Electricity Saving Tips For Homes And Offices

Solar electric, solar thermal, power generation, inverters, grid, off-grid: clearing the cobweb

By on January 21, 2014

Any new technology can be daunting to understand if one is not very tech savvy. And when it is electrical or for that matter renewables, then it gets scarier. With more people getting interested in solar applications, there is more demand from people to understand the concepts in renewable space. People specially want to understand how they can use these technologies to get over with power cuts and rising electricity cost. As with every other thing in this world, solar science is not a rocket science and it is certainly not difficult to understand the basics. With this article we will try to clear some cobwebs around the basics of solar science.


Solar Electric vs Solar Thermal

Solar energy has multiple applications and it is not necessarily converted into electricity in every case. For e.g. a solar cooker uses heat from sun to cook food, a solar water heater again uses heat from sun to heat water. These are solar thermal applications where heat from the sun is collected and utilized or transferred. No electricity is generated in this case.

Another example is the innovative day-lighting solution we discussed in our previous article (link), which does not convert solar energy but just innovatively moves light from sun using reflective surfaces.

None of the above applications use photovoltaic cells (or PV in short) and are highly efficient systems (efficient in utilizing energy from sun) and are cheap as compared to a photovoltaic application. A PV is required when solar energy is used to generate electricity. PVs are made of silicon and available in 2 types: 1) mono-crystalline 2) poly-crystalline. As per their name, they convert Photo (or light) into Volt (or electricity). Their efficiency in utilizing sun’s energy is much less as compared to thermal or photo applications as explained above. The difference between mono-crystalline and poly-crystalline is that mono-crystalline is made of single silicon crystal whereas multi-crystalline PV is made up of multiple crystals. A mono-crystalline is more efficient in converting solar energy into electricity per sq meter area than a multi-crystalline PV. Thus the space required for the same amount of wattage is less in mono-crystalline PV panel and hence it is costlier than a multi-crystalline PV.

Solar Power Generation

Solar energy can be used to generate electricity in almost any part of the world. The most important thing is availability of some sunlight, which is there everywhere. To generate electricity from sun, you need a solar photovoltaic system. A solar PV system is a long lasting system and can last for 20-30 years. There are 2 types of Solar PV system assemblies that are available:

  1. Off-Grid solution:  An Off-Grid solution is a system that works independently and is not connected to the Grid. Grid over here means the wiring network from the electricity distribution company that provides you electricity. An off-grid solution generates electricity and stores it in a system of batteries and does not provide it back to the grid. A typical off grid solution looks something like shown below:SolarInverter

(Source of photo: http://www.altestore.com/)

In an off-grid solution a PV Module generates electricity that charges the batteries connected to it through a charge controller. The charge controller prevents overcharging of batteries and also makes sure that the batteries do not get discharged at night or cloudy days. There are three types of charge controllers available: 1) Shunt 2) PWM (Pulse Width Modulation) 3) MPPT (Maximum Power Point Tracking). MPPT being the most sophisticated, efficient and thus more expensive and Shunt the simplest, least expensive but less efficient.

The battery bank is the component that needs regular maintenance. Solar systems need deep cycle batteries and cannot be operated on batteries used in automobiles. Life of batteries depends on number of times it is discharged and thus deep cycle batteries are a must. There are multiple types of batteries available in market. The maintenance free ones are the most expensive and they also last no longer than 4-5 years. The other regular lead batteries need to be filled with distilled water regularly for right operation but if maintained well can run for long and are cheaper than maintenance free batteries.

The inverter converts DC current from the battery into AC current that is useful for various appliances in a house. For using with Solar Panels, it can be the same inverter if you have one in your house. There are two types of inverters available in the market: 1) Modified Sine Wave and 2) Pure Sine Wave inverters (more details on inverters available in our article: Choose right inverter for home and maintain it right to manage electricity bills.

