(Published under Creative Commons from Mongabay-India. Read the original article here)