May 30, 2013

How to Calculate and Match Solar Panel, Inverter and Battery Charger Specifications for Acquring Optimal Results

The following post explains through calculations how to select and evaluate the right solar panel, inverter and charger controller combinations for acquiring optimal results in the form of free electricity.

For convenience, let's believe you possess a a hundred watt gadget that you would like to operate with free of charge solar power for ten hours every night.

To determine how large solar panel, batteries, charge controller and inverter it is necessary to have, observe the below conditions.

1. Estimate the amount of electricity required. 100 Watts x 10 hours = 1,000 Watt hours. Which is the absolute power that is necessary.

2. Next figure out how large solar panel you really need. Depending on a ten hour day of luminosity, the approximation is straight forward:
1,000 Watt hours / 10 hours sunlight = 100 Watt solar panel.

The simple truth is that nearly all the summer time days or weeks provide roughly 15 hours of sunshine and winter season you receive roughly 4-5 hours of natural light. Invariably select the worst case predicament for
your solar panel. On those grounds, choose a winter season day of sunshine.
1,000 Watt hours / 5 hours sunlight = 200 Watt solar panel.

(Based on normal United States daily sunlight .)

3. Calculate the optimal size of the batteries which might be essential. 1,000 Watt hours divided by 12 Volts = 83 Amp Hours of reserve battery power. 1,000 / 12 = 83.3
A typical marine deep cycle battery works nicely in this case. Choose much bigger battery to rest assured, assume 100 Amp hours power.

4. To estimate how big solar charge controller you might need, consider your solar panel energy specs, which happens to be a hundred watts divided by twelve Volts.
100 / 12 = 8.3 Amps.
Desirably choose bigger sized units, and therefore utilize a ten Amp solar charge controller.

5. Determine what capacity inverter can be used. That's the hassle-free aspect. You might want to energize a a hundred Watt load, therefore choose an inverter which includes
no less than a hundred Watts steady power standing.


  1. hi sir i have a question that i have a 55w solar panel 50ah lead acid batery i dont have a controler so for how long the batery will be full charged? and also i can run 2w 5 bulbs,40w tvand dvd for how many hours? and also what is the suitable charge controller needed? thanks

    1. Without a charger controller it would be dangerous to charge the battery, or drive any gadget.... not recommended.

  2. Dear Mr. Majumdar

    Can you help me in installing a solar panel at home?

    I have the following data:

    Solar panel wattage: 216 watts
    Electricity required in our home: 106 watts
    Hours of use: it doesn't matter to me as long the hours wont go below 10 hours.
    Hours of sunlight (based on the normal daylight ): Max.- 7 hrs.; Min.- 6 hrs

    Can you fill in the blanks? :
    battery: voltage:___; amp-hours:___
    inverter: wattage:___; voltage: 220

    Can I ask if you can make me a solar charge controller out of the data above?

    And can you add a function to the solar charge controller? : If the sun has enough light,
    the inverter will get the source from the solar panel while the battery is being charged.
    Then the moment the cloud dims, in which the solar panel can't produce enough voltage,
    the relay will change the inverter's source, which is from solar panel to battery. With this function I can protect the appliances from low voltage and use the solar panel during daytime.

    thanks a lot for your kind consideration!!!!

    yours truly
    Eshkariel Tapiador

    1. Dear Achiless,

      I'll try to do it and respond soon.

  3. Replies
    1. Good day Eshkariel,
      you can try calculating the parameters with the help of the data given in the above article. It isn't very difficult if you see.

      I'll try to design the solar charger that you have asked and will let you know soon, pls remind me if i forget, though:)

  4. This comment has been removed by the author.

    1. Good Morning Eshkariel,

      Your calculations look OK to me.

      You can try the inverter that's been covered in this article although it's not a pure sine wave, just a modified one.

      transformer rating could be = required wattage divided by available voltage, this will give the amp rating for the trafo.

      Battery could be rated at = required wattage divided by voltage,this will give the AH of the battery, but make it twice at least for a reasonable back up time.