So in case you have an existing inverter solution and you want to have a PV system integrate to it, you can do that by getting a PV module array and a charge controller and connect it to the existing system.

  1. Grid Connected Solution: A grid-connected solution is simpler and cheaper to install as compared to off-grid solution. It also requires less maintenance, as there are no batteries involved in it. So essentially a grid connected system is similar to the above diagram without a charge controller and a battery bank. Something like this:GridConnected

In this case the electricity generated through the PV array is connected to the inverter as well as the grid. During the daytime when there is ample sun, the electricity generated will be used in the house through the inverter and any extra electricity generated will be sent into the grid. The distribution company can use this extra electricity generated to distribute in other areas. In return the producer of the electricity (the one who has installed the PV system) gets rebate when electricity is used from the grid during the nighttime. This system turns out to be cheaper as it does not involve any batteries for storage and thus require less maintenance as well.

As it does not involve storage, such a system is not good for places where there is lot of power outages during nighttime.

Sizing of a PV system

Sizing of a solar PV system is not very important if you are installing a grid-connected solution. That is because in case your usage is more than what the system installed can generate, then extra electricity required can come from the grid. If your usage is less than what the system has generated, then the extra will go into the grid and you will get rebates on the electricity you use from the grid.

But sizing can be very important for an off-grid system. The number of PV modules, size of battery array and the inverter will depend on the setup that you want to support on it. As per the standards taken everywhere, it is assumed that on a good day a solar PV system can generate electricity only for 5-7 hours. Which means a 1 kW system will generate 5-7 units of electricity on a real good day.

The best thing that can help you in sizing your system is your electricity bill. If you get monthly electricity bills then just take the electricity units on your bill and divide it by 30 (or 31 based on the month) and you get your daily units usage. If you do not have the same, then you need to find out the wattage of all the appliances that you have and use the formula below to calculate daily units:

                        Units = (wattage of appliance) x (number of hours of usage in a day)/1000

Sum the units of all appliances and you will get your daily units.

While sizing make sure that you look at the month when you have the maximum electricity consumption. Please note the electricity consumption changes every month (link). Size your system according to the maximum electricity consumption.



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There Are 20 Comments

  1. Priyank Thakur says:

    Very useful information. I’m planning to set up a grid connected solar power plant in MP soon. Thanks for the information you shared

  2. solariiknight says:

    Hi, you mentioned that 1KW solar panel generates 5-7 units per day. I have to correct you here a little bit – 1KW solar panel generates normally 4 units using a PWM solar charge controller(most common type) and 5 units using a MPPT charge controller. Only if you use a single axis tracker+MPPT inverter/charge controller, you may get 6 units.

  3. kiran says:

    dear sir i am kiran from vijag we are started a business like solar distribution,i have a doubt about the panels what is the difference between china made and india made,at the same time panels are same quality are using the world wide are if any diferences,pls let me know ,thanmiking u sir

  4. Rakesh Kumar Singh says:

    Dear Abhishek,

    Thanks for your reply. I have been seriously looking for some cost effective low maintenance solution

    With a load of 300W, The battery backup is exhausted is 5hrs. To have a backup of 10hrs what should be the quantity (in Watts) of Solar Panel I should be adding to the battery .

    • Abhishek Jain says:


      300W for 5 hours is 1.5 units of electricity. I would say that you need about 250-300 W of solar panel for it.

      Hope this helps.


  5. Rakesh Kumar Singh says:

    Hi abhishek,

    I come from eastern UP and we get only 10 to 12 hr of electricity from the grid. I have a 800VA inverter already installed but it doesn’t gets charged completely to meet our requirement.

    I would like to know if I install a 200W solar panel with charge controller,Will it increase the battery backup

    • Abhishek Jain says:

      Well it will surely increase the battery backup, but you need to analyze your electricity needs before deciding on the size. First thing to evaluate is your consumption. What all do you run on backup? And for how long? Second is to evaluate the size of your battery, can it hold the amount of energy that you need for 10-12 hours. If not then you may have to add some batteries. Finally whatever is the delta which is not getting stored from the grid will have to be generated using solar. A 1 kW solar panel can generate about 5 units of electricity in a day. 200 W will generate 1 unit. You will have to analyze if 1 unit is sufficient for the appliances that you run on inverter.

