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

By on June 17, 2015

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.

Here is a quick video that can guide you on Rooftop Solar PV buying in India:



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46 Comments on "Solar electric, solar thermal, power generation, inverters, grid, off-grid: clearing the cobweb"

If you have any question or comment, please leave a message here. We try to reply to questions in the sequence they come in. We work from Monday-Friday 10AM-7PM. If we know the answer we try to reply to the question within 3 days.

vinay kumar
May 24, 2015

Contact for Solar grid solutions for Institutes, hospitals, malls, industrial areas and large scale plant 200 kva to 10 MW. Our manufacturers have very vaast experience in this field. We provide services across India at very nominal rate which are competitive in market.

For any query, please feel free to contact us at +91-9312700996

mayank tanwar
June 1, 2015

Choose wide range of best quality Generator Batteries, Inverters and Home ups at discounted prices. Batterybhai.com offers a complete range of generator batteries of all brands starting from 90 Ah to 190 Ah. For best generator batteries visit here http://www.batterybhai.com/category/genset-batteries/6

March 17, 2015

Hi All,

We are providing the customized solutions to our customers as per their requirement. We provide free site survey to our customer and design the system after proper site analysis.

We are installing solar projects with minimum space. We are providing solar consultancy to big solar firms. We have a strong team of IIT grads. for designing the system with maximum energy generation. We guarantee the least weighted structure to big solar firms.

We provide world class products (panels, inverter, cables etc.). We design the complete system as per Indian standards.

For any query, please feel free to contact us at [email protected] or +91-8527652687

Next Engineering Solutions

February 27, 2015

I am Gurumoorthy , residing in secunderabad.
Can anybody tell me the details :

1 ) My total load per month is 1000 units ( as per the meter reading )

2 ) Roof area required to install solar power panels;.

3) Cost of the system ( ie control unit , batteries , solar panels , installation etc )

4 ) I want to use the solar power during day time .

5 ) pl. split up the cost for each of the above mentioned items.

Thank U


February 23, 2015

How the connection in solar panel to grid ?

December 15, 2014

Are grid connected systems available in India, for households? If yes, can you also please tell about the benefits that we receive for the current that is fed into the grid?

December 16, 2014

hi Abhishek,

Thank you for the info.
I have found what i was looking for.
The feed in tariff is pretty low. Only INR 3 for unit, in ap

November 16, 2014

Is it safe to battery with existing Electric Inverter to connect Solar Charge Controller through Solar Panels

Krishna shrivastava
November 21, 2014

Dear sir shriikanth ji,
it is fully safe to battery with existing Electric Inverter with connect Solar Charge Controller through Solar Panels.
For more information and any doubt please contact us.

Krishna shrivastava
[email protected]
+91 7415324645

October 8, 2014

I want to set up a small solar power system for my home and for this purpose i made a calculation .Please have a look below:-

1.Power requirement calculation:-

(i) 5 ceiling fan (each consumes 35 watts) so, 5 x35 watt = 175 watts

(ii) 6 LED lightning bulb (each consumes 12 watts) so, 6 x 12 =72 watts

(iii) 2 (32″) LED tv (each consumes 64 watts) so, 64 x 2 = 128 watts

(iv) Miscellaneous item 50 watts
Total power required = 425 watts

Total current needed = 425/12 = 35.4 amp(current) [ i divided 425 watts by 12 because the battery voltage output is 12v )
2.Number of Solar panels required for 425 watt or 35. 41 amps = **8 panel of 100 watts** (as each 100 watt solar panel produce 5 amps).
3. One Charge controller [24 volts/40 amps]
4. One Battery [100AH(amp-hour) 12 volt battery]
5. One solar inverter [500 watt 12DCA to 220ACA]

The whole system would be cost up to Rs.65000

(i need solar power only during day time that`s why i choose 100AH battery for getting constant voltage for solar inverter)

****But before going ahead i wanted you to verify my calculation and requirements and also do correction if needed.*****


October 10, 2014

I need back up hardly for one hour after sunset.
Q. Does solar charge controller will be able to convert 40amps into 5amps(for the purpose charging battery @5amp) and also 17~18 volts into 12 volts.
***(i am making parallel connection between solar panel)***
Q. What happens if battery get charged to 100% during daytime and 425 watts load is still there?(A/C to http://www.freesunpower.com/solar_simulator.php 100AH battery will take roughly 17~20hrs to get charged(@5amp without any load) so as i think 3-4 day will be enough but what happen on the fifth day with a load of 425 watt )?

thanx a lot in advance again!!!

Athar Ansari
October 22, 2014

Dear Shubhankar,
we are a company based in Bareilly (U.P) wherein we provide solar solution assessment and complete system, incase you are located in North India and need us to help you may call me on 9457819102

October 12, 2014

Can i directly use solar power energy to run appliance during sunshine time
I mean SOLAR PANEL[8 unit each, 100watt{5amp}]———>Charge controller[40amp{12/24volt]———–>POWER INVERTER[500watt{12vdc into 220vac}]—–>LOAD[220vac 425watt].

August 1, 2014

OfThaks for the information. can u pl. Let me know the rooftop area required to install the cells for one kw power consumption.

August 3, 2014

Thank u for the reply.

Priyank Thakur
June 15, 2014

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

March 17, 2015

Hi Priyank,

We are providing best solar solutions as per our customer’s requirement. We are providing most efficient and premium quality system. We are designing the system as per Indian standards.

For any query, please feel free to contact us at [email protected] or +91-8527652687

Next Engineering

May 24, 2014

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.