How to Calculate the Amount of Energy needed for a Solar Panel/Inverter

Ok guys, someone asked me this question and i had to see what and how best i can explain this in plain terms.

Electronics is not exactly my thing but i will make this article as easy as possible.

How do i know the number of solar panel needed to charge my 1kva, 24v 200ah battery?

For a 1kva inverter of 24VDC (voltage)
2batteries of 12volts 200AH or 100AH are required
The solar panel needed to charge a 12 volt battery is determined by the numbers of hour of daily average sunlight.
In Nigeria we have an average of 7hrs of sunlight.
However since solar are in wattage, we have to convert the battery also to watt
i.e 12v 200AH =12×200=2400watts
to know how many panels needed to charge a 12volt battery for a day, all we need to do is divide the battery wattage by hours of sunlight daily
=2400watts/7hours of sunlight=343watt solar panel is needed to charge a 12v200AH battery
For a 24v200battery
1solar panel=200 watts
686 watts /200 watts =3.43panel
Hence 4 solar panels are required.
Same is applicable for all other cases of 2kva-20kva.

For the total breakdown of the calculation.
of course there are always loses in the sense that its not all the charges that goes into the battery that are stored.
and for loses i usually keep at between 25-30%, and as for the number of sunlight hours, if you check the write up again you will see I wrote an average of 7hours which could be ≤ 7.
However, since I assume there are 7 peak sunlight hours in Nigeria (which is still debatable) depending on your region in Nigeria.

Therefore to charge your 12v 200AH battery in 7hrs, and also having in mind that battery is @ 10% level it means we charge 90%.

Hence 12v200AH=2400watts
2400×90/100 =2160
2160/7hrs =308watt
taking my charge loss % of 30%

hence 30% of 308watts will give me 92watts

my final sum will therefore be 308+92=400Watts


1. how much energy can a solar panel generate over a given period of time?
2. How much energy can my battery store?
3. How much energy will my appliances use over a given period?

for number 1 question, I have answered in my initial write up “How do i know the number of solar panel needed to charge my 1kva, 24v 200ah battery?

2. how much energy can my battery store?

Battery capacity is measured in Amp Hours (e.g. 100AH). You need to convert this to Watt Hours by multiplying the AH figure by the battery voltage (e.g. 12V). this is just the simple calculation below

A (Battery size in AH) x B (Battery Voltage) = C (Power available in watt hours

For a 100AH, 12V battery the Watt Hours figure is 100(A) x 12(B) = 1200 WH (C)

This means the battery could supply 1200W for 1 hour, 600W for 2 hours or even 10w for 120 hours i.e. the more energy you take, the faster the battery drains or discharges.

Howeve,r you can’t really take all the power from a battery, since once the voltage drops below your equipment’s requirements it will no longer be able to power it. Since I can’t know the battery capacity of everyone, you can please check your battery’s specifications to make sure.

For Lead acid battery’s you will only able be to access around 50% of their rated power. (e.g. a 100Ah battery has 50Ah of usable power)

For Li-ion battery’s you will only be able to get around 80% of their rated power. (e.g. a 100Ah battery has 80Ah of usable power)

Another common question that most people ask regarding the battery issue is

Q. Are car battery’s as good for solar as leisure battery’s?

A. The answer is a capital NO they are NOT. The reason is because a leisure battery has been designed to be discharged and recharge, a Car battery is designed to provide a lot of power quickly but it’s not able to cope with a low internal charge and recover fully.

3. How much energy will my appliances use over a given period?

As We all know, the power consumption of appliances is generally given in Watts (e.g. My small portable TV is around 20W this information can be found on the data sticker behind most electrical items). To calculate the energy you will use over time, just multiply the power consumption by the hours of intended use.

i.e for my 20[i]watts[/i] TV in this example, if on for 2 hours, will take 20 x 2 = 40WH from the battery,
if it is on for 5hrs for example, it will take 5 x 20 =100wh from the battery.

Repeat this for all the appliances you wish to use, then add the results to establish total consumption.
let me quickly do an assumptous calculation below, which you can as well follow below.

TV 20w on for 2 hours per day = 40w per day

Radio 10w on for 5 hours per day = 50w per day

Water pump (20w) on for 20mins per day = 6.66w per day (20mins convert to hrs = 20/60=0.3333 x20 =6.66watts)

Main Light 30w on for 3h per day = 90w per day

Fan 25w on for 2h per day = 50w per day

Total = 236.6w per day

In other to lower your power usage and consumption I advise you swap out halogen lights for LED lights. LED lights generally use 80% less energy for a similar light level. We have a range of 12V LED.

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