I had been toying with the idea of connecting a couple of solar panels to my ancestral house. However, the constant thought of what the return on investment be kept nagging me and I put it off for quite a few months. The house itself is a 80 year old house and until recently had only a single phase supply powering the entire house.
Now that may seem a bit strange but back in the days even a single phase connection was a luxury. Recently I took the house through a much need electrical upgradation and by the time the electrician had finished, I had three phase supply, points for the heavier loads such as airconditioners in all the bed rooms and I had managed to put back into service and old 800VA inverter that had been accumulating dust in one corner. This was also when I revisited the idea of connecting up solar panels once again. The electrician suggest two options - off grid and grid tied and naturally the investment for the grid tied system was nearly 8 times that of an off grid system. Ofcourse the grid tie system would handle the entire house load where as the off grid system would only handle the lighter loads that were connected to the inverter. (This is not because of any electrical limitation but because much of the wiring for the inverter had already been completed and therefore to keep the cost low he suggested that). Naturally the next thing I was curious about was how much it would cost me and I was told the solar panels and charge controllers (including labour) would cost be close to Rs 25,000 and the truss work required to support the three panels (350Watts) would cost me another 35,000 - a total outlay of Rs 60,000 or US $ 1000. This is when I decided to try to find a cheaper solution.
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Step 1: Researching the Options
Thankfully the internet provides enough information about the various types of charge controllers from different manufacturers and while my choice of solar panel or charge controller is not reflective of this make being better than some of the others, I was convinced it should serve my purpose. I chose Su Kam a reputed Indian make primarily because there was a Su Kam dealer right next to my house. Su Kam offered a 25 year warranty on the panels.
My requirement was to find a charge controller that would be compatible with my existing inverter and also allow the bettery to discharge when fully charged. Su Kam seemed to have just the thing I wanted - a new type of charge controller called Solarcon that could convert my makes regular sine wave inverter into a hybrid solar inverter.
Essentially to keep the cost low, I decided to go in for one panel of 100 Watts 12 V rating (Rs 4500)and bought a compatible Solarcon charge controller for around Rs 3500.
I had everything else I needed to connect up electrically. Now the challenge was to overcome the need for truss work to mount the solar panel arrangement. This is where I got innovative and made a massive cost savings. Read on....
Step 2: Arrangement to Mount the Solar Panel
The fabricator who I had called over a few weeks ago had given me an estimate of Rs 35000 to make me a platform of sorts from the terrace area to just above where the red sloping roof was (see pictures).
Then one day while going past a construction site, I saw a couple of workers stand on scaffolding made out of Casuarina and Bamboo poles and I knew almost immediately I had a great idea. I decided to use one corner of my terrace to make a similar scaffolding arrangement and mount my first panel on a long Casuarina pole and stick it out into the sun.
My son a budding mechanical engineer kept arguing it wouldn't work and my answer to him was "the beauty of a solution to a seemingly complex problem lies in its simplicity".
With a total of three Casuarina poles, I made the requisite arrangement for supporting the pole I would mount the solar panel on. The best part about this design was that the poles could be retracted when required to carry out maintenance of the solar panel (replacement, cleaning etc).
In order to mount the panel I got a H shaped bracket fabricated as shown in the picture.
The next challenge was to make sure the solar panels once mounted would move or roll over due to heavy winds or its own weight. That problem too was solved by a simple bolt as shown in the figure.
Total cost of this set up : Rs 900
Rs 600 for the 4 Casuarina Poles,
Rs 300 for the fabrication of the brackets
Although I have mounted only one panel so far, with two more panels I can add on with my existing inverter / battery combination, this is likely to go up to Rs 2700. Now that is very different from the estimate given by the fabricator.
Step 3: Connecting It All Up
The next thing to do was connecting it all up. The Solarcon charge controller ordered through Amazon.in arrived and with its a set of instructions making it easy for almost anyone to connect it up.
For me the important decision to take was
(A) do I relocate my existing inverter and 150Ah battery from where it was to the terrace area - distance of 30 meters . This would also entail having to run a total of 4 cables
(B) do I connect the solar panel and take its two leads up to the inverter and connect the Solarcon there.
My son and I decided to run two wires initially and check its voltage at the other end. If the drop was significant the decision was to go with option (A). I remember during my earlier discussions with the electrician too, he suggested trying to keep the panels as close to the battery and minimize the loss. Being an electrical engineer, I can fully appreciate that.
However, when we ran the two leads and measured the voltage at the end of 30 m, we didn't notice a significant drop in voltage and that simplified things for us.
The rest was merely a question of following instructions and connecting it all up. See figure
Step 4: Setting to Work
I don't have much to write about here because everything just worked perfectly once I had them all connected.
See attached picture. When the battery charges to 14.5 volts the inverter supply is tripped by the charge controller and its starts discharging the battery till the battery voltage drops to 11.4 volts. Then it starts charging again. In doing so, the time that the inverter discharges when there is regular electrical supply available is when I make some savings. At the end of the first day I had made a saving of Rs 3.5. I reckon at that rate it will be about 5 years before I get my money back.
However just to speed up the battery charging process, I intend to procure two more 100 W solar panels and connect them up in parallel to ensure optimum charging of the batteries.
Total cost of setting up my 100 W solar panel and charge controller is as shown below:-
Panel mounting and fabrication - Rs 9,00
Solar Panel - Rs 4,500
Charge controller - Rs 3,500
Wires 2.5 sq mm - Rs 1,000
Total - Rs 10,000 (approximately)
With two more panels this is likely to go up to Rs 21000. I am totally pleased that my solution was not only cost effective but simple. The savings to the tune of Rs 40,000 makes it even more satisfying.
Step 5: Post Script
Its 26 Oct 17 today and I have just installed a second panel in parallel. What that did was take my saving up from Rs 3.6 per day to almost Rs 8 per day. Basically I think it has to do with additional current being available which (a) charges the battery quicker and (b) allows my charge controller to switchover to bypass mode more readily that it would with one panel.
As per my latest calculations, I should be able to break even in about three and a half years.
Limitations with present setup
Having finished this set up, I realized the limitation with this is that I am having to depend on the grid supply to power the lights after sun down. Therefore leaving the two phases that power the heavier loads,
Scope for future improvement
I am currently toying with an idea to see if I can work out a way totally reduce the dependance on the grid supply on this phase -powered during the day by solar.
It might involve buying an extra panel and a seperate battery and designing some additional circuits to turn on and off. However, I think it should be possible.