How to calculate your solar power requirements

How much solar power do you need?


So you want to set your rig up for Solar but you are not sure what size of set up you need? This blog is designed to give you the tools needed to be able to work out exactly what are you are drawing from your rig's batteries and what type of solar set up you need. Knowledge is key when setting up your rig for solar so the more information you have on each and every one of those home comforts devices you plan to take away with you the better. If anyone has a question pop it in the comment section below. I will try my best to answer everyone.


iTechworld Solar Panel


How to work out Watts, Amps and Volts

A larger solar panle will collect more energy in less time, but just how big does the solar panel need to be?

The power consumption of appliances is usually given in Watts. To calculate the energy you will use over time, just multiply the power consumption by the hours of use. For example:

10 watt device used over 3 hours equals 10 x 3 = 30 Watt

How to convert Amps to Watts

The energy in Watts is equal to the electric charge in Amps times the voltage in volts:

Watts = Amps × Volts


If your device doesn’t have the Watts labelled on it, then it should at least have the input Volts i.e. 240V and the Amps AC it draws such as 240V – 1.5A. You can then use the equation Watts Volts x Amps so 240v x 1.5amps = 360 Watts.

How to convert Watts to Amps

The electric charge in Amps is equal to the energy in Watts divided by the voltage in volts (V):

Amps = Watts / Volts


Find the electric charge in Amps when the energy consumption is 300 watts and the voltage is 240 volts.

300 Watts / 240 volts = 1.25 Amps


Do I need a battery?

iTechworld Lithium Battery

Solar panels are commonly used to charge a battery – not to charge a device directly. There are a couple of reasons for having batteries. Solar panels might not generate enough wattage to directly power an appliance, but they can build up a higher wattage via a battery. Secondly a battery can regulate the power going in to the appliance at a constant rate. When solar panels are charging a battery it is usually at a varying rate which could harm an appliance if not regulated.

Battery capacity is measured in Amp Hours (e.g. 120Ah). You need to convert this to Watt Hours by multiplying the Ah figure by the battery voltage (e.g. 12V) – see calculations above.

AH refers to amp hours. This rating is usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps of power for 20 hours or 20 amps of power for 5 hours.

When choosing a battery, keep in mind the equipment you will be powering and the time in which they will be running. Theoretically a 100Ah battery can deliver 5 amps over a 20 hour period (and so on). Taking into account the average small campsite - with a small 45W fridge running for 6 hours, 3 hours of 15W lighting and 20W of other electronic equipment - the minimum consumption to be expected is 335W. Take this wattage and divide it by the voltage, 12V, gives 28Ah. With the aim of leaving 50% in the battery brings the requirement to 56 Ah per day. A smarter battery setup would be to use an iTECH120 lithium battery. This new type of battery is a fraction of the weight of old style AGM batteries. AGM batteries usually weigh 35kg but and iTECH120 battery weighs just 13kg. You can also use more of the battery capacity in an iTECH120 - 80% which means its usable Amp Hour rating is similar to a 200 Amp Hour AGM. Read more about the iTECH120 HERE


What size solar panel do I need? 

280 Watt Solar

Solar Panels power generation is commonly given in Watts e.g. 120 Watts. To calculate the energy it can supply the battery with, divide the Watts by the Voltage of the Solar Panel.

120 Watts / 18v = 6.6 Amps

Please note that Solar Panels are not 12v, I repeat Solar Panels are not 12v. Any one who works out the Amps of a solar panels using 12v as the voltage calculation does not understand solar or has been misinformed. All solar panel voltages should be marked in the item description of our website or on the unit itself.

Check out the iTechworld Solar Panel range HERE


Power Inverter

The power inverter converts your storage battery power into the 240 volts AC that runs your appliances. Unless you only run 12 volt DC appliances you will need a power inverter to supply your AC.

There are 2 types of Inverters

Pure sine wave and Modified sine wave.

The Pure Sine Wave matches the power to that of which you get from your Electricity Supplier, its clean and you can run any appliances safely even sensitive equipment.

The Modified sine wave used to be considered a dirty power but some aren't as bad as they used to be, you can use this inverter type for  things that don't have sensitive electronics for example fridges, cookers, pumps, You may have to be careful with some appliances such as laptops and TVs so check first.

Check out the iTechworld range of inverters HERE

Charge Controllers/Regulators

MPPT Controller

All Solar Panels 30 watts and above need a Solar Charge Controller/Regulator. A Charge Controller/Regulator is necessary to protect the batteries from over charging and supply them with the proper amount of energy to promote long battery life. If the charge isn’t regulated it can have a damaging effect on the battery being charged.

Check out the iTechworld range of Charge Controllers/Regulators HERE


Article author






Hi Ian Can you advise me with this situation, I have a 50lt waeco cfx 12 volt compressor fridge, the book says @ 12 volts current draw is 7.8 amps,( I don’t know if this is on start up or continuous it probably starts very infrequently overnight say 6pm to 6am , 12 hours, I have 120 watts @ 18.6 volts max power in two panels supplying only a 105 amp hour all rivers agm deep cycle battery, do you think this can work overnight if the fridge is not opened often overnight, if not what do you suggest? many thanks for any help kind regards Eric


Hi Ian, Can you tell me what wattage solar panels I require to run 2 × 60 ltr engel fridges. Current draw on these fridges is 4.2 amp maximum. I would also like to run 2 x auxilary batteries. Can i run 2 different battery types from 1 regulator ? or would you recommend 2 seperate systems?


Hi Ian,can you assist me on this, I’am trying buy a 120watts solar panel please specify how regulator and type of battry required.
Thanks and kind regards.


Hi Mate i have 50 w pump 12 volt for fish pond, need to run on solar, what size battery and panel i need so pump can run day and night.



Hi Bob,

I would recommend at least a 160 Watt solar panel with at least one 100a deep cycle battery. Two batteries would be preferable.

Kind regards

maunish parmar#6

Thank u so much for share this information to us….


Hey Ian, looking at a 40l fridge for my troopy that according to the website uses 1-1.5 amps per hour.. I haven’t yet bought a second battery.. Dual set up in place already. Just wondering what kind/size battery and what solar set up would be appropriate and how long it would last?


Hi Ian I have a 160watt solar panel and a 10 amp regulator could you explain what the advantage of going to a bigger panel would be if the maximum output from the regulator is 10 amp ( Why go 200 watt when 10 amp out put is max) ?


Awesome info, very easy to understand and detailed. Keep up the good work my man.

Paul prior#10

Hi Ian .firstly your site is one of the best I have come across about info on solar and power .I’m still trying to get my head around it all .for example if I ran a 500 watt light bulb that is 1.23 amps.for say 10 hrs ? Would 200 ah batteries through 600 watt inverter and a 180 w solar panel be enough?regards paul

Epah francis kuku#11

thanks I’m just new here but I HV learnt a lot.

David Walker#12

Thanks for that itechworld -will read up on what you’ve just sent re batteries & solar panels.


Can I change my existing 95ah battery for one with say 120ah! How will it affect the solar panel set? Many thanks

Patrick Usman#14

Hi, How long will it take 260 watts solar panel to fullly charge a 12volts 200amps battery

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