Solar energy for homes

Solar energy as an option for homes

Background

Much has been said about tapping power from renewable sources and Solar and Wind top the list. I was toying with this idea for perhaps more than a year more for academic interest rather than any commercial viability and looking at both wind and solar. Wind option was dropped since the wind velocities where I stay are not that high to generate power to meet daily requirement. Solar also fascinated me because the number of rainy days is very small in my place and therefore the 'blackout periods' expected to be insignificant.

At the very outset let me make it amply clear that if one is looking for Return On Investment (ROI) in conventional way in this project, the returns are dismal to put it mildly (I have invested Rs 2.4 lakhs and save around Rs 1000 of electricity bill every month i.e. a payback around 20 years). However from a very holistic angle and long term sustainability I am convinced that Solar power makes sense. How long can we enjoy paying electricity bills at subsidized rates? As the availability of natural sources like coal and oil decline, the power generation from these sources will increasingly become costlier in tune with laws of economics. Another point to be noted is that if you are in a location where there are long duration of load shedding, frequent and unpredictable power interruptions, breakdowns and perennial shortage all through the year, it makes sense in considering options for solar power.

I was emboldened to invest in this venture (and just not restrict to academic exercise on designing solar power plants and give lectures on advantages of solar power) because my daughter was also quite supportive to back financially (100%) and did not mind if the experiment failed. Few reputed companies that I had approached had quoted around Rs 4.5 lakhs to meet my needs as they perceived. I was however not totally satisfied with their offers. I thought they had over-designed the unit (may be to ensure that there is no complaint from me later on for non-performance or under performance). Even my volunteering to take the blame for deficient performance for giving a configuration which I thought suited me did not elicit encouraging response - perhaps they did not want to risk their reputation and rightly so. I always felt that I should be able to install a power plant meeting my needs for less than Rs 2.5 lakhs. In my scheme I did not put any extra 'fat' in the design. My reasoning was that if condition necessitated increasing the capacity, I could install additional panels and add extra set of batteries. Why spend money now for an 'imaginary shortfall'? The only unit whose capacity cannot be increased by putting additional numbers is the inverter the sizing of which I was liberal.

The quotation of Rs 4.5 lakhs also did not give me comfort to immediately plunge into the project. So I waited for some government incentives to come before taking the plunge. (It is a different matter that nothing came either from the Central Govt or from the State Govt). Meanwhile I shared my idea among my friends here in Nanjangud and two of them showed lot of interest. I thought, three of us pooling together should act as an incentive for prospective supplier to quote an attractive price. Amongst we three, one lives in his farm house where there would be almost no power available for 14 to 16 hours a day and for him an alternate source of power was a dire necessity. In the last week of January he informed me that he has gone ahead and installed a totally stand alone unit for Rs 1.65 lakhs. I was surprised as to how one can get the system for such a low price. I went, saw and frankly I was conquered.

The proprietor of this party is enthusiastic young man willing to learn and listen. In a way to me it is a startup company which wants to grow and establish its brand. When I gave my details on the power load he came out with a configuration that I had arrived at long time back. What I liked about him is that he is prepared to listen to what you want and supply what you need rather than supply what he wants (may be because he is still to grow - I have always felt that small is beautiful).

The Basics

Now I shall explain the factors that should go into configuring the solar plant. Fundamentally there are three segments in the solar power set up which need to be optimized independently to keep the cost low. By optimization I don’t mean you cut down your comforts but would definitely suggest cut down on luxuries.

A.      Average daily consumption – From our monthly electricity bill, we know average units we consume on a daily basis, e.g. if we consume say 240 to 250 units monthly we can say that the average daily consumption is 8 units. If possible find out how much you can reduce from this consumption if you switch over to LED lights. Lighting load can be reduced by 20% easily with this switch over. Thus if you install 1.5kw panels, on a normal day with sunshine available from say 9Am to 5pm i.e. 8 hours the maximum that you can expect is 1.2kwh. It should be noted that the specifications on the panels is for peak wattage generation i.e. a 250wp panel will generate at its peak 250 watts ('p' after the wattage denotes peak). We should consider not more than 70% of this value available to us for harnessing. Thus taking 70% of peak generation of 1.2kwh we will get 8kwh of energy that day. In my case I have got a max of 7.7 units generation in a day in the last 15 days since the time I am on Solar. Most of the days in the last 15 days, the generation has been around 6.5 units. In these 15 days practically there has been no generation after 3pm since the sky gets overcast with dark clouds (but rains have kept alluding us).

B.      Peak Load – The second component of cost is the inverter. The inverter should meet your peak load. One will have many high power consuming gadgets at home e.g. microwave oven, induction heater, electric geysar, washing machine, grinder/mixer, electric iron, borewell pump, sump pump etc. Estimate how many you need to compulsorily operate simultaneously and which are the ones you can stagger. Think whether when you are operating induction heater, whether you can refrain from using microwave oven, washing machine or starting of the bore well pump. You cannot predict when the Fridge compressor will switch on so let it be like that. Suppose total peak load comes to say 2.5kw from this exercise, go for a 5kw inverter – to take care of any inadvertent starting of gadgets without one’s knowledge exceeding the inverter capacity. Be liberal with inverter capacity sizing since its contribution to cost is the lowest and you cannot increase the capacity of the inverter in modules (like increasing the power generation by installing additional panels and increasing battery back up by adding more number of batteries in future). You will have to replace the inverter with a higher capacity one if there were to be under estimation of peak load requirement.

C.      Battery Backup – Please take the trouble of finding out how many units you consume from 5PM to next day 9AM. Battery capacity should match this requirement. If you can avoid using heavy power consuming items like induction heaters etc in this time interval, you will need less number of batteries and thus incur lower cost. Finish utilization of high power consuming equipments before 3pm.

General

It is advisable to be as accurate as one can be in finding out how much each electrical gadget consumes power. What is written on the name plate may not be reliable (They may be valid under ideal conditions). The nearest analogy is the fuel consumption claimed by the automobile manufacturers. We get much lower mileage than what is indicated in the pamphlets because we don’t drive or operate under ideal conditions. I had bad experience with the bore well pump. The pump claims it has a 1hp motor which ideally should consume 0.75kw but now I find that it consumes more that 2kw i.e. almost near 3hp. So I have landed up in a situation where I have to be very careful as to when I have to start the pump.

There are quite a few other points that I have observed which I shall consolidate and share in due course. If anyone is interested in the ‘calculation’ part of sizing the capacity, most welcome to contact me.

Hope this note gives some idea about the ‘design’ considerations of Solar power system and is comprehensible. For any clarification, never hesitate to contact. Go green, go Solar!!!

My salutations to the Sun God, Albert Einstein who got the Nobel Prize for discovering Photo electric effect and the technologists who developed the photo voltaic cells based on Einstein's discovery.