  5. Replies
    1. eshkariel, I think it's already published in my blog, you can refer to this post for more info:

  6. hello sir I want to run 100 watt inverter on solar panel so how many watts panel require for it???

    1. hello kanu, you can try a 25 watt panel and a 25 AH battery

  7. hello sir I am student from Anand,Gujarat, I
    want to make 100 watt solar
    inverter,so how many watts solar panel and
    battery require for it?

  8. Hello sir. Can you suggest me what are all the components to be bought by me including their grades as I am not much aware of electrical components

    1. Hi Nandula, please specify your requirement specifications....only then I would be able to suggest.

    2. My requirement is making a speed restrictor for vehicles.

    3. you can try the following circuit

  9. I hv a 1000 wt invetor and a 240 solar panel and battery but if I try to connect the invetor it just says faulty Wat cn be the problem with it

    1. your specs are not sufficient for judging the fault...

  10. I have a solar company getting ready to do my solar. I will have 28 lg 315 watt panels. They are giving me a 7600 watt inverter. I asked why my inverter is less wattage than my panels. He said you divide the wattage of the panels by the inverter and get 1.17. He said as long as it's. Between .75 and 1.35. Is this right??

    1. The technician is probably correct. the inverter wattage should be much less than the panel wattage otherwise the solar panel could be forced to run at an inefficient zone causing huge drop in inverter voltage

  11. Hello mr Swagatam.

    I have 8 solar panels of 200watts each. I would like to ask which inverter size is the most suitable for these panels when wired all together.
    Can I use the inverter which come with inbuilt charge controller?
    Which battery sizes and how many pieces do I need to make the wiring.
    Which wiring method would give me the most efficient power outputs.
    Can I use the solar power output out of these 8 panels to run a Panasonic home theater of 13200watts?

    Thanks in advance


    1. Hello Pascal,

      the most suitable inverter that could be used with the mentioned 200 x 8 = 1600 watt panel is around a 1300 watt inverter, 13200watt is out of question, since it's way out of the range of the panel.

      connecting the panels in parallel would be a more convenient option....

      the battery voltage will need to be matched with the panel output if no MPPT is used in the middle, and therefore will need to be wired accordingly.

  12. Sir , I read all posts your blog for calculation , in point #2 , you calculate 1000 wh/ 5 hr sunlight= 200 w but in point #4 , you wrote , 100 w panel /12 v = 8.33 Amp charge controller.why you took 100 w instead of 200 w ???

    1. Jitendra, 200 watt is for countries with weaker average sunlight, and 100 watt is for countries for stronger average sunlight...

      the example is given for a 100watt panel, anybody can easily convert the results for 200watt also....

      there's nothing too difficult or confusing about the calculations.

  13. Sir , second question .your answer to Ms. Achilles Hector should be direct I.e. Battery V = 24 , Amp Hr = 44+@ 24 v , Inverter w = 216+ w , but you replied her to follow calculation as per yr blog.I know you can't calculate for everybody but how can we cross check whether our calculation is right until and unless you or any other reader give her the answer.I request you and atleast one reader to confirm my answer.

  14. Sir, i have 8 panels 250W each in a parallel connection, and 8 batteries 150 Amp. 12V In a Series parallel connection 48V. my Inverter is 48V - 220V pure sine. can i connect it together.

    1. If the panel voltage is within 60V then it would be fine, however if the inverter load is too high then the batteries might not charge other words the inverter load and the battery charging consumption must be less than 250 watt combined


Swagatam Majumdar
Swagatam MajumdarHi Friends, Welcome to my site, a place where you will discover a massive collection of electronic circuit ideas, mostly requested by the dedicated readers and exclusively designed by me for their customized application needs. I have posted more than 1100 circuit designs in this site, if you have a personalized circuit requirement you may feel free to request it through the comment box, if it seems feasible to me then surely you may find it published here with your credentials attached in the post, thanks and please keep reading

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