      Hope this helps.


  6. vbhoj74 says:

    I wanted to install a 1kwh system to feed may requirement here in Kolkata, but the costs are a demotivator. The same off grid system costs Rs 90/w in Kerala while it costs Rs 185/w here, these are after subsidies.

    • Abhishek Jain says:


      It is strange because there are many places in the country where it is Rs 100 or below per watt. A Bijli Bachao reader from Delhi got 1.4 kW system for just Rs 75,000. Agreed that there can be difference in quality between versions but Rs 185/w is expensive. I wonder if you can try getting it from somewhere outside.


      • vbhoj74 says:

        Did that 75k involve any subsidies? Why would one state subsidise it for another? 75k for 1.4kw system is so tempting, I’m holding on wasting on a home ups since the off grid system will double up for it.

        • Abhishek Jain says:


          This was the message we received:

          “Dear Mr. Abhishek,

          Nice & valuable information on Solar Panels. But the cost factor i.e. 200 per watt or 2 lakhs for 1 KW does not allows everyone to install solar panels.

          I live in Delhi and I had installed recently a 1400W (1.4KW) system in just Rs. 76,000/= i.e. almost one fourth of the cost mentioned. I am running all my household electric equipments on it CFLs, Fans, TV, Computer, Washing Machine & Fridge too (but not induction cooker, geyser and airconditioner which require more power).

          I am mentioning my cost structure as follows:

          4 Solar panels of 200W @ 8000/- = Total 800W @ 32,000/-
          4 Solar panels of 150W @ 4000/- = Total 600W @ 16,000/-
          Copper Wiring = 2 bundles @ 2300/- = Total 4,600/-
          600VA Inverter @ 5,000/-
          2 Batteries of 23 plates each @ 7500/- = Total 15,000/-
          2 Iron Stands for holding panels @ 1500/- = Total 3,000/-

          Total Cost : 32000+16000+4600+5000+15000+3000 = 75,600/=

          Hope this information will encourage others to follow. For more help, I can be reached at [email protected]

          Suresh Adhikari”

          Hope this helps.


          • vbhoj74 says:

            Thanks so much, I’ll get in touch with him and see if this works out for me as well.

          • Ashok Bhardwaj says:

            Dear Mr. Adhikari

            Thanks a lot for such a valuable information. I already have inverter with batteries at my home, so is it possible to connect the PV panels directly to the inverter & batteries?


            Ashok bhardwaj

          • anil Reddy says:


    • Ravi Ramakrishnan says:

      Actual material cost of 1 KV system is only less than 130 K. This includes installation and 1 year service as per MNRE norms. If you shall entice your state to subsidise the same we shall install 1 KV sytsems in your state for 30% of 130K. The balance amount as subsidy. I am from Kerala.

      • vbhoj74 says:

        So 130k is without subsidies ? WB gives a 30% subsidy, will you be able to arrange me a 1KW system with 130k-30%?

  7. soundara rajan says:

    I, from Australia, but native of Tamilnadu want to start solar power genration to feed the grid. I want to start 5mw solar power farm.

    I want to have if any data is available, annual production from 1 KW solar panel and the cost of installation without battery.

    • disqus_3 says:

      i am based in chennai, just started my solar business. I can help you out in setting up your plant here. contact me at [email protected]

    • Abhishek Jain says:


      A 1 kW system would generate about 1600-1700 kWH of electricity. You certainly do not need batteries as you are planning to supply to the grid so the cost will come down significantly. Just the solar panels should cost you about Rs 40 per kW (or may be less as you have a bigger requirement and you can negotiate with manufacturers).